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Friction Stir Processing (FSP) is an attractive manufacturing technique to produce Mg matrix composites since it avoids the problem of excessive reactivity between reinforcement and matrix encountered in liquid-phase processing routes. However, the strength of the interface in C-reinforced Mg matrix composites produced by FSP remains to be assessed. A short fibre composite has been fabricated by FSP a stack of a C-fabric between two Mg-AZ91D alloy sheets. In order to elucidate the interplay between matrix hardness and interface bonding strength, the work investigates the influence of heat treatment on the mechanical properties of the composites. An incremental Mori-Tanaka model is developed to analyse the relative roles of heat treatment and C-fibre reinforcement on the flow strength and ductility of the composites in tension and compression. The mean-field model provides an estimate of the stress at the matrix/fibre interface, from which a simple debonding criterion can be derived. Comparison between model predictions and experimental data indicates that damage in the FSP composites is triggered by early interfacial debonding. Based on Finite Element simulations of a tensile test carried out in-situ in a scanning electron microscope, the critical interfacial stress for debonding was identified to be 435 MPa in simple traction but only 250 MPa when damage is governed by shear. This explains the limited strengthening by C fibres observed in heat treated composites. [ABSTRACT FROM AUTHOR]

Machining tools are used in many areas of production. To a considerable extent, the performance characteristics of the tools determine the quality and cost of obtained products. The main materials used for producing machining tools are steel, cemented carbides, ceramics and superhard materials. A promising way to improve the performance characteristics of these materials is to design new nanocomposites based on them. The application of micromechanical modeling during the elaboration of composite materials for machining tools can reduce the financial and time costs for development of new tools, with enhanced performance. This article reviews the main groups of nanocomposites for machining tools and their performance. [ABSTRACT FROM AUTHOR]

A detailed study on micromechanical constitutive modelling of unidirectional fiber reinforced and plain woven textile composites (PWTC) is performed. The primary objective is to compute the equivalent homogenized effective properties of PWTC through its mesoscale model. A novel parallel-series model is proposed, to compute the engineering constants in transverse plane of unidirectional composite, and validated against Chamis approaches, Mori–Tanaka and finite element method results for glass/epoxy composite. Computational homogenization of representative volume element (RVE) of transverse direction unidirectional composite is performed satisfying the periodicity of RVE. The RVE of PWTC is then approximated as cross-ply laminate consisting warp and fill plies, whose averaged properties are computed considering fiber undulations by micromechanics-based models. The bounds of the effective material properties of PWTC are determined employing Voigt and Reuss approximation. The effective engineering constants of glass/epoxy PWTC computed are compared with in-house experiments and found to be closely matching with Voigt model. [ABSTRACT FROM AUTHOR]

Novel non-destructive characterization techniques performed at light sources provide previously inaccessible 3-D mesoscopic information on the deformation of polycrystalline materials. One major difficulty for interpretation of these experiments through micromechanical modelling is the likelihood that processing and/or mounting the sample introduce residual stresses in the specimen. These stresses need to be incorporated into crystal plasticity formulations, for these models to operate directly from microstructural images and be predictive. To achieve this, the initial micromechanical state of each voxel needs to be specified. In this letter we present a method for incorporating grain-averaged residual stresses for instantiation of crystal plasticity simulations. [ABSTRACT FROM AUTHOR]

A two dimensional particle model based on the discrete element method (DEM) is developed for micromechanical modelling of fibre reinforced polymer (FRP) composite laminae under biaxial transverse loads. Random fibre distribution within a representative volume element (RVE) is considered for the micromechanical DEM simulations. In addition to predicting the stress-strain curves of the RVEs subjected to transverse compression and transverse shear stresses against the experimental testing results and other numerical modelling results, the DEM model is also able to capture the initiation and propagation of all micro damage events. Fibre distribution is found to more significantly influence the ultimate failure of composite laminae under transverse shear, while it has much less effect on the failure under transverse compression. The failure envelope of composite laminae under biaxial transverse compression and transverse shear is predicted and compared with Hashin and Puck failure criteria, showing a reasonable agreement. The predicted failure envelope is correlated with the damage evolution and the quantitative analysis of failure events, which improves the understanding of the failure mechanisms. [ABSTRACT FROM AUTHOR]

