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Filippo Ubertini - One of the best experts on this subject based on the ideXlab platform.

  • Micromechanics Modeling of the uniaxial strain sensing property of carbon nanotube cement matrix composites for shm applications
    Composite Structures, 2017
    Co-Authors: Enrique Garciamacias, Antonella Dalessandro, Rafael Castrotriguero, Domingo Perezmira, Filippo Ubertini
    Abstract:

    Abstract Recent advances in the field of Nanotechnology have made possible the development of new smart materials, among which Carbon NanoTube (CNT) cement-based composites are attracting an increasing attention. These composites exhibit strain-sensing capabilities providing measurable variations of their electrical properties under applied mechanical deformations. This unique property, together with the similarity between these composites and structural concrete, suggests the possibility of developing distributed strain-sensing systems with substantial improvements in the cost-effectiveness of large-scale concrete structures. In order to design and optimize self-sensing CNT-based composites, it is therefore essential to develop theoretical models capable of simulating the relationship between external mechanical strains and the effective electrical conductivity. This paper presents a Micromechanics model to predict the piezoresistive properties of CNT cement-based nanocomposites, with the consideration of waviness and non-uniform distributions of nanoinclusions. The origin of the piezoresistive response is attributed to (i) strain-induced changes in the volume fraction, (ii) filler reorientation and, (iii) changes in the tunneling resistance. In order to count on an experimental basis to use as benchmark for validation, several nanocomposite cement-based specimens are manufactured and tested under uniaxial compression.

  • Micromechanics Modeling of the electrical conductivity of carbon nanotube cement-matrix composites
    Composites Part B: Engineering, 2017
    Co-Authors: Enrique García-macías, Rafael Castro-triguero, Antonella D'alessandro, Domingo Pérez-mira, Filippo Ubertini
    Abstract:

    The incorporation of Carbon Nanotubes (CNTs) as nanoinclusions for the development of electrically conductive cement-based composites opens a vast range of possibilities for monitoring of concrete structures. A key issue for the design and optimization of these composites is the development of theoretical models capable of providing a quantitative prediction of their overall electrical conductivity. Experimental results have evidenced the strong influence of the waviness and dispersion of the nanotubes on the overall conductivity of these materials, what makes the consideration of these two phenomena essential for the development of realistic theoretical models. Nevertheless, both waviness and agglomeration have been often neglected in the literature or, when considered, have been reproduced with very simple Modeling approaches not suitable to catch the complexity of the problem at hand. This paper presents an improved Micromechanics model of the effective electrical conductivity of CNT cement-based nanocomposites based on enhanced approaches for reproducing waviness and non-uniform spatial distributions of the nanoinclusions. The two mechanisms that govern the electrical conductivity of these composites, electron hopping and conductive networks, are incorporated in the mixed Micromechanics model. On the basis of scanning electron microscopy inspections, a helical waviness model and a two-parameter agglomeration approach are proposed. In order to assess the accuracy of the proposed analytical model, cement-based specimens have been manufactured and tested for providing data to use as the basis of comparison. In particular, specimens of cement pastes, mortars and concretes with different concentrations of Multi-Walled Carbon Nanotubes (MWCNTs) have been prepared. It is shown that the consideration of straight uniformly distributed nanotubes, as typically done in the literature, leads to an overestimation of the overall conductivity. On the contrary, it is highlighted that the wavy state of the fibers as well as their agglomeration in bundles play a crucial role in the conductivity of cement-based nanocomposites, which is demonstrated by achieving a good fit to the experimental data when using the proposed models for waviness and agglomeration. Overall, the paper highlights the physical mechanisms governing the overall electrical conductivity of cement-based composites with MWCNTs and provides a powerful analytical tool for their design.

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

  • 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 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 facto...

  • computational Micromechanics Modeling of inherent piezoresistivity in carbon nanotube polymer nanocomposites
    Journal of Intelligent Material Systems and Structures, 2013
    Co-Authors: Xiang Ren, Gary D. Seidel
    Abstract:

    It has been observed that carbon nanotubes have a measurable inherent piezoresistive effect, that is to say that changes in carbon nanotube strain can induce changes in carbon nanotube resistivity,...

