采用单纤维十字架结构试样测试分析了SiC纤维增强TC17复合材料横向力学性能,利用SEM对拉伸断口及横切面进行了显微观察,分析了界面失效位置,并结合有限元数值模拟计算,研究了界面损伤失效机制及裂纹扩展规律。结果表明,在横向载荷的作用下,单纤维试样应力-应变曲线的非线性拐点应力为(271±12) MPa,该点是界面完全失效的起始点。基于双线性内聚力模型的有限元分析结果与实验结果一致,表明复合材料界面失效模式为剪切失效,裂纹萌生于反应层和碳涂层的界面。有限元分析预测的裂纹萌生位置在与加载方向成40°~50°的圆周之间,实验中不同最大载荷下裂纹出现在与拉伸方向成24°~68°之间不同位置,预测宽度略小于实验结果,这种差异的主要原因是有限元模拟中界面设定为理想刚性界面且沿周向一致,而实际碳涂层和反应层的界面是非光滑的,沿圆周存在微缺陷。裂纹萌生后,在剪切应力作用下沿轴向和周向同时扩展,在沿周向扩展过程中,0°附近界面在径向拉伸应力作用下先于90°附近界面失效,随后90°附近界面在周向剪切应力作用下失效。界面完全失效后,应力重新分配,随载荷增加,界面张开程度加大,基体局部出现屈服,直至材料完全断裂。

Transverse mechanical properties of titanium matrix composites (TMCs) play an important role during its engineering service. Although SiC_f / TC17 composite is one of the most promising TMC candidates for aeroengine, as we know its transverse properties have not been reported yet until now. In this work, the transverse strength of single SiC fiber reinforced TC17 composite was evaluated using cruciform specimen. The surface and cross-section of fractured specimen were investigated by SEM to determine the failure position during tensile test. Finite element simulation method was also used to analyze the mechanism of interfacial failure and crack propagation. During the transverse tensile test of single fiber specimen, the initial non-linearity in the stress-strain curve occurred at the stress of (271±12) MPa, which indicated the beginning of fiber-matrix interface failure. SEM observation showed that the crack in the center of sample appeared at the interface of reaction layer and carbon coating with a 24°~68° angle to the applied loading direction and its length extended with the increase of the applied stress. The finite element simulation results based on bilinear cohesive element model showed that transverse fracture of composite interface was shear failure mode, which agreed well with the test results. Before the occurrence of non-linearity in the stress-strain curve, the crack initiated at the circular interface between reaction layer and carbon coating with a 40°~50° angle to the applied loading direction. Crack initiation locations in test samples were different with those in simulation samples, because the actual composite interface was rough and some micro-flaws formed in the interface, whereas it was assumed to be an ideal rigid interface for simulation. Then the crack propagated along both circumferential and axial directions because of the shear stress. With the crack growing, the interface close to 0°angle to the applied loading direction failed first caused by the radial tensile stress, whereas the interface near 90° failed later as a result of circumferential shear stress. After complete failure of the interface, stress redistribution occurred around the SiC fiber and the interface separation increased with the increasing of the applied load, which gave rise to the yielding and deforming of the matrix near fiber until the final fracture of the composite.