Cyclic loading/unloading hysteresis behavior of fiber-reinforced ceramic–matrix composites at room and elevated temperatures

In this paper, the cyclic loading/unloading hysteresis behavior of unidirectional C/SiC composite at room and elevated temperatures has been investigated. An approach to predict the hysteresis loops has been developed using the Coulomb friction law to describe the fiber/matrix interface shear stress. The interface debonded length, unloading interface counter-slip length and reloading interface new-slip length were determined by fracture mechanics approach. Based on the slipping range between fibers and matrix in the interface debonded region, the hysteresis loops have been divided into four different cases. The relationship between the hysteresis loops, hysteresis loss energy, interface debonding and interface slipping has been established. The hysteresis loops of unidirectional C/SiC composite have been predicted corresponding to different peak stresses at room and elevated temperatures. With the increase of peak stress, the hysteresis loops at room temperature change from the interface slip Case 2, i.e., the interface partially debonding and fiber partially slipping relative to matrix, to the interface slip Case 3, i.e., the interface completely debonding and fiber partially slipping relative to matrix; however, at an elevated temperature of 800 °C in air atmosphere, the hysteresis loops change from the interface slip Case 2 to Case 4, i.e., the interface completely debonding and fiber completely slipping relative to matrix in the interface debonded region, due to interphase oxidation.