Effect of shear bond failure on the strength ratio in DEM modeling of quasi-brittle materials

Displacement softening has shown to be an effective ingredient to overcome common deficiencies associated with DEM modeling based on bonded spherical particles (Ma and Huang in Int J Rock Mech Min Sci 104:9-19, 2018b). By incorporating a softening path in the normal force-displacement contact law, we show that the softening contact model can not only yield a realistic compressive over tensile strength ratio as high as about 30, but also capture the highly nonlinear failure envelope at the confined extension stress range, typical for quasi-brittle materials such as rocks and concretes. In our previous model, bond breakage at the particle scale is governed by the normal bond strength only. Here, we generalize the model by removing the restriction on the shear bond failure. Formulation of the displacement-softening model is first introduced. Novel features from modeling the behaviors of Berea sandstone without considering shear bond failure are summarized. How material behaviors at both the micro- and macroscale are affected by the inclusion of shear bond failure is then analyzed. Finally, implications of the numerical results in the context of how to calibrate material properties for DEM modeling in general is discussed.