Surface chemistry and reactivity of skin-passed hot dip galvanized coating

La publication originale est disponible sur le site http://www.revue-metallurgie.orgInternational audienceGI coatings are covered by a very thin aluminum layer that precipitates after wiping. Anisotropic growing of zinc crystals during solidification induces a strong basal texture in GI coatings. Skin-pass induced changes in GI coating surface chemistry, crystallography and reactivity have been assessed. Local coating analyses have been performed (XPS, TOF-SIMS) in order to describe local effects of roughness indentation during skin-pass on coating characteristics. A laboratory bi-crushing device supported by XRD and EBSD has been used to analyze the aluminum oxide behaviour during deformation and ageing. Reactivity of such surfaces has been tested using fatty acids

Tribochimie du laminage à froid : étude par ToF-SIMS de la chimisorption sur la tôle des additifs du lubrifiant : Tribologie de la mise en forme des métaux

International audienceLa chimisorption des additifs de lubrifiant de laminage à froid sur un acier et un alliage d'aluminium est étudiée par spectrométrie de masse ToF-SIMS. L'étude préparatoire de l'adsorption des divers additifs permet de mettre en évidence leur rôle individuel, les compétitions d'adsorption, les seuils thermiques de désorption ou de décomposition. Ces résultats sont validés par des essais sur laminoir pilote = The chemisorption of cold rolling oil additives on steel and aluminium surfaces is studied with a mass spectrometry technique, ToF-SIMS. Preliminary experiments underline adsorption competition, and thermal threshold for desorption or decomposition. This results fit well with experimental cold rolling results

Classification des chocolats selon leur empreinte globale fluorescente ?

La nature et la quantité des composés d'arôme présents dans le chocolat varient selon plusieurs critères, comme la variété des fèves de cacao, le processus de production du cacao marchand et le processus de fabrication du chocolat. Evaluées sensoriellement, ces qualités organoleptiques permettent de définir les profils sensoriels des chocolats et de les classer dans des pôles sensoriels caractéristiques. Ces évaluations sont essentielles mais demeurent encore trop longues et onéreuses. Une classification des chocolats à partir de leurs empreintes globales fluorescentes pourrait-elle être une solution alternative pour identifier les pôles sensoriels ? L'objectif de notre étude était de différencier 200 chocolats noirs répartis suivant 4 pôles sensoriels (A, B, C, D) à partir de leur " empreinte globale fluorescente " sans passer par une étape de dégustation associée. Pour ce faire, des analyses spectrales 3D ont été réalisées par Spectrométrie de Fluorescence Frontale sur des échantillons de chocolats fondus à 45°C. Les chocolats ont tous été préparés suivant le même processus de fabrication, évalués sensoriellement puis analysés dans les mêmes conditions opératoires (LO excitation : 250-650 nm_ pas de 5nm ; LO émission 290-800nm_ pas de 2nm). Afin de clarifier les données, un prétraitement des signaux et une gestion des zones non informatives (diffusion Rayleigh) ont été effectués. Par la suite, une analyse exploratoire multiway (PARAFAC) a été réalisée de manière à connaitre l'importance des longueurs d'ondes dans la répartition des classes. Une Analyse en Composante Principale (ACP) a également été réalisée sur l'ensemble des données spectrales afin de voir si une séparation des pôles était visible. Les analyses des empreintes globales fluorescentes ont ainsi permis d'en déduire une répartition fiable des chocolats suivant leur pole sensoriel sans passer par une étape de dégustation. (Résumé d'auteur

WTC2005-64372 ADSORPTION OF A FATTY ACID ONTO A DEFORMED ELECTROGALVANIZED STEEL SHEET

ABSTRACT During forming operation of electrogalvanized steel sheets, the crystallographic orientation of the zinc coating may evolve from a pyramidal texture to a basal one. As a consequence, the adsorption of lubricant additives onto the zinc surface may be altered. Plane-strain compression tests and XRD analysis are carried out to study the texture evolution. After deformation, the samples are cleaned and their reactivity versus fatty acids are measured by ToF-SIMS analysis. It is shown that fatty acids adsorb much more strongly on a pyramidal oriented zinc surface than on a basal one

