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Abstract: The work is devoted to the investigation of fracture processes in the vicinity of an interface crack in functionally graded/homogeneous bimaterials with internal defects subjected to tensile loading and a heat flux. A previously obtained solution () for the case of thermal loading on the same geometry is used as a part of the present solution. The solution is based on the integral equation method and it is assumed that thermal properties of the functionally graded material (FGM) possess exponential form. An asymptotic analytical solution is derived for a special case where an interface crack is larger than internal cracks in the FGM. The stress intensity factors are presented as asymptotic analytical functions of geometry of the problem and material properties. Analyses of the effects of the location and orientation of the cracks and the material non-homogeneity parameters on the stress intensity factors in FGM/homogeneous bimaterials is performed in the presence of thermal and mechanical loading. Examples of some FGM/homogeneous bimaterial are discussed. [Copyright &y& Elsevier]

Abstract: The work is devoted to mathematical modeling of the fracture processes in the vicinity of an interface crack in functionally graded/homogeneous bimaterials with internal defects subjected to a thermal flux. A previously obtained solution (Petrova and Schmauder, 2009, 2011) is used and supplemented with the additional possibility to take into account the crack closure. The solution is based on the integral equation method and it is assumed that thermal properties of the functionally graded material (FGM) have exponential form. For a special case where an interface crack length is much larger than the internal cracks in the FGM an asymptotic analytical solution of the problem is obtained as series of a small parameter (the ratio between sizes of the internal and interface cracks). Analyses of the effects of the location and orientation of the cracks, the material non-homogeneity parameters and the crack closure effects on the thermal stress intensity factors of the interface crack in FGM/homogeneous bimaterials are performed. Examples of some FGM/homogeneous bimaterial combinations (i.e., metal/metal, ceramic/metal) are discussed. [Copyright &y& Elsevier]

Abstract: In this study the elastoplastic behaviour of nanodispersed elastomeric copolymer particle-modified PA6 is investigated. Micromechanical modelling is proposed to predict the elastoplastic response of the PA6/elastomer composite under uniaxial tensile loading. A 3D self-consistent embedded unit cell model is chosen in this work which has been successfully applied for simulating the mechanical behaviour of metal matrix composites (MMCs). This model is applied for the first time to evaluate the elastoplastic behaviour of PA6 matrix composites with varying volume fractions of elastomer. The elastomer particles are idealistically assumed to be spherical. In the model a circular inclusion is surrounded by the PA6 polymer matrix, which is again embedded in the PA6/elastomer composite. This cell was subjected to uniaxial loading. The mechanical behaviour is determined iteratively in a self-consistent manner using updated elastic–plastic data as new input. A detailed experimental procedure (uniaxial tensile tests in combination with the ARAMIS high speed camera systems) for determining the true stress–strain curves of the matrix and the elastomer as input data for the simulation is reported. In addition, a numerical surface model based on the real structure of the elastomer particles is studied numerically for comparison. Two analytical micromechanical composite models are chosen for evaluating the elastic performance of the composite. The predictions from the 3D self-consistent embedded unit cell model are in good agreement with the experimental results. [Copyright &y& Elsevier]

This paper develops an approach to model the deformation and fracture of heterogeneous materials at different scales (including multiscale modeling) within a discrete representation of the medium. Within this approach, molecular dynamics is used for the atomic-scale simulation. The simply deformable distinct element method is applied for simulating at higher length scales. This approach is proposed to be implemented using a general way to derive relations for interaction forces between distinct elements in a many-body approximation similar to that of the embedded atom method. This makes it possible to overcome limitations of the distinct element method which are related to difficulties in implementing complex rheological and fracture models of solids at different length scales. For an adequate description of the mechanical behavior features of materials at the micro- and mesoscales, two kinds of models that consider grain and phase boundaries within the discrete element framework are proposed. Examples are given to illustrate the application of the developed formalism to the study of the mechanical response (including fracture) of materials with multiscale internal structure. The examples show that the simply deformable distinct element method is a correct and efficient tool for analyzing complex problems in solid mechanics (including mechanics of discontinua) at different scales. [ABSTRACT FROM AUTHOR]

Abstract: In this study semi-crystalline polyamide 6 (PA 6) and its composites consisting of a semi-crystalline PA 6 matrix filled with up to 32.9vol.% submicron elastomeric copolymer particles are investigated. The aim of this paper is to show how micro-mechanical modelling can predict the elastic behaviour of these composites from the experimentally observed morphology and determined parameters. Semi-crystalline PA 6 possesses a spherulitic morphology, consisting of a radial assembly of amorphous layers and nano-sized crystalline lamellae. In the continuum mechanical representation of semi-crystalline PA 6, nano-sized crystallite lamellae are considered as a phase which is additionally embedded into the amorphous matrix. The 2D self-consistent embedded cell model was chosen to predict the Young’s modulus of the semi-crystalline PA 6 material. In this model a rectangular lamella is surrounded by an amorphous matrix, which is again embedded in the semi-crystalline PA 6 material with the mechanical behaviour to be determined iteratively in a self-consistent manner. The Young’s modulus of PA 6 has been calculated by an appropriate integration of results of all orientations of the crystalline lamellae. The Young’s modulus of PA 6/elastomer composite is also predicted by a 3D self-consistent embedded cell model. In this model a circular inclusion is surrounded by the PA 6 polymer matrix, which is again embedded in the PA 6/elastomer composite. Good agreement is obtained between experiments and the prediction with the self-consistent embedded cell models. [ABSTRACT FROM AUTHOR]

