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Composite driveshafts have emerged as a potent substitute for traditional driveshafts because of their excellent strength-to-weight and stiffness-to-weight ratios. At the same time, usage of multi-walled carbon nanotubes (MWCNTs) as a reinforcement has gained a great momentum due to their superb mechanical, electrical, and thermal characteristics. In this work, a micromechanical model combining the rule of mixtures and the Halpin-Tsai (H-T) model was used to calculate elastic constants of MWCNTs-added carbon fiber reinforced epoxy resin. This micromechanical model considers the effect of agglomeration, aspect ratio, waviness, and random orientation of MWCNTs. Elastic constants of MWCNTs/epoxy resin calculated by using micromechanical model was compared by experimental results available in the literature. Moreover, finite element analysis (FEA) was carried out to predict the critical torsional buckling load of composite driveshafts for various MWCNTs concentrations and fiber orientation angles. The FEA results were compared with the results obtained theoretically. The results showed that Young's modulus of MWCNTs/epoxy resin calculated by using the micromechanical model follows the experimental findings. When compared to pure carbon fiber-reinforced epoxy resin, E1, E2, E12, and G23 (elastic constants of composite lamina) showed improvements of 0.66%, 27.80%, 49.02%, and 37.50%, respectively, in the case of 10vol.% MWCNTs addition. The ply orientation angle has a more dominant effect on Tcr than the Doi: 10.24012/dumf.1336638 MWCNTs concentration. [ABSTRACT FROM AUTHOR]

Quasi-brittle materials such as rock are rate sensitive materials and their behaviour under dynamic loading is not identical with that under static loading. In this study, numerical Brazilian tensile tests are conducted using a Split Hopkinson Pressure Bar system in an attempt to reproduce the dynamic increase factors (DIF) of the experimental tests. The rock is modelled by a bonded particle system made of spherical particles which interact at the contact points. The numerical results indicate that while the bonded particle system with a simple contact bond model can closely mimic the static behaviour of the sandstone specimens, it lacks what is needed for a rate dependent material. Therefore, a micromechanical model in which the contact bond strength is allowed to vary in proportion to the relative velocity of the involved particles is introduced. It is shown that the modified model can reproduce the physical tests data reported in the literature. In particular, with the application of strength enhancement coefficients in the range of 0–16 × 105, DIF values of 1.1–13 are obtained in the indirect tensile Brazilian tests, and the induced strain rate in the specimen is in 10–1000 s−1 range. Our preliminary study indicates that the model, consistent with the fact reported for the quasi-brittle materials, shows different rate-dependent sensitivity and dynamic strength enhancement in tension and compression. The micromechanical parameters in the proposed model can be adjusted to reproduce the physical rock strength, and that the shape of the reflected and transmitted numerical waves can be modified to approach those in the physical tests. [ABSTRACT FROM AUTHOR]

Abstract A new three-dimensional (3D) micromechanical model is proposed to simulate the arbitrary multidirectional carbon fiber reinforced polymer (CFRP) composite laminates. Carbon fiber is assumed as transversely isotropic and linear elastic, matrix is assumed as isotropic and elastic–plastic. Maximum strain criterion is used to describe the failure of fiber and matrix. The stresses, strains and damage are described in the fiber and matrix levels, but the debonding between the fiber and matrix and the delamination between two plies are not modeled in the present analysis. Numerical analyses of nonlinear mechanical behavior of angle-ply [±θ] 2s under tension are conducted to verify the validity of the present micromechanical model. Numerical results of nonlinear mechanical behavior, negative Poisson's ratio through the thickness direction, and stress distribution on the free edge show good agreement with previous experimental and analytical results. [ABSTRACT FROM AUTHOR]

The effect of water on the hydromechanical behavior of unsaturated granular materials has been studied with a micromechanical model based on thermodynamic principles. A general framework based on the theory of thermodynamics with internal variables for constructing thermodynamically consistent multiscale constitutive relations for unsaturated granular materials has been developed. Within this framework, the microscopic total Helmholtz free energy has been separated between a mechanical and a hydraulic part, each of which is a function of either the elastic displacement or the capillary bridge volume and the distance between particles at the microscale. The inter-particle dissipation of energy, assumed to be frictional in origin, is a function of the incremental plastic displacements at the microscale. Both the microscale Helmholtz free energy and the dissipative energy have been volumetrically averaged to obtain the homogenized energy functions at the macroscale. In accordance with the suggested multiscale thermomechanical framework, a micromechanical model has been constructed to describe the behavior of partially saturated granular soils. This model has considered the deformation of soil skeleton by applying a Coulomb-type criterion at the inter-particle contacts. The hydraulic potential is made to be dependent on the size of the particles and is derived through use of the expression for the water retention curve by assuming that liquid bridges are isotropically distributed within the specimen. The performance of the suggested model has been demonstrated through numerical simulations of the behavior of sand under various degrees of saturation and a wide range of mechanical loadings. [ABSTRACT FROM AUTHOR]

