Impact of adhesive joints for the automotive industry at low and high temperatures

Abstract

In recent years there has been an increasing interest in the automotive industry in applying adhesive bonding in structural components of vehicles. Toughened, high performance adhesives can provide exceptional strength while producing lighter structures and, therefore, improve vehicle safety and efficiency. When adhesive joints are used in this area, some factors such as impact loading and temperature variation have a decisive role. Under these conditions, the joint must provide enough strength to transmit the load without fracturing, and thus assure the car’s integrity. Although several studies have characterized adhesives under both situations separately, very few have considered them at the same time. The objective of this study was to characterize the impact strength of a new crash resistant epoxy adhesive as a function of temperature. To achieve this, single lap joints specimens with ductile adherends were tested under drop weight impact at -20, +23 and +80 ºC, in order to emulate real situations. Induction heating and nitrogen gas cooling systems were designed and implemented to reach homogeneously the high and low temperatures in the overlap. Then, properties of steel were obtained by conducting tensile tests. Bulk adhesive specimens were also tested at high and room temperatures in order to understand the influence of temperature on the adhesive properties. Finally, the results were discussed and analyzed, and a failure prediction was developed. As a result, at room temperature failure was mostly dictated by the adherends yielding due to the high strength of the adhesive. At high and low temperatures, it was found a high decrease in the adhesive strength with an increase of ductility and brittleness, respectively. Thus, in this case it was the adhesive which determined the joints strength. Furthermore, although at room temperature the adherend yielding model gave accurate prediction, at high temperature the values predicted using the static properties of the adhesive were below the experimental due to the adhesive sensitiviy to the high strain-rate.