Comparative study of semi-circular bending tests for modes I and II#br#
fracture characteristics of Xinzhouyao bituminous coal
ZHAO Yixin1，2，SUN Zhuang2，LIU Bin2
(1. Beijing Key Laboratory for Precise Mining of Intergrown Energy and Resources，China University of Mining and Technology(Beijing)，Beijing 100083，China；2. School of Energy and Mining Engineering，China University of Mining and Technology(Beijing)，Beijing 100083，China)
Abstract：In order to study the influence of the crack length and the bedding angle on the characteristics of modes I and II fracture of coal，the specimens with three kinds of crack lengths and five kinds of bedding angles were tested by using the semi-circular bending test method. The influence of the crack length and the bedding angle on the peak load，the fracture toughness and the crack propagation path of modes I and II fracture were analyzed. The acoustic emission signals were monitored and the microcrack damage evolution and macroscopic failure characteristics were obtained. The experimental results indicate that the peak load and the fracture toughness of model II fracture of bituminous coal are respectively greater than those of mode I fracture and KIIC/KIC equals to 1.02. With increasing the dimensionless crack length α，the peak loads of both modes I and II of coal decrease gradually while both KIC and KIIC increase first and then decrease. Both the peak load and the fracture toughness of model II decrease first and increase in a “check” pattern with rising the bedding angle. The crack propagation paths of modes I and II fracture of coal are respectively linear and nonlinear. Beddings have a great influence on the crack growth path of mode II fracture，and the crack propagates along the bedding plane as the bedding angle is 22.5°，45°or 90°. The fracture failure process of modes I and II fracture can be classified to be three stages as compaction，steady crack propagation and unsteady crack propagation. In general，modes I and II fracture present a mixed tensile-shear behavior dominated by tensile cracks. More specifically，the tensile microcracks develop first，then the tensile and shear composite microcracks expand extremely and finally failure occurs.
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2019, Vol. 38 
