Publications – Advanced Composites Laboratory

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2019

Chen, W; Zhang, D
An integrated processing and damage model for predicting failure in a curved composite beam Conference
2019.
Abstract | Links | BibTeX | Tags:
@conference{Chen2019b,
title = {An integrated processing and damage model for predicting failure in a curved composite beam},
author = {W Chen and D Zhang},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85068487020&doi=10.2514%2f6.2019-1204&partnerID=40&md5=0a24d3af174877328fe6f3dcd103f743},
doi = {10.2514/6.2019-1204},
year = {2019},
date = {2019-01-01},
journal = {AIAA Scitech 2019 Forum},
abstract = {An integrated processing-failure model was developed to predict the inter-laminar strength of a plain weave composite flange manufactured using the Resin Transfer Molding (RTM) technique. A multiscale modeling framework was established to exchange the information between different scales. At the global scale, the composite was treated as a single, homoge-neous material, and the global stress and strain fields were solved through a cure-dependent constitutive law using the homogenized composite properties. At the integration point of the homogenized model, a discrete model was created to represent the microstructure of the textile composite, and the cure-induced local stress field was calculated by imposing the strain history obtained from the homogenized model on the boundaries of the discrete model. After the curing process, the discrete model was virtually loaded, and the Smear Crack Approach (SCA) was employed to predict the failure response of the matrix. The current study shows that the curing-induced residual stress has little impact on the composite inter-laminar strength. However, the strength can be reduced by 35% with 1% void content. © 2019, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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An integrated processing-failure model was developed to predict the inter-laminar strength of a plain weave composite flange manufactured using the Resin Transfer Molding (RTM) technique. A multiscale modeling framework was established to exchange the information between different scales. At the global scale, the composite was treated as a single, homoge-neous material, and the global stress and strain fields were solved through a cure-dependent constitutive law using the homogenized composite properties. At the integration point of the homogenized model, a discrete model was created to represent the microstructure of the textile composite, and the cure-induced local stress field was calculated by imposing the strain history obtained from the homogenized model on the boundaries of the discrete model. After the curing process, the discrete model was virtually loaded, and the Smear Crack Approach (SCA) was employed to predict the failure response of the matrix. The current study shows that the curing-induced residual stress has little impact on the composite inter-laminar strength. However, the strength can be reduced by 35% with 1% void content. © 2019, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.
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doi:10.2514/6.2019-1204
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Chen, W; Zhang, D
Improved prediction of residual stress induced warpage in thermoset composites using a multiscale thermo-viscoelastic processing model Journal Article
Composites Part A: Applied Science and Manufacturing, 126 , 2019.
Abstract | Links | BibTeX | Tags:
@article{Chen2019b,
title = {Improved prediction of residual stress induced warpage in thermoset composites using a multiscale thermo-viscoelastic processing model},
author = {W Chen and D Zhang},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85072086100&doi=10.1016%2fj.compositesa.2019.105575&partnerID=40&md5=72cd17914c7f1724398836121b04c01a},
doi = {10.1016/j.compositesa.2019.105575},
year = {2019},
date = {2019-01-01},
journal = {Composites Part A: Applied Science and Manufacturing},
volume = {126},
abstract = {A multiscale thermo-viscoelastic processing model is developed to predict the residual stress development in a thermoset composite due to curing. In the proposed modeling framework, a composite laminate is modeled as discrete layers of homogeneous laminae at the macroscale, while at each integration point of the homogeneous model, the constitutive relations of the lamina are determined through micromechanics using an Extended Concentric Cylinder Assemblage (ECCA) model in conjunction with the correspondence principle of viscoelasticity. Since analytical formulations are employed at the microscale, the proposed multiscale approach can efficiently predict the composite time-, temperature-, and cure-dependent responses during processing. The proposed model is employed to predict the warpage shape of an anti-symmetric laminate due to curing-induced residual stresses. Compared with other elastic processing models, the proposed processing model achieves an improved prediction of the warpage shape due to its capability to consider both curing history and stress relaxation during composite processing. © 2019},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

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A multiscale thermo-viscoelastic processing model is developed to predict the residual stress development in a thermoset composite due to curing. In the proposed modeling framework, a composite laminate is modeled as discrete layers of homogeneous laminae at the macroscale, while at each integration point of the homogeneous model, the constitutive relations of the lamina are determined through micromechanics using an Extended Concentric Cylinder Assemblage (ECCA) model in conjunction with the correspondence principle of viscoelasticity. Since analytical formulations are employed at the microscale, the proposed multiscale approach can efficiently predict the composite time-, temperature-, and cure-dependent responses during processing. The proposed model is employed to predict the warpage shape of an anti-symmetric laminate due to curing-induced residual stresses. Compared with other elastic processing models, the proposed processing model achieves an improved prediction of the warpage shape due to its capability to consider both curing history and stress relaxation during composite processing. © 2019
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doi:10.1016/j.compositesa.2019.105575
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Li, R; Zhang, D
A textile architecture-based hyperelastic model for rubbers reinforced by knitted fabrics Journal Article
Acta Mechanica, 230 (3), pp. 953-964, 2019.
Abstract | Links | BibTeX | Tags:
@article{Li2019953,
title = {A textile architecture-based hyperelastic model for rubbers reinforced by knitted fabrics},
author = {R Li and D Zhang},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85058648459&doi=10.1007%2fs00707-018-2276-2&partnerID=40&md5=3471331dcbca3d2953d9b25089323441},
doi = {10.1007/s00707-018-2276-2},
year = {2019},
date = {2019-01-01},
journal = {Acta Mechanica},
volume = {230},
number = {3},
pages = {953-964},
abstract = {A new anisotropic hyperelastic model has been developed to model the deformation response of a knitted-fabric-reinforced rubber composite. The composite has a sandwich structure with a fiber net layer embedded in two rubber layers. Due to the architecture of the knitted fabric, the composite demonstrates an anisotropic hyperelastic response, which is modeled through a strain energy density function that incorporates the effects of deformed rubbers and stretched fibers. The rubber is considered as a neo-Hookean material, while the knitted fabrics are modeled as cords with negligible stiffness in bending. The effect of reinforcement comes from the conservation of the total length of the fiber cords. In addition, a slack variable is proposed to account for the effect of processing-induced fabric pre-stretch or fabric slack on the resulting composite response. This novel approach enables the determination of the constitutive behavior of the composite in closed form based on the constituent rubber and fiber properties and fabric architectures. The proposed analytical model is validated through a full 3D finite element (FE) model, in which the rubber and fiber reinforcement are modeled explicitly. Since the proposed model captures the key parameters that dictate the deformation response of knitted-fabric-reinforced composites, it can be employed as an efficient modeling tool to guide the design of rubbers and fabric architectures with targeted composite performance. © 2018, Springer-Verlag GmbH Austria, part of Springer Nature.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

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A new anisotropic hyperelastic model has been developed to model the deformation response of a knitted-fabric-reinforced rubber composite. The composite has a sandwich structure with a fiber net layer embedded in two rubber layers. Due to the architecture of the knitted fabric, the composite demonstrates an anisotropic hyperelastic response, which is modeled through a strain energy density function that incorporates the effects of deformed rubbers and stretched fibers. The rubber is considered as a neo-Hookean material, while the knitted fabrics are modeled as cords with negligible stiffness in bending. The effect of reinforcement comes from the conservation of the total length of the fiber cords. In addition, a slack variable is proposed to account for the effect of processing-induced fabric pre-stretch or fabric slack on the resulting composite response. This novel approach enables the determination of the constitutive behavior of the composite in closed form based on the constituent rubber and fiber properties and fabric architectures. The proposed analytical model is validated through a full 3D finite element (FE) model, in which the rubber and fiber reinforcement are modeled explicitly. Since the proposed model captures the key parameters that dictate the deformation response of knitted-fabric-reinforced composites, it can be employed as an efficient modeling tool to guide the design of rubbers and fabric architectures with targeted composite performance. © 2018, Springer-Verlag GmbH Austria, part of Springer Nature.
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doi:10.1007/s00707-018-2276-2
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Chen, W; Zhang, D
An integrated processing and damage model for predicting failure in a curved composite beam Conference
2019.
Abstract | Links | BibTeX | Tags:
@conference{Chen2019c,
title = {An integrated processing and damage model for predicting failure in a curved composite beam},
author = {W Chen and D Zhang},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85068487020&doi=10.2514%2f6.2019-1204&partnerID=40&md5=0a24d3af174877328fe6f3dcd103f743},
doi = {10.2514/6.2019-1204},
year = {2019},
date = {2019-01-01},
journal = {AIAA Scitech 2019 Forum},
abstract = {An integrated processing-failure model was developed to predict the inter-laminar strength of a plain weave composite flange manufactured using the Resin Transfer Molding (RTM) technique. A multiscale modeling framework was established to exchange the information between different scales. At the global scale, the composite was treated as a single, homoge-neous material, and the global stress and strain fields were solved through a cure-dependent constitutive law using the homogenized composite properties. At the integration point of the homogenized model, a discrete model was created to represent the microstructure of the textile composite, and the cure-induced local stress field was calculated by imposing the strain history obtained from the homogenized model on the boundaries of the discrete model. After the curing process, the discrete model was virtually loaded, and the Smear Crack Approach (SCA) was employed to predict the failure response of the matrix. The current study shows that the curing-induced residual stress has little impact on the composite inter-laminar strength. However, the strength can be reduced by 35% with 1% void content. © 2019, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

Close
An integrated processing-failure model was developed to predict the inter-laminar strength of a plain weave composite flange manufactured using the Resin Transfer Molding (RTM) technique. A multiscale modeling framework was established to exchange the information between different scales. At the global scale, the composite was treated as a single, homoge-neous material, and the global stress and strain fields were solved through a cure-dependent constitutive law using the homogenized composite properties. At the integration point of the homogenized model, a discrete model was created to represent the microstructure of the textile composite, and the cure-induced local stress field was calculated by imposing the strain history obtained from the homogenized model on the boundaries of the discrete model. After the curing process, the discrete model was virtually loaded, and the Smear Crack Approach (SCA) was employed to predict the failure response of the matrix. The current study shows that the curing-induced residual stress has little impact on the composite inter-laminar strength. However, the strength can be reduced by 35% with 1% void content. © 2019, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.
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doi:10.2514/6.2019-1204
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Roach, J; Chen, W; Zhang, D
Progressive failure prediction of an l-shaped composite flange subjected to flexural loading Conference
2019.
Abstract | Links | BibTeX | Tags:
@conference{Roach2019,
title = {Progressive failure prediction of an l-shaped composite flange subjected to flexural loading},
author = {J Roach and W Chen and D Zhang},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85068931739&doi=10.2514%2f6.2019-2269&partnerID=40&md5=4875e2fac54f66a94f1384f5b68fd608},
doi = {10.2514/6.2019-2269},
year = {2019},
date = {2019-01-01},
journal = {AIAA Scitech 2019 Forum},
abstract = {This work focuses on the development of a reliable failure model to predict the damage evolution of an angled composite flange under 4-point bending. The experiment was consistent with the American Society for Testing and Materials (ASTM) D6415 specification. Specimens were fabricated and tested according to the standard, and an analytical prediction of the through-thickness, or radial, stress state was obtained. This information was then used to support a progressive failure simulation using a User Defined Material (UMAT) within the Finite Element Method (FEM) framework. Particularly, the through-thickness damage progression is examined and it is shown that a good correlation for both load-deflection, damage type, and damage location is obtained through the use of the Smeared Crack Approach (SCA) [1], implemented through an Abaqus UMAT in a FEM simulation. � 2019 by German Aerospace Center (DLR). Published by the American Institute of Aeronautics and Astronautics, Inc.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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This work focuses on the development of a reliable failure model to predict the damage evolution of an angled composite flange under 4-point bending. The experiment was consistent with the American Society for Testing and Materials (ASTM) D6415 specification. Specimens were fabricated and tested according to the standard, and an analytical prediction of the through-thickness, or radial, stress state was obtained. This information was then used to support a progressive failure simulation using a User Defined Material (UMAT) within the Finite Element Method (FEM) framework. Particularly, the through-thickness damage progression is examined and it is shown that a good correlation for both load-deflection, damage type, and damage location is obtained through the use of the Smeared Crack Approach (SCA) [1], implemented through an Abaqus UMAT in a FEM simulation. � 2019 by German Aerospace Center (DLR). Published by the American Institute of Aeronautics and Astronautics, Inc.
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doi:10.2514/6.2019-2269
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Pham, D C; Lua, J; Sun, H; Zhang, D
A three-dimensional progressive damage model for drop-weight impact and compression after impact Journal Article
Journal of Composite Materials, 2019.
Abstract | Links | BibTeX | Tags:
@article{Pham2019,
title = {A three-dimensional progressive damage model for drop-weight impact and compression after impact},
author = {D C Pham and J Lua and H Sun and D Zhang},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85068361496&doi=10.1177%2f0021998319859050&partnerID=40&md5=b2b6ea78739bbe20817f88ea7c82a4d1},
doi = {10.1177/0021998319859050},
year = {2019},
date = {2019-01-01},
journal = {Journal of Composite Materials},
abstract = {In this paper, an enhanced three-dimensional continuum damage mechanics model is applied to predict the drop-weight impact response and compression after impact failure of a fiber-reinforced polymer composite specimen. The three-dimensional progressive damage model incorporates a three-dimensional maximum stress criterion to predict the intra-ply damage initiation, followed by a fracture-energy-based smeared crack model to capture the post-peak softening behavior. Driven by the dominant through-the-thickness failure under impact loading, a three-dimensional continuum damage model is implemented for the three-dimensional solid element via its explicit material model for Abaqus (VUMAT) to capture the effect of three-dimensional stress state and the interaction of matrix cracking and delamination. Abaqus’ restart analysis capability is used to activate the compression after impact analysis using the final damage state from the dynamic impact analysis. Both the dynamic failure and the compression after impact are demonstrated via a suite of verification examples followed by the sensitivity analysis using distinct impact configurations. The predictive capability of the proposed three-dimensional damage model is first verified using a static open-hole tension test. Applications of the damage model are then demonstrated for simulations of the dynamic drop-weight tests and compression after impact tests. A comparative study on the developed method is performed using the results predicted from the open-source CompDam. A sensitivity study is also performed to demonstrate the impact energy-dependent failure mode. The proposed model has shown its advantages in performing a quick assessment of impact damage and its effects on the residual compressive strength. © The Author(s) 2019.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

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In this paper, an enhanced three-dimensional continuum damage mechanics model is applied to predict the drop-weight impact response and compression after impact failure of a fiber-reinforced polymer composite specimen. The three-dimensional progressive damage model incorporates a three-dimensional maximum stress criterion to predict the intra-ply damage initiation, followed by a fracture-energy-based smeared crack model to capture the post-peak softening behavior. Driven by the dominant through-the-thickness failure under impact loading, a three-dimensional continuum damage model is implemented for the three-dimensional solid element via its explicit material model for Abaqus (VUMAT) to capture the effect of three-dimensional stress state and the interaction of matrix cracking and delamination. Abaqus’ restart analysis capability is used to activate the compression after impact analysis using the final damage state from the dynamic impact analysis. Both the dynamic failure and the compression after impact are demonstrated via a suite of verification examples followed by the sensitivity analysis using distinct impact configurations. The predictive capability of the proposed three-dimensional damage model is first verified using a static open-hole tension test. Applications of the damage model are then demonstrated for simulations of the dynamic drop-weight tests and compression after impact tests. A comparative study on the developed method is performed using the results predicted from the open-source CompDam. A sensitivity study is also performed to demonstrate the impact energy-dependent failure mode. The proposed model has shown its advantages in performing a quick assessment of impact damage and its effects on the residual compressive strength. © The Author(s) 2019.
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doi:10.1177/0021998319859050
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2018

