闭合裂纹断裂的有效剪应力准则

将闭合裂纹表面的有效剪应力引入裂尖应力强度因子的计算，获得了无限大板和有限宽板含中心闭合裂纹在不同裂纹长度、倾角以及摩擦系数下裂纹尖端的应力强度因子值。引入等径向剪应力线 这一概念，建立了闭合裂纹断裂的有效剪应力准则：（1）岩板内闭合裂纹将沿着等 线上双剪应力的和最小的方向扩展；（2）裂纹尖端的应力强度因子KⅡ达到材料的临界值KⅡC，裂纹将开始扩展。该准则成功预测了闭合裂纹的临界起裂角 ，与各种经典复合型断裂准则计算Ⅱ型裂纹起裂角比较，结果较为接近。将其应用于闭合裂纹的断裂判定是安全的。

Effective shear stress criterion for closed-crack fracture

The surface’ effective shear stress of closed-crack is introduced into calculating the stress intensity factor (SIF). The value of SIF is calculated when cracks are in different lengths, different angles and different friction coefficients. Introducing isoline, the effective shear stress criterion is developed as follows: (1) the crack grows up along the direction in which the sum of twin shear stress reached minimum on isoline; (2) the crack begins to grow when the crack tip stress intensity factor KII arrived at critical value KIIC. Accordingly, the proposed criterion successfully predicts critical cracking angle of closed-crack. Compared with other criteria in predicting initiation angles , it shows that the effective shear stress criterion is accurate and secure in predicting closed-crack’ fracture.