Highlights • A micromechanics based model is proposed for the CTE of HFRC. • Model is validated level by level from the cement paste level to HFRC level. • The micromechanical model can provide reasonable predictions on the CTE of HFRC. • Water/cement ratio, hydration degree, aggregate type and fiber type are taken into consideration. Abstract This study is involved with presenting a multi-level micromechanical model for predicting the coefficients of thermal expansion (CTE) of randomly distributed and oriented short hybrid fiber reinforced concrete (HFRC), which includes the cement paste level, concrete level, and HFRC level. In this micromechanical model, the inner products (IP), outer products (OP), calcium hydroxide (CH), unhydrated clinker, sands, aggregates and hybrid fibers are comprehensively considered. A substepping homogenization framework is presented to realize the upscaling from the microstructure to macro HFRC, based on which the overall CTE of HFRC is determined. In addition, the volume fractions of phases at each level are also presented to facilitate the prediction of CTE. Comparisons with experimental data from previous studies are implemented level by level. Subsequently, the influences of the water-cement ratio, the hydration degree, the aggregate property and the fiber property on the CTE are discussed carefully. [ABSTRACT FROM AUTHOR]

As confining pressure increases, crystalline rocks of moderate porosity usually undergo a transition in failure mode from localized brittle fracture to diffused damage and ductile failure. This transition has been widely reported experimentally for several decades; however, satisfactory modeling is still lacking. The present paper aims at modeling the brittle-ductile transition process of rocks under conventional triaxial compression. Based on quantitative analyses of experimental results, it is found that there is a quite satisfactory linearity between the axial inelastic strain at failure and the confining pressure prescribed. A micromechanics-based frictional damage model is then formulated using an associated plastic flow rule and a strain energy release rate-based damage criterion. The analytical solution to the strong plasticity-damage coupling problem is provided and applied to simulate the nonlinear mechanical behaviors of Tennessee marble, Indiana limestone and Jinping marble, each presenting a brittle-ductile transition in stress-strain curves. [ABSTRACT FROM AUTHOR]

This study focuses on the poroelastic behaviour and permeability of tight sandstones, which are characterized by a low porosity, a low gas permeability and a strong sensitivity to in-situ stress. Experimentally the Biot coefficient takes a value close to 1 at low confinement and decreases with increasing confining pressure; the permeability shows an important reduction with increasing confining pressure. This behaviour can be attributed to pore entrapment and to the closure of cracks and joints. Micromechanical models, considering low permeable sandstones as made up of an assemblage of grains with interfaces and pores, reproduce well the observed trends of Biot coefficient and permeability. [ABSTRACT FROM AUTHOR]

Microcracks can affect the mechanical properties of rocks, such as their stiffness and strength. To provide a link between the microstructural parameters and the mechanical behaviour of rock, micromechanical models use parameters that represent a quantitative description of the microcrack population. However, these parameters are difficult to constrain. With the aim of better constraining micromechanical models for rock strength and stiffness, we provide here robust measurements of microcrack characteristics. We developed an algorithm to process optical micrographs of rock, automatically creating binary images of the microcrack network. We applied this procedure to optical micrographs of fine-grained granite samples that have undergone varying degrees of thermal microcrack damage. From these processed images, we calculate the mean microcrack length and the number of microcracks per unit area (and therefore the 2D microcrack density). We also create heat maps showing the spatial distribution of microcracks and their lengths. The results of our automated image analysis are in very good agreement with those of widely-used stereological techniques, and we show that our method can be applied to other rock types (sandstone and andesite) that contain microcracks. Using the measured microcrack characteristics as inputs for Ashby and Sammis’ (1990) 2D micromechanical sliding wing crack model, we predict the uniaxial compressive strength of the granite and compare the predictions with strength measurements made in the laboratory. We find good agreement between the model and the experimental data for granite heated to temperatures below the alpha-beta transition of quartz (~573 °C). Rock strength is overestimated above this threshold, possibly due to variations in fracture toughness, which is considered constant in our modelling. Finally, we use the 2D sliding crack model of David et al. (2012) to infer microcrack density and aspect ratio from the mechanical response of the thermally microcracked samples to cyclic stressing. We show a good agreement between inferred and measured crack densities if a scaling factor is introduced. [ABSTRACT FROM AUTHOR]

