Formation of shear bands in crushable and irregularly shaped granular materials and the associated microstructural evolution

摘要

The Voronoi-based particle generation algorithm and the cohesive crack model have been implemented in the combined finite-discrete method (FDEM), which make it an ideal tool for modeling irregularly shaped, crushable granular materials. Of particular interest in this work is the role of particle crushability in the shear band formation and the associated microstructural evolution of granular materials. Numerical biaxial tests were carried out on an identical particle assembly but with varied particle crushability. The simulated stress-strain-dilation responses are qualitatively in good agreement with the experimental observations. The shear banding pattern is sensitive to the particle crushability, where shear bands are clearly visible in the low crushable assembly, whereas strain localizations are evident in the high crushable assembly, but they fail to form a connected shear zone. In depth micromechanical analyses of the particle-scale information inside and outside the shear bands are presented, including the accumulated particle rotation, void ratio distribution and particle breakage behavior. The particle temperature is defined based on the velocity fluctuations and then used to quantify the deformation structures during shearing. Vortex-like patterns are well recognized in the shear bands, particularly at the end of shearing of the low crushable assembly. Besides, there is a weak positive correlation between the particle rotation and the particle temperature and the relationship between them can be approximated by a power law. Finally, this work suggests that the weakening of friction mobilization outside the shear bands is likely responsible for the macroscopic strain softening. (C) 2016 Elsevier B.V. All rights reserved.