Acoustic emission from plastic deformation of a pure single crystal

Abstract

Acoustic emission (AE) during plastic deformation is analyzed for a pure single crystal neglecting the effects of grain boundaries, impurities, and second-phase particles. Acceleration of a moving dislocation is considered to be the principal AE source. There are two major mechanisms of dislocation motion related to acceleration, initial, and continuous oscillatory motion. Initial motion induced by the creation of mobile dislocations is modeled as a step function of velocity. Continuous oscillatory motion produced by interactions with neighboring dislocations is modeled as a harmonic function. These mechanisms vary with strain and strain rate due to dislocation multiplication. AE can thus be described in terms of strain and strain rate. Annihilation at a free surface is also regarded as an AE source in addition to the initial and oscillatory motions. The kinetic and strain energies stored around a moving dislocation are dissipated during annihilation, and can be related to AE. The frequency spectrum of AE is also determined. A shift of the spectrum to higher frequencies with increasing strain is explained by an increase in the interaction force between dislocations.