Shear Horizontal Wave Generation And Interaction With Defects In Metallic Plates

Ultrasonic guided waves are particularly popular in structural health monitoring and nondestructive testing because they can propagate at large distances with low energy-loss.Lamb waves and shear horizontal waves exist in thin plate-like structures.Lamb waves have various applications in the area of damage detection,while dispersion and multimodal make signal interpretation a challenge.Compared to Lamb waves,SH waves have unique mode as the frequency is under first-order cut-off frequency and its zero-order mode is non-dispersive.Thus,SH waves have well research value and applied foreground in the area of nondestructive testing.According to Navier equation of motion,potential function method and boundary conditions are utilized to solve the dispersion equation for guided waves in plates.Based on guided wave propagation theory and consider the process for guided wave damage detection,it is found that SH waves are advantageous in detecting damage.Based on the piezoelectric coupling effect and constitutive equation,the excitation mechanism of guided wave is studied.A finite element model is built for SH waves generated by a d₃₆ type piezoelectric transducer.The displacement on the surface of the plate which is excited by a d35 and d₃₆ type piezoelectric wafer are extracted and compared in order to certify the great performance of d₃₆ type wafer in exciting and receiving SH waves.The space distribution of guided waves are discussed and it provides theoretical basis for high-efficiency SH excitation in metallic plates.Another finite element model is built for the interaction between SH waves and two types of defects in plates utilizing SH waves generated by a d₃₆ type piezoelectric wafer.Aiming at the detection of cracks in metallic plates,the changes of waveform in SH waves are studied.Similarly,reflection coefficients are taken as the index in evaluating corrosion defects in plates.This paper study the excitation mechanism of d₃₆ type piezoelectric material using numerical simulation and offer an idea for exciting SH waves efficiently.Theinteraction between SH waves and two types of damage in metallic plates is discussed and this provides theoretical foundation for detecting specific sort of damage using SH waves.