Monitoring and damage detection of adhesive bonds with micro-encapsulated markers

The quality and durability of adhesive bonds are affected by aging processes. Therefore, appropriate monitoring for early damage detection is essential for such bonds. For these reasons, we set out to develop an adhesive-based joining technology that makes early detection of potential defects in adhesive bonds possible. In this method, various dyes are added to the adhesive used, which indicate, if the specific load is exceeded. These dyes are micro-encapsulated through different methods, producing capsules of different sizes and wall thicknesses. When an adhesive bond is damaged or overloaded, the capsule would break and the dye would be released. The released colors can be detected optically or with suitable measurement systems. To demonstrate this technology, various experiments were carried out. Firstly, changes in adhesive properties were checked through thermal analysis and then pure substance specimens were produced and tested as means of comparison. Finally, the formulated adhesives were used to produce specimens for compressive shear tests, using glass and aluminium. The advantage of this technology by comparison to conventional nondestructive testing methods is the possibility to detect defects in adhesive bonds before the durability of the adhesive bond itself is affected.