Chapter 11 - Strain Rate Effect on Deformation of Single Crystals at Submicron Scale

Abstract

In this chapter, discrete dislocation dynamics simulations are carried out to investigate the effect of the strain rate on the deformation of finite-sized copper single-crystalline samples under uniaxial compression, tension, and hydrostatic compression. The dislocation structures are found to be less activated under hydrostatic compression compared with uniaxial compression. Although a rate-dependent stress–strain relationship is not observed under hydrostatic compression, the evolution of dislocation density exhibits a significant rate dependence. With an increase in the strain rate, the yield stress of single-crystal copper increases rapidly. A critical strain rate exists in each single-crystal copper block for a given size and dislocation source, below which yield stress is relatively insensitive to the strain rate. The dislocation pattern changes from nonuniform to uniform under a high strain rate. Band-like dislocation walls and their shielding effect on other dislocations are observed in the shocked single-crystal copper. Both fast homogeneous nucleation and avalanche-like dislocation multiplication become involved and lead to the softening of shear stress. By comparing dynamic behavior under different impact speeds, a threshold speed for a dislocation-dominant mechanism is proposed from the computations in this work at around 1000m/s, beyond which effects of other defects such as stacking faults and twinning would be prominent.