In last decades, several computational strategies have been proposed for masonry structures, which form a large fraction of worldwide built heritage. In this study, a micromechanical model is proposed for tuff stone masonry by assuming a periodic composite with two components, namely tuff stones and mortar. A pressure-dependent failure rule was assigned to each component and mechanical properties were assigned according to material test results. The accuracy and robustness of the micromechanical model were assessed by simulating nonlinear response and crack patterns of masonry in different geometrical, boundary and loading conditions related to axial and diagonal compression tests. A satisfactory numerical-experimental comparison was found. Sensitivity to tensile and compressive strengths of masonry components was evaluated. Local limit states were associated with the overall nonlinear response of masonry and were statistically characterised for performance-based assessment. Finally, Monte Carlo simulations were performed to assess the influence of masonry inhomogeneity on experimental test simulations. [ABSTRACT FROM AUTHOR]

Working conditions of casing pipes in drilling rigs can significantly influence the initiation and development of damage in the material, and therefore also the safe service of the entire system. In this work, an integrity assessment of a pipe with initial defect (machined surface crack) is presented. The position of this defect is on the external surface; unlike transport pipes, where internal surface is often endangered due to the contact with the fluid, casing pipes are also often exposed to damages at the external surface. A pipe segment exposed to internal pressure is examined experimentally and numerically, using the finite element method. Experimental setup included tracking of crack mouth opening displacement (CMOD) values, as well as J integral. Criteria for pipe failure are determined on the finite element (FE) models of the pipe; fracture initiation and plastic collapse are considered as failure mechanisms. Several 3D models with different crack sizes are evaluated. 2D plane strain models are also examined, to determine the applicability limits of this simplified approach. Integrity assessment criteria for the analysed geometries are discussed. Assessment of fracture resistance of the pipeline material is also considered in this work. Besides the standard SENB specimens, Ring specimens cut from the pipe are tested, and the results are compared. Both specimen geometries are modelled using local approach to fracture, by application of the micromechanical Complete Gurson model (CGM), developed by Z.L. Zhang. It is shown that the Ring specimens have similar fracture conditions under bending load as SENB specimens. Since they are much simpler to fabricate from the pipe than standard specimens, it is concluded that they can be used for assessment of fracture of the pipes with axial cracks. [ABSTRACT FROM AUTHOR]

A micromechanical modelling based approach by means of a Representative Volume Element (RVE) was employed to predict the flow behaviour and plastic strain of DP600 steel, produced by WISCO. Macroscopic modelling of a classical Bending-Under-Tension (BUT) experiment was employed to acquire strain deformation, and thus the following microscopic modelling was implemented by considering the realistic microstructure morphology. Comparisons between macroscopic behaviour and microscopic behaviour, including strain distribution and stress distribution, were extracted for different boundary conditions of the BUT set-up. The micro–macro modelling approach increases the understanding of the steel microstructure, which will enable this microstructure to be tailored for different applications in automobile industry in the future. [ABSTRACT FROM AUTHOR]

Uniform dispersion of carbon nanotubes (CNTs) is a key issue for utilization of their reinforcement potential in CNT-reinforced metal matrix nanocomposites (MMNCs). It was reported that CNT clusters often exist in MMNCs prepared by various techniques, which reduces the load transfer efficiency between the matrix and reinforcement. In this paper, a new micromechanical constitutive model of CNT-reinforced MMNCs is developed, which takes into account of the influences of CNT clusters and misorientations. The strength values of a CNT/Al nanocomposite predicted by the new model are compared first with experimental data for validation. Then, the developed model is applied to predict the size effect, temperature effect and strain rate effect of the nanocomposite in its overall elastoplastic response. [ABSTRACT FROM AUTHOR]

In micromechanical modelling, covariograms are often used as a statistical analysis to estimate the features or morphological Representative Elementary Volumes (REV), from representative pictures of the initial microstructure (i.e. static covariogram). The aim of this article is to present an extension of the method to the time evolution of the microstructure, through the idea of dynamic covariogram built up of successive pictures of the microstructure along time. The possible enhanced evolution of covariogram parameters is analyzed first from a general point of view. It is then illustrated on the cavitation damage occurring during decompression in rubbers exposed to diffusing gas. [ABSTRACT FROM AUTHOR]

