极端环境下连续碳纤维增韧的陶瓷基复合材料的力学行为

连续纤维增韧的碳化硅复合材料(以下简称C/SiC),作为超高速飞行器热结构使用时,有可能在高温环境下受到高速撞击的作用,因此,掌握其在极端环境(高温、高应变率)下的力学性能是进行结构安全设计的基础。本文采用具有高温实验能力的分离式Hopkinson杆,在293~1273K温度范围内进行了动态压缩力学性能测试,研究了环境温度和加载速率对材料力学性能的影响。结果表明:C/SiC复合材料的高温压缩力学性能主要受应力氧化损伤和残余应力的共同影响。实验温度低于873K时,应力氧化损伤的影响很小,而由于增强纤维和基体界面残余应力的释放使界面结合强度增大,复合材料的压缩强度随温度的升高而增大;当实验温度高于873K时,应力氧化损伤加剧,其对压缩强度的削弱超过残余应力释放对强度的贡献,材料的压缩强度随温度的升高逐渐降低。由于应力氧化损伤受应变率的影响很大,当温度由873K升高至1273K时,高应变率下压缩强度降低的程度要比应变率为0.0001/s时低得多。

Compressive Behaviors of Continuous Carbon Fiber Reinforced Silicon Carbide Composites at High Temperature and High Strain Rate

Continuous fiber reinforced silicon carbide composite (C/SiC) used in ultra-high-speed aircraft structure may be subjected to high-speed impact in high temperature invironment. So, grasp of its mechanical properties under extreme conditions (high temperature, high strain rate) is the basis for safety design of structure. Dynamic compression properties of this composite were measured in temperature range 293-1273K, based on split Hopkinson pressure bar with high temperature capability. The influence of environmental temperature and loading rate on material mechanical properties was studied. Results show that the compressive behavior of 2D C/SiC composite is mainly determined by the combined action of oxidative damage and residual stress. When temperature is below 873K, compressive strength increases with rising temperature due to the release of residual stress existed at interface between fiber and matrix; the oxidative damage has little influence. In contrast, when temperature is higher than 873K, compressive strength decreases with temperature rising due to the exacerbation of oxidative damage; its weakening effect on compressive strength exceeds the contribution of residual stress release. Moreover, since oxidative damage is greatly affected by strain rate, the degradation of compressive strength at strain rate of 10^-4/s and temperatures above 873K is much more obvious than that at higher strain rates.