2011, pp 1049-1069

Nondestructive Testing

Abstract

The objective of any system of nondestructively examining an adhesive joint is to obtain a direct correlation between the strength of the joint (howsoever defined) and some mechanical, physical, or chemical parameter which can readily be measured without causing damage to the joint. Faults may be defined as anything which could adversely affect the short- or long-term strength of a joint. There are two basic areas for examination in properly made joints, the cohesive strength of the polymeric adhesive, and the adhesive strength of the bond between the polymer and the substrate. In addition, voids, disbonds, and porosity create an additional issue for inspection.

During the production phase, and also in service with critical structures, it is essential to use nondestructive tests to assess the quality and fitness for purpose of the product. The nondestructive test will not measure strength directly but will measure a parameter which can be correlated to strength. It is, therefore, essential that a suitable nondestructive test is chosen and that its results are correctly interpreted. Typical defects found in adhesive joints are described and an indication given of their significance. The limits and likely success of current physical nondestructive tests will be described, and future trends outlined.

It is shown that a variety of techniques are available for disbond detection, ultrasonics, and different types of bond tester being the most commonly used. These techniques are very time consuming, especially if large bond areas are to be tested. Monitoring interfacial properties is much more difficult and there is currently no reliable test after the joint is made although there are some indications of a possible way forward using high-powered lasers.