Effect of Temperature on Tensile Strength and Mode I Fracture Toughness of a High Temperature Epoxy Adhesive

Abstract

There has been a growing requirement in the last years, particularly in the aerospace industry, for adhesives to withstand high temperatures. The most important factor to consider when studying the effect of temperature on adhesively-bonded joints is the variation of adhesive mechanical properties with temperature such as the stress–strain curve and the toughness. Adhesive strength and strain show temperature dependence, especially near the glass transition temperature (T g) of the adhesive. Similarly, the fracture toughness is expected to show temperature dependence. In this work, an experimental study was performed to evaluate the effect of the temperature on the adhesive strength and fracture toughness of a high temperature epoxy adhesive. Bulk specimens of cured adhesive were produced and tested in tension at room temperature (RT), 100, 150 and 200°C, in order to obtain a strength profile of the adhesive over this temperature range. Results showed that as the temperature increases the adhesive tensile strength reduces but the ductility increases. Pure mode I adhesive fracture toughness (G Ic) tests were performed on double cantilever beam (DCB) specimens at room (RT) and high temperatures (100, 150 and 200°C) and the fracture toughness G Ic as a function of temperature was obtained. It is shown that at temperatures below T g, the fracture toughness, G Ic, is relatively insensitive to temperature, while above T g (at 200°C) a drastic decrease in fracture toughness was observed.