Acoustic Nonlinearity of Surface Wave in a Fatigued Aluminum Alloy Specimen

Abstract

This paper reports a case study for the evaluation of surface fatigue damage by using the acoustic nonlinearity of surface waves. A measurement system using contact angle beam transducers was constructed to measure the acoustic nonlinearity of surface waves based on the harmonic measurement. In order to prove the general properties of acoustic nonlinearity, dependencies of the second harmonic amplitude on the fundamental frequency amplitude and the propagation distance were tested first, where the effect of frequency-dependent attenuation was compensated for. The results showed good agreement with the theoretical expectations. Next, an aluminum 6061 T6 specimen, of which the surface was damaged by a three-point bending fatigue test, was experimented on and magnitudes of nonlinear parameter, measured before and after the fatigue test, were compared. We could see a clear increase in the nonlinear parameter after the fatigue test at the central position of the specimen, where the surface fatigue damage was expected to be concentrated.