The Research On Ultrasonic Non-Destructive Testing Based On Non-Classical Nonlinearity

The detection and evaluation of damages in critical parts is an essential part of structural health monitoring in industry which has great significance on structural maintenance and avoiding a catastrophic failure.Non-destructive testing methods based on nonlinear theory are often employed to detect early damages whose nonlinear response helps reveal their nature.In this paper,non-classical nonlinear behavior of micro-damaged material is introduced using Preisach–Mayergoyz model?PM model?.A special iterative algorithm is employed to define damaged materials in the simulations and the non-classical nonlinearity of bulk waves and Lamb waves introduced by PM model is evaluated.It is shown that remarkable nonlinearity is observed in Lamb waves after interacting with PM model.As is defined,PM model is a multiscale model consisting of a large number of hysteretic elementary units and different configurations of the units lead to different nonlinearity.Further parameter study proves that PM model is also effective to describe the development of the damages.Therefore,PM model is a suitable model to simulate the micro-cracks in plates.This paper further extends the usage of PM model in bulk wave research and both linear and nonlinear indexes are used to evaluate the influence of PM model in the propagation of bulk waves.Higher harmonic generation is observed in both reflected and transmitted wave packets because of the intermediate layer described by PM model.The parameters of PM model determine the nonlinearity of the layer and therefore effect the fundamental and higher harmonic components,which offers a new method to design nonlinear metamaterials.A method combining the nonlinear analysis and time reversal of Lamb waves to locate micro-cracks in plate-like structures is also presented in the paper.Two different models,the contact acoustic nonlinearity?CAN?and the PM model,are used to simulate a localized damage in a thin plate.Pulse inversion method is employed to extract the second and fourth harmonics induced by the damage and time reversal is performed to compensate the dispersion of S₀ model Lamb waves.By investigating the spatial distribution of harmonic wave packets,the location of micro-cracks will be revealed.The numerical simulations indicate that this method gives accurate locations of the damaged area in a plate.