Static fatigue behavior and life of 2D-C/SiC composites under multistage cyclic axial tension

The multi-stage fatigue characteristics of ceramic matrix composites (CMCs) are of significant importance for the design and evaluation of reusable thermal structures. This study investigates the low-cycle static fatigue behavior, damage-evolution mechanism and lifetime of plain-woven C/SiC composites under axial multi-stage tensile loading conditions. Experimental results show that 2D-C/SiC materials exhibit remarkable anisotropic and nonlinear behaviors: the unloading modulus demonstrates a three-stage degradation trend of “fast-slow-fast” with the increase of cycle numbers, and meanwhile the residual strain accumulates progressively. Scanning Electron Microscope (SEM) analysis reveals that the fracture morphologies of specimens show matrix micro-cracks, interface debonding and fiber pull-out. Based on the shear-lag theory, this study also simulated the cyclic stress-strain behavior through a hysteresis constitutive model and proposed a shear-lag theory based residual strength model. The static fatigue life is predicted by calculating the interface slip stress and matrix crack spacing under different peak loading stresses. The predicted values by the fatigue life model and the strength model are in good agreement with the experimental results. This research supplements original data for 2D C/SiC composites in the field of axial static tensile fatigue properties under multi-stage loading mode and extends the life prediction methods.