纤维段裂试验的界面端应力奇异性研究

纤维段裂试验是测定纤维复合材料界面剪切强度的细观实验方法之一，其试验结果与其他三种细观试验方法(纤维拔出、纤维压人和微珠脱粘)测得的结果各不相符，相差较大。针对该问题，仔细研究了纤维段裂试验过程，可发现如下两个问题，首先是试件中纤维断裂造成的界面端应力奇异性问题；其次是纤维断成临界长度时界面是否脱粘的问题。针对界面端应力奇异性问题，本文建立了界面端轴对称分析模型，运用渐近展开法，推导出求解界面端特征值的特征方程，并由此得到应力奇异性指数随Dundurs常数的变化规律；采用文献[5]所用试件的纤维／基体性能数据，计算出了界面端的应力奇异性指数，并与文献[7]得到的其他三种试验的界面端应力奇异性指数进行比较，发现纤维段裂试件也存在界面端应力奇异性，而且应力奇异性最强，也说明了与其他三种试验结果不具可比性。本文还对纤维断成临界长度时界面是否脱粘的问题，进行了讨论。

Analysis of Stress Singularity of Interface End in Fiber Fragmentation Test

Fiber fragmentation test is one of micro-mechanical test method of interfacial shear strength in fiber composites. Its test results exhibit large discrepancy with those of other three tests (fiber pull-out, micro-indentation and micro-debond tests). It's noticed while study the procedure of fragmentation test that, firstly, there exists stress singularity at interface end due to the fiber broken; secondly, if debond-ing occurs at the interface end as critical length achieved. An axisymmetric model is made to analysis the stress singularity. With the aid of asymptotic and variable separation, a characteristic equation, which could determine the eigenvalue at interface end, is obatained. The relation of stress singularity index and Dundurs parameters is presented by solving the characteristic equation. It's found as comparing the stress singularity indexes corresponding to the specimens of four tests used in Ref. [5] that the fragmentation test has the most serious stress singularity at the interface end. It means the results from the fragmentation test cannot be compared with those from other three methods. The problem, if the debonding occurs at the interface end as critical length achieved, is also discussed.