Attenuation of ultrasonic Rayleigh—Lamb waves by small horizontal defects in thin aluminium plates

The present paper illustrates how horizontal symmetric crack-like defects can be detected rapidly in thin isotropic plates by using longitudinal ultrasonic waves. The use of such longitudinal waves o⁄ers the potential of being signiÞcantly faster for non-destructively detecting defects than conventional ultrasonic techniques, which rely on transverse waves propagating through the thickness of a plate. Computational and analytical methods are used to predict reßection coeƒcients due to the attenuation of a longitudinal ultrasonic wave by physically small defects. It is shown that detectable attenuation (’10%), i.e. reßection coeƒcients, of the lowest order symmetric Rayleigh—Lamb wave (S 0) occurs for a range of small defects (sub-millimeter in length) when using high-frequency waves (MHz range). ( 1998 Elsevier Science Ltd. Al