La préparation endodontique par instrument unique (étude comparative in vitro de la mise en forme canalaire Revo-S® / One Shape®)

LYON1-BU Santé Odontologie (693882213) / SudocSudocFranceF

Experimental investigation of impinging jet erosion on model cohesive granular materials

Erosion of soils affects both natural landscapes and engineering constructions as embankment dams or levees. Improving the safety of such earthen structures requires in particular finding out more about the elementary mechanisms involved in soil erosion. Towards this end, an experimental work was undertaken in three steps. First, several model materials were developed, made of grains (mostly glass beads) with solid bridges at particle contacts whose mechanical yield strength can be continuously varied. Furthermore, for most of them, we succeeded in obtaining a translucent system for the purpose of direct visualization. Second, these materials were tested against surface erosion by an impinging jet to determine a critical shear stress and a kinetic coefficient [2, 3]. Note that an adapted device based on optical techniques (combination of Refractive Index Matching and Planar Laser Induced Fluorescence [3]) was used specifically for the transparent media. Third, some specifically developed mechanical tests, and particularly traction tests, were implemented to estimate the mechanical strength of the solid bridges both at micro-scale (single contact) and at macro-scale (sample) and to investigate a supposed relationship with soil resistance to erosion

Experimental investigation of impinging jet erosion on model cohesive granular materials

Erosion of soils affects both natural landscapes and engineering constructions as embankment dams or levees. Improving the safety of such earthen structures requires in particular finding out more about the elementary mechanisms involved in soil erosion. Towards this end, an experimental work was undertaken in three steps. First, several model materials were developed, made of grains (mostly glass beads) with solid bridges at particle contacts whose mechanical yield strength can be continuously varied. Furthermore, for most of them, we succeeded in obtaining a translucent system for the purpose of direct visualization. Second, these materials were tested against surface erosion by an impinging jet to determine a critical shear stress and a kinetic coefficient [2, 3]. Note that an adapted device based on optical techniques (combination of Refractive Index Matching and Planar Laser Induced Fluorescence [3]) was used specifically for the transparent media. Third, some specifically developed mechanical tests, and particularly traction tests, were implemented to estimate the mechanical strength of the solid bridges both at micro-scale (single contact) and at macro-scale (sample) and to investigate a supposed relationship with soil resistance to erosion

Numerical and experimental modeling of cemented soils

International audienc

High resistivity SOI substrates: how high should we go?

For planar RF structures made on oxidized High Resistivity (HR) Si substrates, it is fundamental to keep the resistivity near the SiO/sub 2 //HR Si interface as high as possible. This paper presents a quantitative analysis of the influence of interface states at the SiO /sub 2//Si contact on the substrate resistivity. The starting materials for this study are raw HR substrates before or after SOI bonding process. These HR Si wafers were fabricated with either a Low (LIO) or a High Interstitial Oxygen (HIO) concentration.Anglai

Erosive phenomena at the mesoscale – Perspectives and challenges using coupled LBM-DEM models

International audienceThe physical phenomena related to the erosion of granular materials by a fluid flow are ubiquitous and often present major challenges and threats to a wide range of civil engineering constructions and infrastructures. Catastrophic earth-dam failures and large sinkholes are just some of the possible outcomes of the different forms of erosion (a.o. surface erosion, suffusion, piping, backwards erosion, etc...) [1]. However, little is known about the actual mechanical origins of erosion, while theassessment of erodibility is generally performed by means of experimental tests and empirical correlations (see e.g. [2]). Here we provide a general overview of some current research models aiming to clarify the micromechanical phenomena and their macromechanical consequences taking place in different erosion scenarios [3, 4]. The employed numerical techniques rely on the coupling of two well-stablished particle methods for the fluid and solid phases, namely the Lattice Boltzmann Method (LBM) and the Discrete Element Method (DEM) respectively. Further ingredients of our numerical models include an elastoplastic cohesion model for intergranular solid bridges [5] and a subcritical debonding model for the simulation of transient damage processes within the soil matrix [6]

Physics of soil erosion at the microscale

We focus here on the major and always topical issue of soil erosion by fluid flows, and more specifically on the determination of both a critical threshold for erosion occurrence and a kinetics that specifies the rate of eroded matter entrainment. A synthetic state-of-the-art is first proposed with a critical view on the most commonly used methods and erosion models. It is then discussed an alternative strategy, promoting the use of model materials that allow systematic parametric investigations with the purpose of first identifying more precisely the local mechanisms responsible for soil particle erosion and second ultimately quantifying both critical onsets and kinetics, possibly through existing or novel empirical erosion laws. Finally, we present and discuss several examples following this methodology, implemented either by means of experiments or numerical simulations, and coupling erosion tests in several particular hydrodynamical configurations with wisely selected mechanical tests

Micromechanical analysis of the surface erosion of a cohesive soil by means of a coupled LBM-DEM model

The elementary mechanisms driving the ubiquitous surface erosion of cohesive geomaterials can be analysed from a micromechanical perspective combining well-known numerical techniques. Here, a coupled model combining the Discrete Element and Lattice Boltzmann methods (DEM-LBM) provides an insight into the solid-fluid interaction during the transient erosion caused by a vertical fluid jet impinging on the surface of a granular assembly. The brittle cementation providing cohesion between the solid grains is described here by means of a simple bond model with a single-parameter yield surface. The initial topology of the surface erosion tends to mimic the profile of fluid velocity directly above the soil surface. We find that both the rate of erosion and the magnitude of eroded mass depend directly on the micromechanical strength of the single solid bonds