An intrinsic time to fracture criterion for amorphous polymers

An energy probability theory of global fracture is formulated using the notion of intrinsic time starting with first principles. Comparisons are made between the theory and experiments on Styrene-Butadiene Rubber, thus explaining various aspects of failure.It is proposed that fracture occurs as a result of accumulation of broken carbon-carbon bonds. When a critical concentration of broken bonds is reached, catastrophic failure begins and the specimen fractures. It is assumed that the probability of fracture of a single carbon-carbon bond is determined by the energy content of the bond. Non-uniform distribution of the free energy of the specimen among bonds is taken into account by means of an exponential distribution function. The intrinsic time measure pertinent to the constitutive equation of the material is used as the time measure of fracture. This allows use of the time-temperature shift principle, applicable to fracture of polymers, and enables the prediction of lifetimes in high strain rate conditions.Finally the theory predicts correctly that, at constant amplitudes, the number of cycles to failure at low frequencies is directly proportional to the frequency and is independent of the latter at high frequencies.