Characterization of Micro-Crack Orientation in a Thin Plate Using Quasi-Static Component Generated by Incident Ultrasonic Lamb Waves

The directivity of the quasi-static component (QSC) is quantitatively investigated for evaluating the orientation of a micro-crack buried in a thin solid plate using the numerical simulation method. Based on the bilinear stress–strain constitutive model, a three-dimensional (3D) finite element model (FEM) is built for investigating the nonlinear interaction between primary Lamb waves and the micro-crack. When the primary Lamb waves at A0 mode impinge on the micro-crack, under the modulation of the contact acoustic nonlinearity (CAN), the micro-crack itself will induce QSC. The amplitude of the QSC generated can be used for directly charactering the micro-crack orientation. The finite element simulation results show that the directivity of the QSC radiated by the micro-crack is closely related to the orientation of the micro-crack, allowing for the characterization of micro-crack orientation without the need for baseline signals. The results indicate that the directionality of the QSC can be used for characterizing the orientation of the micro-crack. The amplitude of the QSC is affected by the contact area between two surfaces of the micro-crack. It is demonstrated that the proposed method is a feasible means for the characterization of micro-crack orientation.