在碳化硅基复合材料中碳纤维的就位强度

在对用断裂镜面法(fracture mirror method)评估纤维就位强度(in-situ strength)的方法进行了评述之后,对此方法进行了修正,即采用纤维束试验确定镜面常数, 将标距长度定义为两倍纤维拔出长度与两倍失效长度之和,采用分级平均统计分析方法确定纤维就位强度的Weibull参数和平均强度。采用修正的断裂镜面法,对聚合物先驱体转化法制备的M40JB纤维增强的碳化硅基复合材料中M40JB纤维的就位强度进行了分析,得到了M40JB纤维的Weibull参数和平均强度,并与未修正的断裂镜面法得到的结果进行了比较。 

IN-SITU STRENGTH OF CARBON FIBERS IN SILICON CARBIDE MATRIX COMPOSITES

The fracture mirror method was modified and applied to evaluation of the in situ strength of fibers in ceramic composites. The most significant modifications include (1) the mirror constant relies on the tensile test of fiber bundles instead of a single fiber test and (2) the gauge length parameter is redefined. Traditionally, the gauge length parameter was considered as mean fiber pull out length. In this study, by analyzing the mechanism of fiber pullout, the parameter was defined as the sum of double pullout length and double ineffective length of the broken fibers and the random parameter was then graded statistically. Based on this method, Weibull parameters and mean in situ strength of the M40JB fiber embedded in SiC matrix composites produced from polymer precursor were obtained. The experimental results show that the Weibull shape parameters of fabricated fibers and in situ ones are nearly identical, but the scale parameter of in situ fiber strength is much lower than that of the fabricated one. That means the flaws position distribution in both fibers does not vary obviously, however, the flaws are deeper in in situ fiber than in fabricated one and that leads the strength of the former fiber to decrease markedly.