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Azoti Wiyao - One of the best experts on this subject based on the ideXlab platform.

  • Constitutive modelling of ductile damage matrix reinforced by platelets-like particles with imperfect interfaces: Application to graphene polymer nanocomposite materials
    'Elsevier BV', 2017
    Co-Authors: Azoti Wiyao, Elmarakbi Ahmed
    Abstract:

    In this paper, the mechanical response of composites consisting of ductile matrix reinforced by platelets-like particles is derived with imperfect interfaces. Due to its flexibility to study imperfect interfaces with limited number of model parameters, the linear spring model LSM is considered. Moreover, the interfacial contribution to the Strain Concentration Tensor within each material phase and inside the average Strain filed is described by a modified Mori-Tanaka scheme. The material nonlinearity is established by the J2 plasticity and Lemaitre-Chaboche damage model. A generalised mid-point rule is used to solve rate equations yielding to anisotropic consistent (algorithmic) tangent operators. To avoid spurious macroscopic stress-Strain response, an isotropisation procedure is adopted during the computation of a modified Eshelby's Tensor. Numerical results are performed on graphene platelets GPL-reinforced polymer PA6 composite. They confirm the possibility to achieve high stiffness with low values of GPL aspect ratio. The accumulated plastic Strain and the damage variable within the matrix are influenced by the GPL volume fraction which is also involved in the softening of the overall response when imperfection is considered at the interface

  • Multiscale modelling of graphene platelets-based nanocomposite materials
    'Elsevier BV', 2017
    Co-Authors: Azoti Wiyao, Elmarakbi Ahmed
    Abstract:

    This work presents a multiscale framework for the elasto-plastic response of platelets-like inclusions reinforced nanocomposite materials. The solution of the heterogeneous material problem is solved by a kinematic integral equation. An imperfect interface is introduced between the particles and the matrix through a linear spring model LSM, leading to a modified Eshelby's Tensor. The interfacial contribution, related to the Strain Concentration Tensor within each material phase and inside the average Strain field, is described by a modified Mori–Tanaka scheme. The non-linear response is established in the framework of the J2 flow rule. An expression of the algorithmic tangent operator for each phase is obtained and used as an uniform modulus for homogenisation purpose. Numerical results are conducted on graphene platelets GPL-reinforced polymer PA6 composite for several design parameters such as GPL volume fraction, aspect ratio and the interfacial compliance. These results clearly highlight the impact of the aspect ratio as well as the volume fraction by a softening in the overall response when imperfection is considered at the interface. Finally, a multiscale simulation is performed on a three bending specimen showing the capability of the developed constitutive equations to be implemented in a finite element FE code

  • Non-linear elastic moduli of Graphene sheet-reinforced polymer composites
    'Elsevier BV', 2016
    Co-Authors: Elmarakbi Ahmed, Jianhua Wang, Azoti Wiyao
    Abstract:

    The non-linear elastic moduli of the Graphene sheet-reinforced polymer composite are investigated using a combined molecular mechanics theory and continuum homogenisation tools. Under uni-axial loading, the linear and non-linear constitutive equations of the Graphene sheet are derived from a Taylor series expansion in powers of Strains. Based on the modified Morse potential, the elastic moduli and Poisson's ratio are obtained for the Graphene sheet leading to the derivation of the non-linear stiffness Tensor. For homogenisation purpose, the Strain Concentration Tensor is computed by the means of the irreducible decomposition of the Eshelby's Tensor for an arbitrary domain. Therefore, a mathematical expression of the averaged Eshelby's Tensor for a rectangular shape is obtained for the Graphene sheet. Under the Mori-Tanaka micro-mechanics scheme, the effective non-linear behaviour is predicted for various micro-parameters such as the aspect ratio and mass fractions. Numerical results highlight the effect of such micro-parameters on the anisotropic degree of the composite

  • Nonlinear Elastic Moduli of Graphene Sheet-Reinforced Polymer Composites for Automotive Applications
    'Elsevier BV', 2016
    Co-Authors: Elmarakbi Ahmed, Jianhua Wang, Azoti Wiyao
    Abstract:

