An experimental investigation has been carried out on double cantilever beam specimens with different bond thicknesses to study the effect of bond thickness on lifetime of adhesive joints under mode I. This paper describes an approach to predict the rate of crack propagation. The approach is based on principles of linear elastic fracture mechanics and uses elevated temperature to accelerate the crack propagation under constant loads. The fracture energy of the joint is studied as a function of bond thickness. The results from short-term tests are analyzed and a simple model has been proposed to predict the variation of two kinetic parameters of the Paris law with bond thickness.