Nonlinear based Time Reversal acoustic applied to crack detection: Simulations and experiments

International audienceIn nondestructive evaluation, Nonlinear Elastic Wave Spectroscopy (NEWS) methods represent powerful tools to explore damaged zones in a sample. The combination of these methods with Time Reversal (TR) process can be used to either increase the stress on the retrofocusing position or to retrofocuse elastic waves on the defect, when only the nonlinear components of the received signal are time reversed. In this paper, we propose two different approaches to detect cracks in metallic samples in coupling NEWS methods and TR process. The first one, NEWS-TR, is defined by sending back only the nonlinear components which are preliminary time-reversed. Two different techniques to filter nonlinear components have been numerically studied: classical harmonic filter and pulse inversion. In these two cases, performances of retrofocusing on different defect positions are analysed and compared. The second approach, TR-NEWS, consists in measuring the nonlinear signature on the focal spot. An experimental study of parametric interaction between two reversed signals (f1 and f2) is led. Measurements of components at f2 − f1 and f2 + f1 around a crack are performed and discussed