A fracture model for assessing tensile mode crack growth resistance of rocks

Abstract

Evaluating the fracture resistance of rocks is essential for predicting and preventing catastrophic failure of cracked structures in rock engineering. This investigation developed a brittle fracture model to predict tensile mode (mode I) failure loads of cracked rocks. The basic principle of the model is to estimate the reference crack corresponding to the fracture process zone (FPZ) based on the maximum normal strain (MNSN) ahead of the crack tip, and then use the effective crack to calculate the fracture toughness. We emphasize that the non-singular stress/strain terms should be considered in the description of the MNSN. In this way, the FPZ, non-singular terms and the biaxial stress state at the crack tip are simultaneously considered. The principle of the model is explicit and easy to apply. To verify the proposed model, laboratory experiments were performed on a rock material using six groups of specimens. The model predicted the specimen geometry dependence of the measured fracture toughness well. Moreover, the potential of the model in analyzing the size effect of apparent fracture toughness was discussed and validated through experimental data reported in the literature. The model was demonstrated superior to some commonly used fracture models and is an excellent tool for the safety assessment of cracked rock structures.

Keywords

• Brittle fracture model
• Fracture toughness
• Maximum normal strain (MNSN)
• Fracture process zone (FPZ)
• Size effect