The application of non-classical fracture mechanics to the growth of dynamic fatigue cracks in a visco-elastic solid is discussed. The ideas developed are used to characterize the results of fatigue crack growth measurements on a range of low -density polyethylenes. The results can be expressed in the form dcdN = BFn where dcdN is the growth of the crack each cycle, F is a fracture mechanics parameter and B, n are constants. Most of the materials studied reveal two distinct regions (with differing values of the constants) linked by a transition zone, and corresponding to brittle and ductile crack propagation respectively. The fatigue life of virgin specimens can be predicted from the crack growth characteristics assuming the existence of intrinsic flaws which (when the predictions are matched to actual fatigue data) are found to correspond in size to the polyethylene spherulites.
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Andrews et al. (1971) studied this question.
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