https://sam.ensam.eu:443 The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material. Fri, 12 Jun 2026 11:01:48 GMT 2026-06-12T11:01:48Z http://hdl.handle.net/10985/7934 Multiscale fatigue damage characterization in short glass fiber reinforced polyamide-66 ARIF, Muhamad Fatikul; CHEMISKY, Yves; ROBERT, Gilles; FITOUSSI, Joseph; MERAGHNI, Fodil; SAINTIER, Nicolas This paper aims at studying fatigue damage behavior of injection molded 30 wt% short glass fiber reinforced polyamide-66 composite (PA66/GF30). The evolution of dynamic modulus, hysteresis area, cyclic creep and temperature during fatigue tests were analyzed and discussed. Damage analyses by X-ray micro-computed tomography (lCT) technique on interrupted fatigue tests at several percentages of total fatigue life were performed to further understand the damage mechanisms and evolution during fatigue loading. It can be observed that experimental results related to the evolution of dynamic modulus, strain, temperature and energy dissipation are important and consistently complement each other for damage evaluation of PA66/GF30. During fatigue loading, diffuse damage occurs over the entire specimen though the damage does not necessarily exhibit the same level between different locations inside the specimen. The lCT analysis of voids characteristics demonstrates that the damage continuously increases during fatigue loading. The damage is developed notably along fiber interface in the form of fiber/matrix interfacial debonding. Wed, 01 Jan 2014 00:00:00 GMT http://hdl.handle.net/10985/7934 2014-01-01T00:00:00Z ARIF, Muhamad Fatikul CHEMISKY, Yves ROBERT, Gilles FITOUSSI, Joseph MERAGHNI, Fodil SAINTIER, Nicolas This paper aims at studying fatigue damage behavior of injection molded 30 wt% short glass fiber reinforced polyamide-66 composite (PA66/GF30). The evolution of dynamic modulus, hysteresis area, cyclic creep and temperature during fatigue tests were analyzed and discussed. Damage analyses by X-ray micro-computed tomography (lCT) technique on interrupted fatigue tests at several percentages of total fatigue life were performed to further understand the damage mechanisms and evolution during fatigue loading. It can be observed that experimental results related to the evolution of dynamic modulus, strain, temperature and energy dissipation are important and consistently complement each other for damage evaluation of PA66/GF30. During fatigue loading, diffuse damage occurs over the entire specimen though the damage does not necessarily exhibit the same level between different locations inside the specimen. The lCT analysis of voids characteristics demonstrates that the damage continuously increases during fatigue loading. The damage is developed notably along fiber interface in the form of fiber/matrix interfacial debonding. http://hdl.handle.net/10985/10354 Fatigue damage in short glass fiber reinforced PA66: Micromechanical modeling and multiscale identification approach DESPRINGRE, Nicolas; CHEMISKY, Yves; MERAGHNI, Fodil; FITOUSSI, Joseph; ROBERT, Gilles The paper presents a new micromechanical high cycle fatigue visco-damage model for short glass fiber reinforced thermoplastic composites, namely: PA66/GF30. This material, extensively used for automotive applications, has a specific microstructure which is induced by the injection process. The multi-scale developed approach is a modified Mori-Tanaka method that includes coated reinforcements and the evolution of micro-scale damage processes. The description of the damage processes is based on the experimental investigations of damage mechanisms previously performed by the authors and presented elsewhere [M.F. Arif et al. "In situ damage mechanisms investigation of PA66/GF30 composite: Effect of relative humidity." Composites Part B: Engineering, Volume 61: 55-65, 2014]. Damage chronologies have been proposed involving three different local degradation processes: fiber-matrix interface debonding/coating degradation, matrix microcracking and fiber breakage. Their occurrence strongly depends on the microstructure and the moisture content. The developed model integrates these damage kinetics and accounts for the complex matrix viscoelasticity and the reinforcement orientation distributions induced by the process. Each damage mechanism is introduced through an evolution law involving local stress fields computed at the microscale. The developed constitutive law at the representative volume element scale is implemented into the finite element code Abaqus using a User MATerial subroutine. The model identification is performed via reverse engineering, taking advantage of the multiscale experimental results: in-situ SEM tests as well as quantitative and qualitative μCT investigations. Experimental validation is achieved using high cycle strain controlled fatigue tests. Thu, 01 Jan 2015 00:00:00 GMT http://hdl.handle.net/10985/10354 2015-01-01T00:00:00Z DESPRINGRE, Nicolas