Skin tribology: Science friction?

The application of tribological knowledge is not just restricted to optimizing mechanical and chemical engineering problems. In fact, effective solutions to friction and wear related questions can be found in our everyday life. An important part is related to skin tribology, as the human skin is frequently one of the interacting surfaces in relative motion. People seem to solve these problems related to skin friction based upon a trial-and-error strategy and based upon on our sense for touch. The question of course rises whether or not a trained tribologist would make different choices based upon a science based strategy? In other words: Is skin friction part of the larger knowledge base that has been generated during the last decades by tribology research groups and which could be referred to as Science Friction? This paper discusses the specific nature of tribological systems that include the human skin and argues that the living nature of skin limits the use of conventional methods. Skin tribology requires in vivo, subject and anatomical location specific test methods. Current predictive friction models can only partially be applied to predict in vivo skin friction. The reason for this is found in limited understanding of the contact mechanics at the asperity level of product-skin interactions. A recently developed model gives the building blocks for enhanced understanding of friction at the micro scale. Only largely simplified power law based equations are currently available as general engineering tools. Finally, the need for friction control is illustrated by elaborating on the role of skin friction on discomfort and comfort. Surface texturing and polymer brush coatings are promising directions as they provide way and means to tailor friction in sliding contacts without the need of major changes to the produc

Matériaux – Procédés – Simulation

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3D finite element simulation of TIG weld pool

MCWASP XIII - 17–22 June 2012, Schladming, AUtricheInternational audienceThe aim of this paper is to propose a three-dimensional weld pool model for themoving gas tungsten arc welding (GTAW) process, in order to understand the main factorsthat limit the weld quality and improve the productivity, especially with respect to the weldingspeed. Simulation is a very powerful tool to help in understanding the physical phenomena inthe weld process. A 3D finite element model of heat and fluid flow in weld pool consideringfree surface of the pool and traveling speed has been developed for the GTAW process. Cast3Msoftware is used to compute all the governing equations. The free surface of the weld poolis calculated by minimizing the total surface energy. The combined effects of surface tensiongradient, buoyancy force, arc pressure, arc drag force to drive the fluid flow is included inour model. The deformation of the weld pool surface and the welding speed affect fluid flow,heat flow and thus temperature gradients and molten pool dimensions. Welding trials study ispresented to compare our numerical results with macrograph of the molten pool

Contribution numérique pour l’optimisation d’un mode opératoire de soudage – Identification d’une source de chaleur équivalente

L’utilisation d’un chanfrein étroit pour le soudage de composants lourds tels que ceux utilisés dans l’industrie nucléaire et particulièrement par AREVA, requiert la maîtrise de plusieurs paramètres et plus spécifiquement du retrait. La prédiction par la simulation numérique peut alors s’avérer utile pour la définition de modes opératoires de soudage. Le principal objectif de cette étude est d’identifier par méthode inverse les paramètres d’un modèle thermique 3D pour une configuration de soudage MAG multipasse en chanfrein étroit profond sur un acier bas carbone. La simulation de la géométrie des zones fondues ainsi que du champ de température dans le métal solide passe par l’optimisation d’un problème multiobjectif. L’optimisation du modèle numérique se base sur des résultats expérimentaux obtenus grâce à une instrumentation fine réalisée sur une maquette de soudage. Le modèle de source de chaleur 3D retenu après optimisation est une combinaison de deux sources de chaleur volumiques. Ce modèle peut alors être utilisé comme chargement pour des analyses thermiques, thermo-métallurgiques ou thermomécaniques, notamment pour la prédiction des retraits

Contribution numérique pour l’optimisation d’un mode opératoire de soudage – Identification d’une source de chaleur équivalente

International audienc