Fatigue predictions for VA (variable amplitude) spectra are currently based on the Miner-Pålmgren rule using S-N data obtained from CA (constant amplitude) test data. The Miner-Pålmgren rule is a linear damage accumulation rule, in which the “damage” is the reciprocal of the fatigue life at a given stress level, so not a physical damage.
The Miner-Pålmgren rule is widely used for almost a century now but does have some fundamental shortcomings:
- Fatigue damage is indicated by a single damage parameter only, n/N, which does not depend on the damage size.
- No interaction and sequence effects (notch root plasticity) are not included.
The Miner rule and an engineering approach to overcome a part of the shortcomings (related to cycles below the fatigue limit) are discussed in a white paper that can be downloaded from this page.
The article is part of a chapter in the book Guidelines for Fatigue Life Analysis (2nd Edition).
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