Investigating the influence of various three-point bending specimen configurations on rock fracture parameters testing: an experimental study

Abstract

The fracture parameters of rocks, including fracture toughness and fracture energy, represent their resistance to crack propagation under external stress. These parameters play a critical role in engineering design, construction safety, geological mechanics research, and rock material assessment. This study determined the fracture parameters of granite under Mode I loading conditions using notched semicircular bend (NSCB) and single-edge notched beam (SENB) specimens. Although there was little difference between the initial and unstable fracture toughness values of the two specimen configurations, significant differences were observed in the fracture process and other fracture parameters. For example, the NSCB specimen exhibits a higher elastic modulus, and it witnessed rapid failure after reaching the peak load, whereas the SENB specimen displayed a more gradual failure process with a distinct post-peak stage. This may be one of the reasons for the higher fracture energy in the NSCB specimen than in the SENB specimen. Based on finite element analysis and the extraction of the tangential stress at the crack tip region, the application of the maximum tangential stress fracture criterion provided a robust explanation for the coherence observed in the unstable fracture toughness test results between the two specimen configurations.