The Experts below are selected from a list of 1368 Experts worldwide ranked by ideXlab platform

Javier Llorca - One of the best experts on this subject based on the ideXlab platform.

  • Computational Micromechanics Modeling of Polycrystalline Superalloys: Application to Inconel 718
    Integrated Computational Materials Engineering (ICME), 2020
    Co-Authors: A. Cruzado, Javier Llorca, Javier Segurado Escudero
    Abstract:

    A virtual testing methodology to obtain the mechanical response of a polycrystal as function of its microstructure is presented and applied to an Inconel 718 Ni-based superalloy. The mechanical behavior of the polycrystal for a given deformation history is obtained by the finite element simulation of the response of representative volume elements of the microstructure subjected to that particular deformation history. The microstructural information defining the representative volume elements (grain size distribution and texture) was obtained from standard metallographic characterization techniques. The behavior of the alloy crystals is given by a phenomenological crystal plasticity model, whose parameters were obtained using two different strategies, micropillar compression for the parameters defining the monotonic behavior and an inverse optimization strategy (using experimental macroscopic cyclic stress-strain curves) for the parameters controlling the cyclic deformation. From the macroscopic viewpoint, the material response under monotonic and cyclic deformation was in good agreement with the experimental data. At the micro level, the values of the local fields resolved throughout the volume elements were used to generate fatigue indicator parameters, which were able to determine the most critical points in the microstructure to initiate a fatigue crack. These fatigue indicator parameters were calibrated by comparison with a few experimental fatigue tests and then used to predict the effect of loading conditions (strain ranges and ratio) and microstructure (grain size) on the fatigue life of the superalloy. Overall, the strategy shows how a balanced combination of micromechanical and macromechanical tests together with the application of Computational homogenization strategies can be used to predict the mechanical behavior of Ni-based superalloys taken into account the influence of the microstructure.

  • transverse cracking of cross ply laminates a Computational Micromechanics perspective
    Composites Science and Technology, 2015
    Co-Authors: Miguel Gonzalez Herraez, Ferran Naya, Javier Llorca, C. S. Lópes, Carlos Gonzalez, Diego Mora
    Abstract:

    Abstract Transverse cracking in cross-ply carbon/epoxy and glass/epoxy laminates in tension is analyzed by means of Computational Micromechanics. Longitudinal plies were modeled as homogenized, anisotropic elastic solids while the actual fiber distribution was included in the transverse plies. The mechanical response was obtained by the finite element analysis of a long representative volume element of the laminate. Damage in the transverse plies was triggered by interface decohesion and matrix cracking. The simulation strategy was applied to study the influence of ply thickness on the critical stress for the cracking of the transverse plies and on the evolution of crack density in 0 2 / 90 n / 2 s laminates, with n = 1, 2, 4 and 8. It was found that the transverse ply strength corresponding to the initiation and propagation of a through-thickness crack was independent of the ply thickness and that the transverse strength of carbon/epoxy laminates was 35% higher than that of the glass fiber counterparts. In addition, the mechanisms of crack initiation and propagation through the thickness as well as of multiple matrix cracking were ascertained and the stiffness reduction in the 90° ply as a function of crack density was computed as a function of the ply thickness.

  • Computational Micromechanics strategies for the analysis of failure in unidirectional composites
    Numerical Modelling of Failure in Advanced Composite Materials, 2015
    Co-Authors: F. Naya, Carlos Gonzalez, Claudio S. Lopes, Javier Llorca
    Abstract:

    This chapter summarises the current state of the art on the application of Computational Micromechanics to study the mechanical behaviour of unidirectional plies. We outline the simulation strategies to determine the strength and toughness of unidirectional plies together with the experimental techniques to determine the properties of the constituents (matrix, fibres and interfaces). Several examples in unidirectional plies under matrix-dominated failure conditions are presented and the future developments in Computational Micromechanics of composites are briefly summarised.