Syntactic foams are lightweight composite materials that find extensive application as core materials for sandwich panels in marine and aerospace structures. While several models have been proposed to analyze the elastic response and failure of these composites at small strain rates, the understanding of syntactic foam behavior at high strain rates remains elusive. In this work, we simulate the response of polymer-glass syntactic foams under high strain rate compressive loading conditions, by using a three-dimensional micromechanical model consisting of fifty hollow spheres randomly dispersed in the matrix material. The mechanical response of the matrix is described by generalizing a phenomenological viscoplastic constitutive model from the literature to the three-dimensional stress state. The filler behavior is assumed to be linear elastic until brittle failure, which is predicted on the basis of a structural criterion for glass microballoons. The collapse of the first glass microballoon is hypothesized to trigger the failure of the whole composite. Such a micromechanical model is implemented in the commercial finite element code ABAQUS. We focus on glass-vinyl ester syntactic foams and perform a parametric study to elucidate the roles of strain rate, microoballoon density, and microballoon volume fraction on the compressive modulus, strain energy, and effective strength. Comparisons between model findings and available experimental data are presented to assess the accuracy of the proposed numerical model. Our results enable the study of syntactic foam behavior at high strain rates, for a wide range of strain rates, microballoon densities, and microballoon volume fractions. This knowledge is expected to aid in the design of lightweight composite materials subjected to high strain rate compressive loading. [ABSTRACT FROM AUTHOR]

In this article, the nonlinear vibration frequencies of functionally graded carbon nanotube-reinforced composite doubly curved shell panels under elevated thermal environment are numerically investigated using finite element method. The doubly curved carbon nanotube-reinforced shell panel has been modeled mathematically using higher-order kinematics theory and Green–Lagrange geometrical nonlinear strains. The properties of the individual constituents of the graded composite are assumed to be temperature dependent. In addition, the properties of the media are obtained based on the modified rule of mixture. The carbon nanotubes are dispersed nonuniformly through the thickness direction. The large deformation kinematic effects on the structural responses are counted by including all the nonlinear higher-order terms in the formulation. The desired nonlinear responses are computed numerically using our in-house computer code in conjunction with the direct iterative scheme. The convergence and the accuracy of the present numerical model have been checked by solving various numerical examples. Nonlinear mechanical responses were affected by several other design parameters and explored numerically for the thickness ratios, volume fractions, temperature loading, type of geometries, and type of grading under the uniform thermal environment. [ABSTRACT FROM AUTHOR]

By means of the experimental method, micromechanical model and Finite Element Method (FEM), this paper studied the compressive behaviors of the three-dimensional random fibrous (3D RF) material in the through-the-thickness (TTT) and in-plane (IP) directions at elevated temperatures. The compressive experiments showed that the fracture strength and Young's modulus of the 3D RF material in the TTT and IP directions decrease as increasing temperature. The specimens fracture through breaking the fibers under the bending deformation, while almost all the bonding zones keep intact. A simple micromechanical model and a FEM model are developed to simulate the mechanical properties of the 3D RF material. The micromechanical model ignores the randomness of the fibers, while in the FEM model special attention is drawn to the influence of the morphological characteristic. Numerical results from the micromechanical model and FEM model agree well with the observations from the compressive experiments. [ABSTRACT FROM AUTHOR]

A nondestructive technique for evaluating the strength of hull elements of submersibles is described. The technique is based on the micromechanical model of temporal dependences of the parameters of acoustic emission that is registered under an original novel technique of loading of a cylindrical hull section. The technique is also suitable for assessing the information value of resource-related acoustic-emission diagnostic indicators. [ABSTRACT FROM AUTHOR]

This study presents a new micromechanical model to investigate the effects of thermal residual stresses and interfacial properties on the transverse behaviors of SiC/Ti composites with different microstructures. In this model, the fiber-matrix interface is modeled by the bilinear cohesive zone model. The interface model is introduced into the generalized method of cells, which has the advantage of computational accuracy and efficiency. At the same time, the generalized method of cells is extended to consider thermal residual stresses within the fiber and matrix phases. Thermal residual stresses are found to have a significant influence on the transverse behaviors of the composites. Compared with the perfect interface, the transverse behaviors of the composites with weak interface bonding are much lower. Moreover, with the increase of fiber fraction, the stiffness of the composites increases before debonding occurs while the saturation stress decreases. The predicted results using the circular fiber model and considering thermal residual stresses are more consistent with the experimental values compared with the results using the square or elliptical fiber model. When the stress concentration factor is considered and the interface is weakly bonding, the strength predictions are much better than the results using the perfect bonding. [ABSTRACT FROM AUTHOR]

