The acoustoplastic effect in metals was routinely utilised in industrial processes involving forming, machining and joining, but the underlying mechanism was still not well understood. There were earlier suggestions that dislocation mobility was enhanced intrinsically by the applied ultrasound excitation, but in subsequent deliberations it was routinely assumed that the ultrasound merely adds extra stresses to the material without altering its dislocation density or intrinsic resistance to deformation. In this study, a dislocation dynamics simulation was carried out to investigate the interactions of dislocations under the combined influence of quasi-static and oscillatory stresses. Under such combined stress states, dislocation annihilation was found to be enhanced leading to larger strains at the same load history. The simulated strain evolution under different stress schemes also closely resembles certain previously obtained experimental observations. The discovery here goes far beyond the simple picture that the ultrasound effect was merely an added-stress one, since here, the intrinsic strain-hardening potency of the material was found to be reduced by the ultrasound, through its effect on enhancing dislocation annihilation.

Understanding Acoustoplasticity Through Dislocation Dynamics Simulations. K.W.Siu, A.H.W.Ngan: Philosophical Magazine, 2011, 91[34], 4367-87