Low temperature debonding of toughened structural adhesive joints: A new approach to repairs in the automotive industry

With the increase in lightweight construction in car bodies, has come an increase in the use of structural adhesives. These are advantageous in terms of safety, design and comfort, but become problematic, when repairs or recycling are needed. This paper investigates the use of low temperatures to debond toughened structural adhesives. Using dynamic mechanical thermal analysis (DMTA) and the time-temperature superposition principle, the glass transition temperatures of the tougheners was determined for load rates typical in debonding operations. Wedge impact tests at low temperatures were then used to replicate debonding with a chisel in a workshop setting. It was found that, for the tested adhesives, there existed a temperature under which the cleavage force dropped significantly, the crack growth became unstable and the debonding occurred with no deformation of the substrate`s arms. The glass transition temperature of the tougheners was found to provide a good guideline for this debonding temperature. Scanning electron microscope images showed that at low temperature, the stiffened tougheners tended to debond from the matrix, greatly diminishing the toughening mechanisms as a result. These finding can be used to determine practical debonding windows for quick and clean repairs in workshops.