Effect of Localized Plastic Deformation on Higher Harmonic Guided Wave Mode Generation in Plate

The effect of the evolving microstructure of the material in a plate, including localization of plastic deformation, is investigated with respect to generation of higher harmonic ultrasonic guided wave modes. Study of nonlinear ultrasonic guided waves indicates that a select number of primary wave modes will generate cumulative secondary modes sensitive to the microstructure of the material. Two such mode pairs – S1/S2 and SH1/S1 – are investigated with the help of nonlinear finite element analysis. The result of localized microstructure evolution is demonstrated for the S1/S2 mode pair. These findings will be useful for the detection of precursors to macroscale damage such as fatigue cracks.