In situ monitoring of plastic deformation using ultrasound

Ultrasound has long been used as a non-destructive tool to test for the brittle fracture of materials. Could it be used as a similar tool to test for ductile failure? This study reports results of local measurements of the speed of shear waves, $v_T$, in aluminum under standard testing conditions at two different locations on the same sample, as a function of stress. There is a clear change in $v_T$ at the Yield stress, consistent with a proliferation of dislocations. This measurement provides a quantitative, continuous relation between dislocation density and externally applied stress.