Chen, W; Zhang, D
A micromechanics-based processing model for predicting spring-in angle of a resin transfer molded composite flange Conference
2018.
Abstract | Links | BibTeX | Tags:
@conference{Chen2018b,
title = {A micromechanics-based processing model for predicting spring-in angle of a resin transfer molded composite flange},
author = {W Chen and D Zhang},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85061750108&partnerID=40&md5=8d726e035058b0d3685ca7479ee7c8ad},
year = {2018},
date = {2018-01-01},
journal = {CAMX 2018 - Composites and Advanced Materials Expo},
abstract = {An integrated composite processing model has been developed to predict the spring-in angle of an L-shaped composite flange manufactured using a Resin Transfer Molding (RTM) technique. The curved composite laminate consists of 16 plies of plain-weave laminae made of AS-4 carbon fibers and EPON 862 epoxy. The curing and demolding processes of the composite are simulated using heat transfer and stress analyses in a 3D Finite Element (FE) modeling framework that incorporates resin cure kinetics, cure-dependent resin properties, and textile architecture-based composite constitutive relations. In this study, the composite is modeled as discrete layers of homogeneous, orthotropic material using the FE analysis, while the cure-dependent constitutive relation is determined based on the microstructure of the textile composite. An Extended Concentric Cylinder Assemblage (ECCA) micromechanics is used to compute the thermo-mechanical properties of each fiber tow, and the results are subsequently used to compute the effective composite properties based on the strain energy equivalence. By incorporating the resin cure kinetics model and cure-dependent composite thermal properties into the heat transfer analysis, the evolution of temperature and Degree Of Cure (DOC) during processing can be solved, which are subsequently used as predefined fields in the stress analysis to predict the residual stress development during cure. Both thermal strains and chemical strains due to cure shrinkage are incorporated into the cure-dependent composite constitutive law. Finally, the demolding and cutting processes are simulated to predict the spring-in angle of the L-shaped flange after the manufacturing cycle. The proposed processing model is validated by comparing the predicted spring-in angles against the experimental measurements. © 2018. Used by CAMX The Composites and Advanced Materials Expo. CAMX Conference Proceedings. Dallas, TX.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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An integrated composite processing model has been developed to predict the spring-in angle of an L-shaped composite flange manufactured using a Resin Transfer Molding (RTM) technique. The curved composite laminate consists of 16 plies of plain-weave laminae made of AS-4 carbon fibers and EPON 862 epoxy. The curing and demolding processes of the composite are simulated using heat transfer and stress analyses in a 3D Finite Element (FE) modeling framework that incorporates resin cure kinetics, cure-dependent resin properties, and textile architecture-based composite constitutive relations. In this study, the composite is modeled as discrete layers of homogeneous, orthotropic material using the FE analysis, while the cure-dependent constitutive relation is determined based on the microstructure of the textile composite. An Extended Concentric Cylinder Assemblage (ECCA) micromechanics is used to compute the thermo-mechanical properties of each fiber tow, and the results are subsequently used to compute the effective composite properties based on the strain energy equivalence. By incorporating the resin cure kinetics model and cure-dependent composite thermal properties into the heat transfer analysis, the evolution of temperature and Degree Of Cure (DOC) during processing can be solved, which are subsequently used as predefined fields in the stress analysis to predict the residual stress development during cure. Both thermal strains and chemical strains due to cure shrinkage are incorporated into the cure-dependent composite constitutive law. Finally, the demolding and cutting processes are simulated to predict the spring-in angle of the L-shaped flange after the manufacturing cycle. The proposed processing model is validated by comparing the predicted spring-in angles against the experimental measurements. © 2018. Used by CAMX The Composites and Advanced Materials Expo. CAMX Conference Proceedings. Dallas, TX.
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Chen, W; Zhang, D
A multi-physics processing model for predicting residual stress development in unidirectional fiber-reinforced composites Conference
(210049), 2018.
Abstract | Links | BibTeX | Tags:
@conference{Chen2018d,
title = {A multi-physics processing model for predicting residual stress development in unidirectional fiber-reinforced composites},
author = {W Chen and D Zhang},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85044596084&doi=10.2514%2f6.2018-0901&partnerID=40&md5=f232f25a916c62a1a76a2ebd24a4caf9},
doi = {10.2514/6.2018-0901},
year = {2018},
date = {2018-01-01},
journal = {AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2018},
number = {210049},
abstract = {A novel cure cycle is proposed with view to reducing the residual stress buildup in composites during manufacturing processes. The key is to relax the residual stress when the resin is under the viscoelastic deformation region. This requires the design of a cure cycle that is based on the evolution of the degree of cure (DOC) predicted by the resin cure kinetics. In this paper, a non-symmetric composite was used to illustrate the curing-induced residual stress. A multi-physics and multiscale composite processing model was employed to predict the residual stress development. At the macroscale, the composite was modeled as discrete layers of homogeneous, transversely isotropic laminae, while micromechanics was implemented at the subscale to compute the effective lamina responses based on the fiber and matrix properties through an extended cylinder assemblage (ECCA) model. The composite temperature and DOC distributions were solved by incorporating resin cure kinetics into heat transfer analysis, which were used in the subsequent stress analysis to determine the cure-dependent composite responses, including cure-dependent modulus, thermal strain, and chemical shrinkage. According the output of the processing model, the residual stress inside the panel manufactured using the proposed cure cycle was significantly smaller than that of the panel cured under the conventional cure cycle, which agrees with the experimental result. © 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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A novel cure cycle is proposed with view to reducing the residual stress buildup in composites during manufacturing processes. The key is to relax the residual stress when the resin is under the viscoelastic deformation region. This requires the design of a cure cycle that is based on the evolution of the degree of cure (DOC) predicted by the resin cure kinetics. In this paper, a non-symmetric composite was used to illustrate the curing-induced residual stress. A multi-physics and multiscale composite processing model was employed to predict the residual stress development. At the macroscale, the composite was modeled as discrete layers of homogeneous, transversely isotropic laminae, while micromechanics was implemented at the subscale to compute the effective lamina responses based on the fiber and matrix properties through an extended cylinder assemblage (ECCA) model. The composite temperature and DOC distributions were solved by incorporating resin cure kinetics into heat transfer analysis, which were used in the subsequent stress analysis to determine the cure-dependent composite responses, including cure-dependent modulus, thermal strain, and chemical shrinkage. According the output of the processing model, the residual stress inside the panel manufactured using the proposed cure cycle was significantly smaller than that of the panel cured under the conventional cure cycle, which agrees with the experimental result. © 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.
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doi:10.2514/6.2018-0901
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Chen, W; Li, C; Zhang, D
A multi-physics processing model for predicting sping-in angle of a resin transfer molded composite flange Conference
(210049), 2018.
Abstract | Links | BibTeX | Tags:
@conference{Chen2018e,
title = {A multi-physics processing model for predicting sping-in angle of a resin transfer molded composite flange},
author = {W Chen and C Li and D Zhang},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85044619580&doi=10.2514%2f6.2018-1898&partnerID=40&md5=d066a2f9a5457d873345b3b95bbce956},
doi = {10.2514/6.2018-1898},
year = {2018},
date = {2018-01-01},
journal = {AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2018},
number = {210049},
abstract = {An integrated composite processing model has been developed to predict the springin angle of an L-shaped composite flange manufactured using a Resin Transfer Molding (RTM) technique. The curved composite laminate consists of 16 plies of plain-weave laminae made of AS-4 carbon fibers and EPON 862 epoxy. The curing and demolding processes of the composite are simulated using heat transfer and stress analyses in a 3D finite element (FE) modeling framework that incorporates resin cure kinetics, cure-dependent resin properties, and textile architecture-based composite constitutive relations. In this study, the composite is modeled as discrete layers of homogeneous, orthotropic material using the finite element analysis (FEA), while the cure-dependent constitutive relation is determined based on the microstructure of the textile composite. An extended concentric cylinder assemblage (ECCA) micromechanics is used to compute the thermo-mechanical properties of each fiber tow, and the results are subsequently used to compute the effective composite properties based on the strain energy equivalence. By incorporating the resin cure kinetics model and cure-dependent composite thermal properties into the heat transfer analysis, the evolution of temperature and degree of cure (DOC) during processing can be solved, which are subsequently used as predefined fields in the stress analysis to predict the residual stress development during cure. Both thermal strains and chemical strains due to cure shrinkage are incorporated into the cure-dependent composite constitutive law. Finally, the demolding and cutting processes are simulated to predict the spring-in angle of the Lshaped flange after the manufacturing cycle. The proposed processing model is validated by comparing the predicted spring-in angles against the experimental measurements. © 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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An integrated composite processing model has been developed to predict the springin angle of an L-shaped composite flange manufactured using a Resin Transfer Molding (RTM) technique. The curved composite laminate consists of 16 plies of plain-weave laminae made of AS-4 carbon fibers and EPON 862 epoxy. The curing and demolding processes of the composite are simulated using heat transfer and stress analyses in a 3D finite element (FE) modeling framework that incorporates resin cure kinetics, cure-dependent resin properties, and textile architecture-based composite constitutive relations. In this study, the composite is modeled as discrete layers of homogeneous, orthotropic material using the finite element analysis (FEA), while the cure-dependent constitutive relation is determined based on the microstructure of the textile composite. An extended concentric cylinder assemblage (ECCA) micromechanics is used to compute the thermo-mechanical properties of each fiber tow, and the results are subsequently used to compute the effective composite properties based on the strain energy equivalence. By incorporating the resin cure kinetics model and cure-dependent composite thermal properties into the heat transfer analysis, the evolution of temperature and degree of cure (DOC) during processing can be solved, which are subsequently used as predefined fields in the stress analysis to predict the residual stress development during cure. Both thermal strains and chemical strains due to cure shrinkage are incorporated into the cure-dependent composite constitutive law. Finally, the demolding and cutting processes are simulated to predict the spring-in angle of the Lshaped flange after the manufacturing cycle. The proposed processing model is validated by comparing the predicted spring-in angles against the experimental measurements. © 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.
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doi:10.2514/6.2018-1898
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Pham, D C; Cui, X; Lua, J; Zhang, D
A continuum damage description for a discrete crack modeling approach for delamination migration in composite laminates Conference
(210049), 2018.
Abstract | Links | BibTeX | Tags:
@conference{Pham2018b,
title = {A continuum damage description for a discrete crack modeling approach for delamination migration in composite laminates},
author = {D C Pham and X Cui and J Lua and D Zhang},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85044569315&doi=10.2514%2f6.2018-1222&partnerID=40&md5=58216cfac9f11a3d294590ed79dbc0b4},
doi = {10.2514/6.2018-1222},
year = {2018},
date = {2018-01-01},
journal = {AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2018},
number = {210049},
abstract = {A three-dimensional discrete crack embedded within a continuum damage mechanics (CDM) model is developed for an effective characterization of delamination migration in composite laminates subjected to static loading. 3D Hashin failure criterion is implemented for damage initiation prediction under a 3D stress state. Matrix crack initiation criteria coupled with a maximum principal stress direction are employed to determine the location and orientation of a discrete matrix crack within an element. Given the orientation of the initiated matrix crack, the resulting stiffness degradation is characterized in the local principal stress coordinate system and an energy driven failure mechanism is included to capture the crack growth. By coupling the cohesive model for delamination and the discrete damage embedded CDM for matrix cracking, their synergistic interaction can be captured during the simulation of the delamination migration. The predictive capability of the enhanced modeling strategy is examined through simulation of a delamination migration in a cross-ply tap laminate. The predicted results are compared with the experimental data published by NASA and good agreements are achieved in terms of load displacement curve and the location of crack branching. © 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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A three-dimensional discrete crack embedded within a continuum damage mechanics (CDM) model is developed for an effective characterization of delamination migration in composite laminates subjected to static loading. 3D Hashin failure criterion is implemented for damage initiation prediction under a 3D stress state. Matrix crack initiation criteria coupled with a maximum principal stress direction are employed to determine the location and orientation of a discrete matrix crack within an element. Given the orientation of the initiated matrix crack, the resulting stiffness degradation is characterized in the local principal stress coordinate system and an energy driven failure mechanism is included to capture the crack growth. By coupling the cohesive model for delamination and the discrete damage embedded CDM for matrix cracking, their synergistic interaction can be captured during the simulation of the delamination migration. The predictive capability of the enhanced modeling strategy is examined through simulation of a delamination migration in a cross-ply tap laminate. The predicted results are compared with the experimental data published by NASA and good agreements are achieved in terms of load displacement curve and the location of crack branching. © 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.
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doi:10.2514/6.2018-1222
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Chen, W; Zhang, D
A micromechanics-based processing model for predicting residual stress in fiber-reinforced polymer matrix composites Journal Article
Composite Structures, 204 , pp. 153-166, 2018.
Abstract | Links | BibTeX | Tags:
@article{Chen2018153,
title = {A micromechanics-based processing model for predicting residual stress in fiber-reinforced polymer matrix composites},
author = {W Chen and D Zhang},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85050624281&doi=10.1016%2fj.compstruct.2018.07.016&partnerID=40&md5=1fc3c8a541a15af29a3673007341f8ba},
doi = {10.1016/j.compstruct.2018.07.016},
year = {2018},
date = {2018-01-01},
journal = {Composite Structures},
volume = {204},
pages = {153-166},
abstract = {An experimentally validated, multi-physics and multi-scale processing model was developed to predict the residual stress buildup in a polymer matrix composite during manufacturing. At the macroscale, the composite was modeled as discrete layers of homogeneous, transversely isotropic laminae, while micromechanics was implemented at the subscale to compute the effective lamina responses based on the fiber and matrix properties through an Extended Concentric Cylinder Assemblage (ECCA) model. The composite temperature and Degree of Cure (DOC) distributions were solved by incorporating resin cure kinetics into heat transfer analysis, which were used in the subsequent stress analysis to determine the cure-dependent composite responses, including cure-dependent modulus, thermal strain, and chemical shrinkage. This integrated processing model was applied to predict the cure-induced warpage of a non-symmetric laminate. The proposed model, which incorporates resin cure kinetics, cure-dependent constitutive law, and tool-part interaction, demonstrates good agreement with the experiment on the prediction of the warpage curvatures. © 2018 Elsevier Ltd},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

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An experimentally validated, multi-physics and multi-scale processing model was developed to predict the residual stress buildup in a polymer matrix composite during manufacturing. At the macroscale, the composite was modeled as discrete layers of homogeneous, transversely isotropic laminae, while micromechanics was implemented at the subscale to compute the effective lamina responses based on the fiber and matrix properties through an Extended Concentric Cylinder Assemblage (ECCA) model. The composite temperature and Degree of Cure (DOC) distributions were solved by incorporating resin cure kinetics into heat transfer analysis, which were used in the subsequent stress analysis to determine the cure-dependent composite responses, including cure-dependent modulus, thermal strain, and chemical shrinkage. This integrated processing model was applied to predict the cure-induced warpage of a non-symmetric laminate. The proposed model, which incorporates resin cure kinetics, cure-dependent constitutive law, and tool-part interaction, demonstrates good agreement with the experiment on the prediction of the warpage curvatures. © 2018 Elsevier Ltd
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doi:10.1016/j.compstruct.2018.07.016
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Heimbach, B; Tonyali, B; Zhang, D; Wei, M
High performance resorbable composites for load-bearing bone fixation devices Journal Article
Journal of the Mechanical Behavior of Biomedical Materials, 81 , pp. 1-9, 2018.
Abstract | Links | BibTeX | Tags:
@article{Heimbach20181,
title = {High performance resorbable composites for load-bearing bone fixation devices},
author = {B Heimbach and B Tonyali and D Zhang and M Wei},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85042225085&doi=10.1016%2fj.jmbbm.2018.01.031&partnerID=40&md5=131a091248294549a10c11f4fb212cc7},
doi = {10.1016/j.jmbbm.2018.01.031},
year = {2018},
date = {2018-01-01},
journal = {Journal of the Mechanical Behavior of Biomedical Materials},
volume = {81},
pages = {1-9},
abstract = {Bone fractures are some of the most common injuries annually, and many require a fixation device to help properly heal. The present study focuses on developing a bioresorbable composite that has high strength and stiffness for bone fixation applications. To achieve this, a design of experiments was performed, testing the effect of long fiber reinforcement type, matrix type, matrix amount, and particle reinforcement amount on the flexural properties of the composite. Based on these results, the ideal resorbable long fiber reinforcement, particle reinforcement, and matrix material are degummed silk fibroin, hydroxyapatite, and polylactic acid, respectively. Through further optimizations of the particle reinforcement phase a flexural modulus and strength of 13.7 GPa and 437 MPa, respectively, was achieved. Both values are among the highest found in literature, with the strength far exceeding the requirement for a fixation device and the highest for such a bioresorbable composite material, showing great promise for use as a bioresorbable fixation device. © 2018},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

