A vibration fatigue analysis model considering interaction effects

In the typical vibration fatigue problem, the excited structure is usually subjected to variable amplitude loading in the fatigue weakness area, which is of the random nature.The fatigue life estimation under vibratory loads is generally studied in the frequency domain, which does not take into account the sequence or memory effect. Due to high nonlinearity of the fatigue damage evolution, it is difficult but useful to analyze the fatigue process under the vibration loading in the time-domain.In this paper a time-based method is proposed to analyze the fatigue crack growth behavior under variable amplitude loading caused by vibration.This approach is based on our proposed equivalent plastic zone concept and the generalized crack closure model,which is derived from plasticity in the vicinity of crack tip (such as monotonic and reverse plastic zone). The memory or loading interaction effect on the fatigue crack growth can be accounted for well by using the proposed method. A set of experimental data in Al 7075-T6 under “Christmas Tree” loading, a typical vibration loads condition, are used to validate the method. And then additional experimental data in Al 2024-T3 under block loading are also employed for model validation. The predictions have a very good agreement with the testing data, which are also compared withthose of NASGRO equation. Finally, some conclusions are given based on current investigation.