This paper concerns with the micromechanical modelling of closed-cell polymeric foams (M130) using Laguerre tessellation models incorporated with realistic foam cell size and cell wall thickness distributions. The cell size and cell wall thickness distributions of the foam were measured from microscope images. The Young’s modulus of cell wall material of the foam was characterised by nanoindentation tests. It is found that when the cell size and cell wall thickness are assumed to be uniform in the models, the Kelvin, Weaire–Phelan and Laguerre models overpredict the stiffness of the foam. However, the Young’s modulus and shear modulus predicted by the Laguerre models incorporating measured foam cell size and cell wall thickness distributions agree well with the experimental data. This emphasizes the fact that the integration of realistic cell wall and cell size variations is vital for foam modelling. Subsequently the effects of cell size and cell wall thickness variations on the stiffness of closed-cell foams were investigated using Laguerre models. It is found that the Young’s modulus and shear modulus decrease with increasing cell size and cell wall thickness variations. The degree of stiffness variation of closed-cell foams resulting from the cell size dispersion and cell wall thickness dispersion are comparable. There is little interaction between the cell size variation and cell wall thickness variation as far as their effects on foam moduli are concerned. Based on the simulation results, expressions incorporating cell size and cell wall thickness variations were formulated for predicting the stiffness of closed-cell foams. Lastly, a simple spring system model was proposed to explain the effects of cell size and cell wall thickness variations on the stiffness of cellular structures. [ABSTRACT FROM AUTHOR]

A finite element micromechanical model of a high strength composite material is subjected to a range of loading conditions to demonstrate its ability to predict failure. An investigation into the relative magnitude and distribution of the normal and shear stresses within the interface region of a single fibre embedded in a matrix region is compared to that of a multi-fibre representative volume element, where the fibre placement is statistically equivalent to that of a real material. A study is subsequently undertaken in which the relative magnitudes of the shear and normal strengths of the fibre–matrix interface are varied under transverse tension and shear. The results are interpreted with relation to the yield strength of the matrix. The predicted performance of the composite is shown to compare well with published experimental data, under transverse tension and in-plane shear. It is concluded that a single set of interface strength parameters can be used to represent the behaviour of the composite material. The results also show that interfacial shear strengths are expected to be equal, and higher than the interfacial normal strength. [ABSTRACT FROM PUBLISHER]

In this study, the authors present a micromechanical finite element modelling approach to the analysis of a set of ultrafine-grained polycrystalline copper structures. The models take into account both realistic grain distribution and the number of refinement passes of the microstructure. The grain size effect is successfully predicted, with non-uniform deformation and shear localization reproduced during global plastic flow in agreement with experimental observations. The models provide a useful tool with which to interpret damage and fracture mechanisms occurring in ultrafine-grained structures. [ABSTRACT FROM AUTHOR]

Abstract: A micromechanical model of a composite material is subjected to in-plane shear, in order to quantify the shear hardening effect reported in the literature for this deformation state. Solutions for elastic and elastic–plastic models under the same shear loading are presented, using large and small deformation kinematics. The fibres are modelled as transversely isotropic linear elastic and the matrix is assumed to behave according to the Mohr–Coulomb yield criterion. The stress generated in the fibres during loading is investigated for each of the different models. Elastic–plastic matrix material behaviour permitted additional rotation of the fibres in comparison to the elastic model. This rotation was seen to produce the observed strain hardening under in-plane shear. [Copyright &y& Elsevier]

Abstract: A multi-site micromechanical modelling of the effective thermo-elastic properties of heterogeneous materials is derived from the proposed thermo-elastic integral equation. The fundamental solution based on the Green function of elasticity problem is used to derive a general expression of elastic and thermal strain concentration tensors. This approach enables the development of specific models such as multi-site Mori–Tanaka, self-consistent or generalized self-consistent schemes. The main advantage of the model resides in its capability to take into account the morphology as well as the topology of composites’ reinforcements. Sensitivity of the model predictions to some parameters has been analysed using the Generalized Mori–Tanaka (GMT) approximation. Its predictions have been compared to previous investigations to underline the effect of morphology and topology of reinforcements on the anisotropy of the global material properties. [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]

Abstract: The main characteristics of quasi-isothermal diffusive transformation from austenite to pearlite in a 100C6 steel have been determined from experimental tests. The parameters of constitutive laws and kinetics of phase transformation of different micromechanical models of phase transformation could then be identified. The models are classified according to the prevailing assumptions: mean- or full-field approach, regular or heterogeneous microstructural morphology, macro-homogeneous constitutive laws or crystal plasticity. A comparative analysis in terms of transformation-induced plasticity (TRIP) is performed in order to conclude on the relevance of the different models as regards experiments and to show how the principal assumptions of TRIP modelling can affect the predictions. [Copyright &y& Elsevier]