CHEMISKY, Yves MERAGHNI, Fodil FITOUSSI, Joseph ROBERT, Gilles The paper presents a new micromechanical high cycle fatigue visco-damage model for short glass fiber reinforced thermoplastic composites, namely: PA66/GF30. This material, extensively used for automotive applications, has a specific microstructure which is induced by the injection process. The multi-scale developed approach is a modified Mori-Tanaka method that includes coated reinforcements and the evolution of micro-scale damage processes. The description of the damage processes is based on the experimental investigations of damage mechanisms previously performed by the authors and presented elsewhere [M.F. Arif et al. "In situ damage mechanisms investigation of PA66/GF30 composite: Effect of relative humidity." Composites Part B: Engineering, Volume 61: 55-65, 2014]. Damage chronologies have been proposed involving three different local degradation processes: fiber-matrix interface debonding/coating degradation, matrix microcracking and fiber breakage. Their occurrence strongly depends on the microstructure and the moisture content. The developed model integrates these damage kinetics and accounts for the complex matrix viscoelasticity and the reinforcement orientation distributions induced by the process. Each damage mechanism is introduced through an evolution law involving local stress fields computed at the microscale. The developed constitutive law at the representative volume element scale is implemented into the finite element code Abaqus using a User MATerial subroutine. The model identification is performed via reverse engineering, taking advantage of the multiscale experimental results: in-situ SEM tests as well as quantitative and qualitative μCT investigations. Experimental validation is achieved using high cycle strain controlled fatigue tests. http://hdl.handle.net/10985/17326 In situ X-ray tomography investigation on damage mechanisms in short glass fibre reinforced thermoplastics: Effects of fibre orientation and relative humidity ROLLAND, Héloise; SAINTIER, Nicolas; WILSON, Pablo; MERZEAU, Jonathan; ROBERT, Gilles Damage mechanisms of reinforced polyamide 6,6 have been studied in 3D through in situ X-ray tomography tensile tests. 3D pictures of the microstructure have been taken during tensile tests to catch damage evolution in the bulk of material. The effects of relative humidity and orientation sampling are particularly investigated in this paper. Main mechanisms have been identified such as fibre failure, debonding, damage at fibre ends and matrix damage (cavitation, fibrillation, damage growth). Qualitative observations reveal that the mechanisms are very sensitive to orientation sampling and relative humidity of the specimen. A specific procedure was developed to propose a quantitative analysis of the results. This analysis shows that identified mechanisms not only have different proportions but also have different kinetics according to relative humidity and orientation sampling of the specimen. Sun, 01 Jan 2017 00:00:00 GMT http://hdl.handle.net/10985/17326 2017-01-01T00:00:00Z ROLLAND, Héloise SAINTIER, Nicolas WILSON, Pablo MERZEAU, Jonathan ROBERT, Gilles Damage mechanisms of reinforced polyamide 6,6 have been studied in 3D through in situ X-ray tomography tensile tests. 3D pictures of the microstructure have been taken during tensile tests to catch damage evolution in the bulk of material. The effects of relative humidity and orientation sampling are particularly investigated in this paper. Main mechanisms have been identified such as fibre failure, debonding, damage at fibre ends and matrix damage (cavitation, fibrillation, damage growth). Qualitative observations reveal that the mechanisms are very sensitive to orientation sampling and relative humidity of the specimen. A specific procedure was developed to propose a quantitative analysis of the results. This analysis shows that identified mechanisms not only have different proportions but also have different kinetics according to relative humidity and orientation sampling of the specimen. http://hdl.handle.net/10985/16475 Fatigue damage mechanisms of short fiber reinforced PA66 as observed by in-situ synchrotron X-ray microtomography ROLLAND, Héloise; SAINTIER, Nicolas; RAPHAEL, Ilan; LENOIR, Nicolas; KING, Andrew; ROBERT, Gilles The understanding of fatigue damage mechanisms of short fiber reinforced thermoplastics are a key issue in order to optimize material processing and propose physically based multiscale fatigue damage models. The presented work aims at a fine description of 3D damage development as observed by synchrotron X-ray microtomography. Damage processes at the micro and mesoscale are fully described in order to extract the elementary damage mechanisms, their sequence and kinetics. The effects of local fiber configuration and orientation are particularly detailed. From observations it is clearly