Kissing bonds in adhesive joints: a holistic approach for nonlinear ultrasonic detection, joint mechanics and surface chemistry

A kissing bond is an adhesive bonding defect in which the adhesive and the substrate are in contact or coupled though a weak bond or thin layer. They are thought to arise from either contamination of the surfaces during manufacture or various forms of environmental attack. When adhesives are used for safety critical applications the current approach is to undertake extremely careful process control. None-the-less premature failure of adhesive joints still occurs and kissing bonds are the most likely cause. In addition to this, one of the limiting factors preventing the more widespread use of adhesive bonding is the lack of quantitative non-destructive testing procedures capable of detecting kissing bonds. However, despite this need, the physical nature of the kissing bonds and their failure mechanics are unknown. This lack of knowledge acts as a fundamental barrier to progress and inhibits the design of appropriate NDT procedures. This project aims to investigate the phenomena of kissing bonds in adhesive joints and redress this lack of current understanding. The project will take a holistic approach and obtain 1) a detailed understanding of the physical nature of kissing bonds; 2) an understanding of how kissing bonds lead to a mechanical failure and; 3) undertake an investigation into their detectablity using both current state-of-the-art methods (high frequency ultrasonics) and using nonlinear ultrasonics which is an exciting emerging technology.