A set of three criteria is presented: One for crack nucleation, one for crack propagation, and one for yielding. In combination these three criteria simply explain known data on long-life fatigue, especially the strong effect of mean stress on the notch factor and nonpropagating cracks. Criteria for propagation and yielding are given only in first approximation; the former because a first approximation seems adequate, the latter because of lack of data on yielding in fatigue.

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