  • Finite deformation of incompressible fiber-reinforced elastomers: A Computational Micromechanics approach
    Journal of the Mechanics and Physics of Solids, 2009
    Co-Authors: Joaquín Moraleda, Javier Segurado, Javier Llorca
    Abstract:

    Abstract The in-plane finite deformation of incompressible fiber-reinforced elastomers was studied using Computational Micromechanics. Composite microstructure was made up of a random and homogeneous dispersion of aligned rigid fibers within a hyperelastic matrix. Different matrices (Neo-Hookean and Gent), fibers (monodisperse or polydisperse, circular or elliptical section) and reinforcement volume fractions (10–40%) were analyzed through the finite element simulation of a representative volume element of the microstructure. A successive remeshing strategy was employed when necessary to reach the large deformation regime in which the evolution of the microstructure influences the effective properties. The simulations provided for the first time “quasi-exact” results of the in-plane finite deformation for this class of composites, which were used to assess the accuracy of the available homogenization estimates for incompressible hyperelastic composites.

  • Effect of interface fracture on the tensile deformation of fiber-reinforced elastomers
    International Journal of Solids and Structures, 2009
    Co-Authors: Joaquín Moraleda, Javier Segurado, Javier Llorca
    Abstract:

    AbstractThe influence of interface properties (strength and toughness) on the tensile behavior of fiber-reinforced elastomers deformed perpendicularly to the fibers was studied using Computational Micromechanics. Numerical simulations were performed by means of the finite element analysis of a representative volume element of the composite microstructure. The effect of finite deformations and of interface fracture was included in the simulations, the latter through a bidimensional and quadratic interface element inserted at the fiber/matrix interfaces. A parametrical study was carried out to assess the effect of interface strength and toughness on the tensile strength and damage micromechanisms. It was found that the onset of damage and tensile strength were controlled by interface strength while the evolution of damage depended on interface toughness

Miguel Gonzalez Herraez - One of the best experts on this subject based on the ideXlab platform.

  • Computational Micromechanics model for the analysis of fiber kinking in unidirectional fiber-reinforced polymers
    Mechanics of Materials, 2020
    Co-Authors: Miguel Gonzalez Herraez, Claudio S. Lopes, Andrew C. Bergan, C Gonzalez
    Abstract:

    Abstract A Computational Micromechanics (CMM) model is developed to analyze fiber kinking, which is a failure mechanism that takes place in fiber-reinforced composites when they are loaded under longitudinal compression. The CMM model consists of a single AS4 carbon fiber with an initial misalignment embedded in an 8552 polymer matrix. The deformation of the model is governed by periodic boundary conditions (PBC). The relatively simple CMM model enables the evaluation of the role played by initial misalignment of the fiber, shear yielding of the matrix and fiber-matrix debonding. A novel microscale experimental technique devoted to the characterization of the longitudinal compressive strength of the fibers, X c f , is developed. By exercising the model and comparing it with several models in the literature, the nonlinear shear response of the composite lamina is shown to play a fundamental role not only in the prediction of the compressive strength Xc, but also during the post-peak regime in terms of residual stress σr and fiber rotation φ. Finally, the influence of the fiber-matrix interface damage (not considered in most other fiber kinking models) on the fiber kinking phenomenon is assessed through a parametric study.

  • A microstructures generation tool for virtual ply property screening of hybrid composites with high volume fractions of non-circular fibers – VIPER
    Composites Part A: Applied Science and Manufacturing, 2020
    Co-Authors: Miguel Gonzalez Herraez, Javier Segurado, C Gonzalez, Claudio S. Lopes
    Abstract:

    Abstract Within the framework of Computational Micromechanics (CMM), a simulation toolset is being developed to predict the mechanical behavior of fiber-reinforced polymers from the measured properties and spatial distribution of the different phases and interfaces in the composite. Towards this end, a numerical methodology is proposed herein for the generation of 2D periodic microstructures with arbitrary fiber geometries. A major advantage of the approach presented in this work is the ability of generating high volume fractions of non-circular fibers very efficiently. The underlying algorithm is based on the minimization of fiber overlapping by dynamic translation and rotation of the fibers until intersections are eliminated. The randomness of the microstructures obtained is assessed by means of multiple spatial descriptors.

