Elastic Constants for Unidirectional Boron-Epoxy Composites

The use of unidirectional boron-epoxy composites to reinforce highly stressed or damaged regions in defence aircraft structures is increasing rapidly [1]. Critical nondestructive evaluation problems related to such repair technology include the need to ensure the integrity of the bond between the composite reinforcement and the substrate, and to detect and measure the depth of a crack underneath the reinforcement. Among possible ultrasonic techniques, leaky interface waves have shown promise for the measurement of adhesive bond strength [2], and could also allow extension to second-layer cracks of crack depth measurement techniques such as Rayleigh wave spectral modulation [3,4]. However, it is first necessary to measure elastic constants, C;1, for the composite, as these constants are needed to determine whether leaky interface waves occur for a particular composite/substrate combination.