Simulation and analysis of subharmonics and tail effect for ultrasonic nondestructive evaluation of closed cracks

Subharmonics are generated at closed cracks by the nonlinear effect of large-amplitude ultrasound. This effect has the possibility of more accurate detection and evaluation of closed cracks. Also, it was reported that the tail part of the transmitted wave through the cracks has a peculiar wave, which is called the tail effect. Thus far, the mechanisms of the tail effect have not been revealed. In this paper, we introduced a realistic input wave into the previous model, which shows the interaction between closed cracks and large-amplitude ultrasound. As a result, we reproduced both the subharmonics and the tail effect for the first time. Furthermore, the mechanism was verified by comparing the input and output waveforms and using a potential energy diagram. Based on these findings, we proposed novel approaches for nondestructive evaluation of closed cracks.