    The non-linear elastic moduli of the Graphene sheet-reinforced polymer composite are investigated using a combined molecular mechanics theory and continuum homogenisation tools. Under uni-axial loading, the linear and non-linear constitutive equations of the Graphene sheet are derived from a Taylor series expansion in powers of Strains. Based on the modified Morse potential, the elastic moduli and Poisson’s ratio are obtained for the Graphene sheet leading to the derivation of the non-linear stiffness Tensor. For homogenisation purpose, the Strain Concentration Tensor is computed by the means of the irreducible decomposition of the Eshelby’s Tensor for an arbitrary domain. Therefore, a mathematical expression of the averaged Eshelby’s Tensor for a rectangular shape is obtained for the Graphene sheet. Under the Mori–Tanaka micro-mechanics scheme, the effective non-linear behaviour is predicted for various micro-parameters such as the aspect ratio and mass fractions. Numerical results highlight the effect of such micro-parameters on the anisotropic degree of the composite

  • Micromechanics Modelling of Graphene Platelets Reinforced Polymer Composite Materials With Imperfect Interfaces
    'ASME International', 2016
    Co-Authors: Azoti Wiyao, Elmarakbi Ahmed
    Abstract:

    This work investigates the elasto-plastic response of platelets-like inclusions reinforced polymer composites showing an imperfect interface. The solution of the heterogeneous material problem is solved through a kinematic integral equation. To account for the interfacial behaviour, a linear spring model LSM is adopted, leading to an expression of the modified Eshelby's Tensor. As a consequence, the interfacial contributions with respect to the Strain Concentration Tensor within each phase as well as in the average Strain field are described by a modified version of the Mori-Tanaka scheme for the overall response. The non-linear response is established in the framework of the J2 flow rule. An expression of the algorithmic tangent operator for each phase can be obtained and used as uniform modulus for homogenisation purpose. Numerical results are conducted on graphene platelets GPL-reinforced polymer PA6 composite for several design parameters such as GPL volume fraction, aspect ratio and the interfacial compliance. These results clearly highlight the impact of the aspect ratio as well as the volume fraction by a softening in the overall response when imperfection is considered at the interface. Present developments are analytical-based solutions. They constitute a theoretical framework for further multi-scale applications in automotive. The crashworthiness simulation incorporating an influence of the interfacial behaviour on the Strain energy absorption SEA is of interest

Elmarakbi Ahmed - One of the best experts on this subject based on the ideXlab platform.

  • Constitutive modelling of ductile damage matrix reinforced by platelets-like particles with imperfect interfaces: Application to graphene polymer nanocomposite materials
    'Elsevier BV', 2017
    Co-Authors: Azoti Wiyao, Elmarakbi Ahmed
    Abstract:

    In this paper, the mechanical response of composites consisting of ductile matrix reinforced by platelets-like particles is derived with imperfect interfaces. Due to its flexibility to study imperfect interfaces with limited number of model parameters, the linear spring model LSM is considered. Moreover, the interfacial contribution to the Strain Concentration Tensor within each material phase and inside the average Strain filed is described by a modified Mori-Tanaka scheme. The material nonlinearity is established by the J2 plasticity and Lemaitre-Chaboche damage model. A generalised mid-point rule is used to solve rate equations yielding to anisotropic consistent (algorithmic) tangent operators. To avoid spurious macroscopic stress-Strain response, an isotropisation procedure is adopted during the computation of a modified Eshelby's Tensor. Numerical results are performed on graphene platelets GPL-reinforced polymer PA6 composite. They confirm the possibility to achieve high stiffness with low values of GPL aspect ratio. The accumulated plastic Strain and the damage variable within the matrix are influenced by the GPL volume fraction which is also involved in the softening of the overall response when imperfection is considered at the interface

  • Multiscale modelling of graphene platelets-based nanocomposite materials
    'Elsevier BV', 2017
    Co-Authors: Azoti Wiyao, Elmarakbi Ahmed
    Abstract:

    This work presents a multiscale framework for the elasto-plastic response of platelets-like inclusions reinforced nanocomposite materials. The solution of the heterogeneous material problem is solved by a kinematic integral equation. An imperfect interface is introduced between the particles and the matrix through a linear spring model LSM, leading to a modified Eshelby's Tensor. The interfacial contribution, related to the Strain Concentration Tensor within each material phase and inside the average Strain field, is described by a modified Mori–Tanaka scheme. The non-linear response is established in the framework of the J2 flow rule. An expression of the algorithmic tangent operator for each phase is obtained and used as an uniform modulus for homogenisation purpose. Numerical results are conducted on graphene platelets GPL-reinforced polymer PA6 composite for several design parameters such as GPL volume fraction, aspect ratio and the interfacial compliance. These results clearly highlight the impact of the aspect ratio as well as the volume fraction by a softening in the overall response when imperfection is considered at the interface. Finally, a multiscale simulation is performed on a three bending specimen showing the capability of the developed constitutive equations to be implemented in a finite element FE code

  • Non-linear elastic moduli of Graphene sheet-reinforced polymer composites
    'Elsevier BV', 2016
    Co-Authors: Elmarakbi Ahmed, Jianhua Wang, Azoti Wiyao
    Abstract:

    The non-linear elastic moduli of the Graphene sheet-reinforced polymer composite are investigated using a combined molecular mechanics theory and continuum homogenisation tools. Under uni-axial loading, the linear and non-linear constitutive equations of the Graphene sheet are derived from a Taylor series expansion in powers of Strains. Based on the modified Morse potential, the elastic moduli and Poisson's ratio are obtained for the Graphene sheet leading to the derivation of the non-linear stiffness Tensor. For homogenisation purpose, the Strain Concentration Tensor is computed by the means of the irreducible decomposition of the Eshelby's Tensor for an arbitrary domain. Therefore, a mathematical expression of the averaged Eshelby's Tensor for a rectangular shape is obtained for the Graphene sheet. Under the Mori-Tanaka micro-mechanics scheme, the effective non-linear behaviour is predicted for various micro-parameters such as the aspect ratio and mass fractions. Numerical results highlight the effect of such micro-parameters on the anisotropic degree of the composite

  • Nonlinear Elastic Moduli of Graphene Sheet-Reinforced Polymer Composites for Automotive Applications
    'Elsevier BV', 2016
    Co-Authors: Elmarakbi Ahmed, Jianhua Wang, Azoti Wiyao
    Abstract:

    The non-linear elastic moduli of the Graphene sheet-reinforced polymer composite are investigated using a combined molecular mechanics theory and continuum homogenisation tools. Under uni-axial loading, the linear and non-linear constitutive equations of the Graphene sheet are derived from a Taylor series expansion in powers of Strains. Based on the modified Morse potential, the elastic moduli and Poisson’s ratio are obtained for the Graphene sheet leading to the derivation of the non-linear stiffness Tensor. For homogenisation purpose, the Strain Concentration Tensor is computed by the means of the irreducible decomposition of the Eshelby’s Tensor for an arbitrary domain. Therefore, a mathematical expression of the averaged Eshelby’s Tensor for a rectangular shape is obtained for the Graphene sheet. Under the Mori–Tanaka micro-mechanics scheme, the effective non-linear behaviour is predicted for various micro-parameters such as the aspect ratio and mass fractions. Numerical results highlight the effect of such micro-parameters on the anisotropic degree of the composite

  • Micromechanics Modelling of Graphene Platelets Reinforced Polymer Composite Materials With Imperfect Interfaces
    'ASME International', 2016
    Co-Authors: Azoti Wiyao, Elmarakbi Ahmed
    Abstract:

    This work investigates the elasto-plastic response of platelets-like inclusions reinforced polymer composites showing an imperfect interface. The solution of the heterogeneous material problem is solved through a kinematic integral equation. To account for the interfacial behaviour, a linear spring model LSM is adopted, leading to an expression of the modified Eshelby's Tensor. As a consequence, the interfacial contributions with respect to the Strain Concentration Tensor within each phase as well as in the average Strain field are described by a modified version of the Mori-Tanaka scheme for the overall response. The non-linear response is established in the framework of the J2 flow rule. An expression of the algorithmic tangent operator for each phase can be obtained and used as uniform modulus for homogenisation purpose. Numerical results are conducted on graphene platelets GPL-reinforced polymer PA6 composite for several design parameters such as GPL volume fraction, aspect ratio and the interfacial compliance. These results clearly highlight the impact of the aspect ratio as well as the volume fraction by a softening in the overall response when imperfection is considered at the interface. Present developments are analytical-based solutions. They constitute a theoretical framework for further multi-scale applications in automotive. The crashworthiness simulation incorporating an influence of the interfacial behaviour on the Strain energy absorption SEA is of interest

L C Brinson - One of the best experts on this subject based on the ideXlab platform.