  • Computational Micromechanics of fiber kinking in unidirectional frp under different environmental conditions
    Composites Science and Technology, 2017
    Co-Authors: F. Naya, Miguel Gonzalez Herraez, C. S. Lópes, S. Van Der Veen, C Gonzalez, F. Pons
    Abstract:

    Abstract The determination of ply properties of Fiber Reinforced Polymers (FRP) for particular operational environmental conditions in aeronautical applications is mandatory in order to fulfill current industry stringent certification requirements. However, the traditional experimental approach requires massive investments of resources and time. From the behaviour obtained experimentally, constitutive equations including failure criteria are then devised to be used in the design of FRP structures. The ply longitudinal behaviour under compression is generally the most difficult to measure and characterize. In this work, an alternative coupled experimental-Computational Micromechanics approach is proposed to determine the longitudinal compression properties of unidirectional FRP plies under different environmental conditions. This methodology includes experimental characterization of matrix and fiber/matrix interface, combined with numerical simulations of realistic microstructures. The interface decohesion is simulated using cohesive-frictional interactions. A pressure dependent, elasto-plastic model that includes tensile damage is employed to capture the matrix nonlinear behaviour. The numerical predictions match the experimentally-obtained ply properties available in the literature in a remarkable way and suggest that virtual ply property characterization is a mature and reliable approach to conduct screening of materials.

  • Computational Micromechanics evaluation of the effect of fibre shape on the transverse strength of unidirectional composites an approach to virtual materials design
    Composites Part A-applied Science and Manufacturing, 2016
    Co-Authors: Miguel Gonzalez Herraez, C. S. Lópes, Carlos Gonzalez, Guzman R De Villoria, J Llorca, T Varela, J Sanchez
    Abstract:

    Abstract Computational Micromechanics of composites is an emerging tool required for virtual materials design (VMD) to address the effect of different variables involved before materials are manufactured. This strategy will avoid unnecessary costs, reducing trial-and-error campaigns leading to fast material developments for tailored properties. In this work, the effect of the fibre cross section on the transverse behaviour of unidirectional fibre composites has been evaluated by means of Computational Micromechanics. To this end, periodic representative volume elements containing uniform and random dispersions of 50% of parallel non-circular fibres with lobular, polygonal and elliptical shapes were generated. Fibre/matrix interface failure as well as matrix plasticity/damage were considered as the fundamental failure mechanisms operating at the microscale under transverse loading. Circular fibres showed the best averaged behaviour although lobular fibres exhibited superior performance in transverse compression mainly due to the higher tensile thermal residual stresses generated during cooling at the fibre/matrix interface.

  • transverse cracking of cross ply laminates a Computational Micromechanics perspective
    Composites Science and Technology, 2015
    Co-Authors: Miguel Gonzalez Herraez, Ferran Naya, Javier Llorca, C. S. Lópes, Carlos Gonzalez, Diego Mora
    Abstract:

    Abstract Transverse cracking in cross-ply carbon/epoxy and glass/epoxy laminates in tension is analyzed by means of Computational Micromechanics. Longitudinal plies were modeled as homogenized, anisotropic elastic solids while the actual fiber distribution was included in the transverse plies. The mechanical response was obtained by the finite element analysis of a long representative volume element of the laminate. Damage in the transverse plies was triggered by interface decohesion and matrix cracking. The simulation strategy was applied to study the influence of ply thickness on the critical stress for the cracking of the transverse plies and on the evolution of crack density in 0 2 / 90 n / 2 s laminates, with n = 1, 2, 4 and 8. It was found that the transverse ply strength corresponding to the initiation and propagation of a through-thickness crack was independent of the ply thickness and that the transverse strength of carbon/epoxy laminates was 35% higher than that of the glass fiber counterparts. In addition, the mechanisms of crack initiation and propagation through the thickness as well as of multiple matrix cracking were ascertained and the stiffness reduction in the 90° ply as a function of crack density was computed as a function of the ply thickness.

Claudio S. Lopes - One of the best experts on this subject based on the ideXlab platform.

  • Computational Micromechanics model for the analysis of fiber kinking in unidirectional fiber-reinforced polymers
    Mechanics of Materials, 2020
    Co-Authors: Miguel Gonzalez Herraez, Claudio S. Lopes, Andrew C. Bergan, C Gonzalez
    Abstract:

    Abstract A Computational Micromechanics (CMM) model is developed to analyze fiber kinking, which is a failure mechanism that takes place in fiber-reinforced composites when they are loaded under longitudinal compression. The CMM model consists of a single AS4 carbon fiber with an initial misalignment embedded in an 8552 polymer matrix. The deformation of the model is governed by periodic boundary conditions (PBC). The relatively simple CMM model enables the evaluation of the role played by initial misalignment of the fiber, shear yielding of the matrix and fiber-matrix debonding. A novel microscale experimental technique devoted to the characterization of the longitudinal compressive strength of the fibers, X c f , is developed. By exercising the model and comparing it with several models in the literature, the nonlinear shear response of the composite lamina is shown to play a fundamental role not only in the prediction of the compressive strength Xc, but also during the post-peak regime in terms of residual stress σr and fiber rotation φ. Finally, the influence of the fiber-matrix interface damage (not considered in most other fiber kinking models) on the fiber kinking phenomenon is assessed through a parametric study.

