Selective Generation of Lamb Wave Modes in a Finite-Width Plate by Angle-Beam Excitation Method

Abstract

A Lamb wave in a plate with a finite width has both thickness and width modes, whereas only thickness modes exist in an infinitely wide plate. The thickness and width modes are numerously formed in a finite-width plate, and they all have different cut-off frequencies, wave velocities, and wave structures. These different characteristics can be utilized in various applications, but a selective generation method for a particular Lamb wave mode in a finite-width plate has not been sufficiently studied, and only a method using multiple elements has been reported. This paper presents the selective generation of a certain Lamb wave mode in a finite-width plate by an angle-beam excitation method using single or dual wedges. In the proposed generation method, a specially designed wedge with grooves or a patch having insulation layers is employed for partial acoustic insulation of the ultrasonic energy incident into the plate. The feasibility of the proposed method was investigated through finite element method (FEM) simulations for Lamb wave excitation and propagation, and then experimentally demonstrated by the measurement of Lamb wave propagation using a laser scanning vibrometer.

Impact Damage Detection in Patch-Repaired CFRP Laminates Using Nonlinear Lamb Waves

“…Lamb waves are often utilized in the acoustic guided wave modes of thin laminate structures, wherein the wavelengths of Lamb waves have the same magnitude as the plate thickness. Lamb wave propagation has dispersive, multimodal characteristics [ 23 ]. The dispersive characteristics of Lamb waves can be directly described by a dispersion curve, which depicts the relationship between the group velocity or phase velocity in Lamb waves and the frequency-thickness product.…”

Excitation and Reception of Higher-Order Guided Lamb Wave’s A1 and S1 Modes in Plastic and Composite Materials

“…However, application of higher-order modes could allow better detection and characterization of defects characteristic of planar plastic and composite structures. There are already some publications describing application of higher-order guided waves for detection of wall thickness reduction and crack-like defects, however only in metallic structures [ 13 , 14 , 15 , 16 ]. For example, P. Khalili and P. Cawley analyzed symmetric S 0 mode at ~1.5 MHz-mm and shear horizontal SH 0 and SH 1 modes at ~3 MHz-mm in the 10 mm thick steel plate and determined that they can be suitable for detection of shallow defects [ 15 ].…”