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Bone fractures are some of the most common injuries annually, and many require a fixation device to help properly heal. The present study focuses on developing a bioresorbable composite that has high strength and stiffness for bone fixation applications. To achieve this, a design of experiments was performed, testing the effect of long fiber reinforcement type, matrix type, matrix amount, and particle reinforcement amount on the flexural properties of the composite. Based on these results, the ideal resorbable long fiber reinforcement, particle reinforcement, and matrix material are degummed silk fibroin, hydroxyapatite, and polylactic acid, respectively. Through further optimizations of the particle reinforcement phase a flexural modulus and strength of 13.7 GPa and 437 MPa, respectively, was achieved. Both values are among the highest found in literature, with the strength far exceeding the requirement for a fixation device and the highest for such a bioresorbable composite material, showing great promise for use as a bioresorbable fixation device. © 2018
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Chen, W; Zhang, D
A micromechanics-based processing model for predicting spring-in angle of a resin transfer molded composite flange Conference
2018.
Abstract | Links | BibTeX | Tags:
@conference{Chen2018e,
title = {A micromechanics-based processing model for predicting spring-in angle of a resin transfer molded composite flange},
author = {W Chen and D Zhang},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85061750108&partnerID=40&md5=8d726e035058b0d3685ca7479ee7c8ad},
year = {2018},
date = {2018-01-01},
journal = {CAMX 2018 - Composites and Advanced Materials Expo},
abstract = {An integrated composite processing model has been developed to predict the spring-in angle of an L-shaped composite flange manufactured using a Resin Transfer Molding (RTM) technique. The curved composite laminate consists of 16 plies of plain-weave laminae made of AS-4 carbon fibers and EPON 862 epoxy. The curing and demolding processes of the composite are simulated using heat transfer and stress analyses in a 3D Finite Element (FE) modeling framework that incorporates resin cure kinetics, cure-dependent resin properties, and textile architecture-based composite constitutive relations. In this study, the composite is modeled as discrete layers of homogeneous, orthotropic material using the FE analysis, while the cure-dependent constitutive relation is determined based on the microstructure of the textile composite. An Extended Concentric Cylinder Assemblage (ECCA) micromechanics is used to compute the thermo-mechanical properties of each fiber tow, and the results are subsequently used to compute the effective composite properties based on the strain energy equivalence. By incorporating the resin cure kinetics model and cure-dependent composite thermal properties into the heat transfer analysis, the evolution of temperature and Degree Of Cure (DOC) during processing can be solved, which are subsequently used as predefined fields in the stress analysis to predict the residual stress development during cure. Both thermal strains and chemical strains due to cure shrinkage are incorporated into the cure-dependent composite constitutive law. Finally, the demolding and cutting processes are simulated to predict the spring-in angle of the L-shaped flange after the manufacturing cycle. The proposed processing model is validated by comparing the predicted spring-in angles against the experimental measurements. © 2018. Used by CAMX The Composites and Advanced Materials Expo. CAMX Conference Proceedings. Dallas, TX.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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An integrated composite processing model has been developed to predict the spring-in angle of an L-shaped composite flange manufactured using a Resin Transfer Molding (RTM) technique. The curved composite laminate consists of 16 plies of plain-weave laminae made of AS-4 carbon fibers and EPON 862 epoxy. The curing and demolding processes of the composite are simulated using heat transfer and stress analyses in a 3D Finite Element (FE) modeling framework that incorporates resin cure kinetics, cure-dependent resin properties, and textile architecture-based composite constitutive relations. In this study, the composite is modeled as discrete layers of homogeneous, orthotropic material using the FE analysis, while the cure-dependent constitutive relation is determined based on the microstructure of the textile composite. An Extended Concentric Cylinder Assemblage (ECCA) micromechanics is used to compute the thermo-mechanical properties of each fiber tow, and the results are subsequently used to compute the effective composite properties based on the strain energy equivalence. By incorporating the resin cure kinetics model and cure-dependent composite thermal properties into the heat transfer analysis, the evolution of temperature and Degree Of Cure (DOC) during processing can be solved, which are subsequently used as predefined fields in the stress analysis to predict the residual stress development during cure. Both thermal strains and chemical strains due to cure shrinkage are incorporated into the cure-dependent composite constitutive law. Finally, the demolding and cutting processes are simulated to predict the spring-in angle of the L-shaped flange after the manufacturing cycle. The proposed processing model is validated by comparing the predicted spring-in angles against the experimental measurements. © 2018. Used by CAMX The Composites and Advanced Materials Expo. CAMX Conference Proceedings. Dallas, TX.
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Li, R; Zhang, D
A visco-hyperelastic constitutive model for fiber-reinforced rubber composites Conference
5 , 2018.
Abstract | Links | BibTeX | Tags:
@conference{Li20182957,
title = {A visco-hyperelastic constitutive model for fiber-reinforced rubber composites},
author = {R Li and D Zhang},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85059399209&partnerID=40&md5=e8008748e769b68336b468966967b6ac},
year = {2018},
date = {2018-01-01},
journal = {33rd Technical Conference of the American Society for Composites 2018},
volume = {5},
pages = {2957-2965},
abstract = {The focus of this study is to develop a fabric architecture-based constitutive model to predict the time-dependent mechanical behavior of a knitted-fiber-reinforced rubber. The rubber composite has a sandwich structure consisting of a fabric layer embedded into two rubber layers. Here, the rubber is a visco-hyperelastic material, while the fibers tend to be linear elastic with little extensibility. The rubber composite shows a nonlinear, anisotropic constitutive response under finite strawin and stress relaxation under constant deformation, which is modeled through a novel strain energy function. The anisotropic behavior comes from the conservation of the total length of the fiber cords. The strain energy function comprises two parts to define both the static behavior and the time-dependent response. This approach enables the determination of the constitutive behavior of the rubber composite based on the constituent material properties and geometry, such as the viscoelastic properties of the rubber and the fiber architecture. The proposed strain-energy-based approach is validated through a full Finite Element (FE) model on basis of a Representative Unit Cell (RUC), in which the textile reinforcement and rubber layers are modeled explicitly. © 2018 33rd Technical Conference of the American Society for Composites 2018. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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The focus of this study is to develop a fabric architecture-based constitutive model to predict the time-dependent mechanical behavior of a knitted-fiber-reinforced rubber. The rubber composite has a sandwich structure consisting of a fabric layer embedded into two rubber layers. Here, the rubber is a visco-hyperelastic material, while the fibers tend to be linear elastic with little extensibility. The rubber composite shows a nonlinear, anisotropic constitutive response under finite strawin and stress relaxation under constant deformation, which is modeled through a novel strain energy function. The anisotropic behavior comes from the conservation of the total length of the fiber cords. The strain energy function comprises two parts to define both the static behavior and the time-dependent response. This approach enables the determination of the constitutive behavior of the rubber composite based on the constituent material properties and geometry, such as the viscoelastic properties of the rubber and the fiber architecture. The proposed strain-energy-based approach is validated through a full Finite Element (FE) model on basis of a Representative Unit Cell (RUC), in which the textile reinforcement and rubber layers are modeled explicitly. © 2018 33rd Technical Conference of the American Society for Composites 2018. All rights reserved.
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Chen, W; Zhang, D
A Multi-Scale Viscoelastic Processing Model for Predicting Residual Stress Buildup in Thermoset Composites Conference
1 , 2018.
Abstract | Links | BibTeX | Tags:
@conference{Chen2018329,
title = {A Multi-Scale Viscoelastic Processing Model for Predicting Residual Stress Buildup in Thermoset Composites},
author = {W Chen and D Zhang},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85059315582&partnerID=40&md5=a5ddd8e3311ce4201bba97f774cc01a6},
year = {2018},
date = {2018-01-01},
journal = {33rd Technical Conference of the American Society for Composites 2018},
volume = {1},
pages = {329-345},
abstract = {The focus of this paper is to develop an experimentally validated viscoelastic processing model to predict the residual stress buildup and stress relaxation in fiber reinforced composites in the curing process. Providing elastic properties of carbon fiber and cure-dependent viscoelastic properties of the resin, the effective viscoelastic properties of the composite are calculated based on the correspondence principle of viscoelasticity, and the Rule of Mixtures (ROM) is used to compute the composite properties in the frequency domain. The computed composite properties are then incorporated in a viscoelastic constitutive law to capture the cure-induced residual stress. The accuracy of our proposed processing model is assessed by comparing the deformed shape of the composite part predicted by the finite element model to that of a laminate fabricated using Vacuum Assisted Resin Transfer Molding (VARTM) technique. Compared with our previous elastic models, the proposed viscoelastic processing model is able to provide more accurate predictions on the cure-induced warpage of the composite part after demolding. © Copyright© (2018) by DEStech Publications, Inc. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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The focus of this paper is to develop an experimentally validated viscoelastic processing model to predict the residual stress buildup and stress relaxation in fiber reinforced composites in the curing process. Providing elastic properties of carbon fiber and cure-dependent viscoelastic properties of the resin, the effective viscoelastic properties of the composite are calculated based on the correspondence principle of viscoelasticity, and the Rule of Mixtures (ROM) is used to compute the composite properties in the frequency domain. The computed composite properties are then incorporated in a viscoelastic constitutive law to capture the cure-induced residual stress. The accuracy of our proposed processing model is assessed by comparing the deformed shape of the composite part predicted by the finite element model to that of a laminate fabricated using Vacuum Assisted Resin Transfer Molding (VARTM) technique. Compared with our previous elastic models, the proposed viscoelastic processing model is able to provide more accurate predictions on the cure-induced warpage of the composite part after demolding. © Copyright© (2018) by DEStech Publications, Inc. All rights reserved.
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Chen, W; Zhang, D
A multi-physics processing model for predicting residual stress development in unidirectional fiber-reinforced composites Conference
(210049), 2018.
Abstract | Links | BibTeX | Tags:
@conference{Chen2018g,
title = {A multi-physics processing model for predicting residual stress development in unidirectional fiber-reinforced composites},
author = {W Chen and D Zhang},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85044596084&doi=10.2514%2f6.2018-0901&partnerID=40&md5=f232f25a916c62a1a76a2ebd24a4caf9},
doi = {10.2514/6.2018-0901},
year = {2018},
date = {2018-01-01},
journal = {AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2018},
number = {210049},
abstract = {A novel cure cycle is proposed with view to reducing the residual stress buildup in composites during manufacturing processes. The key is to relax the residual stress when the resin is under the viscoelastic deformation region. This requires the design of a cure cycle that is based on the evolution of the degree of cure (DOC) predicted by the resin cure kinetics. In this paper, a non-symmetric composite was used to illustrate the curing-induced residual stress. A multi-physics and multiscale composite processing model was employed to predict the residual stress development. At the macroscale, the composite was modeled as discrete layers of homogeneous, transversely isotropic laminae, while micromechanics was implemented at the subscale to compute the effective lamina responses based on the fiber and matrix properties through an extended cylinder assemblage (ECCA) model. The composite temperature and DOC distributions were solved by incorporating resin cure kinetics into heat transfer analysis, which were used in the subsequent stress analysis to determine the cure-dependent composite responses, including cure-dependent modulus, thermal strain, and chemical shrinkage. According the output of the processing model, the residual stress inside the panel manufactured using the proposed cure cycle was significantly smaller than that of the panel cured under the conventional cure cycle, which agrees with the experimental result. © 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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A novel cure cycle is proposed with view to reducing the residual stress buildup in composites during manufacturing processes. The key is to relax the residual stress when the resin is under the viscoelastic deformation region. This requires the design of a cure cycle that is based on the evolution of the degree of cure (DOC) predicted by the resin cure kinetics. In this paper, a non-symmetric composite was used to illustrate the curing-induced residual stress. A multi-physics and multiscale composite processing model was employed to predict the residual stress development. At the macroscale, the composite was modeled as discrete layers of homogeneous, transversely isotropic laminae, while micromechanics was implemented at the subscale to compute the effective lamina responses based on the fiber and matrix properties through an extended cylinder assemblage (ECCA) model. The composite temperature and DOC distributions were solved by incorporating resin cure kinetics into heat transfer analysis, which were used in the subsequent stress analysis to determine the cure-dependent composite responses, including cure-dependent modulus, thermal strain, and chemical shrinkage. According the output of the processing model, the residual stress inside the panel manufactured using the proposed cure cycle was significantly smaller than that of the panel cured under the conventional cure cycle, which agrees with the experimental result. © 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.
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Pham, D C; Lua, J; Zhang, D
3D progressive failure modeling of drop-weight impact on composite laminates Conference
1 , 2018.
Abstract | Links | BibTeX | Tags:
@conference{Pham20181,
title = {3D progressive failure modeling of drop-weight impact on composite laminates},
author = {D C Pham and J Lua and D Zhang},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85059327690&partnerID=40&md5=0b0dd4bba420d227a4547f138640cfd6},
year = {2018},
date = {2018-01-01},
journal = {33rd Technical Conference of the American Society for Composites 2018},
volume = {1},
pages = {1-11},
abstract = {Composite laminates are susceptible to out-of-plane impact loads due to the lack of reinforcement in the through-thickness direction. Unlike the localized damage induced by a high velocity impact where the incident energy is dissipated near a contact area, low velocity impact damage involves multiple failure mechanisms such as matrix cracking, fiber breakage, and widespread interface delaminations. Depending on the extent of damage, significant reduction in the load-bearing capability of the structure has been observed. The prediction of composite impact damage resistance by a reliable progressive damage analysis tool is essential to reduce intensive and expensive certification tests at structural level. In this work, an enhanced explicit 3D damage model is implemented via VUMAT in Abaqus to perform a dropweight impact simulation of a [454/04/-454/904]s Hexply AS4/8552 composite laminate. The impact-induced damage and its extent are captured by a 3D Continuum Damage Model (CDM) coupled with an energy driven failure mechanism. The developed module provides a unified solution process for the impact response prediction followed by the residual strength prediction under compression within an explicit solver. Two examples are selected to demonstrate the capability of the progressive failure analysis under dynamic and static loading: 1) a drop-weight test; and 2) an open-hole tension test. Numerical predictions from the developed VUMAT are compared with the test data and predictions using the open source CompDam code developed by NASA. © Copyright© (2018) by DEStech Publications, Inc. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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Composite laminates are susceptible to out-of-plane impact loads due to the lack of reinforcement in the through-thickness direction. Unlike the localized damage induced by a high velocity impact where the incident energy is dissipated near a contact area, low velocity impact damage involves multiple failure mechanisms such as matrix cracking, fiber breakage, and widespread interface delaminations. Depending on the extent of damage, significant reduction in the load-bearing capability of the structure has been observed. The prediction of composite impact damage resistance by a reliable progressive damage analysis tool is essential to reduce intensive and expensive certification tests at structural level. In this work, an enhanced explicit 3D damage model is implemented via VUMAT in Abaqus to perform a dropweight impact simulation of a [454/04/-454/904]s Hexply AS4/8552 composite laminate. The impact-induced damage and its extent are captured by a 3D Continuum Damage Model (CDM) coupled with an energy driven failure mechanism. The developed module provides a unified solution process for the impact response prediction followed by the residual strength prediction under compression within an explicit solver. Two examples are selected to demonstrate the capability of the progressive failure analysis under dynamic and static loading: 1) a drop-weight test; and 2) an open-hole tension test. Numerical predictions from the developed VUMAT are compared with the test data and predictions using the open source CompDam code developed by NASA. © Copyright© (2018) by DEStech Publications, Inc. All rights reserved.
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Roach, J; Chen, W; Zhang, D
Effects of manufacturing-induced residual stress on the strength of an L-shaped laminated textile composite flange Conference
1 , 2018.
Abstract | Links | BibTeX | Tags:
@conference{Roach2018111,
title = {Effects of manufacturing-induced residual stress on the strength of an L-shaped laminated textile composite flange},
author = {J Roach and W Chen and D Zhang},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85059309609&partnerID=40&md5=66565cf20937bf116bcdcdfeb47a8a2b},
year = {2018},
date = {2018-01-01},
journal = {33rd Technical Conference of the American Society for Composites 2018},
volume = {1},
pages = {111-122},
abstract = {Polymer Matrix Composites (PMC) use is increasing in several industries due to their attractiveness relative to weight savings. Fabrication of this material system type requires a cure cycle, performed at elevated temperatures, that induces residual stresses at post-cure due to significant mismatch of fiber and matrix material properties. An integrated has been developed encompassing heat transfer analysis, a viscoelastic constitutive law, and cure kinetics to predict the residual stress distribution and corresponding geometric change after demolding. This paper summarizes efforts performed toward enhanced understanding of these residual thermal stress effects on the delamination type of failure for an angled composite flange under 4-point bending. This study paves the way for fully coupling the composite manufacturing process with structural performance through an Integrated Computational Materials Engineering (ICME) framework. A higher-fidelity Finite Element Model (FEM), developed to include progressive failure, captures failure modes within the element formulations directly, effectively eliminating the need for a priori specification of discrete delamination zones. The ability to incorporate failure directly within the element structure is particularly notable where laminates may not realistically permit a high number of interfacial layers or where geometry may be complex. The study examines woven textile laminates (e.g. plain and satin weaves) at this stage of the effort using FEM validated with ASTM standard physical testing monitored through load-deflection history and Digital Image Correlation (DIC) data. © Copyright© (2018) by DEStech Publications, Inc. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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Polymer Matrix Composites (PMC) use is increasing in several industries due to their attractiveness relative to weight savings. Fabrication of this material system type requires a cure cycle, performed at elevated temperatures, that induces residual stresses at post-cure due to significant mismatch of fiber and matrix material properties. An integrated has been developed encompassing heat transfer analysis, a viscoelastic constitutive law, and cure kinetics to predict the residual stress distribution and corresponding geometric change after demolding. This paper summarizes efforts performed toward enhanced understanding of these residual thermal stress effects on the delamination type of failure for an angled composite flange under 4-point bending. This study paves the way for fully coupling the composite manufacturing process with structural performance through an Integrated Computational Materials Engineering (ICME) framework. A higher-fidelity Finite Element Model (FEM), developed to include progressive failure, captures failure modes within the element formulations directly, effectively eliminating the need for a priori specification of discrete delamination zones. The ability to incorporate failure directly within the element structure is particularly notable where laminates may not realistically permit a high number of interfacial layers or where geometry may be complex. The study examines woven textile laminates (e.g. plain and satin weaves) at this stage of the effort using FEM validated with ASTM standard physical testing monitored through load-deflection history and Digital Image Correlation (DIC) data. © Copyright© (2018) by DEStech Publications, Inc. All rights reserved.
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Favata, J; Zhang, D; Shahbazmohamadi, S
3-D X-ray tomography for in-situ characterization of progressive damage response of carbon fiber laminates subject to mechanical loadings Conference
2 , 2018.
Abstract | Links | BibTeX | Tags:
@conference{Favata2018748,
title = {3-D X-ray tomography for in-situ characterization of progressive damage response of carbon fiber laminates subject to mechanical loadings},
author = {J Favata and D Zhang and S Shahbazmohamadi},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85059297827&partnerID=40&md5=80d29a80adbbeba561ec71baa4aaaf24},
year = {2018},
date = {2018-01-01},
journal = {33rd Technical Conference of the American Society for Composites 2018},
volume = {2},
pages = {748-755},
abstract = {Composite laminates possess heterogeneous microstructures which make characterization and modeling a great challenge, particularly in their failure response to different loadings. One of the most emerging research areas involves the development of a robust, high-fidelity, physics-based model to predict the progressive damage response of composites under mechanical loading. In the literature, many failure models have been developed with a view to predicting various failure modes observed in composites, including fiber breakage, fiber kinking, matrix cracking, and delamination between plies. Digital image correlation (DIC) techniques have been widely used to identify hot spots and failure evolution by tracking the surface strain histories. Although this method can capture crack propagation, the application is limited to determining surface intra-ply damage, and the resolution is generally not fine enough to capture the failure at the fiber level. The most viable approach to produce data of value for the formulation and validation of composite material models would need to be fully 3-D and in-situ. In this experiment, a proof of concept approach to study carbon fiber laminates with 3-D X-ray tomography and in-situ tensile loading is proposed and developed. Test results revealed information regarding through-ply cracking and its impact on catastrophic failure of the specimen. Based on the results of this experiment, the implementation of 3-D data correlation (digital volume correlation) can be evaluated as a way to quantify the load- and time-based material changes that lead to failure. Additionally, other types of loadings including temperature, compressive loading, and 3-point/4-point bending can be considered for future studies. © 2018 by DEStech Publications, Inc. All rights reserved..},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