• A new perspective considering filler distribution was provided in micromechanical modeling of asphalt mastic. • Three viscoelastic micromechanical models of asphalt mastic were improved. • The effects of various parameters on the distribution of the shear modulus ratio were investigated. • The improved models can determine the spatial distribution characteristic of effective properties for asphalt mastic. • A key dimensionless diameter that has a significant effect on effective shear modulus of asphalt mastic exists. This study aims to provide a new perspective into the consideration of filler distribution characteristic in micromechanical modeling of asphalt mastic through combining fractal microstructure. To do this, three viscoelastic micromechanical models were improved by the preliminarily combination between micromechanical equivalence and fractal statistic principles. Particle size distribution (PSD) of filler was tested by a laser particle size analyzer. Asphalt mastics with different filler concentrations were fabricated. Dynamic shear moduli of asphalt and asphalt mastics was tested by a dynamic shear rheometer. The PSD of the circles intercepted by the plane and dimensionless area of the intercepted asphalt matrix were analyzed. The dynamic shear modulus ratio of asphalt mastic to binder were calculated based on the improved models. The effects of various parameters on the distribution of the ratio were investigated. Results show that the shifted R-R distribution function is capable of capturing the PSD of filler. The dimensionless area increases with increasing dimensionless diameter, but decreases with increasing filler volume fraction. The shear modulus ratio shows a three-stage reduction trend with dimensionless diameter, replying that the shear modulus of asphalt mastic appears as a random distribution in space. Meanwhile, the spatial distribution is influenced by filler volume fraction and thus there has difference between the stiffening effects of filler on various local regions in asphalt mastic. Poisson's ratio of binder plays an enhanced role in the stiffening effect of filler, which is affected by the spatial locations within asphalt mastic. Modulus and Poisson's ratio of limestone filler and modulus of binder have little effect on the distribution of the shear modulus ratio. The combination of micromechanical modeling and fractal characteristic is capable of determining the spatial distribution characteristic of effective properties for asphalt mastic. The local homogenization of asphalt mastic in terms of the modulus and its influence on properties of asphalt mixture should be focused on and conducted in future. [ABSTRACT FROM AUTHOR]

The dynamic mechanical properties of PBX1314 and its binder are systematically investigated. Based on split-Hopkinson pressure bar technique, the experimental results of PBX1314 and its binder are obtained under high strain rate. A constitutive theory is developed for modeling the mechanical response of dynamically loaded PBX1314 binder. To accomplish this aim, the PBX1314 binder is assayed by relaxation tests at different temperatures, in order to apply the time-temperature superposition principle (TTSP) and raise the master curves, based on WLF equation. The rate dependence of mechanical response of the polymer binder is accounted for by a generalized Maxwell viscoelasticity model. The basis for this work is Mori and Tanaka's effective medium theory. The grains in this analysis are assumed to be spherical and uniformly distributed in the binder. The relaxation constitutive relations of particulate reinforced composites are investigated by Laplace transformation and the corresponding principle. The theoretical prediction coincides with experimental results. [ABSTRACT FROM AUTHOR]

In this paper, a micromechanical model for connective soft tissues based on the available histological evidences is developed. The proposed model constituents i.e. collagen fibers and ground matrix are considered as hyperelastic materials. The matrix material is assumed to be isotropic Neo-Hookean while the collagen fibers are considered to be transversely isotropic hyperelastic. In order to take into account the effects of tissue structure in lower scales on the macroscopic behavior of tissue, a strain energy density function (SEDF) is developed for collagen fibers based on tissue hierarchical structure. Macroscopic response and properties of tissue are obtained using the numerical homogenization method with the help of ABAQUS software. The periodic boundary conditions and the proposed constitutive models are implemented into ABAQUS using the DISP and the UMAT subroutines, respectively. The existence of the solution and stable material behavior of proposed constitutive model for collagen fibers are investigated based on the poly-convexity condition. Results of the presented micromechanics model for connective tissues are compared and validated with available experimental data. Effects of geometrical and material parameters variation at microscale on macroscopic mechanical behavior of tissues are investigated. The results show that decrease in collagen content of the connective tissues like the tendon due to diseases leads 20% more stretch than healthy tissue under the same load which can results in connective tissue malfunction and hypermobility in joints. [ABSTRACT FROM AUTHOR]

