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The nonlinear ultrasonic nondestructive testing (NNDT) using contact acoustic nonlinearity (CAN) has been developed over the last decade. However, although the nonlinear waves such as higher- and sub-harmonics are considered as generated by the interaction of the crack faces such as clapping motion or friction, the mechanism of generation has not been understood clearly from theoretical view point yet. 1-D and 2-D numerical simulations and 3-D axisymmetric problems have been conducted so far. However, no full 3-D analysis has been done. Therefore, in this research, the boundary integral equations for an interface crack with nonlinear boundary conditions in three dimension is formulated, and solved numerically using time-domain boundary element method. The Fourier spectra of received wave are evaluated by means of far-field scattered waves because the received points are usually located far from the defects in NDT.

Nondestructive evaluation; Elastic wave; Time-domain BEM