Evaluation of interfacial characteristics of adhesive joints by ultrasonic reflection technique

Abstract

This paper presents a method to simultaneously estimate the interfacial stiffnesses between the adhesive and the adherends of an adhesive joint, and the adhesive thickness by combining the experimental measurement based on the ultrasonic reflection method and theoretical analysis. The interfacial stiffnesses and the adhesive thickness were evaluated for an aluminum adhesive joint to study the effects of contamination of the release agent. The optically observed thickness of the adhesive is in good agreement with the theoretical results, indicating that the estimation is appropriate. The interfacial stiffness of the interface contaminated by the release agent was estimated to be approximately 24% of the properly bonded interface. In addition, double-cantilever beam tests were performed on different specimens to evaluate the mode I fracture toughness. The results showed that the mode I fracture toughness decreased to 10% of that of the properly bonded interface owing to the contamination. The results suggest that the reduction in the mode I fracture toughness induced by adherend contamination can be detected by identifying the decrease in the interfacial stiffness based on the proposed method.