Cette étude expérimentale présente l’étude du comportement mécanique d’un polyamide 66 (PA66) renforcé par des fibres de verre courtes fréquemment utilisées dans l’industrie automobile. Afin d’étudier l’influence de la teneur en humidité, de la quantité de fibres de verre introduite dans la matrice et de la vitesse de déplacement, une série d’essais de traction a été réalisée sur du polyamide renforcé ou non avec des fibres de verre courtes à différents fractions volumiques : 10, 20 et 30 wt%. Les résultats montrent la dépendance du matériau aux différents paramètres cités précédemment. La technique de thermographie infrarouge (IR) a été utilisée pour déterminer l’évolution de la température à la surface des matériaux au cours des essais de traction. Un processus de localisation de la dissipation thermique a pu être identifié à partir des images thermiques.

In water supply installations, noise pollution often occurs. As a basic component of a system, a flush valve may frequently be a source of noise and vibration generated by cavitation or high turbulence levels. During valve closing or valve opening, cavitation can be a problem. In order to decrease the noise and to improve the design inside a flush valve, some experimental and numerical analyses were carried out in our laboratories. These analyses led to some improvements in the design of the valves. Cavitation occurrence was more specifically addressed, using numerical simulation, and this is the main aim of the present paper. Particularly, the use of a simplified numerical test without cavitation model is compared with one using a cavitation model. In order to define potential cavitation risks in some parts of the valve, it has been found that a simplified approach provides an accurate overview. Computational Fluid Dynamics (CFD) simulations of cavitating flow of water through an industrial flush valve were performed using the Reynolds averaged Navier-Stokes (RANS) equations with a near-wall turbulence model. The flow was assumed turbulent, incompressible and steady. Two commercial CFD codes (Fluent 6.3 and Star CCM+ 3.04.009) were used to analyse the effects of inlet pressure as well as mesh size and mesh type on cavitation intensity in the flush valve.

In mass production, the customer defines the constraints of assembled products by functional and quality requirements. The functional requirements are expressed by the designer through the chosen dimensions, which are linked by linear equations in the case of a simple stack-up or non-linear equations in a more complex case. The customer quality requirements are defined by the maximum allowable number of out-of-tolerance assemblies. The aim of this paper is to prove that quality requirements can be accurately predicted in the design stage thanks to a better knowledge of the statistical characteristics of the process. The authors propose an approach named Advanced Probability based Tolerance Analysis (APTA), assessing the defect probability (called PD) that the assembled product has of not conforming to the functional requirements. This probability depends on the requirements (nominal value, tolerance, capability levels) set by the designer for each part of the product and on the knowledge of production devices that will produce batches with variable statistical characteristics (mean value, standard deviation). The interest of the proposed methodology is shown for linear and non-linear equations related to industrial products manufactured by the RADIALL SA Company.

An analytical solution to compute the 3D steady state temperature distribution in a bearing ring is presented in this paper. The ring is formed by a hollow cylinder of finite length. Its radial external surface is subjected to localized, identical heat sources, equally spaced in the azimuth direction. This surface is also subjected to convective cooling while as the internal surface is maintained at a uniform temperature. The developed solution is explicit and does not impose any restriction on the geometrical or physical parameters.

La méthodologie proposée pour l’étude du comportement de matériaux cellulaires sous sollicitation dynamique est abordée par une approche multi-échelles. Le comportement des mousses polymères étudiées dépend du matériau constitutif, et de sa structure poreuse. Les matériaux cellulaires de l’étude sont constitués de grains millimétriques poreux; le cœur de ces grains est constitué de cellules microscopiques. La méthodologie proposée vise à reproduire la morphologie multi-échelles du matériau cellulaire, celles des grains et des cellules, d’implémenter des modèles de comportement simples à ces différentes échelles afin de reproduire les phénomènes physiques complexes observés et la réponse macroscopique du matériau. L’observation et l’analyse des phénomènes locaux est un travail préparatoire à la modélisation multi-échelles. Cet article décrit les méthodes expérimentales et numériques qui ont été développées pour l’observation fine de la structure des matériaux cellulaires, et quantifier des déformations et des dommages de ces structures à l’échelle des cellules et des grains. Deux approches de modélisation ont été ensuite envisagées; un modèle éléments-finis pour décrire la structure des grains, et une autre approche numérique plus originale qui s’appuie sur la méthode des éléments discrets pour représenter la structure microscopique des cellules.

