International audienceThe aim of this work is to focus on the StokesDarcy coupled problem in order to simulate numerically, with the finite element method, composite manufacturing processes based on liquid resin infusion. In this study, a macroscopic description is used. The computational domain can be divided into two non-miscible sub-domains: a purely fluid domain and a porous medium. In the purely fluid domain, the fluid flows according to the Stokes equations, while in the porous medium, the fluid flows into the preforms according to the Darcy equations. Specific conditions have to be considered on the fluid/porous medium interface. The corresponding weak formulation is obtained by summing up the variational forms of the Stokes and Darcy equations over the whole domain. It is solved by a mixed velocity/pressure finite element method. In the purely fluid domain, a first-order mixed P1+/ P1 finite element is used. However, in the porous medium, the LadysenskayaBrezziBabuska stability condition is not satisfied, and a P1/P1 finite element is preferred. It is stabilized with the Hughes Variational Multiscale formulation. The originality of our approach is two fold. First, one single unstructured mesh is considered for the whole domain. Second, the interface between the purely fluid domain and the porous medium is represented by a level-set function. The level-set framework is also used to capture the resin flow front. At the end of this paper, numerical simulations of such manufacturing processes by resin infusion/injection are presented

Under repeated impact loadings -shot peening process, surface mechanical attrition treatment, erosive wear -metallic surfaces undergo severe plastic deformation which leads sometimes to a local change of their microstructure. These mechanically attrited structures (MAS) exhibit very interesting physical properties: high hardness, better tribological properties, etc. Consequently it is of primary importance to understand the mechanism explaining how these MAS are created and grow under such loadings. In this article, this mechanism is investigated with the help of a coupled experimental and finite element approach. First, the MAS are generated on an AISI1045 steel with a micro-impact tester which allows to know the impact energy and the location of impacts with a very good accuracy. The evolution of the MAS shape as a function of the impact number is presented. Then, the finite element investigation is presented. It is shown that a macroscopic stabilized elastic regime is reached after one hundred impacts. It also appears that a close cycle of plastic strain is observed locally in the zone where material transformation should happen during this regime. The severe plastic deformation achieved after a given number of cycles may thus explain the material transformation. Based on these results, we propose a mechanism based on a plastic strain threshold to explain the growth of the MAS. The resulting MAS size and shape appear to be in very good agreement with the experimental results. Finally, we conclude on the influence of the mechanical parameters that are involved in the proposed mechanism.

International audienceWithin the framework of the sintering process simulation, this paper proposes a numerical strategy for the direct simulation of the matter transport by surface diffusion. A level-set method is used to describe the topological changes which arise at the free boundary of the sintering particles. The surface velocity is found to be proportional to the surface Laplacian of the curvature, that is, proportional to the fourth-order derivative of the level-set function. Consequently, both curvature and velocity must be computed carefully and with accuracy. Finally, three-dimensional simulations are shown and investigated

Cet article expose un modèle numérique permettant de simuler par éléments finis les procédés par infusion de résine au travers de renforts fibreux. Ce modèle nécessite le couplage entre un écoulement dans un milieu poreux (Darcy), non poreux (Stokes) et la déformation élastique de préformes. Une méthode level-set permet de décrire les interfaces fixes ou mobiles de couplage. Mots clés -Stokes -Darcy, matériaux composites, level-set.