Debonding techniques in metal joints using imbedded additives

Abstract

Adhesive bonding as a joining technique for hybrid materials and joints in general has many advantages, such as even stress distribution, a large area connection and no damage to the individual components. However, for recycling or replacing the individual components easier debonding can be useful. This can be done by weakening the adhesive layer with a specific stimulus. It is important that the boundary conditions of the component are fulfilled during operation.

The present work focuses on various options for adhesive debonding in metal joints. In particular, two promising methods of imbedding additives in the adhesive layer are investigated. The first one is the addition of thermally expandable particles (TEPs), which can be activated at a certain higher temperature, leading to a weakening of the adhesive layer and thus contributing to an easy debonding. The second method is the addition of thermally expandable graphite (TEG) to the adhesive layer, which is based on the same debonding concept as the TEPs. Laser treated Ti-6Al-4V was used as the metal component and different epoxy resins as well as a polyurethane adhesive were tested. In addition, different weight percentages of the particles were tested and compared. Tensile shear strengths and fracture surfaces were examined and evaluated to identify successful methods and approaches. Some variations that were tested, did not meet the desired requirements. A promising combination turned out to be the variation of TEG with Polyurethane and RTM6. The addition of 15 wt% resulted in an easy debonding after expansion of the particles, while the strength of the unexpanded specimens remained high enough. The investigated approaches can also be transferred to other material combinations including hybrid materials.