The ultrasonic vibration characteristics of adhesive joints

Abstract

The natural frequencies of the longitudinal (through thickness) modes of an adhesive joint have been predicted using receptance analysis and measured using ultrasonic spectroscopy. Excellent agreement has been obtained between the predicted and measured frequencies of joints with a wide range of adhesive thicknesses and moduli. At low adhesive thicknesses, the modes tend to occur in pairs, but, at higher thickness, this pairing no longer occurs. This phenomenon has been explained in terms of the mode shapes of the different modes and the role of the adhesive layer in determining their frequencies. The variation of the apparent vibration damping with adhesive thickness has also been explained in terms of the mode shapes of the joint. The results indicate that it should be possible to calculate the thickness and modulus of the adhesive layer from measurements of the resonant frequencies of the joint. This would represent a significant advance in the nondestructive testing of adhesive joints.