Génie mécanique
Evaluation of residual stresses in titanium alloy welded by tig using ultrasonic method and effect of the microstructure on the lcr elastic wave
This study consists to determine the superficial residual stresses on Ti-6Al-4V titanium alloy sheets (e = 2 mm) welded by Tingsten Inert Gaz (TIG) process. The residual stresses can increase the fatigue cracks propagation. We will focus in the method of measurements based on ultrasonic using longitudinal critically refracted (Lcr) waves. This method is based on the acoustoelastic effect, which measure the velocity variation of the elastic waves according to the stress state of the material. This can be achieved through a calibration test to determinate the acoustoelastic coefficient (K).The results show a tensile stresses in the melted zone (MZ), heat affected zone (HAZ) and compression stresses in base metal (BM). The microstructure effect acts on the acoustoelastic constant K. The correction of t0 corrects the overestimated residual stresses in the (HAZ) and (MZ). Voir les détails
Mots clés : Titanium alloy, welding, residual stresses, Ultrasonic, microstructure
Determination des contraintes résiduelles par la méthode ultrasonore d’un alliage d’aluminium soudé par FSW
L’aluminium et ses alliages occupent une place importante dans l’industrie particulièrement l’aéronautique. En tenant compte de la sensibilité de ces secteurs nous incite à étudier leur comportement mécanique sous l’effet des procédés de soudage, ses derniers induisent des contraintes résiduelles qui jouant un rôle important dans la tenue mécanique des assemblages.En vu de réduire la probabilité de défaillance, une maintenance préventive est imposé pour estimé le niveau de contraintes admissible par la structure en service en utilisant l’une des récentes méthodes de contrôle non destructive à savoir la méthode ultrasonore. L’évaluation des contraintes résiduelles par ultrasons repose sur l'effet acoustoélastique qui traduit la dépendance de la vitesse de propagation des ondes acoustiques en fonction de l'état de déformation du solide. Les contraintes résiduelles sont déterminées sur des tôles en alliage d’aluminium (2024 T3) de 3 mm d’épaisseur soudé par le procédé de soudage Friction malaxage (FSW). Elles prennent un profile de forme "M" dans lequel les contraintes maximales en tension se trouvent aux extrémités de l’épaulement de l’outil (ZATM) . Voir les détails
Mots clés : Alliage d’aluminium 2024-T3, soudage FSW, contraintes résiduelles, méthode ultrasonore
Influence du courant de soudage TIG sur la microstructure et les propriétés mécaniques d'un alliage d’aluminium 2024 T3
L’utilisation des alliages d’aluminium prend de l’ampleur grace à leurs faible masse associé aux propriétés mécaniques élevées. Cependant, les problèmes rencontrés lors de de soudage limitent son application dans plusieurs domaines. Dans cette étude, des investigations microstructurales et de microduretés ont été menées sur des plaques minces en alliage d’aluminum 2024 T3 par le procédé TIG. Voir les détails
Mots clés : soudage, alliage d’Aluminium, TIG, microstructure
Numerical Study of Thermal Effects in the Hydrodynamic Behavior of Textured Journal Bearings
The journals bearing characteristics with texture presence on the bearing surface are investigated. The thermal effect has been studied. The used numerical approach in this analysis is Finite Difference Method. The textured bearing performance enhancement passes essentially by a minimum film thickness and a friction torque improvement through an appropriate surface texture geometry and right texture distribution on the bearing surface. It is found that the simulation results are in good concordance with those issued from the litterature. The obtained results by considering the temperature effect are more realisti Voir les détails
Mots clés : Hydrodynamic lubrication, journal bearing, texturation, dimple
Comparative analysis of surface texturing effect on the performance of hydrodynamic journal bearings
Understanding the influence of surface texturation on journal bearing performances inevitably involves experimental investigations pending being followed by a numerical modeling of the problem. This work consists to model and to understand the evolution of journal bearing characteristics with and without presence of textures on the bearing surface. The numerical approach based on the finite difference method is used in this analysis. Improving performance of textured bearing with spherical dimples suggest that contact characteristics such as minimum film thickness, maximum pressure, and friction torque may be improved through an appropriate surface texture geometry and appropriate texture distribution on the contact surface. The results of our simulations are in good agreement with those obtained experimentally [1]. Voir les détails
Mots clés : Journal bearings, Reynolds equation, Hydrodynamic lubrication, Stribeck curve, texture
The texture effect on the static characteristics of hydrodynamic journal bearings
Understanding the influence of surface texturationon journal bearing performances inevitably involvesexperimental investigations pending being followed by anumerical modeling of the problem. This work consists to modeland to understand the evolution of journal bearingcharacteristics with and without presence of textures on thebearing surface. The numerical approach based on the finitedifference method is used in this analysis. The results of oursimulations are in good agreement with those obtainedexperimentally by Xiaobin. Voir les détails
Mots clés : Cavitation, friction, hydrodynamics, Journal bearings, lubrication, numerical analysis, surface texture, Thin films, tribology
