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een neglected due to the strong density of thedomain and the higher influence of diffusion.3 APPLICATIONS3.1 SSD Study in abrasion process.zyPeriodical boundariesUpper wallDegradableFirst bodyImposed velocityAbrasive particlesLower wallxFig.2 Simulated domain3.1.a Simulated domainThe studied material is silica. According to fig. 2,the upper first body (Silica piece to be surfaced) isconstituted by spheres linked together by elasticsolid joints. This first body is linked to the upperwall. A normal load is applied to the upper wallwhich is free to move along axis z. The lower firstbody (tool) is simply defined as a lower rigid wallmade of adjacent spheres. A constant velocity alongx is applied to the lower wall. The abrasive particlesare plates composed by 4 adjacent spheres linked byan elastic non breakable solid link.The effect of abrasive size and abrasive quantitythrough the contact are studied. Abrasive size is thesame than silica particles (*1) or twice silicaparticles (*2). Table 1 summarizes the studied cases.Nb of Abra. plates abrasive sizeCase ‘DiscreteBig’ 6 *2Case ‘LayerOfLittle’ 39 *1Case ‘DiscreteLittle’ 19 *1Case ‘L.ayerOfbig’ 24 *2Table 1 :Abrasive layer definition.3.1.b ResultsCalculations are carried out till a certain amount ofsilica particle is removed from the silica volume, bythe effect of broken links. The fixed amount is 150particles. Broken links through the volume areplotted in terms of the distance from the surface.Curves fig. 3 show the results. The thickness isdivided by particle mean radius.Nb/unit of Volume10 010 -110 -210 -31 : DiscreteBig2 : DiscreteLittle3 : LayerOfLittle4 : LayerOfBig12 45 0 10 5 15 10 20 15 25 20 3025Dimensionless ThicknessFig.3 :Number of broken joint through the thicknessThe number of broken joints decreases exponentiallywith the depth. It greatly depends on abrasivegeometrical properties and quantity. A little numberof big abrasive particles creates more residual cracksin the material. These results are qualitatively inaccordance with experimental results [9]. This firstsimple study demonstrates how discrete elementsimulations have the ability to simulate theformation of a great number of cracks and the linkbetween sub surface damage and abrasive properties.33.2 FSW joint characterization50+100454035-10V low302520150 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1V high0% 50%100%Fig.4 : quality of mixture in an FSW joint.Simulating friction Stir welding requires thesimulation of material flow, material mixture, toolmaterialcontact and thermo mechanical coupling.D.E.M. could be in that case an interesting tool,because it has been widely used to simulate mixtureof true granular flow. A first simulation is carriedout with a tool that passes through two bodiesinitially in contact (two colours in fig.4). The bodiesare simulated by an assembly of cohesive sphericalparticles. The particles of the two bodies are able tomix thanks to the rotating tool that pass through theinterface. Fig.4 shows the result, in terms of mixturequality for two cases. For one simulation thetranslation velocity has the same order of magnitudethan the rotating velocity. For the other one thetranslation velocity is largely less than rotatingvelocity. It is found that the quality of mixture is