  • Computational Micromechanics Modeling of piezoresistivity of carbon nanotube polymer nanocomposites
    Behavior and Mechanics of Multifunctional Materials and Composites 2012, 2012
    Co-Authors: Xiang Ren, Gary D. Seidel
    Abstract:

    It has been observed that carbon nanotubes (CNT) have a measurable inherent piezoresistive eect, that is to say that changes in carbon nanotube strain can induce changes in its resistivity, which may lead to observable macroscale piezoresistive response of nanocomposites. In this paper, the focus is on Modeling the eect of inherent piezoresistivity of carbon nanotubes on the nanocomposites piezoresistive behavior by using computational Micromechanics techniques based on nite element analysis. The computational results show the magnitude of the piezoresistive coecients needed for the piezoresistive response of the macroscale nanocomposites to be comparable with experimental data in literature if inherent piezoresistive eect of CNTs is the only driving force for the piezoresistive response of the macroscale nanocomposites.

  • Micromechanics Modeling of functionally graded interphase regions in carbon nanotube polymer composites
    47th AIAA ASME ASCE AHS ASC Structures Structural Dynamics and Materials Conference, 2006
    Co-Authors: Gary D. Seidel, Dimitris C Lagoudas, Sarah Jane V Frankland, Thomas S Gates
    Abstract:

    The effective elastic properties of a unidirectional carbon fiber/epoxy lamina in which the carbon fibers are coated with single-walled carbon nanotubes are modeled herein through the use of a multi-scale method involving the molecular dynamics/equivalent continuum and Micromechanics methods. The specific lamina representative volume element studied consists of a carbon fiber surrounded by a region of epoxy containing a radially varying concentration of carbon nanotubes which is then embedded in the pure epoxy matrix. The variable concentration of carbon nanotubes surrounding the carbon fiber results in a functionally graded interphase region as the properties of the interphase region vary according to the carbon nanotube volume fraction. Molecular dynamics and equivalent continuum methods are used to assess the local effective properties of the carbon nanotube/epoxy comprising the interphase region. Micromechanics in the form of the Mori-Tanaka method are then applied to obtain the global effective properties of the graded interphase region wherein the carbon nanotubes are randomly oriented. Finally, the multi-layer composite cylinders Micromechanics approach is used to obtain the effective lamina properties from the lamina representative volume element. It was found that even very small quantities of carbon nanotubes (0.36% of lamina by volume) coating the surface of the carbon fibers in the lamina can have a significant effect (8% increase) on the transverse properties of the lamina (E22, k23, G23 and G12) with almost no affect on the lamina properties in the fiber direction (E11 and v12).

Dallas N. Little - One of the best experts on this subject based on the ideXlab platform.

  • Dynamic Modulus Prediction of Asphalt Concrete Mixtures Through Computational Micromechanics
    Transportation Research Record, 2015
    Co-Authors: Pravat Karki, Dallas N. Little
    Abstract:

    This paper presents a computational Micromechanics Modeling approach to predict the dynamic modulus of asphalt concrete mixtures. The Modeling uses a finite element method combined with the micromechanical representative volume element (RVE) of mixtures and laboratory tests that characterize the properties of individual mixture constituents. The model treats asphalt concrete mixtures as heterogeneous with two primary phases: a linear viscoelastic fine aggregate matrix (FAM) phase and a linear elastic aggregate phase. The mechanical properties of each phase were experimentally obtained by conducting constitutive tests: oscillatory torsion tests for the viscoelastic FAM phase and quasistatic nanoindentation tests for the elastic aggregate particles. Material properties of each mixture phase were then used in the finite element simulation of two-dimensional mixture microstructures obtained from digital image processes of asphalt concrete mixtures. Model simulations were compared with the experimental dynamic...

  • Damage-Induced Modeling of Asphalt Mixtures through Computational Micromechanics and Cohesive Zone Fracture
    Journal of Materials in Civil Engineering, 2005
    Co-Authors: Yong-rak Kim, D. H. Allen, Dallas N. Little
    Abstract:

    This paper presents a computational Micromechanics Modeling approach to predict damage-induced mechanical response of asphalt mixtures. Heterogeneous geometric characteristics and inelastic mechanical behavior were taken into account by introducing finite element Modeling techniques and a viscoelastic material model. The Modeling also includes interface fracture to rep resent crack growth and damage evolution. The interface fracture is modeled by using a micromechanical nonlinear viscoelastic cohesive-zone constitutive relation. Fundamental material properties and fracture characteristics were measured from simple laboratory tests and then incorporated into the model to predict rate-dependent viscoelastic damage behavior of the asphalt mixture. Simulation results demonstrate that each model parameter significantly influences the mechanical behavior of the overall asphalt mixture. Within a theoretical framework of Micromechanics, this study is expected to be suitable for evaluating damage-induced performance of asphalt mixtures by measuring only material properties and fracture properties of each mix component and not by recursively performing expensive laboratory tests that are typically required for continuum damage mechanics Modeling.

