偏轴载荷下连续SiC纤维增强钛基复合材料的拉伸行为研究

Study on Tensile Behavior of Continuous SiC Fiber Reinforced Titanium Matrix Composites Under off-Axis Loading

连续SiC纤维增强钛基(SiCf/Ti)复合材料是未来高性能动力装置的关键材料之一。针对SiCf/Ti复合材料中纤维与试样轴向载荷常存在一定偏轴角度的问题,通过室温拉伸、有限元模拟和断口表征研究了偏轴角度对SiCf/TC17复合材料力学性能和失效机理的影响。根据SiCf/TC17复合材料力学性能、断口形貌和应力分布可以定义一个临界偏轴角度,其数值约为1°。结果表明,随偏轴角度的增加,复合材料试样的抗拉强度下降,且当偏轴角度超过临界值时,抗拉强度下降速率增加。复合材料的失效机制与偏轴角度相关,当偏轴角度小于临界值时,试样断口由数个平坦的断面组成,纤维拔出和界面开裂程度都较低,纤维断面基本垂直于轴线,为典型的正应力断裂形貌;当偏轴角度大于临界值时,断口的起伏程度增加,纤维拔出和界面开裂现象都更加明显,部分纤维开始出现剪切断裂,表明拉剪耦合在断裂中起到重要作用。因此,对于SiCf/TC17复合材料轴向试样而言,应将纤维与试样整体的偏轴角度控制在临界值内,以获得有效的性能测试数据。

Continuous SiC fiber-reinforced titanium-based(SiC_(f)/Ti)composites are one of the key materials for future high-performance power devices.To address the problem that the axial loading of fibers and specimens in SiC_(f)/Ti composites often exists at a certain off-axis angle,the influence of the off-axis angle on the mechanical properties and failure mechanism of SiC_(f)/TC17 composites was investigated using room temperature tensile,finite element simulation and fracture characterization.The results show that a critical off-axis angle can be defined based on the mechanical properties,fracture morphology and stress distribution of SiC_(f)/TC17 composites,and its value is about 1°.The tensile strength of the composite specimens decreased with the increase of the deflection angle,and the decreasing rate of tensile strength increased when the deflection angle exceeded the critical value.The failure mechanism of the composite material is related to the off-axis angle.When the off-axis angle is smaller than the critical value,the specimen fracture consists of several flat sections,the degree of fiber pullout and interfacial cracking is low,and the fiber section is basically perpendicular to the axis,which is a typical positive stress fracture;when the off-axis angle is larger than the critical value,the degree of undulation of the fracture increases,and the phenomena of fiber pullout and interfacial cracking become more obvious,and some of the fibers start to appear shear fracture,indicating that tension-shear coupling plays an important role in fracture.Therefore,for the axial specimens of SiC_(f)/TC17 composites,the off-axis angle between the fibers and the specimen as a whole should be controlled within the critical value in order to obtain effective performance test data.