Evaluation of the Curing of Structural Adhesives by Ultrasonic Interface Waves Correlation with Strength

An ultrasonic interface wave can be excited at the interface between two solid bodies, joined by a thin adhesive film. The velocity of the interface wave is con trolled by the shear modulus of the adhesive, and hence the interface wave can be used for evaluation of the curing of the adhesive. This method makes it possible to perform measurements in situ at the required temperature and pressure. The technique allows a clear recording of all phases of the curing pro cess : softening of the prepreg and its transition to the liquid phase, and the beginning and the termination of the polymerization reaction. It is shown that the ultrasonic data satisfactorily predict changes in the mechanical bond strength in the course of curing.