A strategy for fatigue life estimation under variable amplitude loading in consideration of load sequence based on damage mechanics

Most mechanical and structural components are typically subjected to variable amplitude loading during their entire life. For practical purpose, it is computationally advantageous to approximate the load sequence by blocks of cycles with constant amplitude and stress ratio. But the indispensable influence on life evaluation of the correlation characteristics between individual load processes can be ignored in many cases. The paper first reviews the historical achievements on the equivalence disposal and life-prediction models applied for variable amplitude loading. Based on the idea of Gaussian copula type model, the fatigue life process can be discretized into blocks. The dependence character is described with correlation length. Then an ameliorated model based on Corten-Dolan accumulated damage rule is introduced to draw to the equivalent stress range. Using the disposed stress sequence, a life estimation algorithm based on damage mechanics is presented, during which the coupling between damage field and stress field is considered to deduce the damage evolution equation. Finally, the strategy discussed above is applied examplarily to a practical case.