Implementation of a Discrete Element Method for the space-time modeling of loading in the case of a soft shock: qualitative approach

The aim of this study is to modelize the space-time loading induced on a target by a deformable impactor, in the case of a ”soft” shock.The originality of this work resides in the use of discrete elements to model the behaviour of the impactor, where large displacements an ddeformations can occur .A qualitative analysis is then developed to describe the changes in load applied to the target, as a function of the parameters relevant to such a shock.AN

Modèle par éléments discrets pour l’étude du comportement dynamique d’un matériau élastique.

Le comportement mécanique des matériaux est généralement simulé par des approches issues de la mécanique des milieux continus. Cependant, lorsqu’il s’agit de simuler des phénomènes de multi fissurations voir de multi fracturations, les modèles de la mécanique discrète s’avèrent mieux adaptés, car ils prennent en compte naturellement les discontinuités générées par les interfaces. La difficulté est alors de s’assurer qu’une approche par éléments discrets (DEM) permet bien de retrouver le comportement mécanique au sens de la mécanique des milieux continus. Cet article propose une méthodologie permettant, à partir des données connues du matériau à simuler (module de Young, coefficient de Poisson, célérité de propagation des ondes), de quantifier les paramètres « microscopiques » du modèle DEM

Tensile response of the muscle-tendon complex using discrete element model

Tear of the muscle-tendon complex (MTC) is one of the main causes of sport injuries (De Labareyre et al. 2005). However, the mechanisms leading to such injury are still unclear (Uchiyama et al. 2011). Before modeling the tear of the MTC, its behavior in tensile test will be first studied. The MTC is a multi-scale, non isotropic and non continuous structure that is composed of numerous fascicles gathered together in a conjunctive sheath (epimysium). Many MTC models use the Finite Element Method (FEM) (Bosboom et al. 2001) to simulate MTC’s behavior as a hyperviscoelastic material. The Discrete Element Method (DEM) used for modeling composite materials (Iliescu et al. 2010) could be adapted to fibrous materials as the MTC. Compared to FEM, the DEM could allow to capture the complex behavior of a material with a simple discretization scheme in terms of concept and implementation as well as to understand the influence of fibers’ orientation on the MTC behavior. The aim of this study was to obtain the force/displacement relationship during a numerical tensile test of a pennate muscle model with DEM

A discrete element model to investigate sub-surface damage due to surface polishing

International audienceLarge high-power laser facilities such as megajoule laser (LMJ) or National Ignition Facility (NIF) are designed to focus about 2 MJ of energy at the wavelength of 351 nm, in the center of an experiment chamber. The final optic assembly of these systems, operating at 351 nm is made of large fused silica optics working in transmission. When submitted to laser at the wavelength of 351 nm, fused silica optics can exhibit damage, induced by the high amount of energy traversing the part. The created damage is a set of micro-chips that appear on the optic surface. Current researches have shown that this damage could be initiated on pre-existing sub-surface damages created during the optics manufacturing process. It is then very important to understand, for various set of manufacturing parameters, what are the key parameters for sub-surface damage. The presented work details the development of a simplified model to investigate the polishing process. Both silica (the material to be polished) and the abrasive particles are modeled using a discrete element approach. This numerical tool allows following the evolution of micro-cracks inside the material during the abrasion process. It is shown how the mechanical properties (pressure), the abrasive properties (shape and quantity of abrasive particles) and the system properties (filtration) have an influence on the sub-surface properties at the end of the process