This paper presents thermohydrodynamic solutions for a finite-width journal bearing with single axial groove on the crown by considering turbulent effects in lubricant film. Appropriate governing equations and boundary conditions are used for the fluid flow and heat transfer process occurring in finite full journal bearings. A general computer program is developed to numerically solve the set of governing equations. Results are provided for THD characteristics of journal bearing in terms of Reynolds number, clearance ratio and eccentricity ratio. Good agreement with published experimental results was achieved. The results indicate that the bearing temperature field and pressure field are considerably influenced by the journal bearing parameters.

L’assemblage des rails de chemin de fer se fait généralement à travers un procédé de soudage par aluminothermie. Ce procédé consiste en la coulée de métal de jonction entre les deux extrémités de rails à assembler. La qualité de cet assemblage dépend étroitement des conditions de la réalisation qui sont généralement difficiles à respecter. En effet, les techniques classiques de contrôle des rails, mettent souvent, en évidence la présence des défauts de soudure dans la jonction. Selon les observations, ces défauts peuvent être classés en deux types : défauts d’adhésion (ou défauts de collage) et défauts de porosité (ou défauts de soufflures multiples). Chacun de ces défauts, peut constituer un site privilégié de concentration des contraintes. Selon le niveau de ces contraintes, des éventuels processus d’endommagement risquent de se développer et mettant le rail hors service. Il semble donc nécessaire de modéliser le comportement mécanique de ces soudures avec ces défauts en vue de les classer par leur criticité. Dans cette étude, nous avons donc modélisé avec un même chargement et avec les mêmes conditions aux limites, la jonction de soudure pour chaque type de défaut. Les résultats obtenus sont très concluants et permettent de bien orienter l’approfondissement de notre analyse coté paramètres de soudage.

The present paper is concerned with the thermoelectric behaviour of CFRP composite samples subjected to DC currents in view of developing experimental and modelling tools for the characterisation of the thermo-electro-mechanical behaviour of composite materials for aircraft applications. DC currents up to 8 A are injected through the specimens end sides by employing several different electrode techniques whose performances are assessed and compared. Sample and electrode contact resistances are measured for different values of the injected current. The transient and permanent temperatures fields promoted by the injected currents are experimentally measured by infrared thermography. The temperature fields are simulated numerically by a thermoelectric coupled model employing the ABAQUS® FE commercial code; temperatures can be also approximately calculated by a simple lumped parameter model discarding thermal conduction. The comparison between simulations by the models and measurements allows employing the simplified model as a tool to design thermo-electro-mechanical tests.

This paper investigates the flow boiling heat transfer in microchannels with the aim of developing compact cooling systems which can be adapted to miniaturized power components. Nano- and micro-surface treatments were used as innovative techniques to improve the heat transfer performance as well as to delay the intermittent dryout. It was observed that the micro-structured surfaces show significant enhancements (up to 85%) in heat transfer compared to the smooth surfaces. Especially, using the highly-wetted structured surface, the intermittent dryout is improved.

The paper concerns the transient thermal behavior of a conrod bearing in an automotive engine subjected to various running conditions. The thermal model is oil shear and contact friction heat generation components. The first part of the paper covers some of the industrial and scientific aspects related to bearings seizure, and emphasizes the importance of removing this failure mechanism as early as the incipient development stages of new automotive engines. The second part concerns several of the broad array of factors that approximate a seizure mechanism. In the third and final part, the mathematical model for conrod bearings seizure is revealed. The objective of the paper is to confirm the conrod seizure model’s utility, complementary with more refined approaches such as the thermo-elasto-hydrodynamic approach.

This paper explores analytically the nonlinear dynamic behavior of rotors. Coupled nonlinear equations of motion are formulated using Hamilton’s principle. The rotor model is composed of a rigid disk and a flexible shaft which is characterized as a beam of circular cross section. Various influences are taken into account like the effect of higher order large deformations, rotary inertia, gyroscopic effect, rotor unbalance and the effect of a dynamic axial force. Forced response due to a mass unbalance is presented first for the linear analysis and then perturbation techniques are used to solve the complete equations of motion including nonlinear terms. Method of multiple scales is applied to examine the nonlinear behaviour of the rotor system. Resonant curves are plotted for different possible resonance conditions. It is concluded that the higher order large deformations and axial force acting dynamically on the rotor have a significant effect on its nonlinear response. This response varies for different parameters of the rotor like an unbalance mass and diameter of the shaft.

