Dislocation Dynamics and Steady Plastic Wave Profiles in 6061-T6 Aluminum

Abstract

Under certain conditions, plastic wave profiles in 6061-T6 aluminum may achieve a constant wave velocity and steady shape within a few millimeters from the impact surface in a plate-impact experiment. The finite rise time of the steady plastic wave is assumed to be controlled by the motion of dislocations within the solid. The theory of steady-propagating waves is presented and theoretically determined wave profiles are compared with those measured experimentally by means of laser interferometry. These studies provide information on dislocation velocity and multiplication under conditions of shock-wave compression. In particular, if the mobile dislocation density is assumed to be a function of plastic strain alone, the dislocation velocity is found to be proportional to (τ−τ0)n, where τ is the applied shear stress, τ0 is a back stress, and n is a constant approximately equal to 2. Thus, it appears that a linear relationship between dislocation velocity and shear stress, which has been found to apply for strain rates less than 10−2 μsec−1 in aluminum, may not be sufficient to describe rate-dependent behavior at strain rates greater than 10−2 μsec−1, which are achieved in shock-wave compression.