Enrique García-macías - One of the best experts on this subject based on the ideXlab platform.

  • Micromechanics Modeling of the electrical conductivity of carbon nanotube cement-matrix composites
    Composites Part B: Engineering, 2017
    Co-Authors: Enrique García-macías, Rafael Castro-triguero, Antonella D'alessandro, Domingo Pérez-mira, Filippo Ubertini
    Abstract:

    The incorporation of Carbon Nanotubes (CNTs) as nanoinclusions for the development of electrically conductive cement-based composites opens a vast range of possibilities for monitoring of concrete structures. A key issue for the design and optimization of these composites is the development of theoretical models capable of providing a quantitative prediction of their overall electrical conductivity. Experimental results have evidenced the strong influence of the waviness and dispersion of the nanotubes on the overall conductivity of these materials, what makes the consideration of these two phenomena essential for the development of realistic theoretical models. Nevertheless, both waviness and agglomeration have been often neglected in the literature or, when considered, have been reproduced with very simple Modeling approaches not suitable to catch the complexity of the problem at hand. This paper presents an improved Micromechanics model of the effective electrical conductivity of CNT cement-based nanocomposites based on enhanced approaches for reproducing waviness and non-uniform spatial distributions of the nanoinclusions. The two mechanisms that govern the electrical conductivity of these composites, electron hopping and conductive networks, are incorporated in the mixed Micromechanics model. On the basis of scanning electron microscopy inspections, a helical waviness model and a two-parameter agglomeration approach are proposed. In order to assess the accuracy of the proposed analytical model, cement-based specimens have been manufactured and tested for providing data to use as the basis of comparison. In particular, specimens of cement pastes, mortars and concretes with different concentrations of Multi-Walled Carbon Nanotubes (MWCNTs) have been prepared. It is shown that the consideration of straight uniformly distributed nanotubes, as typically done in the literature, leads to an overestimation of the overall conductivity. On the contrary, it is highlighted that the wavy state of the fibers as well as their agglomeration in bundles play a crucial role in the conductivity of cement-based nanocomposites, which is demonstrated by achieving a good fit to the experimental data when using the proposed models for waviness and agglomeration. Overall, the paper highlights the physical mechanisms governing the overall electrical conductivity of cement-based composites with MWCNTs and provides a powerful analytical tool for their design.

Wenbin Yu - One of the best experts on this subject based on the ideXlab platform.

  • Variational asymptotic Micromechanics Modeling of heterogeneous magnetostrictive composite materials
    Composite Structures, 2013
    Co-Authors: Zhong Yifeng, Wenbin Yu, Zhou Xiao-ping
    Abstract:

    Abstract A new Micromechanics model is developed to predict the effective properties as well as the local fields of heterogeneous magnetostrictive composite materials using the variational asymptotic method for unit cell homogenization (VAMUCH), a recently developed Micromechanics Modeling technique. Starting from the total magnetic enthalpy of the heterogenous continuum, we formulate the Micromechanics model as a constrained minimization problem taking advantage of the fact that the size of the microstructure is small compared to the macroscopic size of the material. To handle realistic microstructures in engineering applications, we implement this new model using the finite element method. A few examples are used to demonstrate the application and accuracy of the proposed theory and the companion computer program-VAMUCH.

  • Variational asymptotic Micromechanics Modeling of heterogeneous piezoelectric materials
    Mechanics of Materials, 2008
    Co-Authors: Tian Tang, Wenbin Yu
    Abstract:

    Abstract In this paper, a new Micromechanics model is developed to predict the effective properties and local fields of heterogeneous piezoelectric materials using the variational asymptotic method for unit cell homogenization (VAMUCH), a recently developed Micromechanics Modeling technique. Starting from the total electric enthalpy of the heterogenous continuum, we formulate the Micromechanics model as a constrained minimization problem using the variational asymptotic method. To handle realistic microstructures in engineering applications, we implement this new model using the finite element method. For validation, a few examples are used to demonstrate the application and accuracy of this theory and the companion computer program – VAMUCH.