Simultaneous nondestructive estimation of thickness and longitudinal wave velocity of adhesive layers in adhesive joints through air-coupled ultrasonic testing

Abstract

This paper proposes a nondestructive method for the simultaneous estimation of the thickness and longitudinal wave velocity of an adhesive layer using a transmission coefficient spectrum, including amplitude and phase spectra measured via air-coupled ultrasonic testing to confirm adhesive joint reliability. The method correctly estimated the values of the adhesive layer from the transmission coefficient spectrum experimentally, unlike the conventional estimation using only the amplitude spectra. The absolute values of the estimation errors of thickness and longitudinal wave velocity obtained using this method were 1.3–12.1% and 0.4–6.1%, respectively. The proposed method can be useful for the quality assurance of adhesive joints.