An event-based simulation for optimizing one-way car-sharing systems

Car-sharing systems allow registered users to use cars spread throughout an urban area: vehicles are at their disposal anytime they need one against some amount of money per minute rental. The customer avoids some issues linked to the ownership of a car such as insurance fees, maintenance or parking. Such a system is beneficial for the society in terms of environmental, energetic impacts and congestion. It completes the urban transportation service by allying the efficiency of public transportation and the flexibility of owning a vehicle. Car-sharing systems can be classified in different families depending on the rental conditions. For instance, free-floating systems allow people to park the vehicles anywhere in city area whereas non-free floating impose to users to park them inside stations with limited number of allowed spots. In this last family, another differentiating feature is the "one-way/two-way" characteristic: two-way systems force the user to return the car to the location where it was picked-up whereas one-way systems allow drop-off at any station. We focus in this research mainly on non-free-floating one-way electric systems. The system operations naturally induce imbalances in the distribution of vehicles that need to be corrected by performing relocations. Our aim is to model and simulate those operations to first analyze the way the system evolves with time and then to test different management policies for operations and especially relocations in order to both maximize customers' satisfaction and make the operation of the system sustainable for the operator

Simulation and optimization of one-way car-sharing systems with variant relocation policies

Car-sharing is a transportation service consisting of vehicles distributed over an urban area that any driver registered to the system can use. This paper focuses on one-way electric car-sharing systems. The success of such systems relies strongly on operations management and attractive rental conditions. Immediate availability and possibility of reservation in advance are key points. This induces strong constraints for the operator especially when some stations attract more trips as a destination than as an origin and vice versa. These imbalances must be corrected by performing vehicle relocations in a smart way to maximize vehicle availability and minimize operator’s costs. In order to understand the demand patterns and explore relocation possibilities, an event-based simulator is built in C#. We develop a new relocation strategy to minimize the demand loss due to vehicle unavailability. Implemented in parallel to rentals, it relies on the regular update of the relocation plans based on an optimization framework which utilizes the current state of the system and partial knowledge of near-future demand. This strategy is compared to three other strategies on a case study based on real data from Nice, France. We show that it maximizes the number of served demand and succeeds in keeping the system in a balanced state contrary to the other strategies considered

On-line proactive relocation and regulation strategies for one-way station-based car-sharing systems

This study examines the on-line proactive planning of relocations in a one-way station-based electric car-sharing system that implements a complete parking reservation policy. A Markovian model that utilizes reservation information is formulated in order to estimate the expected near-future shortages of vehicles and parking spots at each station. The outcome of the model is used in algorithms for staff-based and user-based relocations. The proposed algorithms are tested in a simulation environment using data derived from a real-world car-sharing system. In addition, in collaboration with a car-sharing operator, the algorithms are test in the field

On-line proactive relocation strategies in station-based one-way car-sharing systems

In this work, we study the integration of relocation activities and system regulations in the operation of one-way car-sharing systems. Specifically, we consider the on-line proactive planning of relocations in a one-way station-based car-sharing system that implements a complete journey reservation policy. Under such policy, a user’s request is accepted only if at the booking time, a vehicle is available at the origin station and a parking spot is available at the destination station. If a request is accepted, the vehicle is reserved until the user arrives at the vehicle and the spot is reserved until the user returns the vehicle. Each parking spot may be in one of the following states: empty free spot, empty reserved spot, available vehicle and reserved vehicle. The reserved vehicles/spots provide additional information regarding spots/vehicles that are about to become available. We thus propose utilizing this information in order to plan relocation activities and implement impactful demand shifting strategies. We devise two relocation policies and two demand shifting strategies that are based on the evaluation of the near future states of the system. Using a purpose-built event based simulation, we compare these polices to a state-of-the-art inventory rebalancing policy. An extensive numerical experiment is performed in order to demonstrate the effectiveness of the proposed policies under various system configurations

Dynamic prediction-based relocation policies in one-way station-based carsharing systems with complete journey reservations

In this paper, we study the operations of a one-way station-based carsharing system implementing a complete journey reservation policy. We consider the percentage of served demand as a primary performance measure and analyze the effect of several dynamic staff-based relocation policies. Specifically, we introduce a new proactive relocation policy based on Markov chain dynamics that utilizes reservation information to better predict the future states of the stations. This policy is compared to a state-of-the art staff-based relocation policy and a centralistic relocation model assuming full knowledge of the demand. Numerical results from a real-world implementation and a simulation analysis demonstrate the positive impact of dynamic relocations and highlight the improvement in performance obtained with the proposed proactive relocation policy