La modélisation de l'usure superficielle nécessite la mise en place d'un outil numérique de calcul des puissances dissipées lors du roulement sous charge de galets sur des pistes de came [1]. Compte tenu des dispersions relatives aux défauts géométriques et aux paramètres mal connus comme le coefficient de frottement par exemple, l'étude s'oriente vers une approche probabiliste [2] où le nombr e de cas simulés devient très grand et hors d'atteinte en des temps de calcul CPU raisonnables par une approche exacte. L'utilisation d'une approche simplifiée est alors nécessaire pour le calcul de la puissance dissipée dans le cas non hertzien généré par l'usure. Pour quantifier la précision (ou l'incertitude) d'une telle approche, nous présentons et discutons les choix qui ont été réalisés ; en particulier, l'approche simplifiée proposée par Kalker [3] est comparée avec les solutions de l'approche exacte, puis nous proposons des améliorations aux approches semi-hertziennes déjà utilisées dans [4] ou [5].

The use of composite laminates is increasing in these days due to desired directional properties and low densities in comparison of metals. Delamination is a major source of failure in composite laminates where a crack like entity can initiate and propagate between different layers of composite laminates under given loading conditions. Damage mechanics based theories are employed to simulate the delamination phenomena between composite laminates. These damage models are inherently local and can cause the concentration of stresses around the crack tip. In the present study integral type non-local damage formulation is proposed to avoid the localization problem associated to damage formulation. A comprehensive study is carried out for the selection of different non-local variables. Finite element simulations based on proposed non-local damage models and classical local damage model are performed and results are compared with available experimental data for UD IMS/924 Carbon/fiber epoxy composite laminate.

In the present paper an experimental investigation of drag reduction on in-line tubebundles with a configuration of seven by seven with a pitch ratio of 1.44 has beenperformed. Two longitudinal grooves are placed on the external surface of the circularcylinders as a passive control. The experiment is carried out using a subsonic windtunnel. The pressure distributions for various azimuthal angles along the tubes aremeasured using a multi-channel differential pressure. Drag forces are also determinedusing a combined wire-strain gauge balance. The pressure drops are deduced from theresulting drag forces. The results obtained show an unexpected reduction in the pressuredrop for the tube bundles. A reduction of 36.5% in the pressure drop for a Reynolds numberof 1.33 × 104 is found compared to the configuration without grooves. Somecorrelations for the pressure drop are proposed.

This study presents a new simple lumped model for analyzing the thermally induced seizure of fully lubricated eccentric circumferential groove journal bearings (CGJB). The model represents a significant upgrade of a previous seizure lumped model developed by Pascovici & Kucinschi, in 2002. Main upgrades consist of: eccentric operation, introduction of hydrodynamic lubricant flow rate component, and evaluation of friction power losses based on the short bearing theory with Barwell’s hypothesis on the divergent zone. The viscosity–temperature variation is replaced with Tipei’s viscosity-clearance relationship, as in the previous model. The decrease of viscosity, as a consequence of temperature increase, does not always limit clearance loss, and the seizure process ends with a concentric journal-bushing merged system. Although CGJB’s are less sensitive to this seizure mechanism, the threat still exists and must be avoided. As a result, bearing designers and users should check whether if several safe-operation criteria are met. A recent Institute Pprime experiment on CGJB’s provided a base set of operating parameters, from which numerical simulations have been performed to determine in what conditions the CGJB fails, under thermally induced seizure.

Dans le processus de fabrication par enlèvement de matière sur machines-outils, l'apparition des vibrations est inévitable. Dans les situations où l'amplitude dépasse les limites de la précision dimensionnelle, le phénomène vibratoire est préjudiciable. L'étude expérimentale présentée ici permet d'identifier les principaux paramètres relatifs au comportement dynamique du système usinant. La localisation des déplacements de la pointe de l'outil dans un plan est démontrée grâce aux résultats expérimentaux. L'existence de ce plan et les corrélations avec les caractéristiques élastiques du système usinant permettent de simplifier le modèle dynamique 3D. Avec l'approche expérimentale réalisée, un modèle dynamique est proposé en concordance avec les résultats expérimentaux.