evidenced that cavitation plays a major role in the fatigue damage process as it triggers all elementary damage mechanisms observed at the microscale. It is also shown that a characteristic length appears in the fatigue damage development. This internal length is in the order of magnitude of the spherulite size, suggesting a strong impact of the spherulite size on the fatigue damage development. Finally the effect of local fiber orientation on the micro and meso crack orientation is presented. Mon, 01 Jan 2018 00:00:00 GMT http://hdl.handle.net/10985/16475 2018-01-01T00:00:00Z ROLLAND, Héloise SAINTIER, Nicolas RAPHAEL, Ilan LENOIR, Nicolas KING, Andrew ROBERT, Gilles The understanding of fatigue damage mechanisms of short fiber reinforced thermoplastics are a key issue in order to optimize material processing and propose physically based multiscale fatigue damage models. The presented work aims at a fine description of 3D damage development as observed by synchrotron X-ray microtomography. Damage processes at the micro and mesoscale are fully described in order to extract the elementary damage mechanisms, their sequence and kinetics. The effects of local fiber configuration and orientation are particularly detailed. From observations it is clearly evidenced that cavitation plays a major role in the fatigue damage process as it triggers all elementary damage mechanisms observed at the microscale. It is also shown that a characteristic length appears in the fatigue damage development. This internal length is in the order of magnitude of the spherulite size, suggesting a strong impact of the spherulite size on the fatigue damage development. Finally the effect of local fiber orientation on the micro and meso crack orientation is presented. http://hdl.handle.net/10985/25885 Viscoelastic–viscoplastic model with ductile damage accounting for tension–compression asymmetry and hydrostatic pressure effect for polyamide 66 SATOURI, Soheil; CHATZIGEORGIOU, George; MERAGHNI, Fodil; ROBERT, Gilles This paper proposes a model for predicting the complex inelastic mechanical response of polyamide 66. Polyamide 66 is a semi-crystalline pressure-sensitive polymer that exhibits asymmetric yielding behavior, in which the yield strength is slightly higher in compression. With this in mind, an �� 1 -�� 2 yield function considering the asymmetric behavior and the hydrostatic pressure effect is presented and integrated into a phenomenological viscoelastic–viscoplastic model accounting for ductile damage. The corresponding thermodynamic framework and constitutive laws are discussed. Then, an experimental approach is presented to identify the model parameters through mechanical tests with different loading paths to capture the active mechanisms. The experimental findings obtained from uni-axial and multi-axial (tension-torsion) mechanical tests and the numerical model are used in an optimization algorithm to identify the model parameters. A parametric analysis is performed to study the effect of the asymmetric behavior on the state variables under different loading conditions using the identified parameters. The present model responses are in good agreement with the experimental data, and the combination of the experimental and numerical results demonstrates and statesthe asymmetric behavior of polyamide at relative humidity (RH) of 50%, which is captured by the suggested model. It is also worth pointing out that the parametric study conducted on a notched plate using finite element simulations showcases the structural computation capabilities of the proposed model. Sat, 01 Mar 2025 00:00:00 GMT http://hdl.handle.net/10985/25885 2025-03-01T00:00:00Z SATOURI, Soheil CHATZIGEORGIOU, George MERAGHNI, Fodil ROBERT, Gilles This paper proposes a model for predicting the complex inelastic mechanical response of polyamide 66. Polyamide 66 is a semi-crystalline pressure-sensitive polymer that exhibits asymmetric yielding behavior, in which the yield strength is slightly higher in compression. With this in mind, an �� 1 -�� 2 yield function considering the asymmetric behavior and the hydrostatic pressure effect is presented and integrated into a phenomenological viscoelastic–viscoplastic model accounting for ductile damage. The corresponding thermodynamic framework and constitutive laws are discussed. Then, an experimental approach is presented to identify the model parameters through mechanical tests with different loading paths to capture the active mechanisms. The experimental findings obtained from uni-axial and multi-axial (tension-torsion) mechanical tests and the numerical model are used in an optimization algorithm to identify the model parameters. A parametric analysis is performed to study the effect of the asymmetric behavior on the state variables under different loading conditions using the identified parameters. The present model responses are in good agreement with the experimental data, and