10. Fatigue Life Analysis of Strain Loadings Using Effective Strain Damage Approach with the Consideration of Cycle Sequence Effects

This paper presents fatigue life determination of automobile coil spring subjected to variable amplitude loading by considering the loading sequence effect. Fatigue failure of automobile coil spring is common occurrence that is subjected to random loading due to road conditions. Load sequence effect was found to have more significant effects in the automobile coil spring strain signals with many high amplitude events. Strain time histories of coil spring were acquired via road tests on various road conditions. To determine the effect of load sequence on fatigue life, effective strain damage model was also applied in fatigue life assessment and compared with strain-life models. Results illustrated that the lowest fatigue life of between 1.19 and 2.93 × 10³ blocks was found in the industrial road signal. This owes to the high amplitude events contributing to high fatigue damage. The fatigue life of highway signals predicted using this significantly effective model is close to the predicted value using strain-life models. This is mainly because the load sequence effect was not dominant from the highway signal due to the absence of high amplitude events. Finally, the load sequence effect was found to have more significant effects in strain signals that had many high amplitude events.