“Nonlinear ultrasonic characterization of dislocation-based damage in metals”
The field of nondestructive evaluation (NDE) aims to evaluate damage in structures and materials before failure occurs. However, current NDE techniques are limited to evaluating damage late in the component life, and damage oftentimes goes undetected. On the other hand, nonlinear ultrasonic wave propagation results from an ultrasonic wave nondestructively interacting with dislocation-based damage in materials. Such dislocation-based damage forms long before and ultimately leads to crack initiation, crack propagation, and/or component failure. This means that nonlinear ultrasound (NLU) is sensitive to very early damage that occurs on the nano-scale, well before larger defects form, and long before component failure. While NLU has clear potential as an NDE technique, experimental ultrasonic and modeling challenges prevent NLU from reliably and accurately evaluating dislocation-based damage. This presentation discusses our group’s recent efforts in distilling a fundamental link between dislocation-based damage and nonlinear ultrasonic wave propagation during monotonic or cyclic loading, by experimentally probing the ultrasonic response in situ during loading and interpreting this with systematic materials characterizations. Applications to characterizing fatigue damage, evaluating rolling contact fatigue, and quality control of additively manufactured metals will also be discussed.