平纹编织C/SiC复合材料的失效判据

通过Arcan夹具拉伸实验,研究了平纹编织C/SiC复合材料的唯象强度特性,根据实验结果提出了一种椭圆形失效判据,可以反映拉压强度的差异,以及压缩和剪切同时作用时裂纹面闭合引起最大容许剪应力的回升.结果表明：椭圆形判据和实验结果在第一象限吻合良好,说明椭圆判据在第一象限内对平纹编织C/SiC是适用的.用线弹性有限元方法分析了Arcan拉伸实验中试样的应力状态和分布,并讨论了夹具刚度的影响.分析表明：试样缺口区域剪切应力分布均匀,大小接近平均剪应力;正应力在边缘有应力集中,中央应力约为平均正应力的77%.由于纤维增强陶瓷基复合材料存在微弱缺口敏感性,Arcan圆盘测出的强度略低于均匀拉伸结果.采用系数对测出的强度进行了修正.

PHENOMENAL FAILURE CRITERIA OF A PLAIN WOVEN C/SiC COMPOSITE

The strength of a plain-weave C/SiC composite was measured by the Arcan fixture tensile test. According to the test results, a quadratic equation was suggested to describe the failure criteria of the plain-woven C/SiC composite. The criteria take into account the inequality between tensile strength and compression strength, and shear stress recovery due to crack closure that is caused by the co-action of compression and shearing. The Arcan fixture test results agree well with the theory in the first quadrant. The stress states and stress distribution of butterfly specimen were analyzed according to the linear elastic finite element method. The effect of fixture stiffness was discussed. It was found that the shear stress is distributed uniformly at the average shear stress level, while there is the normal stress concentration in the notch root. The normal stress in the center is only 77% of the average value. Due to the weak notch sensitivity of ceramic matrix composites, the strength measured from the Arcan specimens is just a little lower than that from uniform-stress tensile tests. The results from Arcan tests were corrected with a factor.