Localization And Characterization Of Local Micro-defects Using Nonlinear Ultrasonic Guided Waves Mixing

New requirements has been raised in industrial nondestructive testing field with the development of nuclear power industry and aeronautical inertia:first,detection of early material defects;second,Localization and imaging of defects.Nonlinear Lamb waves mixing can satisfy these requests.Meanwhile,Lamb waves mixing can weaken the nonlinear effect of measuring devices compared to second harmonic generation.In this paper,Lamb waves mixing mode triplets is selected based on the internal resonance criteria for 1 mrm thick aluminum plate,the properties of mixing signal and defect's characterization and localization with mixing signal is analyzed through numerical and experimental method.Main work in this paper are as fellows:The internal resonance conditions to generate a cumulative harmonic is obtained by solving waves equation in a homogeneous,isotropic,stress-free elastic plate with perturbation and modal decomposition,they are phase matched and nonzero power flow.Mixing signal's propagating direction is determined two source's wave number through wave vector analysis.A program is written based on phase matched and nonzero power flow.Lamb waves mixing mode triplets are select for 1 mm thick aluminum plate based on internal resonance conditions.A special mode triplet is investigated through numerical method.Simulation results identifies that sum frequency signal S1 at 1.82MHz arises in mixing zone and it's propagating direction is consistent with SO at 1.13MHz.The interaction between Lamb waves mixing signal and defects is investigated.Results indicate that mixing signal is sensitive for defects in mixing zone and can be employed to detect early material micro defects.The feasibility about local defect's localization and imaging using Lamb waves mixing is investigated.Image from scanning with mixing signal is consistent with real defect.The propagation of mixing signal will influent imaging.Mixing signal generation through Lamb waves nonlinear interaction is investigated from the perspective of experiment.Different mixing mode with same material and mode at different material are analyzed for verifying the commonality of Lamb waves mixing...