Entropy Production during Fatigue as a Criterion for Failure. The Critical Entropy Threshold: A Mathematical Model for Fatigue.
Annual rept. no. 1, 15 Aug 82-14 Aug 83,
NEBRASKA UNIV LINCOLN COLL OF ENGINEERING AND TECHNOLOGY
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A mathematical model of fatigue crack nucleation is described using the irreversible thermodynamics to quantify the damage caused by plastic straining. The model is based on the hypothesis that the entropy gain which results from dynamic irreversible plastic straining is a material constant. A random model of internal friction is used to calculate the irreversible part of the hysteresis energy dissipation rate, enabling the quantification of uncertainty through the variance of the dynamic plastic strain. In this manner, the mathematical model for fatigue crack nucleation provides an estimate for longevity including confidence intervals under arbitrary temperature, environment, and loading history. The model explains the existence of an endurance limit. Although this analysis was conducted for an uncracked material leading to time estimates for crack nucleation, the theory can easily be extended to the case of crack propagation using the methods of fracture mechanics. Author