Close
Composite laminates possess heterogeneous microstructures which make characterization and modeling a great challenge, particularly in their failure response to different loadings. One of the most emerging research areas involves the development of a robust, high-fidelity, physics-based model to predict the progressive damage response of composites under mechanical loading. In the literature, many failure models have been developed with a view to predicting various failure modes observed in composites, including fiber breakage, fiber kinking, matrix cracking, and delamination between plies. Digital image correlation (DIC) techniques have been widely used to identify hot spots and failure evolution by tracking the surface strain histories. Although this method can capture crack propagation, the application is limited to determining surface intra-ply damage, and the resolution is generally not fine enough to capture the failure at the fiber level. The most viable approach to produce data of value for the formulation and validation of composite material models would need to be fully 3-D and in-situ. In this experiment, a proof of concept approach to study carbon fiber laminates with 3-D X-ray tomography and in-situ tensile loading is proposed and developed. Test results revealed information regarding through-ply cracking and its impact on catastrophic failure of the specimen. Based on the results of this experiment, the implementation of 3-D data correlation (digital volume correlation) can be evaluated as a way to quantify the load- and time-based material changes that lead to failure. Additionally, other types of loadings including temperature, compressive loading, and 3-point/4-point bending can be considered for future studies. © 2018 by DEStech Publications, Inc. All rights reserved..
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Chen, W; Li, C; Zhang, D
A multi-physics processing model for predicting sping-in angle of a resin transfer molded composite flange Conference
(210049), 2018.
Abstract | Links | BibTeX | Tags:
@conference{Chen2018h,
title = {A multi-physics processing model for predicting sping-in angle of a resin transfer molded composite flange},
author = {W Chen and C Li and D Zhang},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85044619580&doi=10.2514%2f6.2018-1898&partnerID=40&md5=d066a2f9a5457d873345b3b95bbce956},
doi = {10.2514/6.2018-1898},
year = {2018},
date = {2018-01-01},
journal = {AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2018},
number = {210049},
abstract = {An integrated composite processing model has been developed to predict the springin angle of an L-shaped composite flange manufactured using a Resin Transfer Molding (RTM) technique. The curved composite laminate consists of 16 plies of plain-weave laminae made of AS-4 carbon fibers and EPON 862 epoxy. The curing and demolding processes of the composite are simulated using heat transfer and stress analyses in a 3D finite element (FE) modeling framework that incorporates resin cure kinetics, cure-dependent resin properties, and textile architecture-based composite constitutive relations. In this study, the composite is modeled as discrete layers of homogeneous, orthotropic material using the finite element analysis (FEA), while the cure-dependent constitutive relation is determined based on the microstructure of the textile composite. An extended concentric cylinder assemblage (ECCA) micromechanics is used to compute the thermo-mechanical properties of each fiber tow, and the results are subsequently used to compute the effective composite properties based on the strain energy equivalence. By incorporating the resin cure kinetics model and cure-dependent composite thermal properties into the heat transfer analysis, the evolution of temperature and degree of cure (DOC) during processing can be solved, which are subsequently used as predefined fields in the stress analysis to predict the residual stress development during cure. Both thermal strains and chemical strains due to cure shrinkage are incorporated into the cure-dependent composite constitutive law. Finally, the demolding and cutting processes are simulated to predict the spring-in angle of the Lshaped flange after the manufacturing cycle. The proposed processing model is validated by comparing the predicted spring-in angles against the experimental measurements. © 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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An integrated composite processing model has been developed to predict the springin angle of an L-shaped composite flange manufactured using a Resin Transfer Molding (RTM) technique. The curved composite laminate consists of 16 plies of plain-weave laminae made of AS-4 carbon fibers and EPON 862 epoxy. The curing and demolding processes of the composite are simulated using heat transfer and stress analyses in a 3D finite element (FE) modeling framework that incorporates resin cure kinetics, cure-dependent resin properties, and textile architecture-based composite constitutive relations. In this study, the composite is modeled as discrete layers of homogeneous, orthotropic material using the finite element analysis (FEA), while the cure-dependent constitutive relation is determined based on the microstructure of the textile composite. An extended concentric cylinder assemblage (ECCA) micromechanics is used to compute the thermo-mechanical properties of each fiber tow, and the results are subsequently used to compute the effective composite properties based on the strain energy equivalence. By incorporating the resin cure kinetics model and cure-dependent composite thermal properties into the heat transfer analysis, the evolution of temperature and degree of cure (DOC) during processing can be solved, which are subsequently used as predefined fields in the stress analysis to predict the residual stress development during cure. Both thermal strains and chemical strains due to cure shrinkage are incorporated into the cure-dependent composite constitutive law. Finally, the demolding and cutting processes are simulated to predict the spring-in angle of the Lshaped flange after the manufacturing cycle. The proposed processing model is validated by comparing the predicted spring-in angles against the experimental measurements. © 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.
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doi:10.2514/6.2018-1898
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Ahmed, S; Cao, P; Zhang, D; Tang, J
Damage detection of textile composite structures using the piezoelectric impedance method Conference
5 , 2018.
Abstract | Links | BibTeX | Tags:
@conference{Ahmed20183408,
title = {Damage detection of textile composite structures using the piezoelectric impedance method},
author = {S Ahmed and P Cao and D Zhang and J Tang},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85059423689&partnerID=40&md5=4cc53f326cd345bb2c49501ce5fae044},
year = {2018},
date = {2018-01-01},
journal = {33rd Technical Conference of the American Society for Composites 2018},
volume = {5},
pages = {3408-3426},
abstract = {Structural health monitoring of aerospace structures is becoming vital as lightweight composite materials are increasingly used in aero-structures. Composites have various types of failure modes, which make it even more important to identify damage compared to isotropic materials. Therefore, on-site health monitoring is one of the most preferred methodologies for detecting internal crack or damage at its initial stage to enhance operating safety and reduce repair cost. Recently, piezoelectric transducers are on high demand for on-site health monitoring because of its high bandwidth sensitivity. They simultaneously perform as actuators and sensors and embedded on the structure. The electrical impedance or admittance changes according to modification in mass, stiffness or damping properties of the host body. In this study, plain-weave textile composites are utilized to demonstrate capability of piezoelectric transducer. The elastic properties of composite are determined using the Concentric Cylinder Assemblage micromechanics model. Finite element modeling is done in ANSYS APDL to observe electrical admittance variation around natural frequency. Delamination and intra-ply damage cases are studied. Delamination is separation of adjacent plies and damage is reduction of stiffness in the whole structure. Modal frequency of the structure decreased with delamination and damage level increment within the body. Pre-preg manufacturing method is carried out to fabricate composite panel from which samples are cut for testing according to ASTM standards. Piezoelectric test provided voltage drop across the resistor that denoted the coupling effect of the patch with the host structure. Electrical admittance plot expressed response to body deformation actuated by the piezoelectric transducer. Results from finite element modeling and experimentation assert that piezoelectric impedance technique is efficient in detecting damage or delamination within the composite structure. © 2018 33rd Technical Conference of the American Society for Composites 2018. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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Structural health monitoring of aerospace structures is becoming vital as lightweight composite materials are increasingly used in aero-structures. Composites have various types of failure modes, which make it even more important to identify damage compared to isotropic materials. Therefore, on-site health monitoring is one of the most preferred methodologies for detecting internal crack or damage at its initial stage to enhance operating safety and reduce repair cost. Recently, piezoelectric transducers are on high demand for on-site health monitoring because of its high bandwidth sensitivity. They simultaneously perform as actuators and sensors and embedded on the structure. The electrical impedance or admittance changes according to modification in mass, stiffness or damping properties of the host body. In this study, plain-weave textile composites are utilized to demonstrate capability of piezoelectric transducer. The elastic properties of composite are determined using the Concentric Cylinder Assemblage micromechanics model. Finite element modeling is done in ANSYS APDL to observe electrical admittance variation around natural frequency. Delamination and intra-ply damage cases are studied. Delamination is separation of adjacent plies and damage is reduction of stiffness in the whole structure. Modal frequency of the structure decreased with delamination and damage level increment within the body. Pre-preg manufacturing method is carried out to fabricate composite panel from which samples are cut for testing according to ASTM standards. Piezoelectric test provided voltage drop across the resistor that denoted the coupling effect of the patch with the host structure. Electrical admittance plot expressed response to body deformation actuated by the piezoelectric transducer. Results from finite element modeling and experimentation assert that piezoelectric impedance technique is efficient in detecting damage or delamination within the composite structure. © 2018 33rd Technical Conference of the American Society for Composites 2018. All rights reserved.
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Sun, H; Heimbach, B; Wei, M; Zhang, D
Progressive damage analysis of a bioresorbable composite subject to three-point bending Conference
5 , 2018.
Abstract | Links | BibTeX | Tags:
@conference{Sun20183361,
title = {Progressive damage analysis of a bioresorbable composite subject to three-point bending},
author = {H Sun and B Heimbach and M Wei and D Zhang},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85059379095&partnerID=40&md5=411515e58d745d070506e15902f277ff},
year = {2018},
date = {2018-01-01},
journal = {33rd Technical Conference of the American Society for Composites 2018},
volume = {5},
pages = {3361-3379},
abstract = {The focus of this paper is to investigate the deformation response of a new class of bioresorbable composites used for bone fixation devices under flexural loading. The Digital Image Correlation (DIC) technique are utilized to map the deformation history and identify the damage locations. Since the damage propagation path needs to be calculated by the simulation, a fracture energy based Smeared Crack Approach (SCA) is revisited and implemented in the Finite Element Analysis (FEA). In the new SCA model, 2D crack morphology incorporating two crack components are discussed. In addition, the stress degradation rule after the damage initiation is revised to guarantee the energy conservation. Compared with the analytical solution, the new SCA model is validated by the benchmark examples of the Double-Cantilever Beam (DCB) and the End Notched Flexure (ENF) simulations. The results demonstrate the predictive capability of the SCA to capture both the mode-I and mode-II failure modes. The new SCA model is further employed to predict the failure response of the bioresorbable composite under three-point bending, which shows a good correlation with the experiment. Based on the FE simulation results, a linear regression model is developed to elucidate the effect of critical stress and fracture energy on the resulting flexural response. The numerical methods in this paper can be used as an efficient tool in designing the bioresorbable composite for controlled mechanical performance. © 2018 33rd Technical Conference of the American Society for Composites 2018. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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The focus of this paper is to investigate the deformation response of a new class of bioresorbable composites used for bone fixation devices under flexural loading. The Digital Image Correlation (DIC) technique are utilized to map the deformation history and identify the damage locations. Since the damage propagation path needs to be calculated by the simulation, a fracture energy based Smeared Crack Approach (SCA) is revisited and implemented in the Finite Element Analysis (FEA). In the new SCA model, 2D crack morphology incorporating two crack components are discussed. In addition, the stress degradation rule after the damage initiation is revised to guarantee the energy conservation. Compared with the analytical solution, the new SCA model is validated by the benchmark examples of the Double-Cantilever Beam (DCB) and the End Notched Flexure (ENF) simulations. The results demonstrate the predictive capability of the SCA to capture both the mode-I and mode-II failure modes. The new SCA model is further employed to predict the failure response of the bioresorbable composite under three-point bending, which shows a good correlation with the experiment. Based on the FE simulation results, a linear regression model is developed to elucidate the effect of critical stress and fracture energy on the resulting flexural response. The numerical methods in this paper can be used as an efficient tool in designing the bioresorbable composite for controlled mechanical performance. © 2018 33rd Technical Conference of the American Society for Composites 2018. All rights reserved.
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Pham, D C; Cui, X; Lua, J; Zhang, D
A continuum damage description for a discrete crack modeling approach for delamination migration in composite laminates Conference
(210049), 2018.
Abstract | Links | BibTeX | Tags:
@conference{Pham2018c,
title = {A continuum damage description for a discrete crack modeling approach for delamination migration in composite laminates},
author = {D C Pham and X Cui and J Lua and D Zhang},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85044569315&doi=10.2514%2f6.2018-1222&partnerID=40&md5=58216cfac9f11a3d294590ed79dbc0b4},
doi = {10.2514/6.2018-1222},
year = {2018},
date = {2018-01-01},
journal = {AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2018},
number = {210049},
abstract = {A three-dimensional discrete crack embedded within a continuum damage mechanics (CDM) model is developed for an effective characterization of delamination migration in composite laminates subjected to static loading. 3D Hashin failure criterion is implemented for damage initiation prediction under a 3D stress state. Matrix crack initiation criteria coupled with a maximum principal stress direction are employed to determine the location and orientation of a discrete matrix crack within an element. Given the orientation of the initiated matrix crack, the resulting stiffness degradation is characterized in the local principal stress coordinate system and an energy driven failure mechanism is included to capture the crack growth. By coupling the cohesive model for delamination and the discrete damage embedded CDM for matrix cracking, their synergistic interaction can be captured during the simulation of the delamination migration. The predictive capability of the enhanced modeling strategy is examined through simulation of a delamination migration in a cross-ply tap laminate. The predicted results are compared with the experimental data published by NASA and good agreements are achieved in terms of load displacement curve and the location of crack branching. © 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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A three-dimensional discrete crack embedded within a continuum damage mechanics (CDM) model is developed for an effective characterization of delamination migration in composite laminates subjected to static loading. 3D Hashin failure criterion is implemented for damage initiation prediction under a 3D stress state. Matrix crack initiation criteria coupled with a maximum principal stress direction are employed to determine the location and orientation of a discrete matrix crack within an element. Given the orientation of the initiated matrix crack, the resulting stiffness degradation is characterized in the local principal stress coordinate system and an energy driven failure mechanism is included to capture the crack growth. By coupling the cohesive model for delamination and the discrete damage embedded CDM for matrix cracking, their synergistic interaction can be captured during the simulation of the delamination migration. The predictive capability of the enhanced modeling strategy is examined through simulation of a delamination migration in a cross-ply tap laminate. The predicted results are compared with the experimental data published by NASA and good agreements are achieved in terms of load displacement curve and the location of crack branching. © 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.
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doi:10.2514/6.2018-1222
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2017

