Statistical Miner’s Rule Based On Equivalent Statistical Moment Of Fatigue Damage

Traditional deterministic methods are unable to deal with the dispersion in the process of fatigue damage accumulation. It is necessary to introduce the concept of probability and statistics fatigue into fatigue life prediction. In order to obtain proper uncertain fatigue cumulative damage rule, this paper found out the real distribution of instantaneous fatigue cumulative damage and raised a simple probability cumulative damage theory by matching equivalent moments on the foundation of analyzing existing fatigue cumulative damage rules and evaluating experimental data.The paper reviewed the uncertainty in fatigue life prediction methods of structure. Besides, the existing fatigue damage accumulation rules was roughly classified and summarized in this paper. As the basis of conventional fatigue life prediction, the linear fatigue accumulative damage theories for metal materials were classified and reviewed systematically in aspects of theoretical basis, material constants, parameters introduced, etc. and major typical models were listed. Furthermore, several sets of variable loading tests of metal materials under two-level spectrum loading, multiple-level spectrum loading and random spectrum loading were carried out to verify the major typical models. The applicable scopes and application effects were compared and discussed according to theoretical basis and the accuracy. This paper considered the inner and external dispersion in the process of fatigue damage accumulation and modified the deterministic Miner rule by taking the dispersion into the three essential elements of fatigue damage accumulation theories into account. Finally, a convenient and practical statistical quantitative fatigue damage model was obtained. A comparison analysis about experimental results and predicted results by using the model proposed by this paper under two-levels loading of 45# steel and multi-level block spectrum loading of LC4 CS was presented. The results indicated that the proposed model can describe the distribution of instantaneous cumulative damage and predict fatigue life accurately.