Crystal orientation effect on dislocation nucleation and multiplication in FCC single crystal under uniaxial loading

Molecular dynamics simulations are applied to study the effects of orientation and the presence of structural defects on the compression/tension (C/T) asymmetry of copper single crystals. In addition to the perfect crystal, crystals with stacking fault tetrahedra, as a representative internal defect, are considered to investigate both homogeneous and heterogeneous deformation mechanisms. Both the normal stresses to the slip plane and the relative values of Schmid factor in compression and tension impact the C/T asymmetry. The presence of an SFT lowers the applied stress required for plastic deformation, but this effect is highly dependent on the crystal orientation and loading direction. The reduction in yield stress is larger in compression than in tension for almost all orientations. Results show that in general a structural defect would decrease the C/T asymmetry in copper, corresponding closely to previous experiments. The reduction in yield stress in tension is less sensitive to defects than that in compression, suggesting that compression test is a more reliable experimental tool for future size dependence studies, since structural defects are the main reason behind the observed size effects in materials. On the other hand, since the reduction in yield stress is almost constant in tension for all orientations, testing in this geometry is more efficient to determine the orientation dependence of the yield stress. (C) 2013 Elsevier Ltd. All rights reserved.