The Non-destructive Testing of Adhesively Bonded Structure: A Review

The types of defect encountered in adhesive joints and the non-destructive testing techniques available to detect them are reviewed. Three types of defect: complete voids or dis-bonds, poor cohesive strength of the adhesive layer and poor adhesion between the adhesive layer and adherend are commonly present. It is shown that a variety of techniques is available for dis-bond and void detection, ultrasonics and sonic vibration being the most commonly used. The detection of poor cohesive and adhesive properties, however, is much more difficult than void and dis-bond detection and is the subject of current research. At present there is only one commercially available instrument which claims to predict cohesive strength. There is no reliable non-destructive test to detect poor adhesion.