Theoretical and experimental evaluation of material nonlinearity in metal plates using Lamb waves

In this study, an equation is proposed considering Lamb wave motion in a plate in order to estimate the nonlinearity in plate material. The equation evaluates material nonlinearity in terms of amplitudes of the fundamental and second harmonics of Lamb waves. Because the Lamb wave second harmonic can be generated in a nonlinear material through the experiments or simulation, the proposed equation is practically useful to estimate the material nonlinearity. Accordingly, authors carried out experiments on pristine 1100‐H14 Aluminium (Al) specimens using Lamb waves and obtained their inherent material nonlinearity using the amplitude‐based equation. Additionally, authors obtained the value of inherent material nonlinearity in 1100‐H14 Al using the constitutive nonlinear stress‐strain relation containing higher order elastic constants. The material nonlinearity parameters estimated using the experimental results and amplitude‐based equation are then compared with that obtained using the constitutive nonlinear equation. The difference between the results is marginal. Thus, using amplitudes of the fundamental and second harmonics of Lamb waves obtained through the experiments, the proposed amplitude‐based equation can be used to estimate the material nonlinearity in metal plates with fair accuracy.