  • High-fidelity Computational Micromechanics of first-fibre failure in unidirectional composites: Deformation mechanisms and stress concentration factors
    International Journal of Solids and Structures, 2020
    Co-Authors: Mostafa Barzegar, Josep Costa, Claudio S. Lopes
    Abstract:

    Abstract Stress redistribution and damage phenomena in the vicinity of the first-fibre break in unidirectional composites under longitudinal tensile loads are investigated by means of high-fidelity Computational Micromechanics based on experimentally characterised material constituents. In this framework, periodic microstructures with statistically representative random fibre packings are analysed, and transient dynamic analyses are performed to take into account the progressive failure and recoiling of a breaking fibre. The effects of mechanisms such as curing residual stresses, fibre/matrix debonding and matrix inelastic deformation on the first-fibre failure process are investigated. The stress concentration factors on intact fibres are found to depend on the statistical failure stress of the breaking fibres, and decrease with increasing strength. For the AS4/8552 composite with average constituent properties, maximum stress concentration factors of 20.6%, 16.1% and 14.2% are predicted, respectively, for fibre volume fractions of 50%, 60%, 70%. Material systems with lower fibre-to-matrix stiffness ratios, such as glass/epoxy, result in lower stress concentration factors. The fibre/matrix interface strength is found to have a limited overall influence on stress redistribution around fibre breakage.

  • A microstructures generation tool for virtual ply property screening of hybrid composites with high volume fractions of non-circular fibers – VIPER
    Composites Part A: Applied Science and Manufacturing, 2020
    Co-Authors: Miguel Gonzalez Herraez, Javier Segurado, C Gonzalez, Claudio S. Lopes
    Abstract:

    Abstract Within the framework of Computational Micromechanics (CMM), a simulation toolset is being developed to predict the mechanical behavior of fiber-reinforced polymers from the measured properties and spatial distribution of the different phases and interfaces in the composite. Towards this end, a numerical methodology is proposed herein for the generation of 2D periodic microstructures with arbitrary fiber geometries. A major advantage of the approach presented in this work is the ability of generating high volume fractions of non-circular fibers very efficiently. The underlying algorithm is based on the minimization of fiber overlapping by dynamic translation and rotation of the fibers until intersections are eliminated. The randomness of the microstructures obtained is assessed by means of multiple spatial descriptors.

  • Computational Micromechanics of the transverse and shear behavior of unidirectional fiber reinforced polymers including environmental effects
    Composites Part A: Applied Science and Manufacturing, 2017
    Co-Authors: F. Naya, Carlos Gonzalez, Claudio S. Lopes, S. Van Der Veen, F. Pons
    Abstract:

    Abstract Qualification of Fiber Reinforced Polymer materials (FRP’s) for manufacturing of structural components in the aerospace industry is usually associated with extensive and costly experimental campaigns. The burden of testing is immense and materials should be characterized under different loading states (tension, compression, shear) and environmental conditions (temperature, humidity) to probe their structural integrity during service life. Recent developments in multiscale simulation, together with increased Computational power and improvements in modeling tools, can be used to alleviate this scenario. In this work, high-fidelity simulations of the material behavior at the micro level are used to predict ply properties and ascertain the effect of ply constituents and microstructure on the homogenized ply behavior. This approach relies on the numerical analysis of representative volume elements equipped with physical models of the ply constituents. Its main feature is the ability to provide fast predictions of ply stiffness and strength properties for different environmental conditions of temperature and humidity, in agreement with the experimental results, showing the potential to reduce the time and costs required for material screening and characterization.

