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

•Non-collinear wave mixing is used for detection and localization of plasticity in aluminum alloy.•The efficiency of wave mixing is significantly affected by the incident angle.•A tolerable deviation (i.e. 4°) of incident angle is proposed based on simulations and experiments.•The proposed deviation is probably suitable for other metals with similar Poisson's ratios.

Non-collinear wave mixing recently has been proposed to detect and localize micro-damage in materials. It is proved sensitive to the interaction angle α of the incident waves. In this work, the relationship between the acoustic nonlinearity parameter χ and the α 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 χ′ 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 χ′ corresponds to a deviation of about 4° 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.