Abstract: Functionally graded materials (FGMs) have great potential as energy absorbing devices, electrical transducers, thermal barriers, etc. Study of the propagation of elastic waves is imperative for a number of such applications. In this paper, a simple one-dimensional model is proposed to study the stress waves in discretely graded media. The model uses spectral approach to determine the stresses due to the incident and reflected waves in FGMs. It has been observed that FGMs attenuate and delay the peak stresses considerably as compared to composites with sharp interfaces. Performance of different number of inner layers on the reflected wave characteristics has been discussed. Stress time history profiles are also presented for Alumina–Aluminum FGMs that are used in armor applications. [Copyright &y& Elsevier]

The present paper deals with a class of functionally graded materials (FGM), called active FGM that has electro-elastically graded material phases. An active FGM system leads to minimization of stress concentration that arises due to mismatch in the electrical and elastic properties of the constituent phases. This work focuses on the characterization of the through thickness stresses of an active FGM subjected to electrical excitation. The structure is comprised of a substrate, an electro-elastically graded layer and an active layer. A formulation for exact solutions of the system based on Euler–Bernoulli theory is presented. Power-law variation of the composition of the two phases in the graded layer is considered. Performance of linearly gradient FGM for a range of stiffness and electrical property ratios of the active and substrate materials have been studied. It is observed that the electrical strain component and the compositional gradation significantly influence the stress characteristics of the active FGM. [Copyright &y& Elsevier]

In order to contribute to the understanding of advanced materials with improved mechanical properties we investigate strengthening and failure processes in iron-graphene composites using molecular dynamics simulations. Graphene sheets are embedded in {110} planes of bulk iron. Tensile tests and shear tests are conducted and evaluated with regard to the orientation of the graphene sheet. It is found that two different failure mechanisms involving interfacial fracture and dislocation nucleation can occur due to tensile load. The shear tests revealed three mechanisms of dislocation-obstacle interaction. The highest strengthening was found for graphene sheet orientations which normal vectors are not orthogonal to the Burgers vector of the interacting dislocation. [Display omitted] • Graphene sheet orientation significantly affects failure and strengthening • High CRSS and low UTS with non zero components in tensile and shear direction • Dislocation interaction with graphene is mostly cutting of the matrix • Cutting results in folding, straining and rotation of the sheet. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations are used to investigate tensile strengths and failure mechanisms of aluminium nanopolycrystals with an average grain diameter of 8 nm containing dissolved Ni, Cu, Mg or Ti atoms. It is shown that tensile strengths are influenced by several factors such as stacking fault energies as well as types, concentrations and positions of the dissolved atoms. A strong strengthening was found in case of Cu whereas Ni or Ti lead to a moderate increase of strength, while Mg even lowers the tensile strength. It was found that both dislocation processes as well as grain boundary dominated effects contribute to plastic failure mechanisms. Type and concentration of dissolved atoms possess a significant influence on these failure mechanisms. Whereas alloying with Ni, Cu or Mg supports grain boundary dominated failure processes, dissolved Ti atoms lead to a significant increase of stacking faults and dislocations. [ABSTRACT FROM AUTHOR]

Highlights: [•] We present results from virtual nano-mechanical testing on Cu alloyed α-Fe using Molecular Dynamics (MD) simulations. [•] We investigate the coarsening behaviour of Cu-rich precipitates during thermal ageing and its effect on the material strength. [•] Samples are obtained from a multiscale approach coupling kinetic Monte-Carlo (KMC) and Phase-field Method (PFM) simulations. [•] MD results show the correctness of the multiscale approach, predicting a continuous trend in structure–property correlation. [Copyright &y& Elsevier]

The graphite phase of ferritic cast-iron was assumed to consist of randomly oriented, rotationally symmetric, ellipsoidal inclusions of same dimensions. Accordingly, a self-consistent one-particle 3D unit cell model was developed to simulate the effect of graphite aspect ratio on cast-iron elastic constants. The cube shaped unit cell is made up of an inner rotational ellipsoid of graphite surrounded by α Fe–2.5%Si matrix in a concentric outer ellipsoid of the same aspect ratio as the inner graphite ellipsoid in order to model the desired graphite content. The remainder of the unit cell is filled up by the cast-iron compound, the elastic behaviour of which is determined self-consistently. In order to obtain elastic properties, the unit cell was subjected to uniaxial loading. Calculations of stress and strain distributions, in dependence on the orientation of the graphite ellipsoid, were carried out by the finite element method using 3D elements. Finally, updated values of Young’s modulus and Poisson’s ratio were derived by employing Hooke’s law. This procedure was repeated, using the updated elastic constants as new input, to get a self-consistent convergent solution. The results are compared with finite element calculations using a conventional one-particle 3D unit cell model with multiphase elements, and an analytical solution given in the literature. Comparison with experimental data shows the relatively wide range of validity and the superiority of the self-consistent method. [Copyright &y& Elsevier]