Zeng, S; Li, R; Freire, S G; Garbellotto, V M M; Huang, E Y; Smith, A T; Hu, C; Tait, W R T; Bian, Z; Zheng, G; Zhang, D; Sun, L
Moisture-Responsive Wrinkling Surfaces with Tunable Dynamics Journal Article
Advanced Materials, 29 (24), 2017.
Abstract | Links | BibTeX | Tags:
@article{Zeng2017,
title = {Moisture-Responsive Wrinkling Surfaces with Tunable Dynamics},
author = {S Zeng and R Li and S G Freire and V M M Garbellotto and E Y Huang and A T Smith and C Hu and W R T Tait and Z Bian and G Zheng and D Zhang and L Sun},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85018604698&doi=10.1002%2fadma.201700828&partnerID=40&md5=d6a8cf5ef182186a23fcb7f403ab1a23},
doi = {10.1002/adma.201700828},
year = {2017},
date = {2017-01-01},
journal = {Advanced Materials},
volume = {29},
number = {24},
abstract = {The wrinkle dynamics (such as reversibility and stability) of human skin are affected by the external stimuli, as well as the skin's structure and mechanical properties. Inspired by these tunable responses, three types of moisture-responsive wrinkle dynamics are achieved, for the first time, through a single film–substrate system. These dynamics include: (1) completely reversible wrinkles formation; (2) irreversible wrinkles formation I: the initially formed wrinkles can be permanently erased and never reappear; and (3) irreversible wrinkles formation II: once the wrinkles form, they can no longer be erased. The key to success is to control the stiffness and thickness ratios of the film and the substrate, and tailor the crosslink degree/gradient of the film to allow for moisture-dependent changes of modulus and swelling degree. These unique responsive dynamics motivate the invention of a series of optical devices triggered by moisture, including anticounterfeit tabs, encryption devices, water indicators, light diffusors, and antiglare films. This study also paves the road for further understanding of the skin wrinkling dynamics and manipulation. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

Close
The wrinkle dynamics (such as reversibility and stability) of human skin are affected by the external stimuli, as well as the skin's structure and mechanical properties. Inspired by these tunable responses, three types of moisture-responsive wrinkle dynamics are achieved, for the first time, through a single film–substrate system. These dynamics include: (1) completely reversible wrinkles formation; (2) irreversible wrinkles formation I: the initially formed wrinkles can be permanently erased and never reappear; and (3) irreversible wrinkles formation II: once the wrinkles form, they can no longer be erased. The key to success is to control the stiffness and thickness ratios of the film and the substrate, and tailor the crosslink degree/gradient of the film to allow for moisture-dependent changes of modulus and swelling degree. These unique responsive dynamics motivate the invention of a series of optical devices triggered by moisture, including anticounterfeit tabs, encryption devices, water indicators, light diffusors, and antiglare films. This study also paves the road for further understanding of the skin wrinkling dynamics and manipulation. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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doi:10.1002/adma.201700828
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Zhang, D; Meyer, P; Waas, A M
An experimentally validated computational model for progressive damage analysis of notched oxide/oxide woven ceramic matrix composites Journal Article
Composite Structures, 161 , pp. 264-274, 2017.
Abstract | Links | BibTeX | Tags:
@article{Zhang2017264,
title = {An experimentally validated computational model for progressive damage analysis of notched oxide/oxide woven ceramic matrix composites},
author = {D Zhang and P Meyer and A M Waas},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85000879104&doi=10.1016%2fj.compstruct.2016.11.001&partnerID=40&md5=12dce26910992624bb4619626831f8a5},
doi = {10.1016/j.compstruct.2016.11.001},
year = {2017},
date = {2017-01-01},
journal = {Composite Structures},
volume = {161},
pages = {264-274},
abstract = {The focus of this paper is to examine the effect of a notch on the failure response of an oxide/oxide ceramic matrix composite (CMC) subjected to room-temperature tensile loading. The CMC is made of aluminosilicate matrix reinforced by 3M Nextel™ 610 alumina fibers (AS/N610) that are woven into an eight-harness satin weave (8HSW) preform. Uniaxial tensile tests were carried out on both un-notched and single-edge-notched tensile (SENT) specimens of two different lay-ups, (0/90)S and (45/0/-45/0)S, using a hydraulically activated load frame. The digital image correlation (DIC) technique was utilized to map the deformation histories and identify the locations of strain concentration for both un-notched and SENT specimens. The experimental results were subsequently used to develop a lamina-level constitutive model for a single 8HSW ply that incorporates damage and fracture mechanics implemented through a finite element (FE) framework. A secant-modulus approach was employed to model the pre-peak nonlinear damage evolution, while the post-peak softening was modeled using the smeared crack approach (SCA). Utilizing the ply properties measured from the un-notched (0/90)S and (45/0/-45/0)S tension tests, the proposed computational model is able to predict the failure strength and strain localization in the SENT specimens. Such a predictive model can aid in the design of CMC structures and accelerate the development of CMCs for engineering applications. © 2016 Elsevier Ltd},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

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The focus of this paper is to examine the effect of a notch on the failure response of an oxide/oxide ceramic matrix composite (CMC) subjected to room-temperature tensile loading. The CMC is made of aluminosilicate matrix reinforced by 3M Nextel™ 610 alumina fibers (AS/N610) that are woven into an eight-harness satin weave (8HSW) preform. Uniaxial tensile tests were carried out on both un-notched and single-edge-notched tensile (SENT) specimens of two different lay-ups, (0/90)S and (45/0/-45/0)S, using a hydraulically activated load frame. The digital image correlation (DIC) technique was utilized to map the deformation histories and identify the locations of strain concentration for both un-notched and SENT specimens. The experimental results were subsequently used to develop a lamina-level constitutive model for a single 8HSW ply that incorporates damage and fracture mechanics implemented through a finite element (FE) framework. A secant-modulus approach was employed to model the pre-peak nonlinear damage evolution, while the post-peak softening was modeled using the smeared crack approach (SCA). Utilizing the ply properties measured from the un-notched (0/90)S and (45/0/-45/0)S tension tests, the proposed computational model is able to predict the failure strength and strain localization in the SENT specimens. Such a predictive model can aid in the design of CMC structures and accelerate the development of CMCs for engineering applications. © 2016 Elsevier Ltd
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doi:10.1016/j.compstruct.2016.11.001
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Li, R; Zhang, D
A fabric architecture based constitutive model for fiber reinforced rubbers Conference
4 , 2017.
Abstract | Links | BibTeX | Tags:
@conference{Li20172930,
title = {A fabric architecture based constitutive model for fiber reinforced rubbers},
author = {R Li and D Zhang},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85047735098&partnerID=40&md5=4105c2382bc3f30665e80beca90ee74e},
year = {2017},
date = {2017-01-01},
journal = {32nd Technical Conference of the American Society for Composites 2017},
volume = {4},
pages = {2930-2939},
abstract = {The focus of this paper is to develop a fabric architecture-based constitutive model for a rubber hose reinforced by knitted fibers. The composite hose is modeled using a representative unit cell (RUC) consisting of a fiber layer embedded in two rubber layers. The rubber is considered as a Neo-Hookean material, while the knitted fibers are modeled by cords with negligible stiffness in bending. The effect of reinforcement comes from the conservation of the total length of the fiber cords. This approach enables the determination of the constitutive behavior of the composite sheet in closed form based on the constituent rubber and fiber properties and geometry. © 2017 by DEStech Publications, Inc.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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The focus of this paper is to develop a fabric architecture-based constitutive model for a rubber hose reinforced by knitted fibers. The composite hose is modeled using a representative unit cell (RUC) consisting of a fiber layer embedded in two rubber layers. The rubber is considered as a Neo-Hookean material, while the knitted fibers are modeled by cords with negligible stiffness in bending. The effect of reinforcement comes from the conservation of the total length of the fiber cords. This approach enables the determination of the constitutive behavior of the composite sheet in closed form based on the constituent rubber and fiber properties and geometry. © 2017 by DEStech Publications, Inc.
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Chen, W; Zhang, D
A micromechanics-based processing model for predicting residual stress in fiber-reinforced composites Conference
2017.
Abstract | Links | BibTeX | Tags:
@conference{Chen2017,
title = {A micromechanics-based processing model for predicting residual stress in fiber-reinforced composites},
author = {W Chen and D Zhang},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85017378282&partnerID=40&md5=33d7293fdc7562b80d08e43dce565fa7},
year = {2017},
date = {2017-01-01},
journal = {58th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2017},
abstract = {The focus of this paper is to develop a micromechanics-based processing model that predicts the residual stress development in a fiber-reinforced composite during the curing process. The effective thermal and mechanical properties of the composite were computed in closed form using the concentric cylinder assemblage (CCA) micromechanics model. The effective composite thermal properties were used to solve the distributions of temperature and degree of cure (DOC) in the composite during the curing process through heat transfer analysis, where the cure kinetics was incorporated as an internal heat generation term. The solved temperature and DOC distributions were implement as pre-defined fields in the subsequent stress analysis of the curing process. The residual stress accumulation during the curing process was computed through the cure constitutive model that encompasses cure-dependent mechanical properties, thermal strains, and cure shrinkage. The proposed composite processing model was applied to predict the deformed shape of a non-symmetric laminate after the curing process. The composite was fabricated using the Vacuum Assisted Resin Transfer Molding (VARTM) technique. The predictive capability of the proposed model is evaluated by comparing the computed curvatures of the panel with the experimental results. © 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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The focus of this paper is to develop a micromechanics-based processing model that predicts the residual stress development in a fiber-reinforced composite during the curing process. The effective thermal and mechanical properties of the composite were computed in closed form using the concentric cylinder assemblage (CCA) micromechanics model. The effective composite thermal properties were used to solve the distributions of temperature and degree of cure (DOC) in the composite during the curing process through heat transfer analysis, where the cure kinetics was incorporated as an internal heat generation term. The solved temperature and DOC distributions were implement as pre-defined fields in the subsequent stress analysis of the curing process. The residual stress accumulation during the curing process was computed through the cure constitutive model that encompasses cure-dependent mechanical properties, thermal strains, and cure shrinkage. The proposed composite processing model was applied to predict the deformed shape of a non-symmetric laminate after the curing process. The composite was fabricated using the Vacuum Assisted Resin Transfer Molding (VARTM) technique. The predictive capability of the proposed model is evaluated by comparing the computed curvatures of the panel with the experimental results. © 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.
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Chen, W; Fan, T -H; Zhang, D
An integrated numerical model for predicting flow and compaction of 2D textile composite in the VARTM process Conference
4 , 2017.
Abstract | Links | BibTeX | Tags:
@conference{Chen20172488,
title = {An integrated numerical model for predicting flow and compaction of 2D textile composite in the VARTM process},
author = {W Chen and T -H Fan and D Zhang},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85047743180&partnerID=40&md5=233bef0d362fbafacde4147668ac79cf},
year = {2017},
date = {2017-01-01},
journal = {32nd Technical Conference of the American Society for Composites 2017},
volume = {4},
pages = {2488-2501},
abstract = {The vacuum assisted resin transfer molding (VARTM) technique is a low-cost alternative to the autoclave process suitable for manufacturing large-scale composite parts. During the VARTM process, carbon fiber sheets are covered by a vacuum bag, and a vacuum pump is utilized to assist the resin flow in the infiltration process. However, when dealing with carbon fiber fabrics with complicated microstructure such as 2D textile fabrics, the gaps between the fiber tows are sometimes not fully saturated by the resin flow, creating starvation areas that potentially compromise the mechanical performance of the composite part. In addition, during the resin infusion process, the cross-linking reaction is activated under the preheated condition, making the material properties of resin both temperature and degree of cure (DOC) dependent. Therefore, the key is to establish a multi-physics model that incorporate heat transfer analysis and cure kinetics into the flow compaction model. In this paper, an integrated flow compaction model is developed to predict the flow front advancement inside the textile fabrics during the VARTM process. The flow velocity and pressure distribution inside the resin flow are governed by the continuity equation and Darcy's law. Due to the fact that the behavior of the resin flow is influenced by the local permeability, which in return is a function of fluid pressure, the flow model and the compaction model are coupled, and they are solved simultaneously to determine the flow behavior of resin inside the fiber fabrics. In the meantime, the viscosity model of the resin is incorporated into the flow compaction model through the material properties of the resin to account for the effects of infusion parameters. Using this flow compaction model, the permeability of the carbon fabrics used in this study is determined by comparing the flow front predicted by the flow compaction model to that observed in the radial injection experiment. Moreover, once the fluid distribution is determined, the local fiber volume fraction and thickness variation of the laminate can be predicted, which are essential input parameters for estimating the residual stress buildup in the stress analysis. © 2017 by DEStech Publications, Inc.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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The vacuum assisted resin transfer molding (VARTM) technique is a low-cost alternative to the autoclave process suitable for manufacturing large-scale composite parts. During the VARTM process, carbon fiber sheets are covered by a vacuum bag, and a vacuum pump is utilized to assist the resin flow in the infiltration process. However, when dealing with carbon fiber fabrics with complicated microstructure such as 2D textile fabrics, the gaps between the fiber tows are sometimes not fully saturated by the resin flow, creating starvation areas that potentially compromise the mechanical performance of the composite part. In addition, during the resin infusion process, the cross-linking reaction is activated under the preheated condition, making the material properties of resin both temperature and degree of cure (DOC) dependent. Therefore, the key is to establish a multi-physics model that incorporate heat transfer analysis and cure kinetics into the flow compaction model. In this paper, an integrated flow compaction model is developed to predict the flow front advancement inside the textile fabrics during the VARTM process. The flow velocity and pressure distribution inside the resin flow are governed by the continuity equation and Darcy's law. Due to the fact that the behavior of the resin flow is influenced by the local permeability, which in return is a function of fluid pressure, the flow model and the compaction model are coupled, and they are solved simultaneously to determine the flow behavior of resin inside the fiber fabrics. In the meantime, the viscosity model of the resin is incorporated into the flow compaction model through the material properties of the resin to account for the effects of infusion parameters. Using this flow compaction model, the permeability of the carbon fabrics used in this study is determined by comparing the flow front predicted by the flow compaction model to that observed in the radial injection experiment. Moreover, once the fluid distribution is determined, the local fiber volume fraction and thickness variation of the laminate can be predicted, which are essential input parameters for estimating the residual stress buildup in the stress analysis. © 2017 by DEStech Publications, Inc.
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Shuai, Q; Chen, W; Zhang, D; Tang, J
On-line detection of composite structural faults utilizing piezoelectric impedance measurement Conference
4 , 2017.
Abstract | Links | BibTeX | Tags:
@conference{Shuai20172643,
title = {On-line detection of composite structural faults utilizing piezoelectric impedance measurement},
author = {Q Shuai and W Chen and D Zhang and J Tang},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85047760893&partnerID=40&md5=ba8aea91980794587b7ed894a49882db},
year = {2017},
date = {2017-01-01},
journal = {32nd Technical Conference of the American Society for Composites 2017},
volume = {4},
pages = {2643-2655},
abstract = {The timely and accurate detection and identification of structural faults during their operations can play a vitally important role in ensuring the safety and sustainability of various structural systems. This mission, however, is inherently difficult, because structural faults/degradations usually have extremely small characteristic lengths with infinitely many possible patterns/profiles. It becomes even more challenging for layered composites due to the lack of understanding of many failure modes peculiar to such structures. In this research, we integrate the piezoelectric transducer into layered composites to facilitate piezoelectric impedance-based damage detection. In order to enhance the measurement quality, several circuitry integration techniques are introduced. © 2017 by DEStech Publications, Inc.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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The timely and accurate detection and identification of structural faults during their operations can play a vitally important role in ensuring the safety and sustainability of various structural systems. This mission, however, is inherently difficult, because structural faults/degradations usually have extremely small characteristic lengths with infinitely many possible patterns/profiles. It becomes even more challenging for layered composites due to the lack of understanding of many failure modes peculiar to such structures. In this research, we integrate the piezoelectric transducer into layered composites to facilitate piezoelectric impedance-based damage detection. In order to enhance the measurement quality, several circuitry integration techniques are introduced. © 2017 by DEStech Publications, Inc.
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Xiao, J; Fang, E; Lua, J; Zhang, D
A multiscale model for fatigue damage prediction of notched composite components Conference
2017.
Abstract | Links | BibTeX | Tags:
@conference{Xiao2017,
title = {A multiscale model for fatigue damage prediction of notched composite components},
author = {J Xiao and E Fang and J Lua and D Zhang},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85017355142&partnerID=40&md5=599fb45c666a20593efaf7eddb119d2b},
year = {2017},
date = {2017-01-01},
journal = {58th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2017},
abstract = {A micro-, continuum-, and discrete- based multiscale progressive damage model was developed for fatigue damage and life prediction of notched composite components. An n-phase concentric cylinder micromechanics model was coupled with a continuum damage and discrete crack framework and implemented through user-defined subroutines within commercial finite element software such as Abaqus. Sub-critical damage evolution was evaluated by decomposing the ply level response into its constituent response variables through the use of a pair of fiber-matrix concentric cylinders with the nonlinear constituent behavior of the matrix. Weighted local matrix strain components were used to determine the macroscopic nonlinear response and update the global stiffness and stresses in the macroscale for the subsequent fracture prediction. Using a stress-life based strength degradation model coupled with intra- and inter- ply failure criteria, evolution of matrix cracking and delamination was predicted under fatigue loading. Numerical studies were performed using the solution modules with the application of the multiscale modeling approach. The results of stiffness degradation and residual strength predictions of open-hole specimens were used to demonstrate the solution fidelity from the application of the multiscale solution approach. © 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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A micro-, continuum-, and discrete- based multiscale progressive damage model was developed for fatigue damage and life prediction of notched composite components. An n-phase concentric cylinder micromechanics model was coupled with a continuum damage and discrete crack framework and implemented through user-defined subroutines within commercial finite element software such as Abaqus. Sub-critical damage evolution was evaluated by decomposing the ply level response into its constituent response variables through the use of a pair of fiber-matrix concentric cylinders with the nonlinear constituent behavior of the matrix. Weighted local matrix strain components were used to determine the macroscopic nonlinear response and update the global stiffness and stresses in the macroscale for the subsequent fracture prediction. Using a stress-life based strength degradation model coupled with intra- and inter- ply failure criteria, evolution of matrix cracking and delamination was predicted under fatigue loading. Numerical studies were performed using the solution modules with the application of the multiscale modeling approach. The results of stiffness degradation and residual strength predictions of open-hole specimens were used to demonstrate the solution fidelity from the application of the multiscale solution approach. © 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.
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Zeng, S; Zhang, D; Huang, W; Wang, Z; Freire, S G; Smith, A T; Huang, E Y; Nguon, H; Yu, X; Sun, L
Sensitive mechanochromisms based on a polymer bilayer structure Conference
2017-May , 2017.
Abstract | Links | BibTeX | Tags:
@conference{Zeng2017979,
title = {Sensitive mechanochromisms based on a polymer bilayer structure},
author = {S Zeng and D Zhang and W Huang and Z Wang and S G Freire and A T Smith and E Y Huang and H Nguon and X Yu and L Sun},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85038624718&partnerID=40&md5=3f73029b362fb914d3556a66bd27692d},
year = {2017},
date = {2017-01-01},
journal = {Annual Technical Conference - ANTEC, Conference Proceedings},
volume = {2017-May},
pages = {979-982},
abstract = {We have designed a series of mechanochromic devices inspired by nature with the capabilities of changing transparency and "switching on/off" luminescence in response to mechanical stimuli. The key to accomplish these excellent optical properties is to control strain-induced surface engineering, that is, the longitudinal cracks opening and transverse invaginated folds. All of these devices are comprised of a rigid thin layer atop polydimethylsiloxane (PDMS) based elastomer, which can be facilely and quickly fabricated. For transparency change mechanochromism, the folds and cracks with excellent light trapping and scattering capabilities can endow high opaqueness to the originally highly transparent samples. The evolution of crack opening and fold-ridge mechanisms are captured through finite analysis that incorporates damage and cracks in the rigid thin layer. For luminescent mechanochromism, the strain-tunable cracks on the UV shield layer act as "gates" to mediate the traveling of UV light to "switch on/off" the luminescence of mechanochromism. This device exhibits a remarkably high strain responsive sensitivity, demonstrating an excellent sensing capability for detecting mechanical failure or damage. All the mechanochromisms also show outstanding durability and reversibility.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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We have designed a series of mechanochromic devices inspired by nature with the capabilities of changing transparency and "switching on/off" luminescence in response to mechanical stimuli. The key to accomplish these excellent optical properties is to control strain-induced surface engineering, that is, the longitudinal cracks opening and transverse invaginated folds. All of these devices are comprised of a rigid thin layer atop polydimethylsiloxane (PDMS) based elastomer, which can be facilely and quickly fabricated. For transparency change mechanochromism, the folds and cracks with excellent light trapping and scattering capabilities can endow high opaqueness to the originally highly transparent samples. The evolution of crack opening and fold-ridge mechanisms are captured through finite analysis that incorporates damage and cracks in the rigid thin layer. For luminescent mechanochromism, the strain-tunable cracks on the UV shield layer act as "gates" to mediate the traveling of UV light to "switch on/off" the luminescence of mechanochromism. This device exhibits a remarkably high strain responsive sensitivity, demonstrating an excellent sensing capability for detecting mechanical failure or damage. All the mechanochromisms also show outstanding durability and reversibility.
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2016