The nonlinear free vibration behavior of functionally graded carbon nanotube reinforced composite flat panel is investigated using temperature dependent material properties for different grading. The carbon nanotube reinforced composite flat panel model has been developed mathematically using the higher-order shear deformation theory and Green-Lagrange nonlinearity. The present mathematical model has included all the nonlinear higher-order terms for the sake of generality. Further, the responses are computed numerically using the direct iteration method in conjunction with the finite element method. The validity and the convergence behavior of the present nonlinear model have been checked and the effect of different design parameters on the nonlinear vibration responses are discussed in detail. [ABSTRACT FROM AUTHOR]

As there has been an increasing trend in using nonwovensnatural fiber in composites, there is a need to find good micromechanical models to represent their behavior. In this study,randomly oriented nonwoven kenaf/epoxy composites at various fiber loading has been fabricated by using resin transfer moulding (RTM) method. Experimental results show that increasing the fiber loading has led to the increment of tensile modulus. The validity of rule of mixtures (ROM) and modified rule of mixtures (MROM) which includes model by Krenchel and Nairn has also been analyzed. ROM has failed to predict the tensile modulus of the composites. Meanwhile, MROM managed to produce an accurate tensile modulus prediction due the inclusion of fiber length factor by Nairn model and fiber orientation factor by Krenchel model. [ABSTRACT FROM AUTHOR]

A micromechanical stick-slip model was developed to characterize the damping response of single-walled carbon nanotube nanocomposites. Depending on the strength of the interfacial bonding and the extent of applied loading, the single-walled carbon nanotube embedded in the matrix may either completely stick to the matrix or partially slide relative to the matrix. The slippage in the interface, together with the contact friction, may lead to the energy dissipation of single-walled carbon nanotube nanocomposites. The effects of the aspect ratio of single-walled carbon nanotube, interfacial bonding strength, volume fraction of single-walled carbon nanotube, and interfacial friction on the damping behavior of single-walled carbon nanotube nanocomposites were accounted for in the micromechanical stick-slip model. In order to validate the analytical model, the energy dissipation was also evaluated using the finite element method. A cylindrical finite element method, with an embedded single-walled carbon nanotube, was developed where the stick-slip behavior of the interface between the single-walled carbon nanotube and surrounding matrix was characterized using a contact element. It was found that the energy dissipation obtained from the finite element analysis agrees with that derived from the micromechanical stick-slip model. Moreover, the energy dissipation may significantly increase, when the single-walled carbon nanotube slippage takes place. The increment of the energy dissipation could be attributed to the interfacial contact friction between the single-walled carbon nanotube and the surround matrix as well as the viscoelastic properties of the matrix materials. [ABSTRACT FROM AUTHOR]

In this study hierarchical micromechanical modeling is presented for prediction of the elastic properties of 2D needled carbon/carbon (C/C) composites. The modeling is based upon the analysis of the representative volume element (RVE) models of the hierarchical microstructure of composites. The prediction procedure consists of two sequential levels covering: (1) unidirectional fiber ply consisting of continuous fibers, matrix and randomly distributed pores and short-chopped fiber felt consisting of matrix and randomly distributed short fibers and pores; (2) needled laminate consisting of homogenous layers of fiber plies and felts and the needling yarn. Mori–Tanaka theory based method and strain energy-based finite element approach are used to calculate the effective properties of constituent materials and overall composites. Predictions are compared with experimentally measured data to verify the proposed model. In addition, a series of numerical predictions are performed to examine the influences of the thickness ratio of short-chopped fiber felt to unidirectional fiber ply and the needling periodicity on the elastic moduli of composites. [ABSTRACT FROM AUTHOR]

This work aims mainly to derive closed-form expressions for the effective properties of layered composites when linear uncoupled and coupled phenomena, such as conduction, elasticity, thermoelectricity and piezomagnetoelectricity, are concerned. In addition, properties may be graded in the direction normal to the layer plane. The remarkable feature of the obtained results is that they are expressed in a unified and very compact way for all uncoupled and coupled linear mechanical and physical phenomena. Our results include as special ones all the relevant results reported up to now in the literature. The key to obtaining our general compact coordinate-free results resides in extending Hill’s interfacial relations for a perfect elastic interface to the setting of an arbitrary finite number of uncoupled and coupled linear phenomena. The effects of the presence of stiffeners and softeners on the effective properties of layered composites are also investigated. In particular, four limiting cases for piezoelectricity are studied in detail. As illustrations, the general results are applied to several coupled phenomena and to functionally graded layered composites. [ABSTRACT FROM PUBLISHER]

