Lamb Wave’s Hybrid Imaging Algorithm And Its Application In Thin-walled Structure Health Monitoring

With the emphasis on safety,structural health monitoring has become a hot research topic.Thin plate structures are widely used in aerospace and other fields,let it become the main object of nondestructive testing.Lamb wave has the characteristics of fast propagation speed,low energy attenuation and sensitive to damage,which is an effective tool for thin plate structure damage detection.In this thesis,the following works has done about damage detection using Lamb waves.1)According to the displacement equation of ultrasonic wave,the dispersion equation of Lamb wave is deduced.According to the dispersion equation,the group velocity dispersion curves and phase velocity dispersion curves of Lamb waves in aluminum plate are plotted.The fluctuation characteristic of the Lamb waves is obtained.2)According to the fluctuation characteristic of Lamb wave,the excitation signal of damage detection is determined.The propagation speed of Lamb wave is verified.Analyzing the principle of incident and reflection of Lamb wave,the formula of damage index is deduced.The damage identification model is established by using the finite element method,and the damage index is calculated under different damage degree.The results show that the damage index formula is correct.The damage threshold D0 is used to identify the damage of the thin plate structure.3)A hybrid imaging algorithm is proposed based on ellipse and hyperbolic method.The basic principle of hybrid imaging algorithm is expounded.The damage localization model is established by finite element method.Respectively,the simulation results were imaged using the hybrid imaging algorithm and ellipse method.According to the imaging results,the hybrid imaging algorithm is more accurate to damage location than the ellipse algorithm.