Acoustic Emission from Single Crystals of LiF and KCl

Abstract

Single crystals of LiF and KCl were subjected to incremental compressive stress along a [100] direction. A continuous record of stress and strain was kept, together with data from ultrasonic damping and acoustic emission measurements. The experimental techniques and the electronic equipment used are discussed in detail. It was found that specimens of LiF exhibited acoustic emission peaks in the macroscopic elastic range having their maximums at a strain of approximately ε₀=10⁻³ and skewed toward larger values of ε. The analysis of this acoustic emission distribution forms the basis for a microscopic deformation model for LiF. It is hypothesized that this distribution should be identical to the distribution of dislocation‐source inverse loop‐lengths. An expression for the probability of observing N acoustic emission bursts while the crystal is being strained from ε to ε+dε is written in terms of inverse loop‐length and used to calculate average values of ε, ρM, and (A₁/A₂), the dislocation strain, mobile dislocation density, and ratio of successive ultrasonic wave amplitudes, respectively. Since no such peak was observed for KCl, the differences in the microscopic deformation mechanisms for that material are emphasized.