Thermal diffusivity identification by 2 nde derivative analysis of transient temperature profile

International audienceThis paper deals with a new method to identify the thermal diffusivity of isotropic materials. Contrary to the flash method, a continuous and constant heating is applied on the rear surface of the sample. An analytical solution of the 1-D transient equation is developed based on Green's function and gives the temperature profile on the opposite surface at the first moments. Regarding the 2 nde derivative of this equation, we found that it reaches a maximum value at a characteristic time tc 2nde which is proportional to the thermal diffusivity α and the sample thickness es. Experiments are performed on a well-known material, ARMCO Iron, to check the feasibility and the accuracy of the identification with noisy temperature measurements. The method is also applied to insulation materials. Uncertainties on the identified values are discussed and rules are given t

Finite element modelling of orthogonal cutting: sensitivity analysis of material and contact parameters

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Role of frozen lubricant film on tribological behaviour and wear mechanisms in grinding

International audienceIn this paper the friction conditions of Minimum Coolant Grinding (MCG) technology are deeply characterized. The MCG is a successful cooling/lubricating system that combines the application of Minimum Quantity of Lubrication (MQL) and CO2 at low temperatures to create a frozen layer of oil able to reach the contact zone. This technique has previously shown promising results to reduce heat generation in grinding process and improve the workpiece finish. A comparison of the energy consumption, forces and wear patterns have been performed between MCG and dry grinding by means of the On-Machine Test Bench. In the work authors have identified that MCG favours the shearing of the material reducing the energy consumption and wear of the abrasive. Differences are highlighted on the size of wear flats, the shape of the debris and the various types of wear mechanisms

Approche thermomécanique de la tribologie à grande vitesse - Application au freinage

This work is supported by International Campus on Safety and Intermodality in Transportation. Objective approach is developed so as to identify causes leading to fading phenomenon and braking tribosystem damage. Simplified brake pad behaviour is studied regarding pressure, sliding speed and temperature expected in automotive braking conditions. This pad is composed by phenolic resin reinforced by spherical steel particles.High Speed Tribology bench allows tribological caracterisation at reduced scale until 40 m.s−1. Disc temperature data are obtained thanks to telemetry system. Temperature field and dissipated heat flux are calculated with inverse heat conduction methods. Contact temperature, mean normal pressure and sliding speed influence on macroscopic friction coefficient is evaluated for pure phenolic resin and simplified composite pin. Pin surface micrographs show that contact zone damaging depend on thermal and mechanical conditions. Particle debonding is studied thanks to mesoscopic numerical model. Materials and cohesive properties are determined by rheological tests in heating chamber under several temperature. Static simulations show that high pressure and high temperature lead to reinforcement interface failure. Correlation between experimental tests on HST and numerical model are found.Les présents travaux s'inscrivent dans la continuité des projets soutenus depuis plusieurs années par le Campus International pour la Sécurité et l'Intermodalité dans les Transports (CISIT CPER). Une approche objective est développée dans ce mémoire afin d'identifier les causes amenant à la perte d'efficacité et à la dégradation du tribosystème de freinage. Le comportement d'une garniture de composition simplifiée, une matrice de résine phénolique renforcée de particules sphériques d'acier, est étudié dans des conditions de pression, vitesse et température de freinage automobile. Le développement de la plateforme High Speed Tribology permet la caractérisation tribologique à échelle réduite pour des vitesses de glissement de plusieurs dizaines de mètres par seconde. L'acquisition de température dans le disque est possible grâce à l'instrumentation d'un dispositif de mesure par télémétrie. Le champ de température surfacique et les flux thermiques dissipés sont identifiés à partir de techniques inverses de conduction de la chaleur. La dépendance du coefficient de frottement macroscopique vis à vis de la température de contact, de la pression moyenne et de la vitesse de glissement est évaluée pour un pion en résine pure et pour le matériau bicomposant. Les observations des surfaces témoignent de l'influence de ces paramètres sur le mode de dégradation de la zone en contact. La décohésion d'un renfort de la matrice est étudiée par le biais d'un modèle numérique à échelle mésoscopique. Les propriétés mécaniques de la résine et de l'interface sont déterminées par des essais rhéologiques dans une étuve pour différentes températures. Les simulations montrent que les hautes pressions et les hautes températures conduisent à la rupture de l'interface matrice - renfort. Des corrélations entre les essais menés sur le HST et le modèle numérique sont présentées

Experimental disc heat flux identification on a reduced scale braking system using the inverse heat conduction method

International audienceThis work focuses on the local heat fluxes on a disc during braking conditions. The generated heat and the temperature field are identified using an inverse heat conduction method coupled to temperature measurements inside the disc. Function specification is used to estimate the boundary conditions in the model without any prior information on the flux intensity and the evolution regarding the time and the position on the sliding surface. Disc heat flux identifications are performed for different braking conditions (sliding speed and normal pressure) on a High-Speed Tribometer. The temperature values are obtained using a telemetry system that allows inductive data transfer. The influence of the braking conditions on the heat repartition and the surface temperature is discussed

Characterization of particulate matter emissions in urban train braking - An investigation of braking conditions influence on a reduced-scale device

International audienceThe particulate matter emissions related to the braking of railway rolling stock are investigated using a reduced scale braking device. Samples of organic materials and cast iron discs are tested for different nominal contact pressures and disc surface temperatures, representative of real conditions. The aim of this work is to investigate the influence of braking conditions on the global amount of particles emitted, their distribution in number and size, and their morphological and chemical characteristics. To be representative, the tested conditions are designed to dissipate the same amount of energy for all the braking events by adjusting the pad application duration. The results show that for the same dissipated energy, a temperature increase above a transition value in the range of 230-280 ∘C depending on the braking conditions modifies the size and number distributions of the generated particles. The results obtained are of interest to better represent their propagation through CFD modelling according to the characteristic of the particle emission