Strain-Rate Dependence of Material Strength: Large Scale Atomistic Simulations of Defective Cu and Ta Crystals

Large$-$Scale molecular dynamics (MD) simulations are used to model shock wave (SW) and quasi$-$isentropic compression (QIC) in defective copper and tantalum crystals. The atomic interactions were modeled employing embedded$-$atom method (EAM) potentials. Quasi$-$isentropic uniaxial compression is achieved by incorporating a strain rate function in the positions and velocities equations of motion. In this new formalism the change in internal energy is exactly equal to the work done in compression. We examined the deformation mechanisms and material strength for strain rates in the $10^{8}-10^{12} s^{-1}$ range for both Cu and Ta defective crystals. Near and far$-$field X$-$ray diffraction simulations were also performed to infer the required resolution for resolving defect densities.