Fatigue hysteresis behavior of unidirectional C/SiC ceramic-matrix composite at room and elevated temperatures

In this paper, the tensile fatigue hysteresis behavior of unidirectional C/SiC composite at room and elevated temperatures in air atmosphere has been investigated. The fatigue hysteresis modulus and fatigue hysteresis loss energy corresponding to different number of applied cycles have been analyzed. Based on the damage mechanism of fiber slipping relative to matrix in the interface debonded region, the fatigue hysteresis loops models based upon the Coulomb friction law instead of a constant fiber/matrix interface shear stress usually assumed in the hysteresis analysis, have been developed. The relationships between the fatigue hysteresis loss energy, fatigue hysteresis loops, interface frictional slip and interface frictional coefficient have been established. When the fiber/matrix interface frictional coefficient degrades, the fatigue hysteresis loss energy first increases to the maximum value, and then decreases to zero; the fatigue hysteresis loops correspond to different interface frictional slip cases. By comparing the experimental fatigue hysteresis loss energy with theoretical computational values, the fiber/matrix interface frictional coefficient corresponding to different number of applied cycles, has been obtained. The variations of fatigue hysteresis modulus, fatigue hysteresis loss energy and interface frictional coefficient as a function of cycle number, have been analyzed for different fatigue peak stresses and test conditions. The fatigue hysteresis loops predicted using the hysteresis loops models and estimated fiber/matrix interface frictional coefficient agreed with experimental results.