Zeng, S; Zhang, D; Huang, W; Wang, Z; Freire, S G; Yu, X; Smith, A T; Huang, E Y; Nguon, H; Sun, L
Bio-inspired sensitive and reversible mechanochromisms via strain-dependent cracks and folds Journal Article
Nature Communications, 7 , 2016.
Abstract | Links | BibTeX | Tags:
@article{Zeng2016,
title = {Bio-inspired sensitive and reversible mechanochromisms via strain-dependent cracks and folds},
author = {S Zeng and D Zhang and W Huang and Z Wang and S G Freire and X Yu and A T Smith and E Y Huang and H Nguon and L Sun},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84978062249&doi=10.1038%2fncomms11802&partnerID=40&md5=74663552821d24b92043e84110ee8310},
doi = {10.1038/ncomms11802},
year = {2016},
date = {2016-01-01},
journal = {Nature Communications},
volume = {7},
abstract = {A number of marine organisms use muscle-controlled surface structures to achieve rapid changes in colour and transparency with outstanding reversibility. Inspired by these display tactics, we develop analogous deformation-controlled surface-engineering approaches via strain-dependent cracks and folds to realize the following four mechanochromic devices: (1) transparency change mechanochromism (TCM), (2) luminescent mechanochromism (LM), (3) colour alteration mechanochromism (CAM) and (4) encryption mechanochromism (EM). These devices are based on a simple bilayer system that exhibits a broad range of mechanochromic behaviours with high sensitivity and reversibility. The TCM device can reversibly switch between transparent and opaque states. The LM can emit intensive fluorescence as stretched with very high strain sensitivity. The CAM can turn fluorescence from green to yellow to orange as stretched within 20% strain. The EM device can reversibly reveal and conceal any desirable patterns.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

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A number of marine organisms use muscle-controlled surface structures to achieve rapid changes in colour and transparency with outstanding reversibility. Inspired by these display tactics, we develop analogous deformation-controlled surface-engineering approaches via strain-dependent cracks and folds to realize the following four mechanochromic devices: (1) transparency change mechanochromism (TCM), (2) luminescent mechanochromism (LM), (3) colour alteration mechanochromism (CAM) and (4) encryption mechanochromism (EM). These devices are based on a simple bilayer system that exhibits a broad range of mechanochromic behaviours with high sensitivity and reversibility. The TCM device can reversibly switch between transparent and opaque states. The LM can emit intensive fluorescence as stretched with very high strain sensitivity. The CAM can turn fluorescence from green to yellow to orange as stretched within 20% strain. The EM device can reversibly reveal and conceal any desirable patterns.
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doi:10.1038/ncomms11802
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Chen, W; Zhang, D
A micromechanics based processing model for the curing response of a unidirectional fiber reinforced composite Conference
2016.
Abstract | Links | BibTeX | Tags:
@conference{Chen2016,
title = {A micromechanics based processing model for the curing response of a unidirectional fiber reinforced composite},
author = {W Chen and D Zhang},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85013966492&partnerID=40&md5=bd88acc83d330ce9dd85b6901ce46675},
year = {2016},
date = {2016-01-01},
journal = {Proceedings of the American Society for Composites - 31st Technical Conference, ASC 2016},
abstract = {A micromechanics based thermal model was developed to predict the temperature and degree of cure (DOC) distribution inside a unidirectional fiber reinforced composite during the curing process. Using the concentric cylinder assemblage (CCA) model as a representation of the composite microstructure, the effective thermodynamic properties of the composite were computed based on the fiber and matrix properties through closed-form expressions. By incorporating the cure kinetics of epoxy as the heat generation term in the thermal analysis, the temperature field of the homogenized composite model was solved based on the prescribed cure cycle at the boundary. Meanwhile, this micromechanics model was implemented at the integration point of the homogenized model to predict the local temperature and DOC fields at the microscopic (fiber-matrix) level. Since the heat flux at the axial direction is negligible, this axisymmetric CCA model can be further reduced to 1D heat transfer problem, which can be efficiently solved through the finite difference method. The proposed homogenization scheme and the 1D heat transfer model were validated through a full 3D finite element model. This study suggests that the curing response is influenced by the size of the composite under the same cure cycle.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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A micromechanics based thermal model was developed to predict the temperature and degree of cure (DOC) distribution inside a unidirectional fiber reinforced composite during the curing process. Using the concentric cylinder assemblage (CCA) model as a representation of the composite microstructure, the effective thermodynamic properties of the composite were computed based on the fiber and matrix properties through closed-form expressions. By incorporating the cure kinetics of epoxy as the heat generation term in the thermal analysis, the temperature field of the homogenized composite model was solved based on the prescribed cure cycle at the boundary. Meanwhile, this micromechanics model was implemented at the integration point of the homogenized model to predict the local temperature and DOC fields at the microscopic (fiber-matrix) level. Since the heat flux at the axial direction is negligible, this axisymmetric CCA model can be further reduced to 1D heat transfer problem, which can be efficiently solved through the finite difference method. The proposed homogenization scheme and the 1D heat transfer model were validated through a full 3D finite element model. This study suggests that the curing response is influenced by the size of the composite under the same cure cycle.
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Zhang, D; Meyer, P; Waas, A M
Effect of notch on the failure response of oxide/oxide ceramic composites Conference
2016.
Abstract | Links | BibTeX | Tags:
@conference{Zhang20161,
title = {Effect of notch on the failure response of oxide/oxide ceramic composites},
author = {D Zhang and P Meyer and A M Waas},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84958549292&partnerID=40&md5=dd7d45f41e9b8f045ed1de32a4c9a0cc},
year = {2016},
date = {2016-01-01},
journal = {57th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference},
pages = {1-12},
abstract = {The focus of this paper is to examine the effect of notch on the failure response of an oxide-oxide ceramic matrix composite (CMC) under both room temperature and elevated temperature. The CMC is made of aluminosilicate matrix reinforced by 3M Nextel™ 610 alumina fibers which are woven into an eight-harness satin weave (8HSW) preform. Uniaxial tensile tests were carried out on both un-notched and single-edge-notched specimens of two different lay-ups, (0/90)s and (45/0/-45/0)s, using a hydraulically activated load frame. For high-temperature tests, a two-zone hot rail box furnace was mounted between the hydraulic grips to precisely control the temperature at 1500 F. Two novel digital image correlation (DIC) techniques were utilized to achieve full-field strain measurements at elevated temperature. A lamina-level constitutive model was developed for a single 8HSW CMC ply, including both pre-peak nonlinear response and post-peak softening. A secant- modulus approach was employed to model the pre-peak nonlinear evolution based upon the experimental result on the un-notched tension tests, while the post-peak softening was modeled using the smeared crack approach (SCA). Using the material properties measured from the un-notched tensile tests, the proposed computational model is able to predict the failure strength and strain localization in a notched specimen. © 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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The focus of this paper is to examine the effect of notch on the failure response of an oxide-oxide ceramic matrix composite (CMC) under both room temperature and elevated temperature. The CMC is made of aluminosilicate matrix reinforced by 3M Nextel™ 610 alumina fibers which are woven into an eight-harness satin weave (8HSW) preform. Uniaxial tensile tests were carried out on both un-notched and single-edge-notched specimens of two different lay-ups, (0/90)s and (45/0/-45/0)s, using a hydraulically activated load frame. For high-temperature tests, a two-zone hot rail box furnace was mounted between the hydraulic grips to precisely control the temperature at 1500 F. Two novel digital image correlation (DIC) techniques were utilized to achieve full-field strain measurements at elevated temperature. A lamina-level constitutive model was developed for a single 8HSW CMC ply, including both pre-peak nonlinear response and post-peak softening. A secant- modulus approach was employed to model the pre-peak nonlinear evolution based upon the experimental result on the un-notched tension tests, while the post-peak softening was modeled using the smeared crack approach (SCA). Using the material properties measured from the un-notched tensile tests, the proposed computational model is able to predict the failure strength and strain localization in a notched specimen. © 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.
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2015