the combination of the experimental and numerical results demonstrates and statesthe asymmetric behavior of polyamide at relative humidity (RH) of 50%, which is captured by the suggested model. It is also worth pointing out that the parametric study conducted on a notched plate using finite element simulations showcases the structural computation capabilities of the proposed model. http://hdl.handle.net/10985/23925 Cycle jump technique combined with mean-field micromechanics towards predicting the cyclic response of PA66/GF composites under viscoelastic- viscoplastic regime and damage mechanisms CHEN, Qiang; CHATZIGEORGIOU, George; ROBERT, Gilles; MERAGHNI, Fodil This work proposes a probabilistic micromechanics damage framework to predict the uniaxial and cyclic stress-strain response and progressive damage in random glass-reinforced polyamide composites. Motivated by different microscopic degradation modes observed experimentally, the damage mechanism in the vicinity of the fibers is characterized by the onset and the coalescence of voids, whose evolution can be formulated through a Weibull probabilistic density function. In contrast, the ductile progressive degradation of matrix initial stiffness is analyzed via the continuum damage theory. Towards this end, a 2N+1-phase Mori-Tanaka (MT) method combined with the transformation field analysis approach (TFA) is established within a unified framework. Moreover, the rate-dependent viscoelastic and viscoplastic response of the polymer matrix phase is formulated through a phenomenological model consisting of four Kelvin-Voigt branches and a viscoplastic branch under the thermodynamics framework. Comparison of numerical predictions with experimental data demonstrates the model’s capabilities. In a second step of this work, the micromechanics scheme is combined with the cycle-jump technique in order to simulate moderate and high cycle fatigue tests. This modeling strategy is validated through comparison with experimental results. Sat, 01 Jul 2023 00:00:00 GMT http://hdl.handle.net/10985/23925 2023-07-01T00:00:00Z CHEN, Qiang CHATZIGEORGIOU, George ROBERT, Gilles MERAGHNI, Fodil This work proposes a probabilistic micromechanics damage framework to predict the uniaxial and cyclic stress-strain response and progressive damage in random glass-reinforced polyamide composites. Motivated by different microscopic degradation modes observed experimentally, the damage mechanism in the vicinity of the fibers is characterized by the onset and the coalescence of voids, whose evolution can be formulated through a Weibull probabilistic density function. In contrast, the ductile progressive degradation of matrix initial stiffness is analyzed via the continuum damage theory. Towards this end, a 2N+1-phase Mori-Tanaka (MT) method combined with the transformation field analysis approach (TFA) is established within a unified framework. Moreover, the rate-dependent viscoelastic and viscoplastic response of the polymer matrix phase is formulated through a phenomenological model consisting of four Kelvin-Voigt branches and a viscoplastic branch under the thermodynamics framework. Comparison of numerical predictions with experimental data demonstrates the model’s capabilities. In a second step of this work, the micromechanics scheme is combined with the cycle-jump technique in order to simulate moderate and high cycle fatigue tests. This modeling strategy is validated through comparison with experimental results. http://hdl.handle.net/10985/23081 Combination of mean-field micromechanics and cycle jump technique for cyclic response of PA66/GF composites with viscoelastic–viscoplastic and damage mechanisms CHEN, Qiang; CHATZIGEORGIOU, George; ROBERT, Gilles; MERAGHNI, Fodil An accelerated micromechanics framework based on the extended Mori–Tanaka transformation field analysis (TFA) and cycle jump technique is proposed to predict the homogenized response of short glass fiber-reinforced polyamide 66 composites (PA66/GF) under a large number of loading cycles (> 100,000 cycles). The extended theory accounts for microscopic viscoelastic–viscoplastic and damage mechanisms, and realistic microstructures induced by the injection molding process. Toward this end, a number of training cycles are first conducted using the extended Mori–Tanaka TFA to obtain the global evolution functions of material state-dependent variables (SDVs) for each phase. These SDVs are extrapolated linearly to a certain jump length with the help of global evolution functions such that direct numerical simulation of the cycles during this interval can be skipped, leading to a large computational cost reduction. After the cycle jump, a set of complete cycles are performed based on the extrapolated SDVs using the Mori–Tanaka TFA simulation to re-establish the global evolution functions. The implementation of the cycle jump procedure is facilitated by introducing an extrapolation control