A new approach of stiffness degradation modeling for carbon fiber-reinforced polymers under cyclic fully reversed bending

Carbon fiber-reinforced polymers are being used in advanced structural applications such as aerospace, automotive, and naval industries. Therefore, there is a rising need for predicting their fatigue life and improving their fatigue behavior. In this study, the fatigue behavior and changes in flexural modulus of bidirectional carbon fiber-reinforced polymers due to cyclic fully reversed bending are investigated. A unique fixture is designed and manufactured to perform fully reversed four-point bending fatigue tests on (0 °/90 °)15 carbon/polyester specimens with a stress ratio of R = −1 and frequency of 5 Hz. The expected downward trend in fatigue life with increasing maximum applied stress was observed in the S–N curves of samples. Based on the decay in the flexural modulus of the specimens, a modified exponential model is proposed to predict the life of carbon fiber-reinforced polymers under fully reversed bending. The empirical constants in the model are calculated based on the results of experiments. The model is applied to predict the fatigue life of the samples that did not fail during the tests and cycle-to-failure of the specimens are found.