Abstract: In order to study the damage and fracture process between particles meso-contact, the tensile damage variable and shear damage variable were introduced into parallel bond model to characterize the deformation, strength and energy evolution characteristics of particle bonding contact based on the Particle Flow Code(PFC3D). According to the maximum stress criterion, the bond damage initiation criterion was determined, and the contact model was redeveloped by C++ language. The results of tensile, shear, bending and torsion tests of single contact were compared with the theoretical results, and the accuracy of the parallel bond contact model considering damage was verified. A three-dimensional meso discrete element model was established to simulate the uniaxial compression test of sandstone and triaxial compression test of granite, showing the applicability and accuracy of the model. Based on this study, the results show that the damage evolution coefficient has a noticeable effect on the elastic range, peak stress and softening rate of the whole stress-strain curve; the evolution process of bond damage, crack germination, propagation and coalescence in different stages of the stress-strain curve was comparatively studied; the evolution law of elastic strain energy and dissipative energy was further studied, and dissipated energy was introduced. It was explained that the larger the damage evolution coefficient is, the faster the decreasing of stress-strain curve is after reaching the peak stress.

Key words: particle discrete element method, linear parallel bond model, micro-damages, cracks evolution, damage energy consumption