Examination of the KAWAI CLD Method for Fatigue Life Prediction of Composites

The Kawai Constant Life Diagram (CLD) method was examined for fatigue life prediction of composite materials. Static and fatigue tests were carried out for open-hole coupon specimens made of unidirectional carbon/epoxy tapes for examining the applicability of the KAWAI modified constant life model. The Goodman method was examined as well. The prediction of the Kawai model was slightly conservative for R-ratios ≥ −1 and un-conservative for R-ratio that equals 10. The Goodman CLD highly overestimated fatigue life for purely tension and tension-compression areas and underestimated fatigue life for R-ratios lower than R = −1. A modified Kawai model was suggested to overcome the un-conservatism of the Kawai model at the pure compression zone of the CLD.