准三维针刺C_f/SiC复合材料室温层向动态压缩力学行为的实验研究

为了研究应变率对准三维针刺碳纤维增韧的碳化硅复合材料(Cf/SiC)层向压缩力学性能的影响,本文利用分离式Hopkinson压杆装置对三维针刺Cf/SiC复合材料进行了应变率为10-4至6.5×103s-1的单轴压缩力学性能测试。实验结果表明,由于材料缺陷,其动态压缩强度分布遵循Weibull分布。破坏时,材料并未表现出典型的脆性破坏,而是在应力达到压缩强度后经历了较大的伪塑性变形才最终破坏。这表明三维针刺Cf/SiC复合材料沿厚度方向针刺的碳纤维有助于提高材料的韧性。同时,材料的压缩强度随应变率的升高显著增大,并与对数应变率近似成线性关系。借助光学显微镜和扫描电镜对压缩断口的观察表明:材料的失效模式随着应变率变化而发生改变。在准静态下,材料主要表现为剪切和分层破坏,而在高应变率下,则主要表现为劈裂。

Experimental Investigation on Laminar Dynamic Compression Behavior of Quasi-3D Needle-Punched Cf/Sic Composite at Room Temperature

To evaluate the influence of strain rate on laminar dynamic compression characteristics of quasi-3D needle-punched C_f/SiC composite, uni-axial compressive experiments were carried out at the strain rate ranging from 10^-4 to 6.5×10³s^-1 at room temperature. Experimental results show that the dynamic compressive strength distribution obeys Weibull distribution due to the inevitable heterogeneous distribution of defects as gas-holes. Catastrophic brittle failure was not observed for the specimens tested at different strain rates. Instead, despite of the decrease of true stress with true strain after the stress reaches its compressive strength, the material still possesses a relatively high load-bearing capacity. It is also found that the compressive strength of the material increases obviously with the strain rate, and presents a linear relation with logarithm strain rate. Optical and scanning electron microscope (SEM) images of specimen's fracture surface indicate that the failure pattern of material varies with the strain rate applied. Under quasi-static loading, shear failure and delamination play important roles in the fracture process. However, split pattern is observed to feature the failure mode under high strain rate dynamic loading.