Effects of loading cycles on fatigue residual strength for 2D needled C/SiC composites

In order to study the failure mechanism under low cycle fatigue loading of ceramic matrix composites, their fatigue behavior was investigated through tests and mesoscopre analysis. The effects of loading cycles on the residual strength after tension-tension fatigue were studied for 2D needled C/SiC composites at room temperature. The fracture morphology and microstructure of the materials were observed by optical microscope and scanning electron microscope. The results show that the 2D needled C/SiC composites present an outstanding fatigue resistance as the loading cycle is over 10⁶ cycles while loading at level of 85% ultimate tensile strength (UTS). With the increase of loading cycles, the residual strength first increases then declines. The fracture analysis shows that the length of pull-out fibers increases as loading cycle increase, which means that in the process of fatigue loading, the bonding strength of fiber/matrix interface declines, which can eliminate the stress nonuniformity in materials and enhance the bearing capacity of the composites, and result in the fatigue strengthening phenomenon of 2D needled C/SiC composites.