Abstract. The stress intensity factors (SIFs) for a infinite volume were corrected by two dimensionless quantities Y I and Y II which were obtained by employing the Boundary Collocation Method (BCM). The expression of the elastic-plastic boundary of a mixed crack for a cracked specimen was formulated based on the Mises yield criterion. Finally, the shape and scale of the plastic zone for tensile-shear cracks and compressive-shear cracks were analyzed and some meaningful conclusions were obtained. The results show that: the shape of a cracked specimen has an significant effect on the plastic zone; the scale of the plastic zone is much smaller than its real scale under the assumption of infinity volume; the orientation angle of a crack affects both the shape and scale of the crack tip plastic zone significantly under tension; the friction between the crack surfaces can reduce the scope of the crack tip plastic zone effectively under compression. IntroductionCurrently, more and more underground engineering projects have been implemented. The investigation on the failure mechanism of deep rock masses has become a hot issue. Under high temperature and pressure condition, the plastic deformation around a crack tip is significant, and this plastic deformation determines crack initiation, propagation and instability [1]. Thus, it is necessary to study the characteristics of the plastic zone under small scale yield condition. Dugdale [2] proposed a D-M model to calculate the size of plastic zone. Jendoubi [3](1991) and Ranganathan [4] (1994) suggested that the shape and size of the plastic zone can be determined by Mises yield criterion. Zhao[5] proposed the effective stress expression and obtained the initial elastic-plastic boundary function around a crack tip. Li [6] introduced the first and second estimations of plastic zone scale in detail. However, the rock specimen used in experimental study was finite, and it is unreasonable to analyze and evaluate the shape and scale of the plastic zone according to the fracture theory based on the assumption of an infinite volume.

No abstract