三维编织SiC/SiC复合材料拉伸和弯曲损伤机制

为了研究三维编织SiC/SiC复合材料损伤机制，开展了室温条件下的单调拉伸和三点弯曲试验。实验前，利用CT扫描手段，明确了三维编织SiC/SiC复合材料试样的编织组织形态。对拉伸和三点弯曲试样的微观分析表明:原生孔洞和微裂纹导致了材料在单调拉伸过程中形成局部应力集中，随着拉伸载荷的增大，基体的横向开裂和纤维束间纵向层间裂纹逐渐演化形成纤维内部裂纹，导致材料最终的脆性断裂失效；在三点弯载荷作用下，表现为剪切、拉压共生的多耦合破坏模式，拉应力一侧首先发生失效，随后在中性面处发生剪切破坏，紧接着失效迅速向上下两侧扩展，直至截面在整个厚度方向发生失效；断口与纤维束的走向相关性很大，裂纹基本上沿着纤维束之间的界面进行扩展，导致最终失效未发生在理论失效位置处。 

Tensile and bending damage mechanism of 3D braided SiC/SiC composites

In order to study the failure mechanism of the 3D braided SiC/SiC composites, the uniaxial tension and three-point bending tests at room temperature were carried out. Before the experiment, the morphology of the braided structure of the 3D braided SiC/SiC specimen was clarified by means of scanning computed tomography (CT). Microscopic analysis of tensile and three-point bending specimens shows that during the tensile process, the local stress concentrations are developed in the material as a result of the primary pores and microcracks. As the tensile load increasing, the cracks in the transverse direction of the matrix as well as the longitudinal interlaminar cracks between the fiber bundles gradually develop into internal fiber cracks form, ultimately resulting in a brittle fracture of the material. Under the three-point bending load, a combination of shear and tension failure mode is found. The failure firstly happens in the bottom side of the specimen with tensile stress. Then, shear occurrs at the neutral surface. After that, the cracking develops towards both of the top and bottom sides, and finally the 3D braided SiC/SiC specimen fails totally. The fracture surface is strong correlative to the direction of the fiber bundle. The crack propagates substantially along the interface between the fiber bundles, which makes the real failure location different from the theoretical prediction position.