Propagation Property Of Ultrasonic Guided Waves In SHM

The propagation characteristic of ultrasonic guided waves in isotropic media is discussed in this paper which is divided into three parts as infinite medium, plate and cylinder. The reflection, transmission and dispersion of guided wave are studied for selection of guided in structural health monitoring (SHM).In infinite media, the share and longitudinal wave equations are derived from Navier’s displacement equation of motion. Ultrasonic waves with oblique incidence to interfaces of different media can be divided to horizontally polarized shear (SH) waves, vertically polarized (SV) waves, longitudinal (L) waves. The reflection coefficients and transmission coefficients of these single incident waves to free boundary interfaces are studied in this paper.In isotropic plates, frequency equations are derived from Navier’s displacement equation of motion with the global matrix method. Waves in plants are divided to SH waves and Lamb waves (coupled waves of SV waves and L waves). The same frequency equations of Lamb waves are derived as Lamb got in1917with global matrix method. The frequency dispersion curves of phase velocity and group velocity as well as wave structures are obtained from frequency equations with numerical method. In order to deal with common situations in engineering, waves in plates immersed in water as well as coated with viscoelastic media are discussed with layer plate method in this paper.In isotropic hollow infinite cylinders, frequency equations are derived from Navier’s displacement equation of motion with the global matrix method. Different with Gazis in1959, guided waves considered propagate not only along axial direction as Gazis discussed but also along circumferential direction. Guided waves in cylinders can be divided into longitudinal waves and torsional waves which are analogous to Lamb waves and SH waves in plates. The frequency dispersion curves of phase velocity and group velocity as well as wave structures are obtained from frequency equations with numerical method. Waves in pipes filled with water as well as coated with viscoelastic media are discussed with layer cylinder method in this paper.