Scanning non-collinear wave mixing for nonlinear ultrasonic detection and localization of plasticity

Non-collinear wave mixing recently has been proposed to detect and localize micro-damage in materials. It is proved sensitive to the interaction angle alpha of the incident waves. In this work, the relationship between the acoustic nonlinearity parameter chi and the alpha is studied by numerical simulations and experimental measurements based on the nonlinear interaction of two shear waves. A single-peak change in the normalized acoustic nonlinearity parameter chi' of the mixing wave versus the incident angle is observed from numerical simulations and then is verified by experiments. The results show a-6 dB decrease of chi' corresponds to a deviation of about 4 degrees in the incident angle. Meanwhile, the detection and localization of plastic deformation is also conducted on an aluminum alloy based on the scanning of non-collinear wave mixing, in which the distribution of the acoustic nonlinearity is similar to that of the plastic strain.