石墨化度对炭/炭复合材料力学性能的影响

通过三点弯曲试验，并借助SEM断口形貌分析，研究了石墨化度对炭/炭复合材料抗弯强度的影响，对其断裂机制进行了探讨．试验所用材料的基体为沥青浸渍炭+少量CVD炭，增强体炭纤维由乱短纤维和成束长纤维织成的炭布构成，长纤维沿X-Y平面分层铺开，长纤维层之间是随机分布的乱短纤维层．研究结果表明当石墨化度不同时，复合材料的断裂机制不同；在所研究的石墨化度范围28.4%～77.3%内，随着石墨化度的提高，材料的抗弯强度呈现加速下降的趋势；当石墨化度为77.3%时，材料的抗弯强度仅为石墨化度为28.4%时的60%．在石墨化度较低(如27.4%和56.8%)时，材料中的长纤维呈现以拔出机制为主，裂纹沿长纤维束层与乱短纤维层之间的界面传播；在石墨化度较高(如70.6%和77.3%)时，材料中的长纤维被横向切断，裂纹切过长纤维向前传播．这对炭/炭复合材料的研究、开发具有指导意义．

Effect of graphitization degree on the mechanical properties of C/C composites

s: The effects of graphitization degree on the mechanical properties of C/C composite have been studied by three points loading mode bending test, and the fracture mechanism has been investigated. There are two kinds of carbon fiber in the composite, i.e. , bunched long carbon fiber layers and random orientated short carbon fiber layers. The experiments demonstrate that the bending strengths increase acceleratively with the increase of graphitization degree of the C/C composite when the graphitization degree falls in the range of 27.4% to 77.3%. It is concluded that the fracture mechanism varies with the graphitization degree. The long carbon fiber is pulled out from the matrixes and the cracks spread forth along the interfaces between the bunched long carbon fiber layers and the random orientated short carbon fiber layers when the graphitization degree is low, which implies that the long carbon fiber layers mainly reinforce the composite. The cracks cut across the long carbon fiber layers and spread forth when the graphitization degree is high in the composite, which implies that the long carbon fiber layers reinforce the composite little.