Dislocation Dynamics and Precursor Attenuation

Abstract

The low‐pressure plane‐wave test in metals provides more sensitive measurements of the effects of strain rate on plastic behavior than rod‐wave tests. Since strain‐rate effects are due to the motion of dislocations in these materials, such tests should lead to an increased understanding of dislocation dynamics. Two current theories of dislocation mechanics are studied in the context of plane‐wave propagation: the Gilman relation in which the dislocation velocity is proportional to the negative exponential of the reciprocal of the resolved shear stress, and the activation‐energy model in which dislocation velocity is proportional to the exponential of the shear stress. These theories are applied to the problem of attenuation of the elastic precursor wave and the results compared with published experimental data. It is shown that both fit the presently available data and cannot be resolved by low‐pressure plastic‐wave tests. The analytical results, however, suggest the appropriate value of impact pressure above which the two theories predict different results for tests of thin specimens.