Nonlinear ultrasound to characterize dislocation-based damage in classical and rolling contact fatigue

Abstract

Material damage in structural components is driven by nano- and micro-scale defects that evolve early in the component’s life. In metals, the interaction of an ultrasonic wave with these nano- and micro-structural defects, such as dislocations, precipitates, and micro-cracks, generates a second harmonic wave that is proportional to the acoustic nonlinearity parameter, which is an absolute and measurable material parameter. These defects are known to cause measurable changes in the nonlinearity parameter, which changes as the nano- and micro-structural defects evolve in the material. This talk will discuss how nonlinear ultrasound (NLU) techniques that measure the nonlinearity parameter can be used as a nondestructive evaluation tool to characterize dislocation-based damage in metals, and thus characterize early-stage damage. Our group’s recent work on using NLU to characterize different types of cyclic loading, classical fatigue and rolling contact fatigue, will be discussed. Specifically, ultrasonic measurements are related directly to materials characterizations on similar length scales to better understand the relationship between the nonlinearity parameter and the dislocation-based damage evolution.