Scattering of the Fundamental Shear Guided Wave From a Surface-Breaking Crack in Plate-Like Structures

S0 Lamb Mode Scattering Studies in Laminated Composite Plate Structures with Surface Breaking Cracks: Insights into Crack Opening Behavior

Ultrasonic-guided waves are attractive for rapid inspection of laminated composite structures, where cracks developed transverse to the loading direction are the severe type of damage. This paper presents studies of the interaction of fundamental symmetric S0 Lamb mode with vertical surface-breaking cracks in laminated composite plate structures. Finite element simulations and experimental investigations are used to study the effect of crack depth on S0 wave reflection behavior. Results show a monotonic rise of the reflection coefficient for different crack depths in a manner that is strongly dependent on the orientation of the plies and transverse ply location in the vicinity of the crack. Scattered wave packets in the reflection regime are captured using an in-plane laser. The S0 Lamb mode's sensitivity is numerically presented for the different crack depths in the long wavelength limit. We also observed that the reflected wave mode depicts the information of the corresponding broken interfaces. An attempt was made to show that this behavior relates to the crack-opening behavior in response to in-plane excitation. The reflection coefficient as a characteristic polynomial is proposed for various orientations. It was observed that the dispersion at receiver nodes makes the analysis challenging for distinguishing the signal from crack faces due to the smaller dimension. The study outcomes show its prospect as a promising NDE tool for crack damage detection in thin laminated plate structures.

Shear horizontal wave transducers for structural health monitoring and nondestructive testing: A review

Shear horizontal (SH) waves are of great importance in structural health monitoring (SHM) and nondestructive testing (NDT), since the lowest order SH wave in isotropic plates is non-dispersive. The SH waves in plates, circumferential SH waves and torsional waves in pipes have remarkable resemblances in dispersion characteristics and wave structures, so the latter two can also be called as SH waves in pipes. This paper reviews the state-of-the-art research on SH wave transducers for SHM and NDT. These transducers are grouped into the following categories: Lorentz-force-based electromagnetic acoustic transducers (EMATs), magnetostrictive EMATs, shear wave piezoelectric wedge transducers, thickness-shear piezoelectric transducers and face-shear piezoelectric transducers. The working principles, applications, merits and limitations of different kinds of SH wave transducers are summarized, with a focus on discussing the various configurations for exciting and receiving directional, omnidirectional SH waves in plates and torsional waves in pipes. This paper is expected to greatly promote the applications of SH waves in SHM, NDT and the related areas such as elastic metamaterials.