界面相多重开裂对纤维强度的影响

INFLUENCE OF MULTIPLE CRACKING IN INTERPHASE ON THE STRENGTH OF FIBERS

当纤维表面的界面相（如涂层）较脆时，纤维发生断裂之前界面相一般会发生多重开裂的损伤，这种损伤裂纹垂直于纤维轴向，故能导致纤维强度下降。本文以四相（纤维，界面相，基体，复合材料）圆柱体模型为基础，并假设界面脱粘后不再传递剪应力。首先用剪切滞后理论求得了界面相发生多重开裂后，纤维、界面相中的应力集中系数，以及界面上的剪应力，并同时考虑了纤维与界面相间界面部分脱粘的影响；然后，假设纤维强度统计特性用Ｗｅｉｂｕｌｌ分布函数表示，从而根据界面相多重开裂在纤维中引起的应力集中系数Ｋ＿ｆ得到广纤维破坏概率的变化。最后利用界面脱粘区的大小，定性研究了界面剪切强度τ＿０对纤维强度的影响，结果表明：存在一个最佳的界面剪切强度τ＿０，使界面相多重开裂对纤维强度的影响最小。

The damage of multiple cracking in the interphase may occur before the fiberbreaking,which causes the strength of the fiber to descrease seriously. In this article,withfour-phase concentric circular cylinder mode(that is,fiber,interphase,matrix and compositematerial),and assuming that the interface between the fiber and the interphase can’ttransfer shear stress after debonding,the stressconcentration of the fiber and the interphasecaused by the multiple cracking were calculated by using of shear-lag method, then withWeibull distribution function,the change of the cumulative probability of fiber failure wasdiscussed.Finally,the influence of the interface shear strength τ_0 on the fiber strength wasstudied.It is found that there is the optimum interface shear strength τ_0.