Microstructure and Mechanical Properties of a Dissimilar GTA Weld between 2205 duplex stainless steel and API X-70 high strength low alloy steel (HSLA)
The duplex stainless steels and HSLA steels are attractive for applications in the oil and gas industry due to their properties. The dissimilar welds are widely used in the petroleum industry for economical reason. However, the welding of dissimilar metals considered difficult, due to the differences in the physical properties of the two metals. The aim of the present study is to investigate the influence of the welding process parameters on the microstructure and mechanical properties of dissimilar weldement of 2205 duplex stainless steel /API X-70 high strength low alloy steel (HSLA) produced by GTA welding. The microstructures of the welded joints were investigated by the optical microscopy (OM), the mechanical properties included hardness, impact and tensile strength was investigated, the fracture surfaces of the tensile specimen were examined by scanning electron microscopy (SEM). From this investigation, it is observed that, the microstructural characteristics and mechanical proprieties of the weld are influenced by the heat input. Voir les détails
Mots clés : GTA welding, Dissimilar welding, heat input, duplex stainless steel, HSLA steel, microstructure, mechanical properties, Fractography
Influence of heat input on microstructure and mechanical properties of Ferritic Stainless Steel welds
Ferritic stainless steels are classified as such because the predominant metallurgical phase present is ferrite. These steels are characterized by good resistance to stress corrosion cracking (SCC), pitting corrosion, crevice corrosion (particularly in chloride environments), higher thermal conductivity, low coefficient of heat dilation and lower cost, when compared to austenitic stainless steels. The combination of low cost and good properties has made ferritic stainless steel more and more attractive in various application fields, such as, heat exchangers, petroleum refining equipment, storage vessels, protection tubes, solar water heaters, and exhaust manifold applications. However, ferritic stainless steel steels are associated with many problems during the welding process. These problems are the martensite formation and grain growth, causing a reduction of ductility and toughness. For these reasons, until recently, the application of this group steels is limited in welded structures. The aim of the work is, first to characterize the weld metal, as variable GTA welding process parameters and optimize the heat input. We focused on improving tensile strength of ferritic stainless steel. The results show that, the heat input has a great influence on microstructure and mechanical proprieties of weld metal. The details of tensile tests, optical microscopic observations, microhardness, and Scanning electron microscopy (SEM) fractography, are discussed. Voir les détails
Mots clés : GTA welding, heat input, ferritic stainless steel, microstructure, mechanical properties, Fractography
Effet du nombre de plis sur le flambement des structures cylindriques minces
Cette étude vise à prévoir l'effet de nombre de pli, épaisseur du stratifié et diamètre de l’entaille, sur le comportement au flambement des structures cylindriques minces fabriquées en matériau composite hybride CARALL (Al/fibre de carbone/epoxy). L'assemblage de l'aluminium avec un stratifié en polymere renforcé en fibre de carbone ont un effet synergique sur plusieurs propriétés mécaniques, d’où leur attirance est considérable dans le domaine aérospaciale. Le flambement de ces structures est induit par une compression axiale qui se traduit par un déplacement imposé. Les résultats obtenus numériquement par le biais du code Abaqus, en utilisant la méthode des éléments finis, montrent que la rigidité des structures à faibles angle d’inclinaison des fibres est améliorée, en augmentant le nombre de plis, Tandis que pour des inclinaisons importantes, il est recommandé d’agrandir l’épaisseur du la couche du stratifié. Voir les détails
Mots clés : Structures cylindriques minces, déplacement imposé, CARALL, flambement.
The influence of addition elements (Ti, B, Zr) on mechanical properties and corrosion resistance of intermetallic alloys FeAl-B2
The FeAl alloys have been the subject of extensive research in the 60s, but because of their excessive fragility, the use of doping by alloying elements has given hope to this alloy family and to relaunch search. In the context of the present work we studied alloys developed on the basis of the intermetallic Fe-Al40 in an arc furnace with adding alloying elements (Ti, B, Zr). This study aims to improve the mechanical strength and the corrosion resistance of this materials at ambient temperature.The microstructures were examined by the Optical microscope (OM) and scanning electron microscope (SEM). The different phases present in the material were identified by X-ray diffraction (XRD). Numbers hardnesses were determined by Vickers hardness test (HV) and Vickers microhardness measurements. The electrochemical studies were performed in using potentiodynamic polarization curves and the electrochemical impedance spectroscopy (EIS). Microstructural observations indicated the presence of precipitates which result from the introduction of B and Zr. Adding Boron in alloy FeAlTi reduces the hardness, but the combined effect of the (Ti, B, Zr) has led to a structural hardening at low temperature. It was observed that all elements added to the binary alloy FeAl improved the corrosion resistance, but the FeAlTiB alloy present the best features of protection against corrosion. Voir les détails
Mots clés : Intermetallic alloys, FeAl B2, X-ray, mechanical properties.