  • fiber waviness in nanotube reinforced polymer composites ii modeling via numerical approximation of the dilute Strain Concentration Tensor
    Composites Science and Technology, 2003
    Co-Authors: R D Bradshaw, Frank T Fisher, L C Brinson
    Abstract:

    Nanotube-reinforced polymers offer significant potential improvements over the pure polymer with regard to mechanical, electrical and thermal properties. This article investigates the degree to which the characteristic waviness of nanotubes embedded in polymers can impact the effective stiffness of these materials. A 3D finite element model of a single infinitely long sinusoidal fiber within an infinite matrix is used to numerically compute the dilute Strain Concentration Tensor. A Mori–Tanaka model utilizes this Tensor to predict the effective modulus of the material with aligned or randomly oriented inclusions. This hybrid finite elementmicromechanical modeling technique is a powerful extension of general micromechanics modeling and can be applied to any composite microstructure containing non-ellipsoidal inclusions. The results demonstrate that nanotube waviness results in a reduction of the effective modulus of the composite relative to straight nanotube reinforcement. The degree of reduction is dependent on the ratio of the sinusoidal wavelength to the nanotube diameter. As this wavelength ratio increases, the effective stiffness of a composite with randomly oriented wavy nanotubes converges to the result obtained with straight nanotube inclusions. The approach developed in this paper can also be utilized in the analysis of other problems involving nanotube-reinforced polymers, including alternate nanotube representations, viscoelastic response, assessing the effect of low matrix-NT bond strength and in the determination of thermal and electrical conductivity. # 2003 Elsevier Ltd. All rights reserved.

  • Fiber waviness in nanotube-reinforced polymer composites: I. Modulus predictions using effective nanotube properties. Composites Science and Technology, submitted for publication
    2002
    Co-Authors: R D Bradshaw, Frank T Fisher, L C Brinson
    Abstract:

    Nanotube-reinforced polymers offer significant potential improvements over the pure polymer with regard to mechanical, electrical and thermal properties. This article investigates the degree to which the characteristic waviness of nanotubes embedded in polymers can impact the effective stiffness of these materials. A 3D finite element model of a single infinitely long sinusoidal nanotube within an infinite matrix is used to numerically compute the dilute Strain Concentration Tensor. A Mori-Tanaka model utilizes this Tensor to predict the effective modulus of the material with aligned or randomly oriented inclusions. This hybrid finite element-micromechanical modeling technique is a powerful extension of general micromechanics modeling and can be applied to any composite microstructure containing non-ellipsoidal inclusions. The results demonstrate that nanotube waviness results in a reduction of the effective modulus of the composite relative to straight nanotube reinforcement. The degree of reduction is dependent on the ratio of the sinusoidal wavelength to the nanotube diameter. As this wavelength ratio increases, the effective stiffness of a composite with wavy nanotubes converges to the result obtained with straight nanotube inclusions. The approach developed in this paper can also b

Hamid Zahrouni - One of the best experts on this subject based on the ideXlab platform.

  • Incremental mean-fields micromechanics scheme for non-linear response of ductile damaged composite materials
    Composites Part B: Engineering, 2015
    Co-Authors: Adjovi Tchalla, W. L. Azoti, Y. Koutsawa, A. Makradi, S. Belouettar, Hamid Zahrouni
    Abstract:

