On the need to evaluate the probabilistic of fatigue life assessment of random strain loading considering load sequence effects

This study presents a probabilistic method of fatigue life assessment for random strain signals that consider the effect of load cycle sequences. The Effective-Strain-Damage (ESD) model was utilised to calculate the fatigue life of coil spring. The probabilistic approach was used to evaluate the reliability properties of the fatigue life data, indicating that the ESD model estimated lower fatigue life than conventional strain-life models as the load sequence effect encouraged rapid crack propagation. Furthermore, a lower mean-cycle-to-failure (McTF) of 4.53 x 104 blocks to failure was estimated from the ESD-based fatigue life, as it was 7.5-8.1% lower than the McTFs computed from the fatigue life predicted by other models. The results indicated that the coil springs had lower fatigue reliability when the load cycle sequence was included. The McTF can be used as a representation of the reasonable service cycle of the coil spring since the uncertainties of the random loading were considered. Finally, this approach suggested a more appropriate assessment of the life cycle of coil springs subjected to random loading conditions with many uncertainties.