Extending application of asymmetric semi-circular bend specimen to investigate mixed mode I/II fracture behavior of granite

The asymmetric semi-circular bend (ASCB) specimen has been proposed to investigate the cracking behavior in different geo and construction materials and attracted the attention of researchers due to its advantages. However, there are few studies on the fracture toughness determination of rock materials. In this work, a series of fracture tests were performed with the ASCB specimens made of granite. The onset of fracture, crack initiation angle and crack propagating trajectory was analyzed in detail combined with several mixed mode fracture criteria. The influence of the crack length on the mode I/II fracture toughness was studied. A comparison between the fracture toughness ratios predicted by varying criteria and experimental results was conducted. The relationship between experimentally determined crack initiation angles and curves of the generalized maximum tangential stress (GMTS) criterion was obtained. The fracture process of the specimen was recorded with the high-speed camera. The shortcomings of the ASCB specimens for the fracture toughness determination of rock materials were discussed. The results may provide a reference for analysis of mixed mode I and II fracture behavior of brittle materials.

Automated summary

The present study investigates the fracture toughness determination of rock materials using the asymmetric semi-circular bend (ASCB) specimens. A series of fracture tests were conducted on granite ASCB specimens, analyzing the fracture initiation, crack initiation angle, and crack propagating trajectory through various criteria. The influence of crack length on mode I/II fracture toughness was studied, and the comparison between experimental results and predicted fracture toughness ratios was conducted. The relationship between experimentally determined crack initiation angles and curves of the generalized maximum tangential stress (GMTS) criterion was obtained. The fracture process was recorded using a high-speed camera, and the shortcomings of ASCB specimens for fracture toughness determination of rock materials were discussed. The results provide a reference for analyzing mixed mode I and II fracture behavior of brittle materials.