The Effect of Microcrazing on Fatigue Crack Propagation in Polymers
A generalized theory of fatigue crack propagation in polymers is outlined. The theory accounts for fatigue crack propagation through root craze extension accompanied by simultaneous dissemination of microcrazing around the crack-root craze system thereby describing a crack-craze zone (CCZ). In addition to the conventional crack length, the width of CCZ is introduced as a new internal parameter. Applying a special version of the second law of thermodynamics: the principle of minimum thermodynamic forces, these internal parameters are formally described in terms of the reciprocal thermodynamic forces. The rate of crack extension per cycle was found to depend strongly on changes in the width of CCZ. Results of the model are applied to fatigue crack propagation data in polystyrene under various loading conditions and a good description of growth rates is observed.
KeywordsStress Intensity Factor Crack Growth Rate Fatigue Crack Growth Energy Release Rate Fatigue Crack Propagation
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