研究了SiC_f/TC17复合材料的室温、高温(773 K)拉伸性能及其断裂机制. 结果表明: SiC_f/TC17复合材料室温、高温应力-应变曲线受纤维线弹性变形和基体屈服程度影响呈现不同的形状; 室温断裂机制主要是反应层多次断裂、纤维一次断裂和基体脆性断裂等, 高温断裂机制主要是纤维多次断裂、基体韧性断裂和大范围的界面脱黏等; 纤维累计损伤理论适合于对SiC_f/TC17复合材料断裂强度的估测, 其中室温断裂强度符合临界断裂纤维数大于或等于3时的局部承担载荷模型, 高温断裂强度符合均匀承担载荷模型. 结合断裂机制和强度估算结果, 详细论述了SiC_f/TC17复合材料室温、高温拉伸断裂过程.

Tensile properties and fracture mechanisms of SiC_f/TC17 composites at room temperature and 773 K were studied. The results show that fiber elastic deformation and matrix yielding contributed to the shapes of the stress-strain curves of SiC_f/TC17 composites, which were the bilinear appearance at 298 K and the slight curvature at 773 K. Major fracture mechanism of SiC_f/TC17 composites at room temperature were as follows: multiple fractures of the interfacial reaction layer, single fiber fracture, matrix brittle fracture etc.. Typical fracture mechanism of SiC_f/TC17 composites at elevated temperature were as follows: multiple fiber fracture, matrix plastic fracture, interface debonding etc.. Fiber cumulating damage theory was proved to be suitable for estimation of the fracture strength of this composite. The calculations of local loading sharing model while taking three or more fibers failure into account and global loading sharing model were close to the experimental values of room temperature and elevated temperature respectively. In addition, according to fracture mechanisms and strength prediction, tensile fracture process of SiC_f/TC17 composites at room and elevated temperature were explained in detail. At room temperature, multiple fractures of the interfacial reaction layer started at first, and then the weak fiber fractured gradually and randomly. After critical fiber cluster has been formed by nearby broken fibers, the crack extended into the matrix from these fibers. With the increase of load, the fibers and the matrix at the tip of crack gradually destroyed. At the same time, the cracks from other critical fiber clusters were also expanding and connecting to each other. When the crack area has reached the critical level, the remaining fiber and matrix quickly fractured. However, at elevated temperature the matrix yielded firstly, and then multiple fracture randomly of the interfacial reaction layer and the weak fiber occurred sequentially. The crack from broken fiber deflected at interface between fiber and matrix, caused interface debonding. With the increasing of broken fiber number, the micro-cavities of matrix emerged gradually in the stress concentration area. When the total crack area accumulated by the broken fibers and micro-cavities of matrix has reached the critical level, the remaining fiber and matrix quickly fractured.