Investigating the critical aspects of evaluating the material nonlinearity in metal plates using Lamb waves: Theoretical and numerical approach

The present study focuses on critical analysis of various aspects related to the evaluation of amplitude based material nonlinearity parameter ϒ_amp through the numerical simulations and theoretical justifications. Two different materials with distinct nonlinearities are interrogated using Lamb waves in the numerical simulations. The effects of input force amplitude, number of cycles in the tone burst, tone burst windowing functions, material model parameters, excitation frequency, and wave propagation distance on ϒ_amp are studied in detail. Also, gamma_amp estimated for the data obtained from the numerical simulations considering S₀-S₀ mode pair at low frequencies and resonant S₁-S₂ mode pair at higher frequencies are compared with the physics based material nonlinearity parameter ϒ_phy. The difference between the results is marginal. Thus, the nonlinear Lamb wave technique can be effectively used even at low frequencies to estimate the actual material nonlinearity of the (metallic) plate materials with fair accuracy using the proposed nonlinearity models.