The interfacial strength and failure mechanisms of particle-reinforced metal-matrix composites were predicted using a micromechanical model. The micromechanical model was constructed based on the cohesive zone model, and the spherical particle was arranged on the body-centered cubic distribution. The SiC particle-reinforced Al matrix composite was chosen as the model system and its interfacial properties was predicted. It can be seen that a complete interfacial debonding all over the particle could never be reached, and the plastic strain of composite when the interfacial debonding begins to appear shows an increase trend with the increasing of interfacial strength. [ABSTRACT FROM AUTHOR]

This paper develops a micromechanical model to study the mechanical degradation of natural fiber reinforced composites (NFRCs) induced by moisture absorption. Since the moisture absorption and the mechanical degradation of the composite are correlated, a modified Mori–Tanaka method with a damage variable is proposed. A set of micromechanical equations are established to describe the modulus loss of NFRCs. After specifying this model with different inclusion shapes, the overall swelling deformation and the mechanical degradation of the randomly oriented and the unidirectional straight natural fiber reinforced composites are studied in detail. Theoretical predicted results of the randomly oriented straight fiber reinforced composite are compared with experimental ones from literature and a good agreement is obtained. Further numerical results demonstrate that a stiffer matrix can reduce both the moisture absorption and the mechanical degradation of natural fibers. [ABSTRACT FROM AUTHOR]

In this study, a micromechanical model is presented for prediction of the time dependent relaxation modulus of plain weave polymer matrix composites. This model is based upon the analysis of the representative volume element (RVE) of composites. The RVE models are firstly created on two scales consisting of the fiber bundle modeling (fiber-scale) followed by a weave fabric modeling (bundle-scale). The material properties of fiber and matrix are described by linear elastic law and viscoelastic constitutive law respectively. The generalized Maxwell rheological model is used to describe the viscoelastic behavior of matrix. A time dependent strain energy model is then proposed for evaluating the relaxation modulus of composites. Stress relaxation experiments are conducted for plain weave T300 carbon fabric reinforced 5105 AXSON epoxy resin composites with different fiber volume fractions. Predictions are compared with experimentally measured response to verify the proposed model. In addition, a series of numerical simulations are performed to examine the influences of the loading time and fiber volume fraction on the relaxation behavior of composites. [ABSTRACT FROM AUTHOR]

This research is aimed to develop an integrated methodology based on micromechanical model and neural network to predict elastic modulus of 3-D multi-phase and multi-layer (MPML) braided composite. The micromechanical model including two-scale RVC modeling and strain energy model is firstly proposed. A back propagation (BP) neural network model is then developed to map the complex non-linear relationship between microstructural parameters and elastic modulus of the composite. The 3-D braided C/C-SiC composite is used as a case study. Predictions are compared with experimentally measured response to verify the developed technique. The results show that the developed methodology performs well in predicting the properties of the complex 3-D MPML braided composite. [ABSTRACT FROM AUTHOR]

The quantitative interpretation of the extreme dependence of elastic modulus on composition for blends poly(ethylene terephthalate)/poly(butylene terephthalate) has been offered, which uses the percolation theory and fractal analysis. It has been shown that elastic modulus extreme increasing is due to the corresponding growth of shear strength of blends components autohesional bonding. The micromechanical models do not give the indicated effect adequate description. [ABSTRACT FROM AUTHOR]

The mechanical properties of Hot Mix Asphalt (HMA) mixes are often characterized by its viscoelastic behavior. Viscoelasticity coupled with the thermo-mechanical nature of asphalt offers time-temperature dependence to the mechanical properties of HMA mixes. Also, the wide range of distribution of particles, and several orders of magnitude of differences in the mechanical properties between constituents cause a wide range of stress and strain distribution within the microstructure. In this paper, micromechanical modeling has been performed to study the relationship between individual material properties, their interaction within the microstructure, and the macroscopic properties of HMA mix. The analytical model based on N phase self-consistent scheme allows calculating the complex modulus and phase angle of HMA mixes from the mechanical properties of its constituents and designed mix data. In the mix microstructure, aggregates and sand are classified using simple sieve analysis test. Asphalt and sand mastic film thicknesses around the aggregates are calculated for each class and introduced into the model. [ABSTRACT FROM AUTHOR]

