弯曲疲劳后4D-C/C复合材料的抗弯强度及热膨胀性能(英文)

Flexural strength and thermal expansion of 4D carbon/carbon composites after flexural fatigue loading

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。

A four directional carbon/carbon （4D C/C） composite was fabricated by first using liquid phase impregnation carboni-zation （ LPIC） , followed by hot isostatic pressure impregnation and carbonization （ HIPIC） at 75 MPa, and finally high temperature treatment. The flexural properties and fracture behavior of the composite were investigated in the through-thickness direction under static and fatigue loading. The critical fatigue limit of the composite was 80% of the static flexural strength for one million loading cycles at 10 Hz. The failure mechanism of the composite under static flexural loading was dependent on the orientation of the carbon fibers in the tested specimen. Cyclic fatigue loading decreased the interfacial bonding strength and released the inherent stresses in the composite, which increased fiber pull-out, enhanced pseudo-ductility and increased the residual static flexural strength at the ex-pense of a decrease in the flexural modulus. The fatigue loading increased the number of noncritical matrix cracks, increased interfacial debonding, and caused the fracture of filaments in the surviving fatigued C/C composite. These features of the fatigued composite internally accommodated expansion in long direction as the temperature was increased, which resulted in a decrease in its residual thermal expansion.