Modeling of Magnetorheological Fluids by the Discrete Element Method

Magnetorheological (MR) fluids are fluids whose properties vary in response to an applied magnetic field. Such fluids are typically composed of microscopic iron particles ( 1 20 lm diameter, 20 40% by volume) suspended in a carrier fluid such as mineral oil or water. MR fluids are increasingly proposed for use in various mechanical system applications, many of which fall in the domain of tribology, such as smart dampers and clutches, prosthetic articulations, and controllable polishing fluids. The goal of this study is to present an overview of the topic to the tribology audience, and to develop an MR fluid model from the microscopic point of view using the discrete element method (DEM), with a long range objective to better optimize and understand MR fluid behavior in such tribological applications. As in most DEM studies, inter-particle forces are determined by a force-displacement law and trajectories are calculated using Newton’s second law. In this study, particle magnetization and magnetic interactions between particles have been added to the discrete element code. The global behavior of the MR fluid can be analyzed by examining the time evolution of the ensemble of particles. Microscopically, the known behavior is observed: particles align themselves with the external magnetic field. Macroscopically, averaging over a number of particles and a significant time interval, effective viscosity increases significantly when an external magnetic field is applied. These preliminary results would appear to establish that the DEM is a promising method to study MR fluids at the microscopic and macroscopic scales as an aid to tribological design. [DOI: 10.1115/1.4006021

Simulation de la conduction de la chaleur dans un milieu continu par un modèle éléments discrets

Discrete Element Method (DEM) uses a set of discrete elements in order to describe the material under study. The reason is that originally it was conceived to describe granular materials. Thus is naturally adapted to simulate problems like, for example, dry contact, fracturation and mixing. Nevertheless, modelling of a continuous zone may be useful in some of those problems. In that case, the correct physical behaviour of the continuous zone must be ensured. This work, based on the article by W. L. Vargas [1], explains how to simulate heat conduction through a continuous material using a discrete model of the domain

Implementation of a Discrete Element Method for the space-time modeling of loading in the case of a soft shock: qualitative approach

The aim of this study is to modelize the space-time loading induced on a target by a deformable impactor, in the case of a ”soft” shock.The originality of this work resides in the use of discrete elements to model the behaviour of the impactor, where large displacements an ddeformations can occur .A qualitative analysis is then developed to describe the changes in load applied to the target, as a function of the parameters relevant to such a shock.AN

Méthode des éléments discrets : des problèmes multi-corps aux problèmes d’endommagement dynamique complexes.

La méthode des éléments discrets est présentée comme une alternative aux approches de type mécanique des milieux continus pour aborder certains aspects liés aux problèmes dynamiques, notamment la multi fracturation de matériaux fragiles. Des exemples liés à l’usinage des composites et au surfaçage du verre sont présentés. Une extension de la méthode pour étudier le comportement des mousses est ensuite proposée et imagée par des premiers résultats

Congrès français de mécanique (21; 2013; Bordeaux (Gironde))

The indentation response of glasses can be classified into three classes : normal, anomalous and intermediate depending on the deformation mechanism and the cracking response. Silica glass, as a typical anomalous glass, deforms primarily by densification and has a strong tendency to form cone cracks that can accompany median, radial and lateral cracks when indented with a Vickers tip. This is due to its propensity to deform elastically by resisting plastic flow. Several investigations of this anomalous behavior can be found in the literature. The present paper serves to corroborate these results numerically using the discrete element method. A new pressure-densification model involving the discrete element method (DEM) is developed that allows for a quantitative estimate of the densification under very high pressure. This model is then used to simulate the Vickers indentation response of silica glass under various indentation forces. The numerical results obtained compare favorably with past experimental results

A multi-scale coupling method to simulate the silica glass behavior under high pressures

The response of glasses subjected to high pressures can be classified into three classes : normal, anomalous and intermediate depending on the deformation mechanism and the cracking pattern. The silica glass which is the scope of this work is a typical anomalous glass. The numerical study of this behavior with continuum methods (e.g. FEM, CNEM) presents several difficulties and drawbacks. Because, this requires a very small scale analysis. The discrete methods (e.g. MD, DEM) represent a good choice to simulate this behavior. However, these methods are very time consuming (CPU-wise). In this work, a discrete-continuum coupling method is proposed to study the behavior of this brittle material subjected to high pressures. The coupling results, obtained in this work, compare favorably with past experimental results