多向轴编C/C复合材料微结构Micro-CT原位扫描与拉伸破坏机理

Microstructure characterization from X-ray micro-tomography and tensile failure mechanism of 4D in-plane carbon / carbon composites

采用高分辨X射线断层扫描（Micro—CT）技术，对多向轴编C／C复合材料内部微细观结构特征给予统计分析，研究了该材料在室温环境下的拉伸性能与破坏机理。结果表明，4D轴编C／C材料的各向增强纤维束截面形态较规整，走向较平直，未见相互挤压变形；在炭基体、纤维束与基体间的界面层内部随机分布着大量的孔洞、裂纹及脱层等微缺陷，其中界面层内孔洞平均孔径约为138μm，孔隙率高达25％～30％，显著影响界面剪切性能。材料轴向拉伸主要表现为2种失效形式，分别为纤维束棒拔脱和纤维束棒断裂，呈现为假塑性断裂，界面剪切强度、纤维柬拉伸强度是轴向拉伸性能的关键控制因素。径向拉伸以纤维束断裂为主要破坏形式，呈现脆性断裂特性，轴向拉伸非线性较径向显著，纤维束拉伸强度是径向拉伸性能的关键控制因素。

High-resolution X-ray tomography technology was adopted to analyze inner structural features of multi-directional braided carbon/carbon composites.The tensile property and failure mechanism of this material at room temperature were also studied. Results show that the fiber tows of 4-D C/C composites have improved morphology and tend towards straight. Moreover, it is difficult to find interactions which induce deformation.A large number of micro-defects, such as holes and cracks, are randomly distributed in the matrix and the interface region between the fibers and the matrix.The average pore size is 138 μm approximately,and porosity can reach 25% - 30% in interface region, which have a significant impact on shear property of interface. Fiber pull-off and fiber breakage are the main failure mechanisms,which present a pseudo-plastic behavior.Fiber bundle splitting is the main destructional forms of radial stretch, and it shows the characteristics of brittle fracture.It appears dramatic nonlinearity under axial tension.The tensile strength of fiber bundle and bonding strength between fiber and substrate are key factors in tensile strength.