Formulation of Constant Life Diagram for Fatigue Life Prediction of Glass-Carbon/Epoxy Composites

A constant life diagram (CLD) is the most common method for illustrating the relationship between stress ratios, mean stress and alternating stress. In this study, three CLD models are used to illustrate how mean stress and material anisotropy interact for several stress ratios, R = 0.5, 2, 0.1, − 0.5, − 2, and 10 to affect the fatigue life of non-hybrid [NH] 4 and hybrid [H] 4 composites. When modeling fatigue life data using each of these models, the linear piecewise model is found to be the most accurate for predicting the fatigue behavior of [NH] 4 and [H] 4 composites for all stress ratios. Using a linear piecewise model, constant life curves were able to connect all data points for each stress ratio. The S – N curves drawn for each stress ratio reveals that the linear model underestimates the fatigue life of non-hybrid and hybrid composites, resulting in a conservative design. Kawai's model, on the other hand, exaggerates the fatigue life of [NH] 4 and [H] 4 composites, implying an overestimation of fatigue life. As a result, designers can use a linear piecewise model to accurately predict the fatigue strength of fiber-reinforced composites for various stress ratios.