Abstract: This work deals with the development and implementation of a new fatigue model for simulating fatigue effects in skeletal muscles. Basic idea of this modelling strategy is an approach that divides the fibres of a muscle into three groups: fibres in the active state, those that are already fatigued and fibres in the resting state. All fibres are able to switch between the different groups by defining adequate rates. In this way a continuous transfer of fibres between those three states has been described. Rooted on an incompressible, hyperelastic constitutive law with transversely isotropic characteristics the fatigue model has been implemented in the framework of the finite element method. Numerical examples are given in order to illustrate the ability of this model. Further, we validate the model by fatigue experiments of the rat soleus muscle. In doing so, it proves that the model is able to predict physiological observations and mechanical test results. [Copyright &y& Elsevier]

The paper analyzes the mechanical properties of plain-weave composites by employing different micromechanical models. Their in-plane and flexural properties are estimated using analytical approaches, including the rule of mixtures and one-dimensional composite beam and two-dimensional mosaic models. The expressions of effective material properties are obtained for one-, two-, and three-ply woven composites. The results obtained are in agreement with published data. [ABSTRACT FROM AUTHOR]

Abstract: This work aims at developing a new methodology for the reliability assessment of composite structures and their design optimization. It relies on the coupling of well established methods: homogenization scheme for the mechanical modelling of composite materials and reliability methods to account for their inherent variability. Moreover, such approach is based on an accurate treatment of inherent uncertainties of these mechanical systems at various scales, including microscopic and macroscopic levels, that provides new perspectives for structural design. As an illustration, we propose to apply the multi-scale reliability analysis on the case of the Laroin footbridge (France) with carbon–epoxy stay cables. Since the reliability assessment of such structure is evaluated through the fibre failure, numerical simulations require the coupling of reliability methods, finite element modelling to derive macroscopic loading within cables and micromechanics to estimate the effective elastic properties of composite and local responses within constituents. Results demonstrate the feasibility of the coupled approach at a structure scale and its main interests for the optimization phase of materials and engineering structures. [Copyright &y& Elsevier]

In spite of six decades of research, the underlying micromechanisms of deformation of titanium alloys, with their diversity of microstructures and single-crystal behaviour, are still not well understood. Synchrotron X-ray and neutron diffraction allow for the evolution of lattice strain, texture, and phase fractions to be studied in real time. Pure Ti has been shown to deform primarily by twinning as opposed to ⟨c + a> slip, resulting in a characteristic lattice strain response and texture evolution. The addition of > 2.7%Al has been shown to suppress twinning and promote ⟨c + a> slip. In two-phase alloys, the β phase usually carries tensile residual lattice strains of up to ∼⃒ 40% of the macroscopic yield strain. The stability of the β phase with respect to both the α phase and superelastic phase transformations is a strong function of composition and in turn of the shear modulus C′. [ABSTRACT FROM AUTHOR]

Abstract: High-temperature ductility of dual-phase stainless steels is investigated using a micromechanics approach of damage and fracture. Two different microstructures are studied with either a lamellar or a globular morphology of the ferrite phase, the latter being twice as ductile as the former at 1150°C. The high-temperature damage evolution is characterized at different loading rates using notched round cylindrical bars producing different stress triaxialities, supplemented by fractographic analysis. The experimental observations have generated an advanced elasto-viscoplastic micromechanical damage model for both microstructures. With a detailed account of the process of nucleation, growth and coalescence of voids, the model properly captures the effect of stress triaxiality, strain rate, and morphology of the ferritic phase on the high-temperature ductility. The key factor controlling the loss of ductility in the lamellar microstructure is the constraint induced by the harder austenite layer on the softer ferrite zones. [Copyright &y& Elsevier]

Abstract: The effects of grain size and of crack-tip blunting radius on the fracture toughness of tungsten polycrystals are studied by using a combined dislocation dynamics/cohesive zone model (CZM). Two-dimensional dislocation dynamics are employed to analyze crack-tip plasticity and crack propagation is characterized by a CZM. The geometry of the crack and the corresponding boundary conditions are described by means of a boundary element method with dislocation dipoles as fundamental solution. Grain boundaries are introduced as obstacles for dislocation motion. Numerical experiments reveal that the fracture toughness decreases with grain size, because grain boundaries confine the plastic zone. This effect is particularly pronounced at small loading rates, where the unconfined plastic zone is large. Our results also show that fracture toughness scales with the tip radius as the stress concentration at the crack tip is reduced and the plastic zone is enlarged. [Copyright &y& Elsevier]