  • Computational Micromechanics strategies for the analysis of failure in unidirectional composites
    Numerical Modelling of Failure in Advanced Composite Materials, 2015
    Co-Authors: F. Naya, Carlos Gonzalez, Claudio S. Lopes, Javier Llorca
    Abstract:

    This chapter summarises the current state of the art on the application of Computational Micromechanics to study the mechanical behaviour of unidirectional plies. We outline the simulation strategies to determine the strength and toughness of unidirectional plies together with the experimental techniques to determine the properties of the constituents (matrix, fibres and interfaces). Several examples in unidirectional plies under matrix-dominated failure conditions are presented and the future developments in Computational Micromechanics of composites are briefly summarised.

Carlos Gonzalez - One of the best experts on this subject based on the ideXlab platform.

  • Computational Micromechanics of the transverse and shear behavior of unidirectional fiber reinforced polymers including environmental effects
    Composites Part A: Applied Science and Manufacturing, 2017
    Co-Authors: F. Naya, Carlos Gonzalez, Claudio S. Lopes, S. Van Der Veen, F. Pons
    Abstract:

    Abstract Qualification of Fiber Reinforced Polymer materials (FRP’s) for manufacturing of structural components in the aerospace industry is usually associated with extensive and costly experimental campaigns. The burden of testing is immense and materials should be characterized under different loading states (tension, compression, shear) and environmental conditions (temperature, humidity) to probe their structural integrity during service life. Recent developments in multiscale simulation, together with increased Computational power and improvements in modeling tools, can be used to alleviate this scenario. In this work, high-fidelity simulations of the material behavior at the micro level are used to predict ply properties and ascertain the effect of ply constituents and microstructure on the homogenized ply behavior. This approach relies on the numerical analysis of representative volume elements equipped with physical models of the ply constituents. Its main feature is the ability to provide fast predictions of ply stiffness and strength properties for different environmental conditions of temperature and humidity, in agreement with the experimental results, showing the potential to reduce the time and costs required for material screening and characterization.

  • Computational Micromechanics evaluation of the effect of fibre shape on the transverse strength of unidirectional composites an approach to virtual materials design
    Composites Part A-applied Science and Manufacturing, 2016
    Co-Authors: Miguel Gonzalez Herraez, C. S. Lópes, Carlos Gonzalez, Guzman R De Villoria, J Llorca, T Varela, J Sanchez
    Abstract:

    Abstract Computational Micromechanics of composites is an emerging tool required for virtual materials design (VMD) to address the effect of different variables involved before materials are manufactured. This strategy will avoid unnecessary costs, reducing trial-and-error campaigns leading to fast material developments for tailored properties. In this work, the effect of the fibre cross section on the transverse behaviour of unidirectional fibre composites has been evaluated by means of Computational Micromechanics. To this end, periodic representative volume elements containing uniform and random dispersions of 50% of parallel non-circular fibres with lobular, polygonal and elliptical shapes were generated. Fibre/matrix interface failure as well as matrix plasticity/damage were considered as the fundamental failure mechanisms operating at the microscale under transverse loading. Circular fibres showed the best averaged behaviour although lobular fibres exhibited superior performance in transverse compression mainly due to the higher tensile thermal residual stresses generated during cooling at the fibre/matrix interface.

  • transverse cracking of cross ply laminates a Computational Micromechanics perspective
    Composites Science and Technology, 2015
    Co-Authors: Miguel Gonzalez Herraez, Ferran Naya, Javier Llorca, C. S. Lópes, Carlos Gonzalez, Diego Mora
    Abstract:

    Abstract Transverse cracking in cross-ply carbon/epoxy and glass/epoxy laminates in tension is analyzed by means of Computational Micromechanics. Longitudinal plies were modeled as homogenized, anisotropic elastic solids while the actual fiber distribution was included in the transverse plies. The mechanical response was obtained by the finite element analysis of a long representative volume element of the laminate. Damage in the transverse plies was triggered by interface decohesion and matrix cracking. The simulation strategy was applied to study the influence of ply thickness on the critical stress for the cracking of the transverse plies and on the evolution of crack density in 0 2 / 90 n / 2 s laminates, with n = 1, 2, 4 and 8. It was found that the transverse ply strength corresponding to the initiation and propagation of a through-thickness crack was independent of the ply thickness and that the transverse strength of carbon/epoxy laminates was 35% higher than that of the glass fiber counterparts. In addition, the mechanisms of crack initiation and propagation through the thickness as well as of multiple matrix cracking were ascertained and the stiffness reduction in the 90° ply as a function of crack density was computed as a function of the ply thickness.

