Shear stress relaxation through the motion of edge dislocations in Cu and Cu-Ni solid solution: A molecular dynamics and discrete dislocation study

Shear stress relaxation through the motion of multiple edge dislocations in a periodic cell is studied by molecular dynamics and discrete dislocation methods. In both methods, we consider systems with an initial edge dislocation on the parallel slip planes. The initial shear strain is applied to the system along the Burgers vector of the dislocations. The velocity profile for a single edge dislocation fitted from a molecular dynamics (Bryukhanov, 2020) is used as the input to discrete dislocation dynamics. The dependence of shear stress, plastic strain, and plastic strain rate on time are analyzed. We show that when dislocations are sufficiently far from each other, relaxation occurs due to dislocation motion, and dislocation velocity can exceed the anisotropic speed of sound. If the dislocations are closer together, relaxation is due to the growth of stacking faults. We find that the stress at which the stress relaxation mechanism changes decreases with increasing dislocation density. Stress relaxation in a Cu-Ni solid solution occurs faster than in pure Cu due to a higher dislocation velocity in the high-velocity regime. However, the shear stress at which nickel atoms increase the plastic strain rate increases with an increase in dislocation density. The dependence of the relaxation time on the dislocation density obtained in discrete dislocation simulations is approximated using the power law. The elastic interaction between dislocations reduces the exponent of the power law from 1/rho to approximately 1/rho(0.8) for both pure Cu and Cu-Ni solid solutions.

Automated summary

Shear stress relaxation through the motion of multiple edge dislocations is analyzed using molecular dynamics and discrete dislocation methods. It is found that relaxation occurs due to dislocation motion when dislocations are sufficiently far apart, exceeding the anisotropic speed of sound. Dependency of stress relaxation mechanism on dislocation density is shown, with stress decreasing as density increases.