function to allow adaptive jump size control as well as to minimize the extrapolating error. The capabilities of the extended theory with the cycle jump technique have been validated extensively vis-à-vis cycle-by-cycle benchmark calculations under various loading conditions. It has been further verified with the experimental results of actual PA66/GF composites under high-cycle loading beyond which the cycle-by-cycle simulations can achieve. Sun, 01 Jan 2023 00:00:00 GMT http://hdl.handle.net/10985/23081 2023-01-01T00:00:00Z CHEN, Qiang CHATZIGEORGIOU, George ROBERT, Gilles MERAGHNI, Fodil An accelerated micromechanics framework based on the extended Mori–Tanaka transformation field analysis (TFA) and cycle jump technique is proposed to predict the homogenized response of short glass fiber-reinforced polyamide 66 composites (PA66/GF) under a large number of loading cycles (> 100,000 cycles). The extended theory accounts for microscopic viscoelastic–viscoplastic and damage mechanisms, and realistic microstructures induced by the injection molding process. Toward this end, a number of training cycles are first conducted using the extended Mori–Tanaka TFA to obtain the global evolution functions of material state-dependent variables (SDVs) for each phase. These SDVs are extrapolated linearly to a certain jump length with the help of global evolution functions such that direct numerical simulation of the cycles during this interval can be skipped, leading to a large computational cost reduction. After the cycle jump, a set of complete cycles are performed based on the extrapolated SDVs using the Mori–Tanaka TFA simulation to re-establish the global evolution functions. The implementation of the cycle jump procedure is facilitated by introducing an extrapolation control function to allow adaptive jump size control as well as to minimize the extrapolating error. The capabilities of the extended theory with the cycle jump technique have been validated extensively vis-à-vis cycle-by-cycle benchmark calculations under various loading conditions. It has been further verified with the experimental results of actual PA66/GF composites under high-cycle loading beyond which the cycle-by-cycle simulations can achieve. http://hdl.handle.net/10985/23901 Numerical-experimental approach to identify the effect of relative humidity on the material parameters of a rate-dependent damage model for polyamide 66 SATOURI, Soheil; CHEKKOUR, Rabii; CHATZIGEORGIOU, George; MERAGHNI, Fodil; ROBERT, Gilles This work aims at identifying the behavior of polyamide 66 (PA66) under different Relative Humidity (RH) conditions using a phenomenological model that accounts for viscoelastic and viscoplastic rheology coupled to ductile damage. An experimental approach is designed considering different loading conditions, namely: monotonic at several strain rates, loading-unloading, creep-recovery, and cyclic tests. These experiments are chosen to discriminate the various active mechanisms governing the nonlinear behavior of PA66. The thermodynamic background of the phenomenological model, the evolution laws, and the accompanying RH-dependent material parameters are presented and discussed. Using the experimental findings, an optimization algorithm is adopted to identify the model parameters. The latter are investigated with regard to the relative humidity, leading hence to the development of a model that accounts for the effect of RH on all inelastic mechanisms and ductile damage. Validation through experimental data for RH=0%, 25%, 50%, 65%, and 80% reveals that the current model captures the effect of RH and yields mechanical responses in good agreement with experimental findings, notably at higher RH levels. The current numerical-experimental framework presents a unified model for a wide range of humidity conditions and provides a better insight into material properties and rate-dependent inelastic mechanisms under humidity exposure, which typical models do not provide. In addition, the present constitutive law is easily adoptable in micromechanics schemes for the study of polymer based composite materials and structures. Sat, 01 Jul 2023 00:00:00 GMT http://hdl.handle.net/10985/23901 2023-07-01T00:00:00Z SATOURI, Soheil CHEKKOUR, Rabii CHATZIGEORGIOU, George MERAGHNI, Fodil ROBERT, Gilles This work aims at identifying the behavior of polyamide 66 (PA66) under different Relative Humidity (RH) conditions using a phenomenological model that accounts for viscoelastic and viscoplastic rheology coupled to ductile damage. An experimental approach is designed considering different loading conditions, namely: monotonic at several strain rates, loading-unloading, creep-recovery, and cyclic tests. These experiments are chosen to discriminate the various active mechanisms governing the nonlinear behavior of PA66. The thermodynamic background of the phenomenological model, the evolution laws, and the accompanying