Characterization of nonplanar second harmonic lamb waves with a refined nonlinear parameter

Structural health monitoring (SHM) methods based on the cumulative second harmonic Lamb waves show attractive advantages. An ideal nonlinear parameter should allow precise characterization of the cumulative effects of the distributed nonlinear sources such as the material nonlinearity of a plate (MNP), in the presence of other unavoidable localized nonlinear components. While highlighting the deficiencies of the traditional nonlinear parameter (TNP) in the nonplanar cases, a refined nonlinear parameter (RNP) is proposed. Through compensations for the wave attenuation associated with the wave divergence, the new parameter entails a better characterization and differentiation of the cumulative MNP and other noncumulative localized nonlinear sources. Theoretical findings are ascertained by both finite element (FE) simulations and experiments, through tactically adjusting the dominance level of different nonlinear sources in the system. Results confirm the appealing features of the proposed RNP for SHM applications.