A nonlinear constant life model for the fatigue life prediction of composite structures

The constant life diagram (CLD) can predict stress-life curves for various stress ratios under variable amplitude loading by using limited fatigue experimental data. The predictive accuracy of the constant life formulation is very important because fatigue analysis results are significantly affected by the accuracy of the estimated S-N curve. In this study, a nonlinear constant life formulation is developed to estimate more accurate S-N curves for previously developed CLDs. Four CLDs are presented and their predictive accuracies are compared with the proposed model on composite materials fatigue data. The accuracy is compared between actual fatigue data and the predicted S-N curve for the arbitrary load condition, for which no experimental data exists. Finally, the results reveal that the proposed model can predict the most accurate S-N curves with simple calculation processes compared to the results of previous constant life models.