An algorithm of operational modal analysis in time domain is presented for thediscrimination between structural modes, harmonic excitations and spurious modes. Aclassification factor is developed and based on the construction of the damped signal- to-noise ratio which separates the physical modes from the numerical ones. The harmonicexcitations are then recognized at very high power indexes and zero damping. Furthermore, after the modal discrimination, the harmonic spectrum and the estimated frequency responsefunction can be derived. The method can be updated in the time domain either by a shorttime sliding window or a recursive technique to provide the modal monitoring in bothstationary and non-stationary process. An industrial application on a hydro-electricalgenerator is discussed to identify the machine frequencies under operational workingconditions.

Une double enceinte climatique conçue sur le principe de la méthode de la boîte chaudegardée a été mise au point afin d’étudier en laboratoire le comportement thermique ethygrique de différentes configurations de parois en bois. Le dispositif est dotéd’équipements de régulation lui permettant de reproduire des sollicitations climatiquesstationnaires ou dynamiques proches d’un climat réel et de suivre l’évolution des profilsde température et d’humidité dans les parois testées. Dans ce travail, le suivi ducomportement hygrothermique d’une paroi en ossature bois comportant des matériauxhygroscopiques et soumises à différentes conditions est rapporté. Les résultats ont montréque la capacité du dispositif à bien reproduire les conditions imposées a permis demesurer les propriétés importantes de parois en régime permanent (résistance thermique) ettransitoire (amortissement et déphasage thermique). Les essais réalisés ont également misen évidence le comportement hygroscopique des matériaux testés.

La simulation numérique joue un rôle croissant dans la conception des navires à côté des ou associée aux approches réglementaires édictées par les sociétés de classification. Ce texte, non exhaustif, veut illustrer les tendances actuelles et les difficultés rencontrées dans l'approche simulation numérique. Celles-ci sont de plusieurs ordres : problèmes de modélisation liés à la taille des structures et à la nécessité d'une approche multi-échelle, problèmes de méthodologie liés à la complexité de l'environnement, problèmes de couplage fluides structures. Enfin ces études doivent se dérouler dans un temps extrêmement court, avec des informations qui se précisent au cours du déroulement de l'étude, informations entachées d'incertitudes et de dispersions. Les grands codes éléments finis généralistes disponibles sur le marché sont en général utilisés, associés à des outils et développements spécifiques si nécessaire, dans des chaînes de calcul plus ou moins intégrées. Les situations extrêmes ou accidentelles font l'objet d'études assez sophistiquées, nécessitant un travail d'interprétation important.

In recent decades, problems related to the squeeze of fluid films in the presence of aporous medium draw attention of researchers and are the subject of many applied studiesfor industry and biomechanics. Our concerns in this paper are the numerical simulation ofthe viscous shear stresses effects on the fluid film characteristics between two discswith one porous. This study is based on the coupling, at the fluid film-porous discinterface, of the Darcy-Brinkman equations in the porous medium and the modified Reynoldsequation describing the flow in the fluid film. The system of equations obtained isdiscretized by the means of finite differences method and solved numerically using thetechnique of Successive Over-Relaxation (SOR). The results show that the viscous sheareffects increase the radial and the axial fluid film velocities as well as the squeezefilm velocity but decrease the response time. Moreover, these effects are enlarged forsmaller viscous shear parameter and for smaller fluid film thickness.

In this paper, an analytical approach is proposed to model chip formation in the case ofturning process. Numerical simulations of chip genesis are performed in order to fitefficiently the proposed analy- tical model. In particular, cutting edge radius influence,temperature and internal stresses distribution are studied using finite element modelling.Numerical model setting is made with experimental and literature data using forces andchip thickness.

