Temperature Dependence of the Fracture Toughness of Adhesively Bonded Joints

Adhesives used in structural high temperature space and aerospace applications must operate in extreme environments. They need to exhibit high-temperature capabilities in order to maintain their mechanical properties and their structural integrity at the intended service temperature. One class of the adhesives which are able to withstand the temperature extremes that are experienced in the space environment and are able to maintain a good degree of flexibility at very low temperatures are the room temperature vulcanizing (RTV) silicone adhesives. As is known, adhesive strength generally shows temperature dependence. Similarly, the fracture toughness is expected to show temperature dependence. In this study, the pure mode I fracture toughness for adhesive joints bonded with a high temperature RTV silicone adhesive was measured over a wide range of temperatures. Double cantilever beam (DCB) tests were performed on specimens at room temperature (RT), 100 and 200 degrees C. Mode I traction-separation laws were obtained as a function of temperature, directly from the experiments, by differentiation of simultaneously measured data (the J-integral and the end-opening displacement). Results showed that the fracture toughness, the peak cohesive stress and the respective end-opening displacement all decreased with the temperature rise. (C) Koninklijke Brill NV, Leiden, 2010