  • Computational Micromechanics strategies for the analysis of failure in unidirectional composites
    Numerical Modelling of Failure in Advanced Composite Materials, 2015
    Co-Authors: F. Naya, Carlos Gonzalez, Claudio S. Lopes, Javier Llorca
    Abstract:

    This chapter summarises the current state of the art on the application of Computational Micromechanics to study the mechanical behaviour of unidirectional plies. We outline the simulation strategies to determine the strength and toughness of unidirectional plies together with the experimental techniques to determine the properties of the constituents (matrix, fibres and interfaces). Several examples in unidirectional plies under matrix-dominated failure conditions are presented and the future developments in Computational Micromechanics of composites are briefly summarised.

  • a numerical study of the influence of microvoids in the transverse mechanical response of unidirectional composites
    Composites Science and Technology, 2014
    Co-Authors: Danial Ashouri Vajari, Carlos Gonzalez, J Llorca, Brian Nyvang Legarth
    Abstract:

    Abstract The effect of porosity on the transverse mechanical properties of unidirectional fiber-reinforced composites is studied by means of Computational Micromechanics. The composite behavior is simulated by the finite element analysis of a representative volume element of the composite microstructure in which the random distribution of fibers and the voids are explicitly included. Two types of voids – interfiber voids and matrix voids – were included in the microstructure and the actual damage mechanisms in the composite, namely matrix and interface failure, were accounted for. It was found that porosity (in the range 1–5%) led to a large reduction in the transverse strength and the influence of both types of voids in the onset and propagation of damage throughout the microstructure was studied under transverse tension and compression. Finally, the failure locus of the composite lamina under transverse tension/compression and out-of-plane shear was obtained by means of Computational Micromechanics and compared with the predictions of Puck’s model and with experimental data available in the literature. The results show that the strength of composites is significantly reduced by the presence of voids.

Gary D. Seidel - One of the best experts on this subject based on the ideXlab platform.

  • Computational Micromechanics Analysis of Damage Induced Piezoresistivity in Carbon Nanotube-Polymer Nanocomposites Under Cyclic Loading Conditions
    23rd AIAA AHS Adaptive Structures Conference, 2015
    Co-Authors: Adarsh K. Chaurasia, Xiang Ren, Gary D. Seidel
    Abstract:

    The current 2-scale Computational multiscale Micromechanics based exploration of sensing capabilities in carbon nanotube (CNT) polymer nanocomposites focuses on the macroscale piezoresistive response when the nanocomposite undergoes damage. It has been shown that electron hopping at the nanoscale is the primary mechanism behind the observed macroscale piezoresistivity for such nanocomposites. A novel continuum description of the non-continuum electron hopping effect used in the current work enables the use of multiscale continuum Micromechanics based approaches to study nanocomposite piezoresistivity. The current work aims at exploring the effect of nanoscale interfacial damage and local matrix damage on the effective properties of the nanocomposites. The interfacial damage in CNT-polymer nanocomposites is modeled through electromechanical cohesive zones and the local polymer matrix damage is modeled through continuum damage mechanics modeling. The effect of each of these damage mechanisms is studied independently under monotonic and cyclic loading conditions to differentiate between the different damage evolution paths and to explore the evolution of associated effective electrostatic and piezoresistive response.

  • Computational Micromechanics analysis of electron hopping and interfacial damage induced piezoresistive response in carbon nanotube-polymer nanocomposites
    Smart Materials and Structures, 2014
    Co-Authors: Adarsh K. Chaurasia, Xiang Ren, Gary D. Seidel
    Abstract:

