Numerical Study On Macro-&Micro-damage Detection Based On Ultrasonic Guided Waves

As an important non-destructive testing technique,ultrasonic testing has been investigated and applied in many industrial fields such as civil engineering,manufacturing,aerospace engineering.With ultrasound being studied deeply,ultrasonic guided waves technique has drawn increasing attention due to its cost-effective feature and other advantages.In the meantime,nonlinear acoustic techniques are developing dramatically for its higher sensitivity to micro-damages,making it significantly meaningful to study the nonlinear guided wave techniques for materials testing and characterization.This thesis focuses on the propagation of Rayleigh surface wave in curved structures,along with frequency mixing response of Lamb and shear horizontal guided waves in plates regarding macro-and micro-damage detection.The main contents are as follows:(1)Rayleigh surface wave simulation in curved structures,along with wave-macrocrack interaction study.(2)Theoretical study of the guided waves interaction with the classical material nonlinearity in isotropic homogeneous sheet materials.Higher order harmonic waves generation and their propagation patterns are summarized in terms of single excitation of a primary guided wave and dual excitation of two primary guided waves.(3)Phase-matched mode pairs in aluminum plate are searched out according to the theoretical fundamentals,and finite element simulations are performed with regard to different guided wave mixing cases.Higher elastic constants are introduced into the material models to investigate the mechanism of second and third order harmonic generations.The cumulative effects of different harmonic waves at sum-and differencefrequencies are analyzed.Different micro-damage levels in material are simulated through various magnification of higher order elastic constants to study the possibility of damage localization using guided wave mixing method.(4)Numerical simulation based on the interaction of guided waves with contact acoustic nonlinearity are conducted in aluminum plate and CFRP composite laminate.Different contact elastic models are implemented to explore the influence on the second harmonic generation.Closed crack and debonding in these plates are studied in terms of different factors such as depth and size.