There has been a number of initiatives launched in the field of lubrication as potential sources of improvements in energy efficiency in a wide range of engineering products, plant and processes. Attention is being focussed on bearings to improve both performance and efficiency in fields such as automotive, machine tools, industrial and power generation plant. This paper reviews some of the background to these drives and illustrates how a novel design of adjustable fluid film hydrodynamic journal type bearing shows promise to both improve performance and save energy. Theoretical modelling and practical tests have demonstrated clear improvements over conventional fluid film bearings, along with a number of other characteristics offering benefits that may be of interest to designers and users of such bearings.

Cette étude présente une machine frigorifique fonctionnant suivant un cycle à compression-absorption. Le système proposé utilise le couple ammoniac-eau comme fluide frigorigène et opère à trois niveaux de pression. L’absorbeur fonctionne à une pression intermédiaire Pint, prise entre la pression de l’évaporateur (PEV) et celle du condenseur (PCD). Les principaux éléments du système proposé sont modélisés. Les résultats de la simulation numérique sont comparés à ceux relatifs au système conventionnel. L’étude comparative met en évidence les avantages du système objet de cette étude. Elle prouve le double avantage de la pression intermédiaire non seulement dans l’amélioration des performances de la machine à absorption mais aussi dans la réduction de la température du fonctionnement du générateur. Nous avons montré que pour des températures d’évaporation et de condensation prises respectivement à –10 °C et 40 °C, le cycle frigorifique fonctionne à une température du générateur TGE = 75 °C avec un COP de l’ordre de 0,56. La présente étude révèle que pour les mêmes conditions de fonctionnement, la machine frigorifique simple étage, présente un COP qui ne dépasse pas 0,51 avec une température du générateur de l’ordre de 135 °C. Le système hybride présente ainsi le privilège de fonctionner à basse température et de présenter des performances relativement améliorées.

Silicon carbide particulate reinforced aluminum (Al/SiCp) Metal Matrix Composites (MMC) is finding increased applications in Industries due to its unique advantages. Holes are to be drilled in many applications for joining and assembly purposes. Friction drilling is a newer non-traditional hole-making chip less process used to make holes in a single step. The manuscript first discusses the mechanical properties such as tensile strength and micro hardness of Al/SiCp-MMC composites, then it discusses the roundness (hole diameter accuracy) errors on dry friction drilled holes. The parameters considered for the experiments are: the composition of work piece, work piece thickness, spindle speed, and feed rate. The results indicated that the increase in the composition of wt% of SiCp particles increases the tensile strength, hardness. The drilling test results indicated that moderate wt% of SiCp gives better results. Higher spindle speeds and higher feed rates increase the roundness error. The highly influential parameter which affects the roundness error is feed rate. Increase in plate thickness also increases the roundness error in drilling of MMC composites.

Several studies have been carried out in order to describe the impact of water-contaminated lubricants on lubrication performance. One approach considers the water-contaminated oil as a homogeneous lubricant with physical characteristics varying with water concentration. The presented work is being achieved in order to experimentally validate this theory. First investigations showed that the variation of contaminated lubricant viscosity has the most significant effect on lubricating performance. Consequently, the lubricant viscosity is the only parameter taken into account in this study. Thus, based on the rheological measurements, water-in-oil emulsion viscosity has been modelled according to water concentration and temperature. Water concentration was considered relatively to total mass of oil: the mass concentration varied then from 0 to 7% and temperature from 10 to 80 °C. Viscosity modelling was then used to perform the numerical simulations of a hydrodynamic thrust bearing supplied with water contaminated oil. Finally, the experimental validation will be done by measuring various bearing characteristics like the film/pad temperature, the film thickness and the friction torque on a tilting pad thrust bearing test rig.

