Evaluation of adhesive bond Young's modulus during crosslinking using a mechanical method and an ultrasound method

The strength and stability of adhesive bonded structures are related to polymer curing, when crosslinking occurs and leads to adhesive strength, stiffness and durability. Depending on the resin and curing agent used, cure time can vary from minutes to weeks. Methods based on dynamic mechanical analysis (DMA) or calorimetric techniques (DSC, DTA) are valuable for evaluating mechanical properties of adhesives, but are devoted specifically to the polymers alone, and not in situ in adhesive bonds. In this contribution, we have monitored - during crosslinking - the Young's modulus of a slow-curing DGEBA - PAMAM adhesive system, with two non-destructive, in situ, methods used for the characterisation of the adhesive in a bonded system. The first method is based on measurements obtained from strain gauges mounted on one bonded adherend. The second method uses an ultrasound technique based on the through-transmission. Both methods suggest the same curing kinetics.