The present study aims at rate-dependent damage modeling for polymeric composite materials with the rate-dependent constitutive model using a multi-scale approach. Phenomenologically, the nonlinear response of a composite under the in-plane shear loading condition is originated from the viscoplasticity of a matrix and the damage behavior of composite materials. In case of dynamic loading conditions, the strain-rate effects the change of the damage behavior of composite materials, as well as the behavior of the matrix. The enhanced micromechanical model which improves the in-plane shear behavior, is used for analyzing the rate-dependent behaviors of the fiber and matrix constituents. The rate-dependent elastic damage model based on orthotropic continuum damage mechanics theory at the macromechanical level is applied to improve the accuracy of the analysis model. Predictions by presented model are shown to agree fairly well with experimental results over a wide range of strain rates. [ABSTRACT FROM AUTHOR]

2D cross ply magnesium matrix composites were fabricated by melt magnesium infiltration in carbon fiber preform. Carbon fiber uni-directional fabric was used to prepare the carbon fiber preform by alternatively placing fabric in orthogonal way layer by layer. Preform was strengthened by stitching in the perpendicular direction to the fabric layers. The micromechanical model was generated based on the real microstructue of 2D cross ply magnesium matrix composites. The plastic response of 2D cross ply magnesium matrix composites was predicted based on the constructed micromechanical model by applying tensile load in different direction with respect to the fabric direction. Effects of layer mode and packing mode on the plastic response were investigated by numerical simulation. The results showed that composites were strengthened maximally along the fabric direction. Layering mode of fabric played important role on the plastic response of composite. The best layer mode for maximum properties improvement was that perpendicular layer and parallel layer should be used alternatively. The simulated results were verified through corresponding experiments. [ABSTRACT FROM AUTHOR]

Highlights: [•] This paper presents a FE micromechanical model of oxidation in asphalt mixtures. [•] The impact of the void phase on oxidative hardening of mixtures is evaluated. [•] The model includes oxygen diffusion, chemical kinetics and mechanical simulations. [•] Dynamic modulus was numerically computed in the first 5 years of pavement service. [•] Air void content and connectivity strongly impact oxidative hardening in pavements. [Copyright &y& Elsevier]

This paper investigates the stochastic nonlinear flexural response of laminated composite plates resting on a two-parameter Pasternak elastic foundation with Winkler cubic nonlinearity and random system properties subjected to transverse uniform lateral pressure and hygrothermal loading. System properties, such as the lamina material properties, coefficients of thermal expansion, coefficients of hygroscopic expansion, and lateral load, are modeled as basic random variables using a micromechanical model. A higher-order shear deformation theory in the von Kármán sense is used to model the system behavior of the laminated plate. A direct iterative-based nonlinear FEM, in conjunction with the first-order perturbation technique previously developed by the authors, is extended for the hygrothermal problem to obtain the second-order response statistics, i.e., the mean and variance of the nonlinear transverse deflection of the plate. Typical numerical results for the second-order statistics of the nonlinear transverse central deflection of composite plates subjected to uniform temperature and moisture distribution over the plate surface and through the plate thickness are obtained for various combinations of foundation parameters, uniform lateral pressures, staking sequences, volume fraction, aspect ratio, plate thickness ratio, and boundary conditions under environmental conditions. The approach has been compared with those available in the literature and an independent Monte Carlo simulation (MCS). [ABSTRACT FROM AUTHOR]

Highlights: [•] Creep of pure Cu single crystals and of a coarsed grained Cu-1wt.% Sb alloy at 823K. [•] Metallographic and a crystallographic assessment of the Cu–Sb test specimens. [•] Measurements of grain boundary sliding and estimation of the sliding viscosity. [•] Development of a micromechanical polycrystal model for finite element analysis. [•] Fitting of the micromechanical model to the experimental creep data. [Copyright &y& Elsevier]

A 3D anisotropic micropolar continuum model of vertebral trabecular bone is presently developed accounting for the influence of microstructure-related scale effects on the macroscopic effective properties. Vertebral trabecular bone is modeled as a cellular material with an idealized periodic structure made of open 3D cells. The micromechanical approach relies on the discrete homogenization technique considering lattice microrotations as additional degrees of freedom at the microscale. The effective elastic properties of 3D lattices made of articulated beams taking into account axial, transverse shearing, flexural, and torsional deformations of the cell struts are derived as closed form expressions of the geometrical and mechanical microparameters. The scaling laws of the effective moduli versus density are determined in situations of low and high effective densities to assess the impact of the transverse shear deformation. The classical and micropolar effective moduli and the internal flexural and torsional lengths are identified versus the same microparameters. A finite element model of the local architecture of the trabeculae gives values of the effective moduli that are in satisfactory agreement with the homogenized moduli. [ABSTRACT FROM AUTHOR]