RH-dependent material parameters are presented and discussed. Using the experimental findings, an optimization algorithm is adopted to identify the model parameters. The latter are investigated with regard to the relative humidity, leading hence to the development of a model that accounts for the effect of RH on all inelastic mechanisms and ductile damage. Validation through experimental data for RH=0%, 25%, 50%, 65%, and 80% reveals that the current model captures the effect of RH and yields mechanical responses in good agreement with experimental findings, notably at higher RH levels. The current numerical-experimental framework presents a unified model for a wide range of humidity conditions and provides a better insight into material properties and rate-dependent inelastic mechanisms under humidity exposure, which typical models do not provide. In addition, the present constitutive law is easily adoptable in micromechanics schemes for the study of polymer based composite materials and structures. http://hdl.handle.net/10985/23031 Effect of thermo-hygro glycol aging on the damage mechanisms of short glass-fiber reinforced polyamide 66 CHEKKOUR, Rabii; BENAARBIA, Adil; CHATZIGEORGIOU, George; MERAGHNI, Fodil; ROBERT, Gilles This paper aims at studying the effect of ethylene glycol aging on the overall behavior and the damage mechanisms of the Polyamide 66 (PA66) and the short glass fiber reinforced polyamide 66 (PA66/GF). To this end, a proper experimental aging setup is designed and presented for conditioning the samples in glycol at different aging durations. The glycol absorption effect is analyzed through the swelling and the mass variation (uptake). Moreover, monotonic tensile tests are performed to study the glycol aging effect on the PA66 and PA66/GF. SEM (Scanning Electron Microscopy) investigation is then performed to characterize the damage mechanisms and their evolution with the increase of the aging duration. X-ray micro-computed tomography (µCT) observations are also carried out to quantify the damage depending on the aging duration, the material, and the area of interest (AOI). Experimental findings show that the glycol absorption is more important for the PA66 unreinforced matrix than for the short glass fiber reinforced PA66 composite. In addition, the stiffness, as well as the material deformability, are found to be significantly affected by the glycol aging. In terms of composite degradation, the main damage mechanisms are the damage at fiber's end and the fiber-matrix interface, and for the high aging durations, cavitation in the polymer matrix is observed. The X-ray µCT investigation has indicated pronounced damage mostly located at the core and surface of the samples, which is due to the well-known shell-core microstructure of injected PA66/GF composites. All these conclusions lead to infer the significant and irreversible effect of glycol aging on the bulk mechanical behavior and damage mechanisms of the investigated materials. Thu, 01 Dec 2022 00:00:00 GMT http://hdl.handle.net/10985/23031 2022-12-01T00:00:00Z CHEKKOUR, Rabii BENAARBIA, Adil CHATZIGEORGIOU, George MERAGHNI, Fodil ROBERT, Gilles This paper aims at studying the effect of ethylene glycol aging on the overall behavior and the damage mechanisms of the Polyamide 66 (PA66) and the short glass fiber reinforced polyamide 66 (PA66/GF). To this end, a proper experimental aging setup is designed and presented for conditioning the samples in glycol at different aging durations. The glycol absorption effect is analyzed through the swelling and the mass variation (uptake). Moreover, monotonic tensile tests are performed to study the glycol aging effect on the PA66 and PA66/GF. SEM (Scanning Electron Microscopy) investigation is then performed to characterize the damage mechanisms and their evolution with the increase of the aging duration. X-ray micro-computed tomography (µCT) observations are also carried out to quantify the damage depending on the aging duration, the material, and the area of interest (AOI). Experimental findings show that the glycol absorption is more important for the PA66 unreinforced matrix than for the short glass fiber reinforced PA66 composite. In addition, the stiffness, as well as the material deformability, are found to be significantly affected by the glycol aging. In terms of composite degradation, the main damage mechanisms are the damage at fiber's end and the fiber-matrix interface, and for the high aging durations, cavitation in the polymer matrix is observed. The X-ray µCT investigation has indicated pronounced damage mostly located at the core and surface of the samples, which is due to the well-known shell-core microstructure of injected PA66/GF composites. All these conclusions lead to infer the significant and irreversible effect of glycol aging on the bulk mechanical behavior and damage mechanisms of the investigated materials. http://hdl.handle.net/10985/20955 