Influence of pre-fatigue on tensile properties of 3D-C/SiC composites

The tensile tests were conducted at room temperature with a three-dimensional-woven C-fiber-SiC-matrix composite (3D-C/SiC) under 106 sinusoidal tension to tension constant amplitude loading at frequency of 20 Hz and 0.1 stress ratio at 1 300 ℃under 120 MPa,80 MPa,respectively. The tensile fracture morphologies of 3D-C/SiC composite were observed with SEM, and the cracks distribution in the matrix was examined with optical microscope. The result shows that once the maximum fatigue stress is up to 120MPa (more than matrix cracking stress), proportional limit, ultimate tensile strength (UTS), and fracture strain increase by 110%, 17%, and 29%, while elastic modulus decrease 49% compared with vergin composite, respectively, and crack density in matrix and fiber (fiber-bundles) pull-out length of composites increase obviously, otherwise all tensile properties of 3D-C/SiC composites do not change.