Abstract

The Discrete Element Method (DEM) has been used for modeling continua, like concrete or rocks. However, it requires a big calibration effort, even to capture just the linear elastic behavior of a continuum modelled via the classical force-displacement relationships at the contact interfaces between particles. In this work we propose a new way for computing the contact forces between discrete particles. The newly proposed forces take into account the surroundings of the contact, not just the contact itself. This brings in the missing terms that provide an accurate approximation to an elastic continuum, and avoids calibration of the DEM parameters for the purely linear elastic range.

Abstract

A review is given of advancing front techniques for filling space with arbitrary separated objects. Over the last decade, these techniques have reached a considerable degree of maturity and are being used to generate clouds of points for SPH and FPM simulations, as well as spheres, ellipsoids, objects defined by a collection of spheres or polyhedral objects for DEM simulations. Algorithmic as well as implementational aspects are discussed. Techniques to obtain maximum packing, such as closest object placement (during generation) and move/enlarge (after generation) are also considered. Several examples are included that demonstrate the capabilities developed.

Abstract

We present a numerical procedure for elastic and non linear analysis (including fracture situations) of solid materials and structures using the Discrete Element Method (DEM). It can be applied to strongly cohesive frictional materials such as concrete and rocks. The method consists on defining the non-local constitutive equations at the contact interfaces between discrete particles using the information provided by the stress tensor over the neighbour particles. The method can be used with different yield surfaces and in the paper it is applied to the analysis of fracture of concrete samples. Good comparison with experimental results is obtained.

Abstract

This work proposes a fully Lagrangian formulation for the numerical modeling of free-surface particle-laden flows. The fluid phase is solved using the particle finite element method (PFEM), while the solid particles embedded in the fluid are modeled with the discrete element method (DEM). The coupling between the implicit PFEM and the explicit DEM is performed through a sub-stepping staggered scheme. This work only considers suspended spherical particles that are assumed not to affect the fluid motion. Several tests are presented to validate the formulation. The PFEM–DEM results show very good agreement with analytical solutions, laboratory tests and numerical results from alternative numerical methods.

Abstract

Abstract

Powder flowability is a critical parameter for additive manufacturing techniques involving powders. In order to obtain thin and homogenous powder layers, a compromise between grain size and flowability has to be found. Unfortunately, when the grain size decreases, the cohesiveness increases and the flowability decreases. Too often, both the powder spreadability assessment and the optimization of printing parameters are costly empiric processes. In this paper, we describe an original method associating GranuDrum powder flow characterization instrument and DEM numerical simulations to asses the process-ability of powders and to optimize printing parameters like recoater speed, layer thickness or recoater geometry. The powder characterization allows to calibrate the simulation parameters and in particular to quantify the inter-grain cohesiveness. Then, the recoating process is simulated with the calibrated simulations to predict the behaviour of the powder inside the printer. In parallel, the results are validated by testing the powder in a printer equipped with an in-situ powder layer homogeneity tester based on image analysis.

Abstract

Abstract

Abstract

Particle breakage plays an important role in rockfill mechanical behaviour. Under compression or shear, the crushing of particles modifies the grain size distribution and indirectly, the material permeability, their frictional properties and the corresponding critical state. In order to study the breakage of individual particles, several approaches were adopted using discrete element method (DEM). Some considered sub-particles joined by bonding or cohesive forces, other replaced particles, which verified a predefined failure criterion, by an equivalent group of smaller particles. In this paper, using the discrete element method, a new methodology was developed. It consisted of modelling crushable rockfill particles using the clump logic, which was responsible for providing a statistical and spatial variability in the strength and shape of the particles. Particle movements and interactions were determined using DEM, allowing to determined the deformation of the rockfill material. Clumps have a major advantage of severely decreasing the number of contact equations to be solved in the model, resulting in less computer time. A comprehensive study of the brittle failure of single-particle crushing tests is presented. Preliminary tests on particle size evolution were also performed, assuming some simplifications. No attempt was made to simulate the real particle size distribution (PSD), due to the cost of simulating smaller particles. Single-particle crushing tests and oedometer tests were simulated using crushable particles, whose results were in agreement with experimental data.

Abstract