3. Adhesives and Composites
The problem of devising meaningful and reliable methods for nondestructive evaluation of adhesively bonded joints has been the subject of considerable effort for many years. It remains an important and unsolved problem. The use of conventional NOT methods involving ultrasonics is not entirely satisfactory because the thickness of a bond line is small compared with typical acoustic wavelengths and, perhaps more importantly, because the strength and service life of an adhesive bond is dependent on its chemical as well as mechanical properties. That is, an adhesive bond that is mechanically perfect may fail because of chemical degradation initiated at the adhesive/adhered interface.
Wolfram, T. and White, H., "Application of Inelastic Electron Tunneling to the Study of Adhesion" (1977). Proceedings of the ARPA/AFML Review of Progress in Quantitative NDE, July 1975–September 1976. 8.