Nonlinear Ultrasonic Guided Waves for Microstructure Characterization of Hollow Cylinders

The issue of non-destructive characterization of material microstructure with respect to precursors to macroscale damage initiation is addressed. Ultrasonic guided waves are known to be sensitive to material nonlinearity, which is evident through the generation of higher harmonic modes. Thus, nonlinear guided waves have strong potential to identify precursors to macroscale damage and revolutionize condition-based maintenance. Hollow cylindrical waveguides are analyzed herein. As guided waves are multi-modal, the first step in this direction is to identify a primary mode that generates a cumulative higher harmonic mode. The second step is to select transducers to emit the primary mode and receive both primary and secondary modes. After discussing mode and transducer selection, a simulation of second harmonic generation from localized microstructure evolution is presented.