This work gives an overview of the theoretical and experimental achievements of mechatronics applied to fluid film bearings. Compressible and uncompressible fluids are addressed. Rigid and elastic (deformable) bearing profiles are investigated. Hydraulic, pneumatic, magnetic and piezoelectric actuators are used. The ideas of combining control techniques, informatics with hydrodynamic, thermo-hydrodynamic, elasto-hydrodynamic and thermo-elasto-hydrodynamic lubrication techniques are carefully explored in this paper, considering theoretical as well as experimental aspects. The main goal of using controllable fluid film bearings is to improve the overall machine performance by: controlling the lateral vibration of rigid and flexible rotating shafts; modifying bearing dynamic characteristics, such as stiffness and damping properties; increasing the rotational speed ranges by enhancing damping and eliminating instability problems, for example, by compensating cross-coupling destabilizing effects; reducing start-up torque and energy dissipation in bearings; compensating thermal effects. It is shown that such controllable fluid film bearings can act as “smart” machine components and be applied to rotating and reciprocating machines with the goal of avoiding unexpected stops of plants, performing rotor dynamic tests and identifying model parameters “on site”. Emphasis is given to the controllable lubrication (hybrid and active) applied to different types of oil film bearings under different lubrication regimes, i.e., as tilting-pad journal bearings, multi-recess journal bearings and plain journal bearings. After a comprehensive overview of the theoretical and experimental technological advancements achieved in university laboratories, the feasibility of industrial applications is highlighted, trying to foresee the future trends of such mechatronic devices.

Heat release rate fluctuations are the source of combustion instabilities that cause recurrent problems in many combustors. These quantities are difficult to measure and optical techniques are generally implemented. The initial validation of an alternative method is presented in the case of pulsated laminar premixed flames. The technique relies on determining the travel time of ultrasonic waves propagating through the flow. The link between heat release rate fluctuations and perturbations in the travel time of ultrasonic waves is established. Measurements made with this method are compared with optical measurements and an analytical model. A good agreement is obtained for the gain and phase of the transfer function between perturbations in the sound travel time and heat release rate disturbances when the flame is submitted to harmonic modulations of the flow. This work validates the principle of the proposed technique and lays the foundations for future developments.

The focus of this comparative-numerical study is to investigate the effects of advanced cooling hole geometries on film cooling effectiveness. Computational results are presented for a row of coolant injection holes on each side of an asymmetrical turbine blade model near the leading edge. Six film cooling configurations are considered in the present study, namely: (1) a cylindrical film hole, (2) a shaped film hole, (3) a uniform film slot, (4) a convergent film slot, (5) a crescent film hole, and (6) a trenched film hole. All simulations are conducted for the same density ratio of 1.0 and the same inlet plenum pressure. A new parameter, Rc, is defined to measure the rate of blade coverage by the film cooling. Results show that, at the suction side, except for the trenched case, all configurations provide an increase of film effectiveness, specially the crescent slot case which provides the highest increase over the baseline case. On pressure side, the five configurations produce better quality of cooling and an enhancement which reaches 60% for the crescent hole case. The best blade coverage by the film cooling is allotted to the two cases: uniform and converge slot configurations.

Pour situer l’origine d’une anomalie récurrente sur une coque en sandwich tri-couche rotomoulé, une analyse d’instabilité par voilement global est développée. Cette voie est suggérée par la caractérisation de la géométrie du défaut observé et par l’imprédictibilité de son apparition. Le problème thermomécanique est posé dans un cadre non-linéaire en se restreignant à l’évolution au refroidissement en phase solide après que la fraction cristallisée ait atteint le niveau de saturation. Dans le modèle proposé, les non-linéarités liées à l’évolution des propriétés matérielles en fonction de la température et celles associées au contact unilatéral moule/pièce sont considérées. La résolution du problème thermomécanique instationnaire est réalisée par la méthode des éléments-finis au moyen du code Abaqus/Explicit. Le recalage de l’évolution thermique est conduit par un schéma de prédiction-correction de la conductance sur l’interface de contact. Pour l’analyse de la stabilité sous l’effet du chargement thermomécanique, nous appliquons la méthode de perturbation linéaire et les résultats de simulation confirment bien la nature de défaillance suspectée. Les deux premiers modes de voilement calculés sont en bon accord avec les observations dans les conditions réelles du processus.