The critical role played by interface zones in the fracture and failure of composites and other bonded materials is well known. However, the existing nondestructive evaluation methods are not capable of yielding useful quantitative information on either elastic or strength related properties of the interface. The authors are investigating the feasibility of applying an ultrasonic method to determine some of the interface properties nondestructively. The method uses guided waves and is based on the fact that the dispersive properties of these waves are strongly affected by the elastic properties of the interface. A coordinated theoretical and experimental program of research has revealed that the correlation between the interfacial properties and the phase velocity of the guided waves is quite strong and is identifiable at least in laboratory specimens. Some recent results of this research are reported in this paper.

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