    This work is concerned with the modeling of ductile damage behavior in composite materials by the means of the Incremental Micromechanics Scheme (IMS) as Mean-Fields Homogenization (MFH) technique. Indeed, IMS is known for its capability to overcome the well-known accuracy restrictions of the Mori-Tanaka (MT) and Self-Consistent (SC) schemes when a high volume fraction of heterogeneities or/and a high contrast between phases properties is reached. This micromechanics formalism is based on the Eshelby's inclusion concept. The kinematic equation of Dederichs and Zeller (1973) is used as formal solution of the heterogeneous material problem. The nonlinear behavior of the composite is addressed in a general framework based on the kinematic hardening of Lemaitre-Chaboche's ductile damage model. Thus a classical 12 plasticity that accounts for the damage evolution within the microstructure is implemented. The time discretization of all rate relations is solved through a generalized mid-point rule that yields to an anisotropic consistent (algorithmic) tangent modulus. To avoid a stiffer macroscopic stress-Strain response, an isotropization procedure is adopted during the computation of the Eshelby Tensor involved in the IMS modeling. From a computational aspect, the non linear response of the composite is obtained through two interdependent loops: inner and outer. In the inner loop, the IMS determines the global Strain Concentration Tensor that is passed to the outer loop. Then, the macroscopic stress-Strain response is derived using an iterative algorithm based on the Hill-type incremental formulation. Numerical results are obtained considering several heterogeneous materials such as Metal Matrix Composites (MMCs) as well as Carbon fibers reinforced Epoxy Matrix Composites. The model's predictions are compared in most of the cases, with experimental data and predictions obtained from MT-based modeling in the open literature.

R D Bradshaw - One of the best experts on this subject based on the ideXlab platform.

  • fiber waviness in nanotube reinforced polymer composites ii modeling via numerical approximation of the dilute Strain Concentration Tensor
    Composites Science and Technology, 2003
    Co-Authors: R D Bradshaw, Frank T Fisher, L C Brinson
    Abstract:

    Nanotube-reinforced polymers offer significant potential improvements over the pure polymer with regard to mechanical, electrical and thermal properties. This article investigates the degree to which the characteristic waviness of nanotubes embedded in polymers can impact the effective stiffness of these materials. A 3D finite element model of a single infinitely long sinusoidal fiber within an infinite matrix is used to numerically compute the dilute Strain Concentration Tensor. A Mori–Tanaka model utilizes this Tensor to predict the effective modulus of the material with aligned or randomly oriented inclusions. This hybrid finite elementmicromechanical modeling technique is a powerful extension of general micromechanics modeling and can be applied to any composite microstructure containing non-ellipsoidal inclusions. The results demonstrate that nanotube waviness results in a reduction of the effective modulus of the composite relative to straight nanotube reinforcement. The degree of reduction is dependent on the ratio of the sinusoidal wavelength to the nanotube diameter. As this wavelength ratio increases, the effective stiffness of a composite with randomly oriented wavy nanotubes converges to the result obtained with straight nanotube inclusions. The approach developed in this paper can also be utilized in the analysis of other problems involving nanotube-reinforced polymers, including alternate nanotube representations, viscoelastic response, assessing the effect of low matrix-NT bond strength and in the determination of thermal and electrical conductivity. # 2003 Elsevier Ltd. All rights reserved.

  • Fiber waviness in nanotube-reinforced polymer composites: I. Modulus predictions using effective nanotube properties. Composites Science and Technology, submitted for publication
    2002
    Co-Authors: R D Bradshaw, Frank T Fisher, L C Brinson
    Abstract:

    Nanotube-reinforced polymers offer significant potential improvements over the pure polymer with regard to mechanical, electrical and thermal properties. This article investigates the degree to which the characteristic waviness of nanotubes embedded in polymers can impact the effective stiffness of these materials. A 3D finite element model of a single infinitely long sinusoidal nanotube within an infinite matrix is used to numerically compute the dilute Strain Concentration Tensor. A Mori-Tanaka model utilizes this Tensor to predict the effective modulus of the material with aligned or randomly oriented inclusions. This hybrid finite element-micromechanical modeling technique is a powerful extension of general micromechanics modeling and can be applied to any composite microstructure containing non-ellipsoidal inclusions. The results demonstrate that nanotube waviness results in a reduction of the effective modulus of the composite relative to straight nanotube reinforcement. The degree of reduction is dependent on the ratio of the sinusoidal wavelength to the nanotube diameter. As this wavelength ratio increases, the effective stiffness of a composite with wavy nanotubes converges to the result obtained with straight nanotube inclusions. The approach developed in this paper can also b