Synergistic effects of hold time and cyclic loading on fatigue hysteresis loops of fiber-reinforced ceramic-matrix composites at elevated temperatures in oxidizing atmosphere

In this paper, the synergistic effects of the hold time and cyclic loading on the fatigue hysteresis loops of fiber-reinforced ceramic-matrix composites (CMCs) at elevated temperatures in air condition are investigated. Based on the analysis of relative frictional sliding between fibers and the matrix in the fiber/matrix interface oxidation and interface wear region, the interface debonded length, interface counter-slip length and interface new-slip length are determined using the fracture mechanics approach. The fatigue hysteresis loops models are developed considering the synergistic effects of hold time and cyclic loading. The relationships between the fatigue hysteresis loops models and internal multiple fatigue damage mechanisms are established. The effects of fiber volume fraction, matrix crack spacing, fatigue stress levels, hold time and oxidation temperature on the fatigue hysteresis loops shape, location and area, fatigue hysteresis modulus and the fiber/matrix interface slip lengths are investigated. The experimental fatigue hysteresis loops, fatigue hysteresis dissipated energy, fatigue hysteresis modulus and the fiber/matrix interface slip lengths of cross-ply SiC/MAS and 2D SiC/SiC composites under cyclic loading for different hold time at elevated temperatures in air condition are predicted.