The overall mechanical properties of composite materials are dependent on the mechanical response of individual constituents and their interactions while they may be relatively easy to determine. This paper represents a simulation process by which the cyclic stresses and fatigue loadings on its constituents could be predicted for an under fatigue loading lamina. Hence, the unidirectional composites fatigue would be studied through its constituents. The proposed model introduces a new coupled stiffness/strength technique by relating lamina stiffness to the stress field in its constituents. Therefore, the stress field and strength considerations in its constituents could be studied when the lamina stiffness is determined by a non-destructive process. For representing a complete description of the constituents’ properties and their interactions, the effect of fibre/matrix interface debonding was introduced into the model. A number of experiments are conducted to verify the simulated relations. The comparison of theoretical and experimental predictions shows that the results are satisfactorily in good agreement.

This study investigates particle breakage and cracks propagation of non-homogeneous rockfill materials, particularly conglomerates, from a microscale perspective. The conglomerate's materials were gathered from Masjed-E-Soleyman, MES, rockfill dam, Iran. The study of particle breakage in rockfill material has been investigated by several researchers worldwide, both in the laboratory and through numerical simulations. However, the previous research focused on homogeneous rockfill materials, not non-homogeneous ones. The first part of this research investigates crack propagation in conglomerates due to high-stress conditions in a rockfill dam. The second part of the paper evaluates the effects of crack propagation on the MES dam crest settlement. In this paper, the microstructure of conglomerates rockfill was determined by performing a set of XRD analyses. The results revealed that calcite constitutes the majority of the rockfill structure. In accordance with geology science, the calcite has a high potential for breaking, and a numerical simulation was developed to illustrate the fractures and crack propagation in a rockfill dam of 177m in height. The results of this research are useful for understanding the concept of large deformations that occurred in the MES dam and needed rehabilitation measures for preventing dam breakage.

A two-dimensional model has been prepared to analyze the fracture MICROMECHANICS of haversian cortical bone. The interstitial bone has been presented as a matrix and the osteon as a fiber. The justification for such substitutions could be made through similarities between fiber-ceramic composite materials and the human haversian cortical bone. The linear elastic fracture mechanics theory is adopted and the solution for the edge dislocations, as a Green's functions, is used to formulate a system of singular integral equations for the arbitrarily oriented microcrack in the matrix in vicinity of an osteon. The problem is solved for various models and the corresponding stress intensity factors are computed. It is also possible to study the effect of microstructural morphology and heterogeneity of the haversian cortical bone upon the fracture behavior. The results indicate that this effect is limited to vicinity of the osteon. The osteonal effect upon the microcrack could lead to increase or decrease of the stress intensity factor at microcrack tips. This effect is, however, related to mismatch between material properties of tissues and the location of microcrack with respect to the osteon.

Shape memory alloys (SMAs) due to their extraordinary physical and mechanical properties, recently are used to enhance the mechanical properties of composites. In the present paper MICROMECHANICS model based on Eshelby’s equivalent inclusion and Halpin-Tsai model was used in order to predict the elastic properties of randomly oriented shape memory alloy short wires reinforced epoxy. The presented incremental MICROMECHANICS model considers the gradual changes in the elastic modulus of the SMA wires due to martensite phase transformation. Experimental tensile tests were applied to the shape memory alloy short wires/epoxy composites to investigate the accuracy of the model. The MICROMECHANICS results were in good agreement with the experimental results and also the previously reported results in the literature. The effect of shape memory alloy wires volume fraction as well as the aspect ratio of the wires was investigated on the elastic modulus of SMA/epoxy composites. Moreover the effect of orientation of SMA wires on the modulus of composites was studied. MICROMECHANICS results showed that in SMA volume fractions lower than 5%, the minimum acceptable aspect ratio of wires is about 25, However for SMA volume fraction above 15%, aspects ratios above 40 are required in order to enhance the elastic modulus of the composites efficiently.

In this paper, multiscale modeling of Epoxy-based hybrid nanocomposites was performed. Single-walled carbon nanotube and carbon nanoparticle (diamond) were used as reinforcements and the elastic behavior of hybrid nanocomposite was investigated. In the multiscale modeling, at the nanoscale and pico-second time range, molecular dynamics method was used to make an accurate model of the interaction between the nano-scale reinforcements and the polymer matrix to predict the interface behavior more realistically. At the micro and macro scales, micromechanical models were used to predict the elastic properties of the nanocomposites, incorporating the effects of interface behavior. Finite element method was also used to check the accuracy of the results obtained at the macro scale. First, pure thermoset polymer with 75% crosslinking ratio was simulated using molecular dynamics method. Then two nanocomposites, one consisting of a single-walled carbon nanotube and another one containing a carbon nanoparticle (diamond) were simulated to obtain equivalent fiber mechanical properties. Next, a micromechanical model was developed for hybrid nanocomposite using the equivalent fiber and pure thermoset polymer mechanical properties. In addition, the results obtained from the molecular dynamics simulations, along with a correction coefficient were employed in the micromechanical models and finite element simulations. Finally, micromechanical multiscale modeling results were compared with finite element multiscale modeling results and a good agreement was observed. Results suggest that the use of two types of nano-reinforcement together, hybrid nanocomposite, improves nanocomposite mechanical properties.

