Experimental study on the fracture characteristics of sandstone under asymmetric load by using a semi-circular bending specimen

The asymmetric semi-circular bending (ASCB) specimens have garnered attention from researchers due to their straightforward fabrication process and convenient experimental loading, and have been extensively employed for investigating the fracture behavior of building materials. The mixed mode I-II fracture mechanical behavior of sandstone under asymmetric loading was studied by using ASCB specimens. Meanwhile, the effects of dimensionless notch length alpha on fracture toughness, crack propagation path, and crack initiation angle were investigated. The differences between the theoretically predicted and experimental values of fracture toughness ratios, as well as the crack initiation angles, were also analyzed combined with several fracture criteria. The results indicate that the effective fracture toughness Keff first increase and then decrease with increasing dimensionless notch length. When mode II fracture toughness component is dominant, the effect of notch length on fracture toughness is more significant. Furthermore, the effective fracture toughness Keff has a maximum value when the dimensionless notch length is between 0.30 and 0.33. Moreover, the generalized maximum tangential strain (GMTSN) criterion provides better predictive results, especially under pure mode II loading when compared to the generalized maximum tangential stress (GMTS) criterion. This research results have valuable reference for the rational selection of ASCB specimens for fracture experiments and for obtaining reliable experimental results.