Abstract: Establishing structure–property relationships for nanoparticle/polymer composites is a fundamental task for a reliable design of such new systems. A micromechanical analytical model is proposed in the present work, in order to address the problem of stiffness and yield stress prediction in the case of nanocomposites consisting of silica nanoparticles embedded in a polymer matrix. It takes into account an interphase corresponding to a perturbed region of the polymer matrix around the nanoparticles. Its modulus is continuously graded from that of the silica nanoparticle to that of the polymer matrix. Considering the thickness of the third phase as a characteristic length scale, the influence of particle size on the overall nanocomposite behaviour is examined. The key role of the interphase on both the overall stiffness and yield stress is studied and the model output is compared to experimental data of various silica spherical nanoparticle/polymer composites extracted from the literature. The model is also used to examine the influence of interphase features on the overall nanocomposite behaviour. A finite element analysis is then achieved and the numerical results are validated using the analytical predictions. Local stress and strain distributions are analysed in order to understand the phenomena occurring at the nano-scale. [Copyright &y& Elsevier]

Abstract: The effect of size on the mechanical behavior and the void growth rate in a voided single crystal was studied using two-dimensional discrete dislocation dynamics. The simulations were based on the methodology developed by Van der Giessen and Needleman [Van der Giessen E, Needleman A. Modell Simul Mater Sci Eng 1995;3:689], which was extended to non-convex domains through the use of finite elements with embedded discontinuities [Romero I, Segurado J, LLorca J. Modell Simul Mater Sci Eng 2008;16:035008]. Square crystals (in the range 0.5–2.5μm) with an initial void volume fraction of 10% were deformed under plane strain conditions in uniaxial tension, uniaxial deformation and biaxial deformation. The results of the simulations show two size effects, one on the initial flow stress and strain-hardening rate of the voided crystal (“smaller is stronger”) and another on the void growth rate (“smaller is slower”). The magnitude of both size effects increased with triaxiality. The physical micromechanisms responsible for these size effects were elucidated from the simulation results. [Copyright &y& Elsevier]

Abstract: A grain-size dependent accommodation law for polycrystals is deduced from an inclusion/matrix problem (i.e., each grain is seen as embedded in a homogeneous equivalent medium) where plastic strain inside the inclusion is given as a discrete distribution of circular coaxial glide dislocation loops. The loops are assumed constrained at spherical grain boundaries. From thermodynamic considerations specific to a process of identical plastification in all the loops (considered as “super-dislocations”), an average back-stress over the grain is derived. In order to compute the very early stages of plastic deformation in a face-centred cubic polycrystal, this back-stress is incorporated into a diluted model in terms of concentration of plastic grains. Contrary to conventional mean-field approaches, a grain-size effect is obtained for the initial overall strain-hardening behaviour. This size effect results from an intrinsic contribution of intragranular slip heterogeneities on the kinematical hardening. [Copyright &y& Elsevier]

Abstract: The evolution of intergranular lattice strains in a textured, forged bar (Bar) sample of the α−β titanium alloy Ti–6Al–4V has been characterised using in situ X-ray diffraction. A two-phase elastic–plastic self-consistent (EPSC) model has been developed to rationalise the results. Of the orientations analysed, it is found that the {200} β orientation is the most compliant and that load partitions to this orientation during plasticity. The results from the bar material have then been used to predict the response of unidirectionally rolled plate (UD) Ti–6Al–4V. It is predicted that the residual lattice strains in the and orientations will be significantly higher in the UD material. [Copyright &y& Elsevier]

Bimetallic welds (BMWs) play a critical and indispensable role in the primary heat transport piping system of nuclear reactors. The primary heat transport system itself is the critical part of a nuclear reactor. Any failure of this system can lead to very grave consequences, not only speaking of huge monetary losses resulting from non-utilization of the reactor setup, but also immensely valuable and irreparable loss of human life. This paper describes the experimental efforts towards estimation of Gurson material parameters of base metal and weld metal regions of a BMW so as to use the micromechanical modelling approach for addressing the structural integrity issues in BMWs. [ABSTRACT FROM AUTHOR]

