Model for predicting tension-tension fatigue life and residual strength of unidirectional carbon/carbon composites

Based on the random crack core theory and model for predicting the longitudinal tensile strengths of unidirectional composites, the Weibull model describing residual strength distribution of single fiber and the residual strength model of fiber-matrix interfaces were brought in for building the prediction model which can predict tension-tension fatigue life and residual strength of unidirectional composites. The residual strength test of the carbon fiber extracted from the fibers yarn after cyclic tensile fatigue loading was carried out. The two parameters Weibull model of the residual strength of carbon fiber was established. The fiber-matrix interface strength of unidirectional carbon/carbon(C/C) composites was tested. The unidirectional C/C composites analysis results show that the ratios of prediction logarithmic life to test logarithmic life are 0.79, 1.00 and 1.11 under 92.5%, 90.6% and 87.5% stress level, respectively, which indicates that the life prediction model is feasible for fatigue life prediction of unidirectional C/C composites. The error between the predicted value and the experimental value of residual strength is within 10%, which demonstrates that the prediction model of residual strength has high precision.