Improved understanding of the plastic deformation of metals during high-strain-rate shock loading was key to predicting their resulting material properties. This paper presents the results of molecular-dynamics simulations which address two fundamental questions related to materials deformation: the stability of supersonic dislocations and the mechanism of nano-twin formation. The results show that Al plastically deforms by the subsonic motion of edge dislocations when subjected to applied shear stresses of up to 600MPa. Although higher applied stresses initially drive transonic dislocations, this motion was transient, and the dislocations decelerate to a sustained subsonic saturation velocity. Slowing of the transonic dislocation was controlled by the interaction with excited Rayleigh waves. 800MPa marks a critical shear stress at which dislocation glide gives way to nano-twin formation via the homogeneous nucleation of Shockley partial dislocation dipoles. At still higher applied stresses, additional dislocation dipole nucleation produces a mid-stacking fault transformation of the twinned material.

Supersonic Dislocation Stability and Nano-Twin Formation at High Strain Rate. J.A.Y.Vandersall, B.D.Wirth: Philosophical Magazine, 2004, 84[35], 3755-69