Abstract: The grounds of a numerical modelling of the mechanical consequences of diffusive phase transformation in solids have been established by Leblond [Leblond, J.B., Mottet, G., Devaux, J.C., 1986. A theoretical and numerical approach to the plastic behavior of steels during phase transformations I: derivation of general relations, J. Mech. Phys. Solids 34 (4) 395–409] and Ganghoffer [Ganghoffer, J.F., Denis, S., Gautier, E., Simon, A., Sjöström, S., 1993. Finite element calculation of the micromechanics of a diffusional transformation, Eur. J. Mech. A Solids 12 (1) 21–32]: this modelling resorts to the FE method to evaluate the stress and strain fields which ensure the mechanical equilibrium between a diffusionaly growing phase and its parent phase. It has been the subject of a thorough analysis in [Barbe, F., Quey, R., Taleb, L., 2007. Numerical modelling of the plasticity induced during diffusive transformation. Case of a cubic array of nuclei, Eur. J. Mech. A Solids 26, 611–625] which has evidenced the main limit underlying this modelling with regard to physics, relative to the fact that nuclei are implicitly positioned according to a periodic array. The present work proposes, in details, an extension to the case of nuclei instantaneously appearing at random positions in a quasi infinite homogeneous medium. It constitutes a fundamental step towards a numerical modelling explicitly taking into account the crystalline plasticity and the morphology of the transforming medium. [Copyright &y& Elsevier]

Abstract: An efficient full-field formulation based on fast Fourier transforms (FFTs) for the prediction of the viscoplastic deformation of polycrystals is applied to the study of the subgrain texture and microstructure evolution in polycrystalline Cu deformed under tension. Direct input from orientation imaging microscopy (OIM) images is used in the construction of the initial unit cell. Average orientations and misorientations predicted after 11% tensile strain are directly compared with OIM measurements, showing good agreement. The differences between misorientations of surface grains compared with bulk grains are estimated, and the orientation dependence of intragranular misorientations is studied. Measurements and simulations agree in that grains with initial orientation near 〈110〉 tend to develop higher misorientations. This behavior can be explained in terms of attraction towards the two stable orientations and grain interaction. Only models that account explicitly for interaction between individual grains, like the FFT-based formulation, are able to capture these effects. [Copyright &y& Elsevier]

One means of protecting structures involves the panelling of components with foam. Previous work has analysed the response of a low-density aluminium foam to quasi-static, and low velocity impact. In the present work, plate impact experiments are conducted, to observe the transit of a shock through the material. X-ray microtomography was used to obtain microstructural information in three dimensions that was coupled as the input file for hydrocode simulation. This provides insight into mechanisms associated with deformation in the foam. [Copyright &y& Elsevier]

Abstract: The lattice strain evolution in near-β Ti–10V–2Fe–3Al during room temperature tensile loading has been characterised in the as-forged and forged and aged conditions using in situ synchrotron X-ray diffraction. As expected, the fine scale α which precipitates during aging strengthens the β-phase much more effectively than the α present in the forged sample. The behaviour has been modelled using a two-phase elastic–plastic self-consistent (EPSC) model. It is found that the constrained β-phase E 200 increases from 45GPa in the as-forged condition to 88GPa in the forged and aged material. C 11–C 12 increases from 12 to 47GPa due to the increase in β-stabiliser content, in agreement with atomistic predictions. The EPSC models are reasonably successful at reproducing the observed behaviour, but do not provide a complete description of the micromechanics of these materials. [Copyright &y& Elsevier]

