Numerical simulation of the effect of grain fragmentation on the evolution of microstructure quantities

Abstract

In this paper the effect of grain fragmentation of a cohesionless granular material on the change of microstructure quantities is investigated using a micropolar continuum model. To this end the change of the grain size distribution is related in a simplified manner to a reduction of the mean grain diameter, which enters the constitutive equation as the internal length. The additional densification of the grain skeleton is modelled by a reduction of the incremental stiffness, which is related to the so-called solid hardness defined in the sense of a continuum description. The reduction of the mean grain diameter and the solid hardness caused by grain fragmentation is described by corresponding evolution equations, which depend on an increasing mean pressure and an increasing deviatoric stress. The focus of the numerical investigations is on the evolution of microstructure quantities like the void ratio, mean grain diameter and couple stresses under monotonic compression. It is shown that for an initially inhomogeneous distribution of the void ratio polar quantities like microrotations and couple stresses can develop even outside of shear bands. With increasing compression the polar quantities can increase, while the range of fluctuation of the void ratio decreases.

Investigations of granular specimen size effect in interface shear box test using a micro‐polar continuum description

“…Under suppressed dilatancy and high pressures, grain abrasion and crushing also have an important influence on the evolution of the overall shear resistance. 20,21 Thus, the shear resistance may also be influenced by strength, shape and size of the grains. 10 Contrary discussions can be found in the literature for larger normalized roughness values whether the maximum magnitude of mobilised friction angle is determined by the peak value of inter-granular friction angle 22,23 or by the critical friction angle of granular material.…”

Long-Term Behavior of Coarse-Grained Rockfill Material and Their Constitutive Modeling

“…It is an aim of the present paper to propose simple calibration procedures for the material parameters based on standard laboratory tests. As a measure of the state of weathering the so-called "solid hardness of the grain assembly" is a key parameter in the material model proposed [47][48][49][50][51][52]. Particular attention is paid on a refined modeling of the influence of the coupled behavior between the state of weathering, the stress state and the packing density of the rockfill material on the calibration of those material parameters relevant for collapse settlements, long-time creep and stress relaxation.…”