Evaluation Of The Localized Plasticity Using The Mixing Of Counter-Propagating Lamb Waves

The nonlinear interaction of the guided waves has attracted considerable attention since it shows high sensitivity to the material damage at the early stage and can isolate nonlinearity caused by the measurement system. A suitable mode triplet is selected based on resonance conditions, to generate the cumulative difference or sum harmonics. Based on the finite element (FE) simulations, group velocities and wave structure of the primary waves and sum harmonics are measured and they matched well with the desired value. To detect and scan the damaged samples with localized plasticity, experiments are carried out in 2-mm-thickness 6061-T6 aluminum alloy plate. It is demonstrated that the acoustic nonlinearity parameters increase monotonously with the accumulated plasticity, and the distribution of the acoustic nonlinearity parameters agrees well with those of the plasticity.