平纹编织陶瓷基复合材料面内剪切细观损伤行为研究

MESOSCOPIC DAMAGE BEHAVIORS OF PLAIN WOVEN CERAMIC COMPOSITE UNDER IN-PLANE SHEAR LOADING

采用约西佩斯库(Iosipescu)纯剪切试件,研究了平纹编织Si C/Si C和C/Si C复合材料的面内剪切应力-应变行为和细观损伤特性.通过试验获得了材料不同方向上的单调和迟滞应力-应变行为,对比分析了两种材料的剪切损伤特性,结果表明材料的剪切损伤演化规律受热残余应力水平影响严重.由试件断口电镜扫描结果发现剪切加载状态下桥连纤维承受显著的弯曲载荷和变形,据此提出了纤维弯曲承载机制,并结合裂纹闭合效应分阶段阐释了材料的剪切迟滞环形状.基于材料的剪切细观损伤机制,通过两个损伤变量表征了材料的剪切损伤演化进程,得到了材料的面内剪切细观损伤演化模型.对比发现2D-C/Si C复合材料45?方向基体裂纹的起裂应力明显小于2D-Si C/Si C复合材料,而两者0?/90?方向裂纹的起裂应力基本相同.

The in-plane shear mechanical behaviors and mesoscopic damage behaviors of plain woven Si C/Si C and C/Si C composites were investigated with Iosipescu specimens. The materials＇ monotonic and hysteresis stress-strain responses in the various directions were obtained by tests, and the shear damage properties of these two materials were analyzed comparatively. It is found that the shear damage evolutions of materials are affected by residual thermal stress significantly. SEM（scanning electron microscope） photos of fracture surfaces indicate that the bridging fibers withstand significant bending load and deflection. Therefore a fiber bending-bearing mechanism was proposed. And combined with the crack closure effect, the shape of hysteresis loops was elucidated well. By considering the characteristic of mesoscopic shear damage modes, two damage variables were defined to character the shear damage evolution of material. And the shear damage evolution models of these two materials were developed. The results show that the initiation stress for matrix cracks in the 45？direction of 2D-C/Si C composite is much lower than that of 2D-Si C/Si C composite, but the initiation stress values for matrix cracks in the 0？/90？direction are the same for these two materials.