Micro- and macro-mechanical behaviour of DEM crushable materials

Abstract

This paper provides a micro-mechanical commentary on the macroscopic behaviour observed in DEM simulations of the compression of individual crushable grains, and of triaxial tests on assemblies of both crushable and uncrushable grains. A fragmentation ratio is defined to describe the bond breakage processes, and the significance of other micro-mechanical parameters such as sliding contacts ratio, average coordination number, deviator fabric, and internal energies per unit volume is discussed. Three different modes of grain damage were observed: asperity breakage, internal shear cracking, and internal tensile cracking leading to fast fracture. Energy balances both for the compression of a single grain, and for triaxial tests on assemblies of grains, showed that the loss of elastic energy due to bond breakage was a negligible fraction of the significantly enhanced dissipation encountered with crushable materials. This extra dissipation was associated with frictional sliding triggered by the creation of new degrees of freedom among the breaking fragments. Different modes of grain breakage were found to be representative of different regions of soil states of stress defined with respect to the virgin compression line. The secondary role of elastic grain deformability, increasing coordination number but reducing dilatancy, has also been demonstrated.

Energy dissipation in soil samples during drained triaxial shearing

“…Cheng et al (2004) and Bolton et al (2008) quantify energy dissipation in their simulations of agglomerate crushing and use continuum Cam Clay models in their interpretation of the discrete data. Wang & Yan (2012) and Zhou et al (2013) also consider energy in their simulations of crushable agglomerates.…”

Micromechanics-Based Investigation of Fouled Ballast Using Large-Scale Triaxial Tests and Discrete Element Modeling

“…McDowell et al (2006) used the discrete element method to model largescale triaxial experiments of ballast aggregates reinforced with geogrids, and concluded that the DEM approach holds much promise as a tool for investigating granular aggregate assemblies. Bolton et al (2008) used the DEM to simulate triaxial compression shearing tests for both breakable and unbreakable agglomerate assemblies, capturing the influence of confining pressure on the stress-strain and volumetric response. Lu and McDowell (2008) studied the stress-strain response of ballast subjected to monotonic loading using the DEM.…”

Bonded-cell model for particle fracture

“…In contrast, the fragmentation of particles under controlled conditions is used in comminution processes such as the milling of vegetal products or grinding of mineral materials. The evolution of particle size distribution and energy dissipation in such processes depend on many factors such as particle properties (shape, crushability), initial size distribution, loading history, and mobility of the grains during the crushing process [1][2][3][4][5][6][7][8][9].…”

“…Such aggregates may represent real aggregates such as pellets and ceramic compacts or simply be regarded as a toy model for particle fracture. This bonded particle model (BPM) has been employed to investigate the behavior of crushable soils, rocks, fault gouge, and other materials [7,22,[32][33][34][35][36][37][38][39][40][41]. An alternative method consists in replacing a circular or spherical particle at its fracture threshold by several smaller fragments of the same shape [42][43][44][45][46].…”