Numerical Simulation of Fracture Behavior in Granite Using the Tension-Softening Model

Applicability of the tension-softening model to characterize the fracture behavior of rock is examined. Tension-softening-curve measurements were made on three kinds of granite by employing Li’s proposed J-integral-based technique, where the specimen-size effect on measured tension- softening curves was examined by testing CT specimens of several sizes (1.5 inch ~ 6 inchCT). The J -based measuring method is shown to be able to determine the size-independent tension-softening curve by use of laboratory-sized fracture-toughness specimens, providing that the specimen satisfies a minimum size requirement. A series of analyses of fracture-toughness tests on the granites are performed using the tension-softening law determined above, where the boundary-element method is used to simulate the overall fracture behaviors and fracture process zone growth. It is demonstrated that the load-displacement curves simulated for various sized CT and three-point bend specimens compare well with the experimental results, indicating the usefulness of the tension-softening model. These calculations are also used to propose a minimum size requirement for determining a valid tension-softening curve.