Cavitation erosion is a current wear type in hydraulic turbines, on pump impellers, on ship propellers, valves, heat-exchanger tubes and other hydraulic structures in contact with high-velocity liquids subjected to pressure changes. Much effort has been done to optimise the design and operating parameters in order to avoid cavitation wear for the equipment. But, this type of wear has also been observed in mechanical devices which such as plain bearings, seals, orifices in which fluid goes through severe restrictions. Cavitation damage may occur when surfaces in contact with fluid are subjected to vibrations, e.g.: water-cooled Diesel-engine cylinder liner. Sometimes, cavitation can initiate other types of wear such as adhesion or abrasion because of wear particles produced at the friction interface, making the failure analysis more difficult.Cavitation wear mechanisms were showed through three industrial examples. The first one is a hydrodynamic plain bearing which was heavily damaged by cavitation wear due to flow instability. The second one concerns a low speed translating plain bearing. Firstly, abrasion traces were observed on the contact surface. But a deeper study showed that solid particles produced by cavitation wear had been the main cause of the abrasion wear. The last example presents several cases of cavitation damage in oil lubricated plain bearing observed in medium/slow speed diesel engine for marine or power station applications. Because of fluctuation of radial force from crankshaft and instability of lubricant flow, variation of oil pressure can be sufficient to produce bubble inception, collapse and microjet formation process.

Cet article présente une méthodologie d'identification du comportement de mousses polymères hyperélastiques à partir de mesures de champs par corrélation d'images et de la technique d'identification dite méthode des champs virtuels. Dans un premier temps, les constantes élastiques à faible déformation sont identifiées à partir d'un essai de flexion/cisaillement. Ensuite, une loi hyperélastique de type Ogden est identifiée à partir d'un essai de compression uniaxiale. On observe une forte localisation des déformations en raison de l'effondrement élastique des cellules de la mousse, confirmant qu'une approche basée sur la réponse globale force/déplacement ne permettra pas l'identification d'un comportement matériau (effet de structure). Cette étude préliminaire montre le potentiel de la démarche même s'il reste encore beaucoup à faire pour fiabiliser cette approche.

Dans cette étude, on présente une contribution à la modélisation expérimentale etnumérique du comportement élastoplastique endommageable anisotrope de tôles destinées à lamise en forme. L’accent est mis sur la localisation des instabilités plastiques induitespar l’anisotropie plastique et l’endommagement. La procédure d’identification desparamètres matériau du modèle de comportement est basée sur une approche inversed’optimisation s’appuyant sur des essais de traction orientés, associée à des simulationsnumériques (Abaqus/Standard et Matlab). La validation de la procédure proposée a pu êtremenée grâce à une confrontation entre simulations numériques et résultats expérimentauxobtenus sur des éprouvettes caractéristiques des tôles minces texturées en acier doux.L’application est ensuite faite à la simulation de procédés de gonflement hydraulique deces tôles avec prévision de l’endommagement ductile. Plusieurs cas en expansion libre(matrices circulaires et elliptiques) et en expansion dans des cavités de matrice serontprésentés et des comparaisons avec les résultats expérimentaux seront réalisées.

In this paper, we study the phenomena of thermo-chemical imbalance in a reactive mono-dimensional flow composed of a mixture of (79% nitrogen N2 and 21% oxygen O2). We are interested in modeling the physicochemical process that may be encountered in hypersonic flows, as vibrational excitation, dissociation and ionization, also the formation of chemical species to higher temperatures behind a detached strong shock. We put a special emphasis on vibrational relaxation model of CVD coupling. At these high temperatures, collisions electrons-atoms become very effective, taking in account the radiation that requires knowledge and modeling of all physicochemical processes (collisional and radiative). The mathematical model of flows at the atmospheric reentry is governed by Euler stationary equations coupled with the chemical kinetics and the radiative transfer equations. Our computational code is based on the finite differences method that used to discretize and resolve the obtained numerical model, where an appropriate mesh is selected in the relaxation zone in order to determine the flow parameters at each grid position

Impact wear can be defined as the wear of a solid surface due to percussion, which is arepetitive exposure to dynamic contact by another solid body. It has not been studied asextensive as other wear mechanisms and the information on causes and actual data is quitescarce. In the present work an experimental wear tester is designed and used to study theimpact wear phenomenon experimentally. It creates the consecutive impacts between ballsand flat plate. The different ball sizes (up to 30 mm), impact velocities (up to 6m.s-1) and impactangle (10°− 80°) can be tried by tester. The mass lossof plate is measured as the wear parameter. These measurements for different specimensrevealed some aspects of their wearing behaviors. The obtained results could be helpful inoptimal practical designs and explanation of some phenomena associated with impact wear.