Zhang, D; Patel, D K; Waas, A M
A novel two-scale progressive failure analysis method for laminated fiber-reinforced composites Conference
2015.
Abstract | Links | BibTeX | Tags:
@conference{Zhang2015d,
title = {A novel two-scale progressive failure analysis method for laminated fiber-reinforced composites},
author = {D Zhang and D K Patel and A M Waas},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84937859475&partnerID=40&md5=9b2c7dc4473fdc8b92b94b7c3c570cf5},
year = {2015},
date = {2015-01-01},
journal = {56th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference},
abstract = {A novel, two-scale computational model has been developed to predict the progressive damage and failure responses of fiber-reinforced composite laminates using the material properties at the constituent (fiber and matrix) level. These properties were measured from coupon level tests on a unidirectional lamina of the same material system. In the proposed computational scheme, the macroscale finite element analysis (FEA) was carried out at the lamina level of a 3D laminate model, while micromechanical analysis was implemented concurrently at the subscale to compute the local fields at the fiber and matrix scale. Thus, the inuence of matrix microdamage at the microscale manifests as the progressive degradation of the lamina stifiniteness, resulting in the nonlinear evolution of the stress versus strain response, while the lamina stiffness matrix remains positive-definite. The lamina post-peak strain softening response resulting from catastrophic failure modes including fiber tensile breakage, fiber kinking and matrix cracking, were modeled using the smeared crack approach (SCA). The interlaminar failure due to delamination was accounted for through cohesive elements inserted in-between the layers. The predictive capability of the proposed method is illustrated by comparing the computational results with experiment for three different lay-ups of IM-7/977-3 carbon fiber composite laminates subjected to various loading conditions, including both un-notched and open-hole specimens subjected to remote tensile and compressive loading, respectively. © 2015, American Institute of Aeronautics and Astronautics. All Rights Reserved.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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A novel, two-scale computational model has been developed to predict the progressive damage and failure responses of fiber-reinforced composite laminates using the material properties at the constituent (fiber and matrix) level. These properties were measured from coupon level tests on a unidirectional lamina of the same material system. In the proposed computational scheme, the macroscale finite element analysis (FEA) was carried out at the lamina level of a 3D laminate model, while micromechanical analysis was implemented concurrently at the subscale to compute the local fields at the fiber and matrix scale. Thus, the inuence of matrix microdamage at the microscale manifests as the progressive degradation of the lamina stifiniteness, resulting in the nonlinear evolution of the stress versus strain response, while the lamina stiffness matrix remains positive-definite. The lamina post-peak strain softening response resulting from catastrophic failure modes including fiber tensile breakage, fiber kinking and matrix cracking, were modeled using the smeared crack approach (SCA). The interlaminar failure due to delamination was accounted for through cohesive elements inserted in-between the layers. The predictive capability of the proposed method is illustrated by comparing the computational results with experiment for three different lay-ups of IM-7/977-3 carbon fiber composite laminates subjected to various loading conditions, including both un-notched and open-hole specimens subjected to remote tensile and compressive loading, respectively. © 2015, American Institute of Aeronautics and Astronautics. All Rights Reserved.
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Zhang, D; Meyer, P; Waas, A M
Tensile response of oxide/oxide woven ceramic composites Conference
2015.
Abstract | Links | BibTeX | Tags:
@conference{Zhang2015e,
title = {Tensile response of oxide/oxide woven ceramic composites},
author = {D Zhang and P Meyer and A M Waas},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84937856560&partnerID=40&md5=ac1a69ca033030c23b492bda9c7bd0b3},
year = {2015},
date = {2015-01-01},
journal = {56th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference},
abstract = {Room-temperature tensile responses of oxide-oxide woven ceramic matrix composites (CMCs) have been studied for two different lay-ups, including [0/90]s and [+45/0/-45/0]s. The CMC is made of aluminosilicate matrix reinforced by 3M Nextel™ 610 alumina fibers (AS/N610). The dry fiber preform consists of multiple layers of eight-harness satin weave (8HSW) fabric. The digital image correlation (DIC) technique was utilized to map the deformation histories and identify modes of failure for both un-notched and single-edge-notched tension tests. A lamina-level constitutive model was developed for a single 8HSW CMC ply. It is assumed that the pre-peak nonlinear response is only attributed to the in-plane shear. The post-peak strain softening responses were related to the traction-separation laws through the smeared crack approach. Utilizing the ply properties measured from the un-notched [0/90]s and [+45/0/-45/0]s tension tests, the proposed computational model shows accurate predictions for the single-edge-notched tension tests. © American Institute of Aeronautics and Astronautics Inc. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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Room-temperature tensile responses of oxide-oxide woven ceramic matrix composites (CMCs) have been studied for two different lay-ups, including [0/90]<inf>s</inf> and [+45/0/-45/0]<inf>s</inf>. The CMC is made of aluminosilicate matrix reinforced by 3M Nextel™ 610 alumina fibers (AS/N610). The dry fiber preform consists of multiple layers of eight-harness satin weave (8HSW) fabric. The digital image correlation (DIC) technique was utilized to map the deformation histories and identify modes of failure for both un-notched and single-edge-notched tension tests. A lamina-level constitutive model was developed for a single 8HSW CMC ply. It is assumed that the pre-peak nonlinear response is only attributed to the in-plane shear. The post-peak strain softening responses were related to the traction-separation laws through the smeared crack approach. Utilizing the ply properties measured from the un-notched [0/90]<inf>s</inf> and [+45/0/-45/0]<inf>s</inf> tension tests, the proposed computational model shows accurate predictions for the single-edge-notched tension tests. © American Institute of Aeronautics and Astronautics Inc. All rights reserved.
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Zhang, D; Waas, A M; Yen, C -F
Progressive damage and failure responses of hybrid 3D textile composites subjected to dynamic flexural loading Conference
2015.
Abstract | Links | BibTeX | Tags:
@conference{Zhang2015c,
title = {Progressive damage and failure responses of hybrid 3D textile composites subjected to dynamic flexural loading},
author = {D Zhang and A M Waas and C -F Yen},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84966642460&partnerID=40&md5=711d3e27178767023720127c1abb6fd9},
year = {2015},
date = {2015-01-01},
journal = {Proceedings of the American Society for Composites - 30th Technical Conference, ACS 2015},
abstract = {The dynamic flexural response of a hybrid 3D textile composites (H3DTC) was examined through a three-point bend test. The H3DTC contains three different types of constituent fibers, including carbon, glass, and Kevlar that are integrally woven into a single preform. Tests were carried out using a drop tower facility, which can provide different impact velocities by varying the height of the weight that is dropped onto the specimen. High-speed cameras were utilized to record the deformation history and identify the modes of failure. The experimental results show that the development of kink bands in the tows undergoing compressive straining, limits the strength of the H3DTC in flexure, while the final catastrophic failure is due to tow rupture occurring in regions subjected to tensile straining. A global-local multiscale finite element (FE) model was developed to predict the progressive damage and failure response of the H3DTC subjected to low velocity impact. The composite was homogenized as an orthotropic solid at the macroscale, while the damage and failure was incorporated through a mesoscale FE model, which is a collection of repeat unit cells (RUCs) that are composed of fiber tows embedded in a surrounding matrix. A novel micromechanics model was implemented at the fiber-matrix level to compute the fiber tow constitutive responses at the mesoscale. The smeared crack approach (SCA) was employed to model the observed failure modes, including matrix cracking, tow kinking, and tow rupture. The computational results agree well with the experiment. Therefore, the proposed multiscale model can be used as a validated computational tool to understand the effect of textile architecture and constituent properties on the progressive damage and failure responses of 3D textile composites. Copyright © 2015 by DEStech Publications, Inc. and American Society for Composites. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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The dynamic flexural response of a hybrid 3D textile composites (H3DTC) was examined through a three-point bend test. The H3DTC contains three different types of constituent fibers, including carbon, glass, and Kevlar that are integrally woven into a single preform. Tests were carried out using a drop tower facility, which can provide different impact velocities by varying the height of the weight that is dropped onto the specimen. High-speed cameras were utilized to record the deformation history and identify the modes of failure. The experimental results show that the development of kink bands in the tows undergoing compressive straining, limits the strength of the H3DTC in flexure, while the final catastrophic failure is due to tow rupture occurring in regions subjected to tensile straining. A global-local multiscale finite element (FE) model was developed to predict the progressive damage and failure response of the H3DTC subjected to low velocity impact. The composite was homogenized as an orthotropic solid at the macroscale, while the damage and failure was incorporated through a mesoscale FE model, which is a collection of repeat unit cells (RUCs) that are composed of fiber tows embedded in a surrounding matrix. A novel micromechanics model was implemented at the fiber-matrix level to compute the fiber tow constitutive responses at the mesoscale. The smeared crack approach (SCA) was employed to model the observed failure modes, including matrix cracking, tow kinking, and tow rupture. The computational results agree well with the experiment. Therefore, the proposed multiscale model can be used as a validated computational tool to understand the effect of textile architecture and constituent properties on the progressive damage and failure responses of 3D textile composites. Copyright © 2015 by DEStech Publications, Inc. and American Society for Composites. All rights reserved.
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Zhang, D; Waas, A M; Yen, C -F
Progressive damage and failure response of hybrid 3D textile composites subjected to flexural loading, part II: Mechanics based multiscale computational modeling of progressive damage and failure Journal Article
International Journal of Solids and Structures, 75-76 , pp. 321-335, 2015.
Abstract | Links | BibTeX | Tags:
@article{Zhang2015321,
title = {Progressive damage and failure response of hybrid 3D textile composites subjected to flexural loading, part II: Mechanics based multiscale computational modeling of progressive damage and failure},
author = {D Zhang and A M Waas and C -F Yen},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84943455979&doi=10.1016%2fj.ijsolstr.2015.06.033&partnerID=40&md5=12bc1c475468e9e405661b40ee8fe925},
doi = {10.1016/j.ijsolstr.2015.06.033},
year = {2015},
date = {2015-01-01},
journal = {International Journal of Solids and Structures},
volume = {75-76},
pages = {321-335},
abstract = {A mechanics based multiscale computational model is presented to predict the deformation, damage and failure response of hybrid 3D textile composites (H3DTCs) subjected to three-point bending. The geometry of the textile architecture was incorporated in a mesoscale finite element (FE) model, while the H3DTC was homogenized at the macroscale. The mesoscale model is a collection of repeat unit cells (RUCs) that are composed of different types of fiber tows embedded in a surrounding matrix. Matrix microdamage was modeled by a (pre-peak) nonlinear stress versus strain response, using a modified J2 deformation theory of plasticity incorporating a secant-modulus approach. Fiber tow pre-peak nonlinear response was computed using a novel, two-scale model, in which the subscale micromechanical analysis was carried out in closed-form based upon a unit cell of a fiber-matrix concentric cylinder. Consequently, the influence of matrix microdamage developing at the microscale manifests as the progressive degradation of fiber tow stiffness at the mesoscale. The smeared crack approach (SCA) was employed to model the post-peak softening of the constituents due to failure, including matrix macro-cracking, tow kinking, and tow breaking. This method offers a mesh objective result by relating the post-peak softening response to a traction-separation law that is associated with each failure mechanism through a characteristic length. Thus, the total energy release rate during failure in a continuum element is related to the fracture toughness of the material. The load-deflection responses, along with the progressive damage and failure events, including fiber tow kinking and rupture, are successfully predicted through the proposed computational model. In addition, the textile architecture-dependent effect, observed in the asymmetric H3DTCs, is also captured, demonstrating the predictive capability of the proposed modeling scheme. Since all the inputs are from the constituent level, the model is useful in understanding how the macroscopic response of H3DTCs is influenced by textile architecture and constituent properties. The experimental studies are presented in Part I of this two-part sequence (Zhang et al., 2015). © 2015 Elsevier Ltd. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

Close
A mechanics based multiscale computational model is presented to predict the deformation, damage and failure response of hybrid 3D textile composites (H3DTCs) subjected to three-point bending. The geometry of the textile architecture was incorporated in a mesoscale finite element (FE) model, while the H3DTC was homogenized at the macroscale. The mesoscale model is a collection of repeat unit cells (RUCs) that are composed of different types of fiber tows embedded in a surrounding matrix. Matrix microdamage was modeled by a (pre-peak) nonlinear stress versus strain response, using a modified J2 deformation theory of plasticity incorporating a secant-modulus approach. Fiber tow pre-peak nonlinear response was computed using a novel, two-scale model, in which the subscale micromechanical analysis was carried out in closed-form based upon a unit cell of a fiber-matrix concentric cylinder. Consequently, the influence of matrix microdamage developing at the microscale manifests as the progressive degradation of fiber tow stiffness at the mesoscale. The smeared crack approach (SCA) was employed to model the post-peak softening of the constituents due to failure, including matrix macro-cracking, tow kinking, and tow breaking. This method offers a mesh objective result by relating the post-peak softening response to a traction-separation law that is associated with each failure mechanism through a characteristic length. Thus, the total energy release rate during failure in a continuum element is related to the fracture toughness of the material. The load-deflection responses, along with the progressive damage and failure events, including fiber tow kinking and rupture, are successfully predicted through the proposed computational model. In addition, the textile architecture-dependent effect, observed in the asymmetric H3DTCs, is also captured, demonstrating the predictive capability of the proposed modeling scheme. Since all the inputs are from the constituent level, the model is useful in understanding how the macroscopic response of H3DTCs is influenced by textile architecture and constituent properties. The experimental studies are presented in Part I of this two-part sequence (Zhang et al., 2015). © 2015 Elsevier Ltd. All rights reserved.
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doi:10.1016/j.ijsolstr.2015.06.033
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Zhang, D; Waas, A M; Yen, C -F
Progressive damage and failure response of hybrid 3D textile composites subjected to flexural loading, part I: Experimental studies Journal Article
International Journal of Solids and Structures, 75-76 , pp. 309-320, 2015.
Abstract | Links | BibTeX | Tags:
@article{Zhang2015309,
title = {Progressive damage and failure response of hybrid 3D textile composites subjected to flexural loading, part I: Experimental studies},
author = {D Zhang and A M Waas and C -F Yen},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84943455361&doi=10.1016%2fj.ijsolstr.2015.06.034&partnerID=40&md5=464053575dcc7cf6f1b3a15060624073},
doi = {10.1016/j.ijsolstr.2015.06.034},
year = {2015},
date = {2015-01-01},
journal = {International Journal of Solids and Structures},
volume = {75-76},
pages = {309-320},
abstract = {This paper presents an experimental investigation of the deformation responses and failure mechanisms of hybrid 3D textile composites (H3DTCs) subjected to quasi-static three-point bending. The term "hybrid" refers to different constituent fiber tows, including carbon, glass, and Kevlar that are integrally woven into a single preform. Three different hybrid architectures, manufactured by varying the percentages and lay-ups of the constituent fiber tows, were examined to understand the effect of hybridization on the resulting performance enhancement, including the bending modulus, flexural yield stress, and strain to failure. All the architectures show a "plastic-like" nonlinear flexural response, indicating considerable damage tolerance and durability for this class of materials. It has been found that increasing the thickness of the specimens can increase the strain to failure in flexure. For an asymmetric H3DTC, which refers to an architecture that has carbon plies on one side and glass plies on the other (through-the-thickness), an increased flexural yield stress can be achieved by placing the glass on the side that experiences compressive straining in flexure, whereas the failure strain is reduced by placing the carbon on the side which experiences tension. Distributed matrix cracking was observed in regions of predominant tension through a digital image correlation (DIC) technique. Although the experimental results show architecture-dependent responses, fiber tow kinking, which develops on the compressive side of the specimen is determined to be a strength limiting mechanism for this class of materials subjected to flexural loading. The experimental results are subsequently used as a basis for developing a mechanics based multiscale computational model for H3DTC deformation, damage and failure response in flexure. Details of the modeling strategy and the development of damage and failure constitutive models are presented in Part II of this two-part sequence (Zhang et al., 2015). © 2015 Elsevier Ltd. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

Close
This paper presents an experimental investigation of the deformation responses and failure mechanisms of hybrid 3D textile composites (H3DTCs) subjected to quasi-static three-point bending. The term "hybrid" refers to different constituent fiber tows, including carbon, glass, and Kevlar that are integrally woven into a single preform. Three different hybrid architectures, manufactured by varying the percentages and lay-ups of the constituent fiber tows, were examined to understand the effect of hybridization on the resulting performance enhancement, including the bending modulus, flexural yield stress, and strain to failure. All the architectures show a "plastic-like" nonlinear flexural response, indicating considerable damage tolerance and durability for this class of materials. It has been found that increasing the thickness of the specimens can increase the strain to failure in flexure. For an asymmetric H3DTC, which refers to an architecture that has carbon plies on one side and glass plies on the other (through-the-thickness), an increased flexural yield stress can be achieved by placing the glass on the side that experiences compressive straining in flexure, whereas the failure strain is reduced by placing the carbon on the side which experiences tension. Distributed matrix cracking was observed in regions of predominant tension through a digital image correlation (DIC) technique. Although the experimental results show architecture-dependent responses, fiber tow kinking, which develops on the compressive side of the specimen is determined to be a strength limiting mechanism for this class of materials subjected to flexural loading. The experimental results are subsequently used as a basis for developing a mechanics based multiscale computational model for H3DTC deformation, damage and failure response in flexure. Details of the modeling strategy and the development of damage and failure constitutive models are presented in Part II of this two-part sequence (Zhang et al., 2015). © 2015 Elsevier Ltd. All rights reserved.
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doi:10.1016/j.ijsolstr.2015.06.034
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Zhang, D; Patel, D K; Waas, A M
A novel two-scale progressive failure analysis method for laminated fiber-reinforced composites Conference
2015.
Abstract | Links | BibTeX | Tags:
@conference{Zhang2015f,
title = {A novel two-scale progressive failure analysis method for laminated fiber-reinforced composites},
author = {D Zhang and D K Patel and A M Waas},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84937859475&partnerID=40&md5=9b2c7dc4473fdc8b92b94b7c3c570cf5},
year = {2015},
date = {2015-01-01},
journal = {56th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference},
abstract = {A novel, two-scale computational model has been developed to predict the progressive damage and failure responses of fiber-reinforced composite laminates using the material properties at the constituent (fiber and matrix) level. These properties were measured from coupon level tests on a unidirectional lamina of the same material system. In the proposed computational scheme, the macroscale finite element analysis (FEA) was carried out at the lamina level of a 3D laminate model, while micromechanical analysis was implemented concurrently at the subscale to compute the local fields at the fiber and matrix scale. Thus, the inuence of matrix microdamage at the microscale manifests as the progressive degradation of the lamina stifiniteness, resulting in the nonlinear evolution of the stress versus strain response, while the lamina stiffness matrix remains positive-definite. The lamina post-peak strain softening response resulting from catastrophic failure modes including fiber tensile breakage, fiber kinking and matrix cracking, were modeled using the smeared crack approach (SCA). The interlaminar failure due to delamination was accounted for through cohesive elements inserted in-between the layers. The predictive capability of the proposed method is illustrated by comparing the computational results with experiment for three different lay-ups of IM-7/977-3 carbon fiber composite laminates subjected to various loading conditions, including both un-notched and open-hole specimens subjected to remote tensile and compressive loading, respectively. © 2015, American Institute of Aeronautics and Astronautics. All Rights Reserved.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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A novel, two-scale computational model has been developed to predict the progressive damage and failure responses of fiber-reinforced composite laminates using the material properties at the constituent (fiber and matrix) level. These properties were measured from coupon level tests on a unidirectional lamina of the same material system. In the proposed computational scheme, the macroscale finite element analysis (FEA) was carried out at the lamina level of a 3D laminate model, while micromechanical analysis was implemented concurrently at the subscale to compute the local fields at the fiber and matrix scale. Thus, the inuence of matrix microdamage at the microscale manifests as the progressive degradation of the lamina stifiniteness, resulting in the nonlinear evolution of the stress versus strain response, while the lamina stiffness matrix remains positive-definite. The lamina post-peak strain softening response resulting from catastrophic failure modes including fiber tensile breakage, fiber kinking and matrix cracking, were modeled using the smeared crack approach (SCA). The interlaminar failure due to delamination was accounted for through cohesive elements inserted in-between the layers. The predictive capability of the proposed method is illustrated by comparing the computational results with experiment for three different lay-ups of IM-7/977-3 carbon fiber composite laminates subjected to various loading conditions, including both un-notched and open-hole specimens subjected to remote tensile and compressive loading, respectively. © 2015, American Institute of Aeronautics and Astronautics. All Rights Reserved.
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Zhang, D; Meyer, P; Waas, A M
Tensile response of oxide/oxide woven ceramic composites Conference
2015.
Abstract | Links | BibTeX | Tags:
@conference{Zhang2015g,
title = {Tensile response of oxide/oxide woven ceramic composites},
author = {D Zhang and P Meyer and A M Waas},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84937856560&partnerID=40&md5=ac1a69ca033030c23b492bda9c7bd0b3},
year = {2015},
date = {2015-01-01},
journal = {56th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference},
abstract = {Room-temperature tensile responses of oxide-oxide woven ceramic matrix composites (CMCs) have been studied for two different lay-ups, including [0/90]s and [+45/0/-45/0]s. The CMC is made of aluminosilicate matrix reinforced by 3M Nextel™ 610 alumina fibers (AS/N610). The dry fiber preform consists of multiple layers of eight-harness satin weave (8HSW) fabric. The digital image correlation (DIC) technique was utilized to map the deformation histories and identify modes of failure for both un-notched and single-edge-notched tension tests. A lamina-level constitutive model was developed for a single 8HSW CMC ply. It is assumed that the pre-peak nonlinear response is only attributed to the in-plane shear. The post-peak strain softening responses were related to the traction-separation laws through the smeared crack approach. Utilizing the ply properties measured from the un-notched [0/90]s and [+45/0/-45/0]s tension tests, the proposed computational model shows accurate predictions for the single-edge-notched tension tests. © American Institute of Aeronautics and Astronautics Inc. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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Room-temperature tensile responses of oxide-oxide woven ceramic matrix composites (CMCs) have been studied for two different lay-ups, including [0/90]<inf>s</inf> and [+45/0/-45/0]<inf>s</inf>. The CMC is made of aluminosilicate matrix reinforced by 3M Nextel™ 610 alumina fibers (AS/N610). The dry fiber preform consists of multiple layers of eight-harness satin weave (8HSW) fabric. The digital image correlation (DIC) technique was utilized to map the deformation histories and identify modes of failure for both un-notched and single-edge-notched tension tests. A lamina-level constitutive model was developed for a single 8HSW CMC ply. It is assumed that the pre-peak nonlinear response is only attributed to the in-plane shear. The post-peak strain softening responses were related to the traction-separation laws through the smeared crack approach. Utilizing the ply properties measured from the un-notched [0/90]<inf>s</inf> and [+45/0/-45/0]<inf>s</inf> tension tests, the proposed computational model shows accurate predictions for the single-edge-notched tension tests. © American Institute of Aeronautics and Astronautics Inc. All rights reserved.
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2014

