Investigation of the Micromechanical Damage Process in a Granitic Rock Using an Inelastic Bonded Block Model (BBM)

This study numerically investigates the damage process in a granite using an inelastic multiminerallic block model in two-dimensional Universal Distinct Element Code. In addition to the commonly considered calibration targets like uniaxial and triaxial strengths, tensile strength, and Young's modulus, attention was paid to reproduce additional attributes such as postpeak response, residual strengths, and confinement-dependent dilatancy to minimize the nonuniqueness potential of the models. The fracture pattern transitioned from axial cracking to shear banding as the specimen confinement was increased from 0 to 60 MPa. Most notably, the model could exhibit the cohesion-weakening-frictional-strengthening behavior that is typically associated with brittle rocks. The progressive damage mechanism in the unconfined bonded block model (BBM) was subsequently studied using the 2-D digital image correlation (2-D-DIC) approach. To date, the application of the 2-D-DIC approach has been restricted only to real material testing; this study, therefore, is an attempt to extend its applicability to numerical models. It was found that 2-D-DIC is capable of imaging the simulated microcracking process very well and the results were similar to those observed from real testing on a different granitic rock. Lastly, the numerical-based DIC results were analyzed to clarify that even if the point of axial stress-axial strain nonlinearity does not coincide with the point of volumetric strain reversal in unconfined BBMs, the axial stress-axial strain nonlinearity approach should always be used for determining the crack damage threshold in BBMs.