Modelling the wear evolution of a single alumina abrasive grain: Analyzing the influence of crystalline structure

The grinding process is continuously adapting to industrial requirements. New advanced materials have been developed, which have been ground. In this regard, new abrasive grains have emerged to respond to the demands of industry to reach the optimum combination of abrasive-workpiece material, which allows for both the minimization of wheel wear and increased tool life. To this end — and following previous experimental works — the present study models in 3D the wear behavior of Sol-Gel alumina abrasive grain using Discrete Element Methods. It is established that the alumina behaves as a ductile material upon contact due to the effect of high temperature and pressure. This model reproduces the third body generation in the contact, taking into account the tribochemical nature of the wear flat, which is the most harmful type of wear in the grinding process. The evolution of the wear during a complete contact is analyzed, revealing similarities in the wear of white fused alumina (WFA) and Sol-Gel (SG) alumina. However, the SG abrasive grain suffers less wear than the WFA under the same contact conditions. The proposed wear model can be applied to any abrasive-workpiece combination

A constitutive law for dense granular flows

A continuum description of granular flows would be of considerable help in predicting natural geophysical hazards or in designing industrial processes. However, the constitutive equations for dry granular flows, which govern how the material moves under shear, are still a matter of debate. One difficulty is that grains can behave like a solid (in a sand pile), a liquid (when poured from a silo) or a gas (when strongly agitated). For the two extreme regimes, constitutive equations have been proposed based on kinetic theory for collisional rapid flows, and soil mechanics for slow plastic flows. However, the intermediate dense regime, where the granular material flows like a liquid, still lacks a unified view and has motivated many studies over the past decade. The main characteristics of granular liquids are: a yield criterion (a critical shear stress below which flow is not possible) and a complex dependence on shear rate when flowing. In this sense, granular matter shares similarities with classical visco-plastic fluids such as Bingham fluids. Here we propose a new constitutive relation for dense granular flows, inspired by this analogy and recent numerical and experimental work. We then test our three-dimensional (3D) model through experiments on granular flows on a pile between rough sidewalls, in which a complex 3D flow pattern develops. We show that, without any fitting parameter, the model gives quantitative predictions for the flow shape and velocity profiles. Our results support the idea that a simple visco-plastic approach can quantitatively capture granular flow properties, and could serve as a basic tool for modelling more complex flows in geophysical or industrial applications.Comment: http://www.nature.com/nature/journal/v441/n7094/abs/nature04801.htm

Simulation of continuum heat conduction using DEM domains

Currently, almost all material manufacturing processes are simulated using methods based on continuum approaches such as the Finite Element Method (FEM). These methods, though widely studied, face di culties with multi- body, contact, high-strain and high-displacement problems, which are usu- ally found in manufacturing processes. In some cases, the Discrete Element Method (DEM) is used to overcome these problems, but it is not yet able to simulate some of the physics of a continuum material, such as 3D heat transfer. To carry out a realistic simulation of a process, its thermal eld must be properly predicted. This work describes a fast and e cient method to simulate heat conduction through a 3D continuum material using the Discrete Element Method. The material is modelled with spherical discrete elements of di erent sizes to obtain a compact and isotropic domain adequate for carrying out mechanical simulations to obtain straightforward thermal and mechanical coupling. Thermal simulations carried out with the proposed Discrete Element Method are compared to both the analytical and FEM results. This com- parison shows excellent agreement and validates the proposed method

Multiscale description of polymeric foam behavior : a new approach based on discrete element modeling

The mechanical behavior of polymeric foams depends on several parameters, such as temperature, material density, and strain rate. The studied foams are multiscale materials; agglomerated beads (bead scale is millimetric) are composed of microscopic closed cells (a few tens of microns). The response of the material to dynamic loading consists of three regions: an elastic phase, a plastic phase, and densification. The first part of this work has been the identification of the behavior of these multiscale foams in terms of density and strain rate. Some results are presented in this paper. From these first dynamic results, the second step has been the observation and the analysis of the physical phenomena initiated during the yield plateau. Buckling of the bead and cell wall and strong damage localization were studied with several devices and techniques such as high-speed camera, SEM, and microtomography. The final objective is the development of a model adapted to the multiscale structure of the foam. The first step of this numerical approach consists in the modeling of the microstructure. Due to the microscopic discrete aspect of the foam, a Discrete Element Model has been developed to study the relationship between microscopic properties and the macroscopic behavior of foam

Apport des éléments discrets pour la modélisation d’un choc "mou"

Dans le cadre d’essais de choc réalisés avec des impacteurs (( mous )) de type sac de billes, une modélisation utilisant des éléments discrets sphériques est adoptée afin de qualifier l’évolution du chargement appliquée sur la cible