Impact of moisture uptake in uncured bond lines on joints performance

Abstract

Adhesive bonding is a joining technique use to bond two surfaces together by using solidification or hardening that is non-metallic. For example, adhesive joining is mainly used in bonding sheet metal together in the car body in the automotive industry. The advantage of adhesive bonding is that it offers excellent flexibility and toughness. In addition, the risk for crack propagation can be minimized with adhesive bonding due to distributing the stress force over a larger area and reducing the stress concentration on the spotweld. However, moisture and elevated temperature significantly influence adhesive joints' performance. Most research has investigated how uptake moisture in cured bond lines influences the final properties. At Volvo cars, it is essential to understand how the transportation chain between supplier which is bonding the frame together and send it to Volvo cars for curing and assembly influences the mechanical performance of the joint performance and see if the adhesives follow Volvo cars standards before implantation in the production chain. For this thesis, two adhesives are tested, steel-to-steel adhesive and multi-material adhesive, and the following climate are conditions are 25°C/80%RH, 30°C/80%RH, 35°C/90%RH and 40°C/80%RH. The uncured bond lines will be exposed to different humidity and temperature for age-time between 0 to 62 days before being cured and tested. Indication of influences has been seen and increasing the ageing time shows a loss in mechanical properties for both investigated adhesives. Multi-material adhesive for lap shear and T-peel showed a more significant average loss than steel-to-steel adhesive. Also, it has been identified that the number of cycles for failure decreases with age-time for both adhesives. Although today's Volvo Cars standard regarding exposure time for uncured adhesive can be applicable for steel-to-steel adhesive, the multi-material adhesive showed more significant losses and exceeded the acceptable loose limit.