Viscoelastic-viscoplastic homogenization of short glass-fiber reinforced polyamide composites (PA66/GF) with progressive interphase and matrix damage: New developments and experimental validation CHEN, Qiang; CHATZIGEORGIOU, George; ROBERT, Gilles; MERAGHNI, Fodil In this paper, an original probabilistic micromechanics damage framework involving multi-deformation mechanisms, based on the modified Mori-Tanaka and Transformation Field Analysis (MT-TFA) techniques, is developed to predict monotonic and oligocyclic stress-strain responses in short fiber-reinforced polyamide composites. The proposed model allows simulating actual injection-induced fiber arrangement, which is characterized by arbitrary fractions of randomly oriented fibers distributed in the laminate plane. Furthermore, the modified MT-TFA approach employs a phenomenological model consisting of four Kelvin-Voigt branches and a viscoplastic branch, formulated under the thermodynamics framework, to describe the rate-dependent viscoelastic-viscoplastic deformation and the ductile damage of the polymer matrix phase. In addition, the Weibull probabilistic density function is utilized to simulate initiation and coalescence of the void-type discrete damage in the vicinity of the fiber/matrix interphase, induced by the fiber/matrix debonding as observed experimentally. The parameters of the developed model are calibrated against the experimental response of glass/polyamide (PA66/GF35) composites via uniaxial loading/unloading tests, by taking into account the actual fiber orientation density function (ODF). The reliability and efficiency of the modified Mori-Tanaka and TFA scheme are assessed vis-à-vis the separate and hold-out experimental data subjected to uniaxial and oligocyclic loading at various loading rates. Progressive matrix and interphase damage are compared in support of the modified MT-TFA technique’s capabilities to capture the experimentally observed damage mechanisms. To accurately capture the experimental response, the progressive degradation of the load transfer between the fiber and matrix phases is introduced through a reduction of the active fiber length. The latter is introduced by considering the effect of the interphase void-damage content. The new mean-field formulation provides accurate predictions of the overall response under complex loading paths. It can be combined with other techniques in our future work, such as cycle-jump, towards simulating high-cycle fatigue damage in short-fiber composite structures. Sat, 01 Jan 2022 00:00:00 GMT http://hdl.handle.net/10985/20955 2022-01-01T00:00:00Z CHEN, Qiang CHATZIGEORGIOU, George ROBERT, Gilles MERAGHNI, Fodil In this paper, an original probabilistic micromechanics damage framework involving multi-deformation mechanisms, based on the modified Mori-Tanaka and Transformation Field Analysis (MT-TFA) techniques, is developed to predict monotonic and oligocyclic stress-strain responses in short fiber-reinforced polyamide composites. The proposed model allows simulating actual injection-induced fiber arrangement, which is characterized by arbitrary fractions of randomly oriented fibers distributed in the laminate plane. Furthermore, the modified MT-TFA approach employs a phenomenological model consisting of four Kelvin-Voigt branches and a viscoplastic branch, formulated under the thermodynamics framework, to describe the rate-dependent viscoelastic-viscoplastic deformation and the ductile damage of the polymer matrix phase. In addition, the Weibull probabilistic density function is utilized to simulate initiation and coalescence of the void-type discrete damage in the vicinity of the fiber/matrix interphase, induced by the fiber/matrix debonding as observed experimentally. The parameters of the developed model are calibrated against the experimental response of glass/polyamide (PA66/GF35) composites via uniaxial loading/unloading tests, by taking into account the actual fiber orientation density function (ODF). The reliability and efficiency of the modified Mori-Tanaka and TFA scheme are assessed vis-à-vis the separate and hold-out experimental data subjected to uniaxial and oligocyclic loading at various loading rates. Progressive matrix and interphase damage are compared in support of the modified MT-TFA technique’s capabilities to capture the experimentally observed damage mechanisms. To accurately capture the experimental response, the progressive degradation of the load transfer between the fiber and matrix phases is introduced through a reduction of the active fiber length. The latter is introduced by considering the effect of the interphase void-damage content. The new mean-field formulation provides accurate predictions of the overall response under complex loading paths. It can be combined with other techniques in our future work, such as cycle-jump, towards simulating high-cycle fatigue damage in short-fiber composite structures.