Zhang, D; Waas, A M; Yen, C -F
Progressive failure analysis on textile composites Conference
2014.
Abstract | Links | BibTeX | Tags:
@conference{Zhang2014,
title = {Progressive failure analysis on textile composites},
author = {D Zhang and A M Waas and C -F Yen},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84894449831&doi=10.2514%2f6.2014-0157&partnerID=40&md5=fabfe10d09a41ffd4dcd2cbfb88a1e02},
doi = {10.2514/6.2014-0157},
year = {2014},
date = {2014-01-01},
journal = {55th AIAA/ASMe/ASCE/AHS/SC Structures, Structural Dynamics, and Materials Conference},
abstract = {The flexrual response of a layer-to-layer orthogonal interlocked 3D textile composite (3DTC) has been investigated through quasi-static three-point bending. Fiber tow kinking on the compressive side of the fiexed specimens has been found to be a strength limiting mechanism for both warp and weft panels. The digital image correlation technique has been utilized to map the deformation and identify matrix micro-cracking on the tensile side prior to the peak load in the warp direction loaded panels. It is shown that the geometrical characteristics of textile reinforcement play a key role on the mechanical response of this class of material. A mechanism based multiscale computational model that considers the influence of textile architecture has been developed to capture the observed damage and failure characteristics. The fiber tows and surrounding polymer matrix are modeled at the mesoscale, while the 3DTC is homogenized at the macroscale. The pre-peak non- linear response of the fiber tow is modeled using a novel, two-scale model, in which the subscale micromechanical analysis is carried out in close form. The influence of the matrix microdamage at the microscale manifests as the progressive degradation of the fiber tow stiffness at the mesoscale. The post-peak strain softening responses of the fiber tows and the surrounding polymer matrix are modeled through the smeared crack approach (SCA). The load-deflection response, along with the observed damage events, including matrix cracking, tow kinking, and tow tensile breakage, are successfully captured through the proposed computational model. Therefore, the proposed multiscale model is suitable for progressive damage and failure analysis of 3DTCs and specifically to study the influence of textile architecture on macroscopic response.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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The flexrual response of a layer-to-layer orthogonal interlocked 3D textile composite (3DTC) has been investigated through quasi-static three-point bending. Fiber tow kinking on the compressive side of the fiexed specimens has been found to be a strength limiting mechanism for both warp and weft panels. The digital image correlation technique has been utilized to map the deformation and identify matrix micro-cracking on the tensile side prior to the peak load in the warp direction loaded panels. It is shown that the geometrical characteristics of textile reinforcement play a key role on the mechanical response of this class of material. A mechanism based multiscale computational model that considers the influence of textile architecture has been developed to capture the observed damage and failure characteristics. The fiber tows and surrounding polymer matrix are modeled at the mesoscale, while the 3DTC is homogenized at the macroscale. The pre-peak non- linear response of the fiber tow is modeled using a novel, two-scale model, in which the subscale micromechanical analysis is carried out in close form. The influence of the matrix microdamage at the microscale manifests as the progressive degradation of the fiber tow stiffness at the mesoscale. The post-peak strain softening responses of the fiber tows and the surrounding polymer matrix are modeled through the smeared crack approach (SCA). The load-deflection response, along with the observed damage events, including matrix cracking, tow kinking, and tow tensile breakage, are successfully captured through the proposed computational model. Therefore, the proposed multiscale model is suitable for progressive damage and failure analysis of 3DTCs and specifically to study the influence of textile architecture on macroscopic response.
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doi:10.2514/6.2014-0157
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Zhang, D; Waas, A M
A micromechanics based multiscale model for nonlinear composites Journal Article
Acta Mechanica, 225 (4-5), pp. 1391-1417, 2014.
Abstract | Links | BibTeX | Tags:
@article{Zhang20141391,
title = {A micromechanics based multiscale model for nonlinear composites},
author = {D Zhang and A M Waas},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84898026268&doi=10.1007%2fs00707-013-1057-1&partnerID=40&md5=351ebbd0acba10dc02a082baee41e528},
doi = {10.1007/s00707-013-1057-1},
year = {2014},
date = {2014-01-01},
journal = {Acta Mechanica},
volume = {225},
number = {4-5},
pages = {1391-1417},
abstract = {A micromechanics model for fiber-reinforced composites that can be used at the subscale in a multiscale computational framework is established to predict the effective nonlinear composite response. Using a fiber-matrix concentric cylinder model as the basic repeat unit to represent the composite, micromechanics is used to relate the applied composite strains to the fiber and matrix strains by a six by six transformation matrix. The resolved spatial variations of the matrix fields are found to be in good agreement with corresponding finite element analysis results. The evolution of the composite nonlinear response is assumed to be governed by two scalar, strain-based variables that are related to the extreme value of an appropriately defined matrix equivalent strain, and the matrix secant moduli are used to compute the composite secant moduli for nonlinear analysis. The results from the micromechanics model are compared well with a full finite element analysis. The predictive capability of the proposed model is illustrated by two distinct fiber-reinforced material systems, carbon and glass, for the fiber volume fraction varying from 50 to 70 %. Since fully analytical solutions are utilized for the micromechanical analysis, the proposed method offers a distinct computational advantage in a multiscale analysis and is therefore suitable for large-scale progressive damage and failure analyses of composite material structures. © 2014 Springer-Verlag Wien.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

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A micromechanics model for fiber-reinforced composites that can be used at the subscale in a multiscale computational framework is established to predict the effective nonlinear composite response. Using a fiber-matrix concentric cylinder model as the basic repeat unit to represent the composite, micromechanics is used to relate the applied composite strains to the fiber and matrix strains by a six by six transformation matrix. The resolved spatial variations of the matrix fields are found to be in good agreement with corresponding finite element analysis results. The evolution of the composite nonlinear response is assumed to be governed by two scalar, strain-based variables that are related to the extreme value of an appropriately defined matrix equivalent strain, and the matrix secant moduli are used to compute the composite secant moduli for nonlinear analysis. The results from the micromechanics model are compared well with a full finite element analysis. The predictive capability of the proposed model is illustrated by two distinct fiber-reinforced material systems, carbon and glass, for the fiber volume fraction varying from 50 to 70 %. Since fully analytical solutions are utilized for the micromechanical analysis, the proposed method offers a distinct computational advantage in a multiscale analysis and is therefore suitable for large-scale progressive damage and failure analyses of composite material structures. © 2014 Springer-Verlag Wien.
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doi:10.1007/s00707-013-1057-1
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2013

Zhang, D; Waas, A; Yen, C -F
Flexural response of 3D hybrid textile composites Conference
1 , 2013.
Abstract | Links | BibTeX | Tags:
@conference{Zhang2013939,
title = {Flexural response of 3D hybrid textile composites},
author = {D Zhang and A Waas and C -F Yen},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84892905214&partnerID=40&md5=896f0d5cb34ec35de33bbceefee81792},
year = {2013},
date = {2013-01-01},
journal = {28th Annual Technical Conference of the American Society for Composites 2013, ASC 2013},
volume = {1},
pages = {939-956},
abstract = {This paper presents an experimental investigation on the flexural response of 3D hybrid textile composites subjected to quasi-static three-point bending. The term "hybrid" here refers to different constituent fibers, including carbon, glass, and Kevlar, that are integrally woven into a single preform. Three different hybrid architectures, manufactured by varying the percentages and lay-ups of each constituent fiber, were examined to understand the effect of hybridization and the resulting performance enhancement, including the bending modulus, flexural strength, and strain to failure. Although the experimental results show architecture-dependent flexural response, fiber tow kinking on the compressive side of the specimen is determined to be a strength limiting mechanism for this class of materials.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

Close
This paper presents an experimental investigation on the flexural response of 3D hybrid textile composites subjected to quasi-static three-point bending. The term "hybrid" here refers to different constituent fibers, including carbon, glass, and Kevlar, that are integrally woven into a single preform. Three different hybrid architectures, manufactured by varying the percentages and lay-ups of each constituent fiber, were examined to understand the effect of hybridization and the resulting performance enhancement, including the bending modulus, flexural strength, and strain to failure. Although the experimental results show architecture-dependent flexural response, fiber tow kinking on the compressive side of the specimen is determined to be a strength limiting mechanism for this class of materials.
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2012

Pankow, M; Yen, C -F; Rudolph, M; Justusson, B; Zhang, D; Waas, A M
Experimental investigation on the deformation response of hybrid 3D woven composites Conference
2012.
Abstract | Links | BibTeX | Tags:
@conference{Pankow2012b,
title = {Experimental investigation on the deformation response of hybrid 3D woven composites},
author = {M Pankow and C -F Yen and M Rudolph and B Justusson and D Zhang and A M Waas},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84880786978&partnerID=40&md5=ad684f90d7fb6847d9d2f2856c277d9a},
year = {2012},
date = {2012-01-01},
journal = {53rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference 2012},
abstract = {This paper presents results of an experimental investigation on the tensile response of "hybrid" 3D woven composites (H3DWC), where "hybrid" refers to different constituent fibers, including carbon, glass, and kevlar that are integrally woven into a single preform. The H3DWCs are made through a 3D textile weaving process. Five different versions of hybridized architectures were examined to determine the progression of failure under tensile loading. The different types of H3DWC were compared against one another to understand the benefits of hybridization and the resulting performance enhancements. © 2012 by the American Institute of Aeronautics and Astronautics, Inc.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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This paper presents results of an experimental investigation on the tensile response of "hybrid" 3D woven composites (H3DWC), where "hybrid" refers to different constituent fibers, including carbon, glass, and kevlar that are integrally woven into a single preform. The H3DWCs are made through a 3D textile weaving process. Five different versions of hybridized architectures were examined to determine the progression of failure under tensile loading. The different types of H3DWC were compared against one another to understand the benefits of hybridization and the resulting performance enhancements. © 2012 by the American Institute of Aeronautics and Astronautics, Inc.
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Pankow, M; Yen, C -F; Rudolph, M; Justusson, B; Zhang, D; Waas, A M
Experimental investigation on the deformation response of hybrid 3d woven composites Conference
2012.
Abstract | Links | BibTeX | Tags:
@conference{Pankow2012b,
title = {Experimental investigation on the deformation response of hybrid 3d woven composites},
author = {M Pankow and C -F Yen and M Rudolph and B Justusson and D Zhang and A M Waas},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84881402300&partnerID=40&md5=342f6c938423854486b78465d0a63fe9},
year = {2012},
date = {2012-01-01},
journal = {Collection of Technical Papers - AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference},
abstract = {This paper presents results of an experimental investigation on the tensile response of hybrid" 3D woven composites (H3DWC), where hybrid" refers to different constituent fibers, including carbon, glass, and kevlar that are integrally woven into a single preform. The H3DWCs are made through a 3D textile weaving process. Five different versions of hybridized architectures were examined to determine the progression of failure under tensile loading. The different types of H3DWC were compared against one another to understand the benefits of hybridization and the resulting performance enhancements. © 2012 AIAA.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

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This paper presents results of an experimental investigation on the tensile response of hybrid" 3D woven composites (H3DWC), where hybrid" refers to different constituent fibers, including carbon, glass, and kevlar that are integrally woven into a single preform. The H3DWCs are made through a 3D textile weaving process. Five different versions of hybridized architectures were examined to determine the progression of failure under tensile loading. The different types of H3DWC were compared against one another to understand the benefits of hybridization and the resulting performance enhancements. © 2012 AIAA.
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https://www.scopus.com/inward/record.uri?eid=2-s2.0-84881402300&partnerID=40[...]
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Pankow, M; Yen, C -F; Rudolph, M; Justusson, B; Zhang, D; Waas, A M
Experimental investigation on the deformation response of hybrid 3D woven composites Conference
2012.
Abstract | Links | BibTeX | Tags:
@conference{Pankow2012c,
title = {Experimental investigation on the deformation response of hybrid 3D woven composites},
author = {M Pankow and C -F Yen and M Rudolph and B Justusson and D Zhang and A M Waas},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84880786978&partnerID=40&md5=ad684f90d7fb6847d9d2f2856c277d9a},
year = {2012},
date = {2012-01-01},
journal = {53rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference 2012},
abstract = {This paper presents results of an experimental investigation on the tensile response of "hybrid" 3D woven composites (H3DWC), where "hybrid" refers to different constituent fibers, including carbon, glass, and kevlar that are integrally woven into a single preform. The H3DWCs are made through a 3D textile weaving process. Five different versions of hybridized architectures were examined to determine the progression of failure under tensile loading. The different types of H3DWC were compared against one another to understand the benefits of hybridization and the resulting performance enhancements. © 2012 by the American Institute of Aeronautics and Astronautics, Inc.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}

Close
This paper presents results of an experimental investigation on the tensile response of "hybrid" 3D woven composites (H3DWC), where "hybrid" refers to different constituent fibers, including carbon, glass, and kevlar that are integrally woven into a single preform. The H3DWCs are made through a 3D textile weaving process. Five different versions of hybridized architectures were examined to determine the progression of failure under tensile loading. The different types of H3DWC were compared against one another to understand the benefits of hybridization and the resulting performance enhancements. © 2012 by the American Institute of Aeronautics and Astronautics, Inc.
Close
https://www.scopus.com/inward/record.uri?eid=2-s2.0-84880786978&partnerID=40[...]
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Zhang, D; Waas, A M; Pankow, M; Yen, C F; Ghiorse, S
Flexural behavior of a layer-to-layer orthogonal interlocked three-dimensional textile composite Journal Article
Journal of Engineering Materials and Technology, Transactions of the ASME, 134 (3), pp. 31009-1-31009-8, 2012.
Abstract | Links | BibTeX | Tags:
@article{Zhang201231009-1,
title = {Flexural behavior of a layer-to-layer orthogonal interlocked three-dimensional textile composite},
author = {D Zhang and A M Waas and M Pankow and C F Yen and S Ghiorse},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84894470451&doi=10.1115%2f1.4006501&partnerID=40&md5=77a4bfd484bfb0dfa1197e2357a14f2e},
doi = {10.1115/1.4006501},
year = {2012},
date = {2012-01-01},
journal = {Journal of Engineering Materials and Technology, Transactions of the ASME},
volume = {134},
number = {3},
pages = {31009-1-31009-8},
abstract = {The flexural response of a three-dimensional (3D) layer-to-layer orthogonal interlocked textile composite has been investigated under quasi-static three-point bending. Fiber tow kinking on the compressive side of the flexed specimens has been found to be a strength limiting mechanism for both warp and weft panels. The digital image correlation (DIC) technique has been utilized to map the deformation and identify the matrix microcracking on the tensile side prior to the peak load in the warp direction loaded panels. It has been shown that the geometrical characteristics of textile reinforcement play a key role in the mechanical response of this class of material. A 3D local-global finite element (FE) model that reflects the textile architectures has been proposed to successfully capture the surface strain localizations in the predamage region. To analyze the kink banding event, the fiber tow is modeled as an inelastic degrading homogenized orthotropic solid in a state of plane stress based on Schapery Theory (ST). The predicted peak stress is in agreement with the tow kinking stress obtained from the 3D FE model. © 2012 by ASME.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

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The flexural response of a three-dimensional (3D) layer-to-layer orthogonal interlocked textile composite has been investigated under quasi-static three-point bending. Fiber tow kinking on the compressive side of the flexed specimens has been found to be a strength limiting mechanism for both warp and weft panels. The digital image correlation (DIC) technique has been utilized to map the deformation and identify the matrix microcracking on the tensile side prior to the peak load in the warp direction loaded panels. It has been shown that the geometrical characteristics of textile reinforcement play a key role in the mechanical response of this class of material. A 3D local-global finite element (FE) model that reflects the textile architectures has been proposed to successfully capture the surface strain localizations in the predamage region. To analyze the kink banding event, the fiber tow is modeled as an inelastic degrading homogenized orthotropic solid in a state of plane stress based on Schapery Theory (ST). The predicted peak stress is in agreement with the tow kinking stress obtained from the 3D FE model. © 2012 by ASME.
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doi:10.1115/1.4006501
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