LAMB WAVE INTERACTION WITH LAP-SHEAR ADHESIVE JOINTS - THEORY AND EXPERIMENT

Lap-shear joints are made from two plates that overlap in the joint area. In this paper a theoretical and experimental analysis of Lamb wave interaction with such joints is given. In this joint evaluation technique Lamb waves are excited and received outside the joint area and a conclusion about joint quality is drawn based on the phase delay and transmission losses of the ultrasonic signals in the joint. The mode transformation at the joint edges is very important for such tests. This phenomenon is studied in this paper by considering mode conversion on the boundary between the region exterior to the joint area and the two adhesively joined plates inside the joint. The problem is addressed theoretically by the Wiener-Hopf technique for a perfect joint that is represented by a double thickness plate and for a weak joint that is approximated by slip boundary conditions between the two plates in the joint area. This work shows, both theoretically and experimentally, how to select the mode type and frequency of the Lamb modes excited outside the joint to obtain the appropriate mode in the joint area for successful discrimination of bond quality.