Synergistic effects of temperature, oxidation, and stress level on fatigue hysteresis behavior of cross-ply ceramic-matrix composites at room and elevated temperatures under cyclic loading

Abstract

In this paper, the synergistic effects of temperature, oxidation, and stress level on the fatigue hysteresis behavior of cross-ply SiC/CAS ceramic-matrix composites (CMCs) at room temperature and 700 and 850 °C in air atmosphere has been investigated. The relationships between the fatigue hysteresis loops, fatigue hysteresis-dissipated energy, fatigue hysteresis modulus, and the fiber/matrix interface shear stress have been established using the hysteresis loop models considering different matrix cracking modes. The fatigue damage evolution process of SiC/CAS composite under tension–tension fatigue loading has been analyzed using the hysteresis loops. By comparing the experimental fatigue hysteresis-dissipated energy with theoretical computational values, the interface shear stress of SiC/CAS composite were obtained for different cycle numbers and fatigue peak stress. It was found that at elevated temperature in air, the interface shear stress degradation rate is much more affected by the fatigue peak stress than that at room temperature due to interface oxidation. The comparisons of interface shear stress evolution between unidirectional SiC/MAS and SiC/CAS, 2D SiC/SiC, and cross-ply SiC/CAS composites have been analyzed.