Contribution of dislocation dipole structures to the acoustic nonlinearity

Abstract

The ultrasonic nonlinearity created by dislocations in crystals is investigated using two-dimensional dislocation dynamics (DD) simulations. An analytic model of the acoustic nonlinearity parameter, β, of an isolated dislocation dipole is derived using a quasi-static loading assumption. β is predicted to be strongly dependent on the glide stress acting on the dipole, which is not captured by existing models. The technique is extended to an infinite dipole train and an infinite Taylor lattice. β is shown to arise only under the presence of a glide stress. These results contradict the existing model that predicts β of these dipole arrangements to be independent of stress. The analytical models are shown to agree with two-dimensional DD simulations for glide stresses well below the critical stress that causes dissolution of the dipole structure. Several finite sections of the Taylor lattice are modeled with DD and are found to have anomalous scaling behaviors.