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.