Atomistic studies of the responses of composites with thermal residual stresses and defects under uniaxial loading

The thermal residual stresses and plastic deformation caused by the coefficient of thermal expansion (CTE) mismatch in the cooling process play an important role in the physical and mechanical properties of metal matrix composites (MMCs). In this study, the Cu/SiCp composites with and without cooling process are subjected to uniaxial tensile and compressive loadings through molecular dynamics (MD) simulation. We found that the cooling process leads to a decrease in strength and earlier yielding. The mechanical response depends on the temperature drop, and samples cooled from a higher temperature have a lower yield strength. The introduction of reinforcements and thermally induced defects reduce the tension/compression (C/T) asymmetry as compared with that of single crystal and defective Cu. These pre-existing defects can be the source for the initiation of plasticity in early stage of external loading, and the defect evolution shows a C/T asymmetry. For the density of two predominant dislocation types, the Shockley partial increases at the stress buildup stage, while the stair-rod dislocation decreases, regardless of tension and compression. The mechanisms for the dissociation of stair-rod dislocation and incomplete stacking fault tetrahedrons (ISFTs) at the stress buildup stage have been revealed. Our results provide an atomic-scale perspective to understand the influence of thermally residual stresses and defects on mechanical behavior of MMCs.