Fatigue Damage Models And Life Prediction Of Long-Fiber-Reinforced Ceramic Matrix Composites

Fiber reinforced ceramic matrix composites possess high strength and modulus at elevated temperatures. They are becoming the most potential materials for the application on the hot structures of aero engines. To make sure the reliable use of ceramic composites on the aero engine componets, it is necessary to perform the investigation on the tensile and fatigue behavior of ceramic composites. In this paper, the uniaxial tensile behavior, fatigue hysteresis behavior, interface parameter estimation, and life prediction of ceramic matrix composites were investigated.The micromechanical approach to predict the uniaxial tensile stress-strain curve of ceramic composites has been developed. The shear-lag model was used to describe the micro stress field of the damaged composites. The damage models were used to determine the evolution of the micro damage parameters. The tensile stress-strain curves were predicted by combining the shear-lag model with damage models. The uniaxial tensile stress-strain curves of unidirectional, cross-ply, 2D and 2.5D woven ceramic matrix composites were predicted. The results agreed well with the experimental data.The new micromechanical fatigue hysteresis loops models of ceramic composites were proposed. The unloading interface reverse slip length and reloading new slip length were determined by the fracture mechanics approach based on the damage mechanisms of fiber sliding relative to matrix during fatigue loading. The hysteresis loops corresponding to different interface sliding cases were investigated. The hysteresis loops of unidirectional, cross-ply, 2D and 2.5D woven ceramic composites were predicted. The results agreed well with experimental datas.An approach to estimate the interface shear stress of ceramic composites has been proposed. The relationship between the hysteresis loss energy and interface shear stress was derived. By comparing the experimental hysteresis loss energy with computational values, the interface shear stress of unidirectional, cross-ply, 2D and 2.5D woven ceramic composites at aibiemt and elevated temperatures corresponding to different cycles can then be obtained.An approach to predict the fatigue life of ceramic composites based on the interface wear mechanisms has been proposed. By combining the fiber statistical failure model with interface shear stress degradation model and fiber strength degradation model, the fiber failure process during fatigue loading was determined. The S-N curve of unidirectional, cross-ply, 2D and 2.5D woven ceramic matrix composites were predicted. The results agreed well with experimental datas.The uniaxial tensile experiments, loading/unloading tensile experiments and tensile-tensile fatigue experiments of unidirectional and [0/90/0/90/0/90/0/90/0]-C/SiC ceramic composites at ambient and 800°C in air have been performed. The mechanical behavior and damage mechanisms under tensile and fatigue loading were determined. The uniaxial tensile stress-strain curves, fatigue hysteresis loops, interface shear stress during fatigue loading and S-N curves of C/SiC ceramic composites at ambient and elevated temperatures were predicted.