Evaluation of Various Interface Layer Models for Ultrasonic Inspection of Weak Bonds

Abstract

Adhesively joined structures are increasingly used in industry. Effective nondestructive test techniques are therefore necessary for quality control and in service inspection of bonding conditions. Commonly encountered bonding problems can be classified into three types: debonding, cohesive weakness and adhesive weakness. The former two types can be detected by such traditional ultrasonic techniques as pulse echo, through transmission, C-scan, resonance etc. The last type is the most difficult due to physically `perfect ' contact between adhesive and adherent. Several ultrasonic techniques using longitudinal, shear, plate and interface waves etc. have been considered for finding the most sensitive wave type and corresponding experimental parameters [1--8]. High sensitivity was obtained in several cases. To understand the characteristics of wave reflection and refraction on the bond line for evaluating the bonding quality, various boundary conditions and different physical models have been created [9--18]: 1. ideal rigid boundary conditions (or welded bond), considered as perfect bonding, 2. ideal smooth boundary conditions (or kissing bond), considered as a weak bond, 3. weak boundary conditions, the bond between the rigid and smooth limits, 4. intermediate layer between two solid media, to account for weak bonding.