Grain rotation-based analysis method for shear band

Abstract

The grain rotational field is significantly associated with the shear banding process and can be derived easily on the basis of individual grains, which could be an appropriate and convenient quantity in shear band analysis. In this paper, a novel method is proposed for directly analyzing the shear banding process in the granular assembly based on its grain rotational field. Numerical plain strain tests on a dense (S1) and an intermediate dense specimen (S2) are performed using the coupled discrete-element method (DEM) and finite-difference method (FDM). The grain rotational field is statistically characterized by the rotational distribution βv(ω), a new index defined as the volumetric percentage of grains rotating to a greater degree than the rotation ω, in which the high rotation (HR) section basically indicates the grains inside the shear band. A measurement of βv(ω)'s uniformity quantifies the degree of strain localization, and S2 is found to perform a more uniform rotational distribution than does S1. Taking the value of ω at which βv(ω)'s curvature is higher than a threshold as the boundary of the HR section, HR grains are filtered out of the sample, based on which the inclination and thickness of the shear band, as well as two local quantities (average void ratio and coordination number) inside the shear band, are analyzed.