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采用液相浸渍炭化技术,在压力为75MPa下制备出4D-C/C复合材料,并进行高温热处理。研究静态和动态加载条件下,材料沿厚度方向的弯曲性能及断裂行为。结果表明,循环次数达到10×105次、频率为10 Hz时,材料的临界弯曲疲劳极限是静态弯曲强度的80%。静态弯曲加载情况下,C/C复合材料失效机制取决于试样底层炭纤维的取向。循环疲劳载荷作用下,其失效机制包括基体开裂、纤维-基体界面弱化及纤维断裂。复合材料在循环加载过程中界面结合强度降低,并释放内应力,故增强了纤维拔出以及复合材料的假塑性,疲劳加载后其剩余弯曲强度增加10%左右,而模量降低。疲劳载荷引起材料基体缺陷和裂纹数量的增加及纤维断裂,削弱了长度方向上的热膨胀,使材料热膨胀系数降低。
The liquid immersion carbonization technology was used to prepare 4D-C / C composites under the pressure of 75MPa and heat treated at high temperature. The bending behavior and fracture behavior along the thickness of the material under static and dynamic loading conditions were studied. The results show that the critical bending fatigue limit of the material is 80% of the static bending strength when the number of cycles reaches 10 × 10 5 and the frequency is 10 Hz. Under static bending loading, the failure mechanism of C / C composites depends on the orientation of the underlying carbon fibers. Cyclic fatigue loading, the failure mechanism includes matrix cracking, fiber-matrix interface weakening and fiber fracture. The interfacial bonding strength decreases and the internal stress is released during the cyclic loading. Therefore, the fiber pull-out and the pseudoplasticity of the composite are enhanced. The residual flexural strength increases by about 10% and the modulus decreases after fatigue loading. Fatigue loads cause the increase of the matrix defects and crack number and fiber breakage, weakening the thermal expansion in the length direction and reducing the thermal expansion coefficient of the material.