Stochastic Fatigue Damage Accumulation

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Abstract
A study is made of several aspects of the problem of predicting fatigue failure by using the Palmgren‐Miner (PM) approximation, with cycles defined by the rainflow procedure. The stress time history is considered to be a stationary stochastic process, and the term fatigue is considered to refer to crack initiation or crack propagation, or both. It is first shown that PM analysis is consistent with a fairly broad class of theoretical models that give nonlinear growth of damage. Next, simulation results are presented for a bandwidth correction factor, relating damage predicted from rainflow cycles to that predicted from narrowband analysis. It appears that there may be a need to use some bandwidth parameter other than the irregularity factor in order to obtain consistent results for this correction factor. Results are also presented regarding the effect of nonnormality of the stress process. Both analytical and simulation studies show that this effect may be quite significant.

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