In situ nonlinear ultrasonic for very high cycle fatigue damage characterization of a cast aluminum alloy

In this paper, the feedback signal of ultrasonic fatigue system was used to in situ deduce the accumulated fatigue damage via ultrasonic nonlinearity parameter. It was observed that compared with the resonant frequency, the ultrasonic nonlinearity parameter shows a greater sensitivity to fatigue damage like crack initiation and crack propagation. Conventional fatigue testing was carried out and the variation of specimen rigidity and plastic strain of the material were obtained which correlated well with the ultrasonic nonlinearity parameter. Also, the ultrasonic fatigue crack initiation was verified by interrupted test.