EMPIRICAL EQUATION FOR TREATING CUMULATIVE FATIGUE DAMAGE

Cumulative damage in fatigue has received a great deal of attention in recent years and many methods have been developed for predicting fatigue life. However, it does not yield predictions that are in all cases in agreement with the experimental results. In the following a simple equation was developed to interpet the cumulative damage occured by the stress levels and cycles ratio. The derivation is based on analogy and on intuition rather than on well-established natural laws due to the complicated process of cumulative damage and the many factors encountered in it.
Comparison of the results obtained from the proposed empirical equation with the most commonly known methods of linear damage ruleLDR, double linear damage rule DLDR and the experimental results, available in the literature for SAE 4130 steel and maraging 300 CVM steel, proved its true validity. The proposed equation give better life prediction than DLDR and LDR. On average its estimate for life prediction approximately 8% higher or lower than experimental while the DLDR provide estimates 12% high and LDR provide estimates 37% high. However more study is needed to obtain the good perspective of its merits.