The application of woven fabrics in composites manufacturing has increased because of their special mechanical behavior. Due to the complexity of modeling and simulation of these composites, in this research a MICROMECHANICS based analytical model has been developed to predict the elastic properties of woven fabric composites. The present model is simple to use and has a high accuracy in predicting the elastic properties of woven fabric composites. One of the most important effective factors on the modeling accuracy is utilizing a proper homogenization method. Therefore, a new homogenization method has been developed by using a laminate analogy based method for the woven fabric composites. The proposed homogenization method is a multi-scale homogenization procedure. This model divides the representative volume element to several sub-elements, in a way that the combination of the subelements can be considered as a laminated composite. To determine the mechanical properties of laminates, instead of using an iso-strain assumption, the assumptions of constant in-plane strains and constant out of plane stress have been considered. Then, the proposed homogenization model has been combined with a micromechanical model to propose the new micromechanical model. The applied assumptions improve the prediction of mechanical properties of woven fabrics composites, especially the out-of-plane elastic properties. The proposed model is evaluated by comparing the predicted results with five available experimental results available in the literature, and the accuracy of the present model is shown.

In this study, the mechanical and thermal behavior of the nanoreinforced polymer composite reinforced by Montmorillonite (MMT) nanoparticles is investigated. Due to low cost of computations, the 3D representative volume elements (RVE) method is utilized using ABAQUS finite element commercial software. Low-density poly ethylene (LDPE) and MMT are used as matrix and nanoparticle material, respectively. By using various geometric shapes and weight fractions of nanoparticle, the mechanical and thermal properties such as Young’ s modulus, shear modulus, heat expansion coefficient and heat transfer coefficient are studied. Due to addressing the properties of interfacial zone between the matrix and nanoparticle, finite element modeling is conducted in two ways, namely, perfect bonding and cohesive zone. The results are validated by comparing with experimental results reported in literature and a reasonable agreement was observed. The prediction function for Young’ s modulus is presented by employing Genetic Algorithm (GA) method. In addition, Kerner and Paul approaches as theoretical models are used to calculate the Young’ s modulus. It was finally concluded that the magnitude of the Young’ s and shear modules increase by adding MMT nanoparticles. Furthermore, increment of MMT nanoparticles to polymer matrix nanocomposite decrease the heat expansion and heat transfer coefficients.

In this paper, a micromechanical based model is presented to estimate the stress transfer in interphase of three-phase reinforced composites. The symmetric model consists of fiber, matrix and a layer in between them. In this study, composite constituents were considered as linear elastic materials. Also, matrix was treated as isotropic material while the fiber and the interphase were considered as transversely isotropic materials. The stress distribution solutions for intact model and partially debonded model are obtained. A pair of uncoupled partial differentiation equations was obtained in terms of unknown displacement components. The separation of variable with Eigenfunction expansion methods were used to drive the exact solution of the PDE’s. Analytical solutions for the free boundary conditions on the external surface of the matrix are obtained to simulate the pull out test. In both cases, numerical findings revealed a good correlation with the analytical results. By comparing the shear, radial and axial stress components becomes clear that, three- phase composite adopts smaller amounts than of two- phase composites. Also it was shown that the stress field in partially debonded model has small quantities in comparison to the intact model.

The main purpose of the present research is analytical and numerical analyses of graphene/epoxy nanocomposites with a random distribution of nanoparticles. For this purpose, by combining the molecular dynamics and MICROMECHANICS methods, a new approach is presented. The molecular dynamics method is used to model the stiffness of the graphene/epoxy nanocomposites containing one layer of nano graphene embedded in epoxy resin. A multi-scale modeling strategy from macro to meso, then from meso to micro and finally from micro to nano scales is introduced. A representative volume element (RVE) is selected and for a nanocomposite having a single monolayer graphene embedded in epoxy resin, the longitudinal (E11), transverse (E22) and normal (E33) stiffnesses for three RVEs with arbitary graphene size are simulated. The best curve is fitted to each stiffness diagram and stiffnesses of the RVE in three directions with true graphene size are investigated. In order to consider the effect of randomly graphene sheets distribution in epoxy resin, micromechanical approach is used. Finally, the stiffness of the nanocomposites with randomly distributed graphene is calculated. For evaluation of the present approach in this research an experimental program is conducted. The result of the modeling is well agreed with the experimental data.