Combined harmonic generation of feature guided waves mixing in a welded joint

Abstract

In our previous research, the second harmonic generation (SHG) of feature guided waves (FGWs) in a welded joint with material nonlinearity was analyzed theoretically and observed numerically. However, some drawbacks including strict generation criteria, inability of distinguishing nonlinearity, and being unable to localize local defects of SHG-based nonlinear ultrasonic technique, limit the practical testing and application. Wave mixing is a promising alternative to overcome these shortcomings. In this paper, we investigated another acoustic nonlinear response of FGWs, so-called combined harmonic generation (CHG) caused by FGWs mixing in a welded joint. Theoretical analysis of second-order combined harmonic waves induced by two FGWs mixing in a welded joint was firstly implemented based on semi-analytical finite element (SAFE) and perfectly matched layer (PML) methods. Based on the theoretical analysis, four FGW mode triplets, which satisfy the internal resonant conditions, were selected for the observation of CHG caused by FGW mixing in a welded joint from a numerical perspective. CHG induced by FGW mixing with the cumulative growth effect was successfully observed within the mixing zone, which is consistent with the theoretical prediction. This study provides a straightforward analysis not previously available of the process of CHG of FGWs propagating and mixing in a welded joint.