A MODEL FOR THE ULTRASONIC INSPECTION OF COMPOSITE PLATES

This paper presents a theoretical model for calculating elastic waves within layered plates composed of anisotropic materials. The waves are assumed to be generated by an ultrasonic beam incident within a liquid medium onto the top of the plate. The partial waves and their amplitudes are calculated for each layer, taking account of the conditions (perfect adhesion or slip-bonding) at each interface between the layers. These waves are summed to give the total waves travelling within the plate. Plane wave solutions are combined to give the corresponding solutions for bounded beams from finite-sized transducers. The model is used to show how shear and compression resonances may build up within a layered composite plate, and how these are affected by the presence of a thin layer of material such as nylon, and by loss of adhesion between the nylon and the composite layers. The importance of taking into account the transmission and reception characteristics of transducers is illustrated by comparison of plane wave predictions with bounded beam predictions. Resonances predicted using plane wave theory are often broadened sufficiently to appear immeasurable, when transducer characteristics are included. The use of the model for helping to devise ultrasonic techniques to look for delaminations or included material is discussed.