EVALUATION OF FATIGUE DAMAGE USING NONLINEAR GUIDED WAVES

Abstract

An experimental technique to characterize fatigue damage in metallic plates using nonlinear guided waves is presented. It is demonstrated that both phase and group velocity matching is essentially required for the practical generation of nonlinear guided elastic waves. The normalized acoustic nonlinearity of low cycle fatigue damaged aluminum specimens is measured with Lamb waves. A pair of wedge transducers is used to generate and detect the fundamental and second harmonic Lamb waves. The results show that the normalized acoustic nonlinearity measured with Lamb waves is directly related to fatigue damage in a fashion that is similar to the behavior of longitudinal and Rayleigh waves. This normalized acoustic nonlinearity is then compared with the measured cumulative plastic strain to confirm the direct relationship between these two parameters, and to reinforce the notion that Lamb waves can be used to quantitatively assess plasticity driven fatigue damage using established higher harmonic generation techniques.