    Carbon nanotube (CNT)-polymer nanocomposites have been observed to exhibit an effective macroscale piezoresistive response, i.e., change in macroscale resistivity when subjected to applied deformation. The macroscale piezoresistive response of CNT-polymer nanocomposites leads to deformation/strain sensing capabilities. It is believed that the nanoscale phenomenon of electron hopping is the major driving force behind the observed macroscale piezoresistivity of such nanocomposites. Additionally, CNT-polymer nanocomposites provide damage sensing capabilities because of local changes in electron hopping pathways at the nanoscale because of initiation/evolution of damage. The primary focus of the current work is to explore the effect of interfacial separation and damage at the nanoscale CNT-polymer interface on the effective macroscale piezoresistive response. Interfacial separation and damage are allowed to evolve at the CNT-polymer interface through coupled electromechanical cohesive zones, within a finite element based Computational Micromechanics framework, resulting in electron hopping based current density across the separated CNT-polymer interface. The macroscale effective material properties and gauge factors are evaluated using Micromechanics techniques based on electrostatic energy equivalence. The impact of the electron hopping mechanism, nanoscale interface separation and damage evolution on the effective nanocomposite electrostatic and piezoresistive response is studied in comparison with the perfectly bonded interface. The effective electrostatic/piezoresistive response for the perfectly bonded interface is obtained based on a Computational Micromechanics model developed in the authors? earlier work. It is observed that the macroscale effective gauge factors are highly sensitive to strain induced formation/disruption of electron hopping pathways, interface separation and the initiation/evolution of interfacial damage.

  • Computational Micromechanics modeling of piezoresistivity in carbon nanotube polymer nanocomposites
    Composite Interfaces, 2013
    Co-Authors: Xiang Ren, Gary D. Seidel
    Abstract:

    The macroscale piezoresistive response, i.e. the change in electrical resistivity under the application of strain, of carbon nanotube–polymer nanocomposites has been observed to lead to gauge factors which are much larger than the gauge factors of commonly used strain gauges. Whereas most strain gauges rely on geometric effects, the gauge factors of carbon nanotube–polymer nanocomposites are the result of a combination of nanoscale mechanisms, namely electrical tunneling (electron hopping) and carbon nanotube inherent piezoresistivity, which can lead to substantial differences between the nanocomposite resistivity at zero strain and the resistivity under an applied strain. This paper focuses on modeling the piezoresistive effect of carbon nanotube–polymer nanocomposites by using Computational Micromechanics techniques based on finite element analysis. For nanocomposites with aligned carbon nanotubes, an electromechanically coupled code is developed for nominal well-dispersed carbon nanotube representative...

  • Computational Micromechanics Model to Study the Effective Macroscale Piezoresistivity of Carbon Nanotube-Polymer Nanocomposites for Strain and Damage Sensing
    Volume 2: Mechanics and Behavior of Active Materials; Structural Health Monitoring; Bioinspired Smart Materials and Systems; Energy Harvesting, 2013
    Co-Authors: Adarsh K. Chaurasia, Gary D. Seidel, Xiang Ren
    Abstract:

    The formation/disruption of the electron hopping pathways is considered to be one of the dominant mechanisms affecting macroscale effective piezoresistive response of carbon nanotube (CNT)-polymer nanocomposites. In this study, a Computational Micromechanics model is developed using finite element techniques to capture the effect of electron hopping induced conductive pathways at the nanoscale which contribute to the macroscale piezoresistive response of the CNT-polymer nanocomposites. In addition, damage is allowed to evolve at the CNT-polymer interface through electromechanical cohesive zones resulting in disruption of electron hopping pathways in the direction of applied strain. The impact of the electron hopping mechanism and nanoscale interfacial damage evolution on the effective piezoresistive response is studied through the macroscale effective material properties and gauge factors evaluated using Micromechanics techniques based on electrostatic energy equivalence. It is observed that the interfacial damage at the nanoscale results in lower gauge factors as compared to the perfectly bonded interface.

  • Computational Micromechanics modeling of piezoresistivity in carbon nanotube–polymer nanocomposites
    Composite Interfaces, 2013
    Co-Authors: Xiang Ren, Gary D. Seidel
    Abstract:

    The macroscale piezoresistive response, i.e. the change in electrical resistivity under the application of strain, of carbon nanotube–polymer nanocomposites has been observed to lead to gauge factors which are much larger than the gauge factors of commonly used strain gauges. Whereas most strain gauges rely on geometric effects, the gauge factors of carbon nanotube–polymer nanocomposites are the result of a combination of nanoscale mechanisms, namely electrical tunneling (electron hopping) and carbon nanotube inherent piezoresistivity, which can lead to substantial differences between the nanocomposite resistivity at zero strain and the resistivity under an applied strain. This paper focuses on modeling the piezoresistive effect of carbon nanotube–polymer nanocomposites by using Computational Micromechanics techniques based on finite element analysis. For nanocomposites with aligned carbon nanotubes, an electromechanically coupled code is developed for nominal well-dispersed carbon nanotube representative...