The spatial variations in the inclusion size and distribution are examined for a free-cutting steel bloom. Chemical analysis has been carried out on the inclusions using energy-dispersive X-ray analysis and the main findings are reported. It has been observed that inclusions are often associated with a lead tail. Thus an assumption is made that the lead layer becomes liquid or gaseous at hot-forming temperatures. Based on this assumption, a micromechanical finite element model is established and used to model the damage evolution process. Microstructure examinations of hot-tensile-tested specimens are used to compare experimentally the observed inclusion shape and void growth features with those obtained from the micromechanical finite element method. It is concluded that there is no significant inclusion debonding process for the material deformed under hot-forming conditions. The damage growth is directly related to the inclusion size and spacing. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we present a micromechanical approach based on fast Fourier transforms to study the role played by dislocation glide and grain boundary (GB) accommodation in the determination of the plastic behavior of nanostructured materials. For this, we construct unit cells representing self-similar polycrystals with different grain sizes in the nanometer range and use local constitutive equations for slip and GB accommodation. We study the effect of grain size, strain rate and pressure on the local and effective behavior of nanostructured fcc materials with parameters obtained from experiments and atomistic simulations. Predictions of a previous qualitative pressure-sensitive model for the effective yield strength behind a shock front are substantially improved by considering strain partition between slip and GB activity. Under quasiestatic conditions, assuming diffusion-controlled mechanisms at GB, the model predicts a strain-rate sensitivity increase in nanocrystalline samples with respect to the coarse-grained material of the same order as in recently published experiments. [Copyright &y& Elsevier]

Stents are very commonly used in the treatment of coronary heart disease. They are permanent vascular support structures that offer a preferred alternative to bypass surgery in certain situations. The purpose of this work is to examine the mechanical behaviour of a stainless steel balloon expandable stent design using computational micromechanics in the context of the finite element method. Deployment and cardiac pulsing loading conditions are considered. Classical phenomenological plasticity theory (J2 flow theory) and physically based crystal plasticity theory are used to describe the stent material behaviour. Parametric studies are carried out using both constitutive theories with a view to determining important stent deployment characteristics such as recoil and foreshortening. Comparisons of the results obtained using both theories illustrate differences, with the crystal plasticity theory models showing closer agreement to published performance data. The implications of this for stent design are discussed. [Copyright &y& Elsevier]

The fracture process of progressively drawn steels is studied. Results show that drawing affects the phenomenon, so that heavily drawn steels exhibit anisotropic fracture behaviour. A micromechanical model of fracture is proposed to rationalize the results on the basis of the microstructure of the steels after drawing. In slightly drawn steels, the Miller–Smith model of shear cracking in pearlite may be adequate to describe the fracture process. In heavily drawn steels, a fracture propagation step appears, and it may be caused by extremely slender pearlitic pseudocolonies aligned in the drawing direction, with anomalous (very high) local interlamellar spacing which makes them preferential fracture paths with minimum local resistance. [Copyright &y& Elsevier]

In the paper ductile fracture initiation analysis of low-alloyed ferritic steel has been made by application of two micromechanical models: the Rice–Tracey void growth model and the Gurson–Tvergaard–Needleman (GTN) model. The aim of the study was to analyse transferability of micromechanical parameters determined on specimens without initial crack to pre-cracked specimens. A significant part of the research has been carried out through participation in the round robin project organised by the European Structural Integrity Society (ESIS). Tensile tests have been performed on cylindrical smooth specimens and CT specimens. Critical values of micromechanical parameters determined on smooth specimen for both applied models, have been used for prediction of the crack growth initiation in CT specimen. Modelling of the first phase of ductile fracture––void nucleation––has been carried out using quantitative metallographic analysis of non-metallic inclusion content in tested steel. For determination of critical values of model parameters corresponding to ductile fracture initiation a simple procedure has been applied based on a combination of experimental and numerical results. Evaluated J-integral values corresponding to onset of crack growth, Ji, are in good agreement with experimental result and both models have proved to be suitable for determination of the ductile fracture initiation in tested steel. The effect of FE size at a crack tip on Ji-value has been particularly analysed: it has been established that the calculation with FE size corresponding to the mean free path λ between inclusions in steel gives results that are in accordance with the experimental ones. [Copyright &y& Elsevier]

Six different Al–Al3 Ti composites were prepared via the powder metallurgy route. The size and volume fraction of Al3 Ti particles was varied for a systematic investigation of fracture behaviour. The dominant failure mechanism in the composites is particle fracture and void growth starting from the broken particles. In comparison with the pure Al–matrix, an incorporation of Al3 Ti particles reduces the crack initiation toughness and reduces the slope of the crack growth resistance curve. The inter-particle distance was found to be the main microstructural parameter controlling the slope of the crack growth resistance curve. The modified Gurson–Tvergaard–Needleman model (GTN model) was applied to one of the composites. The behaviour of tensile specimens could be successfully modelled, whereas the experimentally observed crack propagation in precracked single edge bend specimens [SE(B)] could not be simulated with the GTN model. [ABSTRACT FROM AUTHOR]