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After several decades, it is still difficult to predict “macroscopic and microscopic (M-m)” residual stresses (RSes) in metal matrix composites (MMCs) after welding. In this work, an enhanced multiscale model is developed to predict the evolution of M-m RSes in MMCs during several thermo-mechanical processes including welding. This multiscale model is capable of handling non-zero initial M-m RSes and integrates the temperature history dependent constitutive model (THDCM) at both macroscale and microscale. Meanwhile, thermal source model of friction stir welding (FSW) is integrated. The extension to other welding thermal source is straightforward. This multiscale model is used to study the generation, inheritance, and evolution of M-m RSes in a SiC/Al composite during quenching, FSW and post-welding heat treatment (PWHT). The effects of initial M-m RSes and material constitutive models on the prediction of M-m RSes are systematically assessed. It is found that using the THDCM and taking into account the initial RSes, this multiscale model shows the best predictions of RSes in the FSW joint of MMCs. The predictions agree with the neutron diffraction measurements reasonably well. It is found that the reduction of RSes during PWHT is mainly caused by the stress relaxation during the solution treatment stage. [ABSTRACT FROM AUTHOR]

A 3D multiscale method is proposed to model the residual stresses in multiphase materials under the hybrid-semiconcurrent multiscale framework. As an illustration, the quenching residual stresses in SiC p /2124Al composite are modeled. The total residual stresses are separated into the macro, elastic misfit and thermal misfit residual stresses by means of the present multiscale model. In this multiscale model, one macroscale model is connected to two microscale models via scale transition boundary conditions. The predicted total residual strains in the metal matrix and the reinforcing particles coincide with reported experimental data very well. The predicted total, macro, elastic misfit and thermal misfit residual stresses agree reasonably well with the reported experimental ones. The present model provides a new tool to gain a deep insight into the residual stresses in multiphase materials. [ABSTRACT FROM AUTHOR]

This study presents a new method to determine both the macroscopic and microscopic (including elastic mismatch, thermal misfit and plastic misfit) residual stresses in metal matrix composite (MMC) welds via neutron diffraction. As an illustration, friction stir welded 17 vol.% SiCp/2009Al-T4 plates were investigated. It is shown that the calculation of the thermal misfit plus plastic misfit residual stresses in the metal matrix of the MMC welds is much more accurate by using the absolute unstrained lattice parameter of the SiC powder sample based on the stress equilibrium condition compared with using that of the unreinforced alloy sample. The profiles of the longitudinal ( L ), transverse ( T ) and normal ( N ) components of the total residual stress in the reinforcement are entirely different from those in the matrix. It was found that the profiles and total variations of the L , T and N components of the total residual stress are dominated by those of the macroscopic residual stress in the matrix, and by those of the elastic mismatch residual stress in the reinforcement, revealing a significant load transfer from the matrix to the reinforcement. The maximum total residual stress in the metal matrix of the FSW 17 vol.% SiCp/2009Al-T4 weld could reach up to ∼69% of the yield strength of the 2009Al-T4 alloy. Increasing the rotation rate has small effects on the basic profiles of the total residual stress, apart from increasing the width of the profiles. [ABSTRACT FROM AUTHOR]

Abstract: The single crystal Ni54Fe19Ga27 shows a martensitic transformation at 281 K on cooling and 283 K on warming. Large jumps in the temperature-dependent resistance curve, temperature-dependent magnetization curve and temperature-dependent thermal conductivity curve are observed at the martensitic transition temperature . Negative magnetoresistance due to spin disorder scattering was observed in Ni54Fe19Ga27 single crystal in all temperature ranges. The Ni54Fe19Ga27 sample exhibited a temperature dependence of thermal conductivity due to atomic disorder above a temperature of 50 K. [Copyright &y& Elsevier]

A finite element (FE) model of particle reinforced metal matrix composite (PRMMC) was developed by considering load transfer, grain refinement, thermal residual stress/strain, plastic strain gradient and damage of the matrix together. This new model provides precise prediction of the tensile stress-strain curves of PRMMC, even when the size of particles varies. Using the new model, the effect of each strengthening mechanism was assessed quantitatively. According to the results, grain refinement is the main reason causing size effect, while strain gradient only causes higher work hardening rate for PRMMC with smaller particles. Load transfer plays a dominant role among other strengthening mechanisms. Residual stress/strain shows steady but small effect in strengthening PRMMC. [ABSTRACT FROM AUTHOR]

Fully dense Ti 5 Si 3 /TiAl composites were successfully in situ synthesized by reactive infiltration using Ti powders and Al–Si alloys as raw materials. Fine Ti 5 Si 3 particles exhibit a unique quasi-network distribution, remarkably hindering the coarsening of α 2 /γ lamellar colonies. Compared to the as-cast samples, the mean size of lamellar colonies is much finer and thus the resulting Ti 5 Si 3 /TiAl composites show the enhanced room temperature elongation, up to 2.5%, while retaining the ultimate tensile strength of 414 MPa. Moreover, Ti 5 Si 3 /TiAl composites display superior high temperature tensile properties. Consequently, the novel Ti 5 Si 3 /TiAl composites have potential for high temperature applications in aeronautics and aerospace. [ABSTRACT FROM AUTHOR]

The material parameters of 17vol.%SiCp/2009Al composite in the Arrhenius-type constitutive equations were calculated using experimental data from hot compression tests. The constitutive equation was then implemented into the finite element software, ABAQUS/Explicit, to calculate the stress, deformation and edge damage in the hot rolling process. The initiation and propagation of edge cracks under the hot rolling condition were studied via the Gurson–Tvergaard–Needleman (GTN) damage model. The influence of the thickness reduction on the strip damage was assessed. The results indicate that the high tensile stress at the edge of the strip causes crack initiation and propagation, and the total reduction has a significant effect on the damage in the hot rolling of the SiCp/2009Al composites. When the reduction is less than 20%, no crack initiates and the damage occurs on the strip surface. With increase of the total reduction to 25% and larger, edge cracks occur and increase gradually. The distribution and direction of edge cracks are closely correlated with the stress components. The hot rolling experiments on 17vol.%SiCp/2009Al composite were conducted to evaluate the simulation results, and it is indicated that the finite element calculation results agreed well with the experimental results. This indicates that the finite element analysis is able to successfully simulate the rolling process and provide important information for the process optimization. [ABSTRACT FROM AUTHOR]