Constitutive modelling of granular soils and interfaces considering their internal state

Abstract

International audienceBy means of the contact dynamics method together with a particle fracture model, in which the particles are cohesive aggregates of irreducible polygonal fragments, we investigate the evolution of particle size distribution in the process of uniaxial compaction of granular materials. The case of single particle breakup under compressive stress is used to test the method and the influence of discretization (number of irreducible fragments). We show that the breaking threshold of the granular assembly scales with the internal cohesion of the particles but it depends also on the initial size distribution and irregularity of polygonal particle shapes. The evolution of size distribution proceeds by consecutive periods of intense particle crushing, characterized by local shattering instability, and periods of little breaking activity. Starting with either monodisperse or power-law distribution of particle sizes, the latter evolves towards a broad distribution of the fragmented particles with a nearly power-law distribution in the range of intermediate particle sizes. Interestingly, a finite number of large particles survive despite ongoing crushing process due to the more homogeneous distribution of forces in the presence of small fragmented particles filling the pores between larger particles

Discrete-element simulations of comminution in rotating drums: Effects of grinding media

“…But, as the internal stresses of the particles are correctly (up to discretization effect) calculated, they yield physically correct estimates of the evolution of size distributions if the debonding criterion is consistent with the classical framework of fracture mechanics, as discussed in [29]. For example, the effects of particle fracture on dilatancy and evolution of the distributions of particle sizes and shapes under shearing, the shattering effect, the slow reduction of the sizes of the largest particles as a result of cushioning effect (redistribution of stresses by smaller fragments) and the power-law distribution of intermediate fragments sizes are observed in the DEM-BCM simulations [30].…”

“…For this reason, we used pentagonal shapes, which have a low number of sides and behave nearly like hexagonal particles. Lower number of sides (squares or triangles) are too specific and lead to pathological local structures [30]. The choice of pentagonal particle shapes is not a crucial parameter for milling since, as a result of particle breakage at the beginning of milling, a variety of different particle shapes are soon generated and therefore the evolution of grinding is mainly governed by a mixture of different particle shapes.The use of polydisperse pentagons prevents also from the creation of local crystallized structures often found in mono-disperse packings of hexagons and squares [37,38,39].…”

Three-dimensional bonded-cell model for grain fragmentation

“…In general, values of λ 0 produce less elongated shapes and tacts). 2D simulations are now capable of reproducing the evolution of cracks and complex geometries of fragments [39,40].…”

Grain breakage under uniaxial compression, through 3D DEM modelling

“…Cheng et al 2003 [7] applied cohesive bonds between small spheres to form spherical grains, removing 20% of the subgrains to induce defects inside the grain and reduce its strength. Nguyen et al 2015 [8] used a two-dimensional Voronoï tessellation to divide a circular grain into smaller polygonal particles and joined them together using cohesive bonds. Cantor et al [9] 2016 used a three-dimensional Voronoï tessellation to divide a spherical grain into polyhedral particles joined together by a cohesive Tresca law.…”