Evaluation of crack orientation using fatigue crack-induced contact acoustic nonlinearity

Abstract

Based on the two-dimensional (2D)1 and three-dimensional (3D)2 analytical models previously developed for interpreting the contact acoustic nonlinearity (CAN) generated due to the modulation from a “breathing” crack in solid media on propagating guided ultrasonic waves (GUWs), this study proposes a new characterization approach, able to orientate a fatigue crack, even when the crack is at its embryo stage. CAN embodied in the scattered Lamb waves and shear horizontal (SH) waves converted from incident GUWs is extracted upon interaction with fatigue cracks, and the unique scattering pattern of CAN is associated with crack slant via the 3D analytical models, whereby the orientation of a fatigue crack can be pinpointed, without making a reference to the baseline signal. Experimental validation of the characterization approach is implemented, in which an undersized fatigue crack is orientated accurately and visualized in the image.