Shrink fits are low-price connections which are widely used in industry and industrialconnections. In designing shrink fits it is important to consider radial interface foroptimized performance and also to choose an accurate method of fabrication and assembling.Parts which have to be assembled are usually exposed to thermo-mechanical loads. Mode andtime duration of heat transfer have a significant effect on required hydraulic force,stress time rate of creation in parts and joint ability to withstand against externalloads. Therefore, planning a set of appropriate thermal and structural procedures hassignificant role in reducing energy consumption, optimized performance and promoting thespeed of parts assembly. Despite of the fact, few researches have been done on shrink fitoperation and design, rather than dimensional design. In this study, shrink fits arestudied in two main processes: first heating and mounting process and then backing to theambient condition. A 3D coupled thermal and structural simulation based on FEM is done oneach process through well-known Solidworks Premium. To evaluate the accuracy, exactanalytical solution of two steel rings shrink fit is compared with the approach outcomes.Results of validated method are used for choosing the most optimum sub processes of shrinkfit fabrication.

Herein we develop a creep test method for characterizing nonlinear viscoelastic behaviour of an elastomer through weak deformation. This approach is based on an expanded Schapery model. Short term creep tests at various stress levels were performed upon specimens composed of a synthetic elastomer. A method to predict the long term creep behaviour using short term creep tests is presented. Experimental results and theoretical predictions are compared.

Early damage detection on structures plays a very important role for ensuring safety and reliability. This paper provides an efficient method based on wavelet transforms in order to detect and localize damage on structures subjected to moving loads such as beams and bridges. A numerical model based on the experimental test-rig utilized in this study is developed by using a finite element commercial software. Different types of damage on the bridge of the numerical model are simulated and transient analyses are performed by incorporating a load which moves constantly along the beam nodes. Continuous wavelet transform diagrams using the vertical acceleration responses show that damage can be identified and localized even with significant percentages of noise. Nevertheless, the method is improved by filtering the signals, removing the border effects, and calculating the total wavelet energy of the beam from the coefficients along the selected range of scales. Thus, the accumulation of wavelet energy could indicate the presence of damage. Finally, laboratory experiments are conducted to validate this work and a good agreement between numerical and experimental results is obtained.

Heat transfer during agitation of Bingham viscoplastic fluid is studied in this paper. The fluid is agitated with an anchor impeller and the heating is made by a jacketed wall of the stirred vessel. Transfers in the agitated vessel, translating hydrodynamic and thermal phenomena, are numerically predicted by means of Computational Fluid Dynamics (CFD) in transient regime. The purpose of this numerical study is to identify the rigid zones and to optimize mixing and heating performances. The Navier-Stokes and energy equations are discretized using finite volume method, and a two-dimensional analysis of the hydrodynamic and transient thermal behaviours generated in the agitated vessel are performed. Fluid rheology is modeled by the Bingham approximation and Papanastasiou’s regularization model. Results show the presence of recirculation zones and permit to explain the unpredicted Nusselt number increasing when Oldroyd number increases. This study shows also the importance of the anchor position on the size and the shape of the rigid zones and on the heating performances.

Braking operation is a process which converts the kinetic energy and the potential energyof the vehicle into other energies. The major part of the mechanical energy is transformedinto heat. During the braking phase, the frictional heat generated at the interfacedisc–pads can lead to high temperatures. This phenomenon is even more important that thetangential stress as well as the relative sliding speeds in contact are important. Theobjective of this study is to analyse the thermal behavior of the full and ventilatedbrake discs of the vehicles using computing code ANSYS. The modeling of the temperaturedistribution in the disc brake is used to identify all the factors and the enteringparameters concerned at the time of the braking operation such as the type of braking, thegeometric design of the disc and the used material. The results obtained by the numericalsimulation are satisfactory compared with those of the specialized literature.