Stochastic fatigue life prediction in C/SiC composites at elevated temperature by micromechanics-based damage model

In this paper, a micromechanical approach is developed to predict the fatigue life and fracture process in different C/SiC composites subjected to different stochastic fatigue loading spectrums at elevated temperatures. Three types of stochastic fatigue load spectrums are considered in the fatigue life prediction at elevated temperature, that is, constant, increasing, and decreasing stochastic stress with cycles. Stress distribution between intact and broken fibers and the broken fibers fraction under stochastic fatigue loading spectrum are determined using the Global Load Sharing criterion considering multiple fatigue damage mechanisms at elevated temperatures. A new damage parameter of fatigue life degradation rate is developed to characterize the effect of stochastic loading on fatigue damage and fracture in C/SiC composites. Relationships between stochastic fatigue loading spectrum, broken fibers fraction, fatigue life, and fatigue life degradation rate in different C/SiC composite are established. Effects of stochastic fatigue loading spectrum type, stress level, and testing temperature on fatigue life degradation rate are discussed. The fatigue life degradation rate is very sensitive to the fiber preform, loading sequence, and testing temperature.