Thermal cracking of Portland cement concrete (PCC) decreases rideability and accelerates deterioration of concrete pavements. Coefficient of thermal expansion (CTE) is one of the most important parameters to evaluate the thermal sensitivity of PCC. The AASHTO mechanistic-empirical pavement design guide (MEPDG) requires CTE as a basic input for concrete pavement design, which has increased interest in studies related to concrete CTE in the United States. Several test methods have been developed and used to determine concrete CTE. Nevertheless, concrete CTE testing is time-consuming. Most of the currently available concrete CTE prediction models are empirical and do not reflect the microstructure of PCC. This paper developed a micromechanical model based on thermal mechanical analysis to predict concrete CTE. Concrete CTE data found in the literature validated the applicability of the developed model. Factors affecting concrete CTE were examined using the proposed model. The model has the potential to estimate concrete CTE for concrete pavement design and to help select appropriate raw materials for PCC to achieve low CTE. [ABSTRACT FROM AUTHOR]

This article presents the hygrothermal effects on the free vibration of laminated composite plates resting on a two-parameter Winkler and Pasternak elastic foundations with random system properties using micromechanical model. System properties such as material properties, hygroscopic expansion coefficients, thermal expansion coefficients and foundation stiffness parameters are modeled as independent basic random variables which are affected by the variation in temperature and moisture based on a micromechanical model of a laminate for accurate prediction of system behavior. A C0 finite element method based on higher-order shear deformation theory has been used for deriving the standard eigenvalue problem. A Taylor series-based mean-centered first-order perturbation technique is used to find mean and standard deviation of the natural frequency subjected to uniform moisture concentration and temperature rise, plate aspect ratio, total number of plies, fiber orientations and elastic foundation parameters with different boundary support under hygrothermal environmental conditions. Typical numerical results have been validated with those available in the literature and independent Monte Carlo simulation. [ABSTRACT FROM AUTHOR]

Electro-thermo-elastic stress analysis of piezoelectric polymeric thick-walled cylinder reinforced by boron-nitride nanotubes subjected to electro-thermo-mechanical fields is presented. The electrothermo-elastic properties of piezoelectric fiber reinforced composite was studied by a modified XY micromechanical model capable of exhibiting full coupling relation between electric, thermal and elastic fields. Assuming piezoelectric fiber reinforced composite material and its composite constituents to be linear, homogenous, orthotropic, and perfectly bonded with uniform applied field, the basic relation for the axisymmetric deformation of a thick-wall cylinder subjected to uniform internal and external pressures, an axial electrical load, a temperature change between inner and outer radius are derived. Although the cylinder has end caps and is free to change length, displacement, strains, and stresses at location far removed from the end caps have been investigated. The stress results suggest that increasing boron-nitride nanotubes content in longitudinal direction reduces the effective stress. Displacement along radial direction indicates an optimum content of 5% boron-nitride nanotube for this. Furthermore, at normal working conditions, the influence of thermal and mechanical fields are much higher than the electric one on the effective stress; hence, this smart structure is best suited for applications as sensors than actuators. [ABSTRACT FROM AUTHOR]

A convenient method to predict the macroscopic elastic performance of composite containing interphase was developed in this paper based on a new modified random sequential adsorption method and multiple nonlinear regression analysis. First, a three-phase micromechanical model with randomly distributed fibers was established with a new modified random sequential adsorption method named the Moving Window Method. Second, the macroscopic elastic behaviors of T300/914C were predicted based on micromechanical parameters of constituent materials using energy method, and the influence of the randomness of fiber distribution on the prediction was analyzed. Third, the effects of interphase thickness, interphase modulus and Poisson’s ratio on the macroscopic elastic properties of the composite were studied by changing these interphase micromechanical parameters gradually within certain ranges. Finally, the multiple nonlinear regression models that describe the relationship between the macroscopic elastic properties of T300/914C and micromechanical characteristic parameters of the interphase were established using a limited number of data from numerical simulation. Results indicate that the relative errors for the longitudinal modulus and the major Poisson's ratio are within ±1% while for the transverse modulus, shear modulus and Poisson’s ratio at cross section, the relative errors are within 5%. [ABSTRACT FROM AUTHOR]