预疲劳对3D-C/SiC复合材料拉伸性能的影响

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

采用应力比为0.1,频率为20Hz的正弦波于1300℃条件下对3D-C/SiC复合材料进行200MPa和80MPa的疲劳实验,在循环106次后在室温对其进行拉伸实验,并通过SEM观察其断口形貌,用光学显微镜观察基体裂纹密度。结果表明,经过200MPa疲劳处理的3D-C/SiC试样的比例极限、抗拉强度和断裂应变值与预疲劳前原始试样相比,分别提高110%,17%和29%,弹性模量比原始试样下降49%,基体裂纹密度和纤维的拔出长度等均明显增加;当最大疲劳应力低于基体开裂应力时,预疲劳处理对3D-C/SiC的拉伸性能几乎没有影响。

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.