An experimental and numerical study of sandstone fractures caused by modified and CCS cutters.

• The modified cutter can generate more connections between the surface and internal cracks and form even larger number of chips. • The modified cutter consumes nearly the same amount of energy as the CCS cutter. • The tensile stress concentrations are responsible for internal and surface crack propagation. Connections between surface and internal cracks are critical to rock fractures between kerfs. To promote rock fracture, a modified cutter containing wedge-shaped cutting teeth was invented. Then, comparison linear cutting tests were performed using a CCS and a modified cutter. The results indicate that the modified cutter can promote surface crack incisions (most frequently initiating from the contact points between cutting teeth and rock) and generate an increased number of chips. The modified cutter consumes nearly the same energy as the CCS cutter. Thus, the cutting efficiency of the modified cutter is higher. To further investigate the underlying mechanism, the dynamic stress evolution between kerfs (using PFC 3D) is studied. The numerical results agree well with laboratory tests in rock fractures and indicate that tensile stress concentrations are responsible for the initiation of internal and surface cracks. In addition, theoretical analysis using elastic–plastic fracture mechanics properly explains the formation of the regularly distributed surface cracks caused by the modified cutter. [ABSTRACT FROM AUTHOR]