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On the connection between Palmgren-Miner’s rule and crack propagation laws

Antonio Papangelo's picture

M.Ciavarella, P.D’Antuono, A.Papangelo

Politecnico di Bari, 70125 Bari, Italy.



The classical Palmgren-Miner’s rule (PM), despite clearly approximate, is commonly applied for the case of variable amplitude loading and to date, there is no simple alternative. In the literature, previous authors have commented that the PM hypothesis is based on an exponential fatigue crack growth law i.e. when da/dN is proportional to the crack size a, the case which includes also Paris law for m = 2, in particular. This is because they applied it by updating the damage estimate during the crack growth. It is here shown that applying PM to the "initial" and nominal SN curve of a cracked structure, results exactly in the integration of the simple Paris’ power-law equation, and more in general to any crack law in the form da/dN = HΔσhan. This leads to an interesting new interpretation of PM rule. Indeed, the fact that PM rule is often considered to be quite inaccurate pertains more to the general case when propagation cannot be simplified to this form (like when there are distinct initiation and propagation phases), rather than in long crack propagation. Indeed, results from well known round-robin experiments under spectrum loading confirm that even using modified Paris’ laws for crack propagation, the results of the "non-interaction" models, neglecting retardation and other crack closure or plasticity effects due to overloads, are quite satisfactory, and these correspond indeed very closely to applying PM, at least when geometrical factors can be neglected. The use of generalized exponential crack growth, even in the context of spectrum loading, seems to imply the PM rule applies. Therefore, this seems closely related to the so called "lead crack fatigue lifing framework". The connection means however that the same sort of accuracy is expected from PM rule and from assuming exponential crack growth for the entire lifetime.

paris-random6.pdf226.04 KB


Mike Ciavarella's picture

Soon we can send you the final form.


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