Génie mécanique
Etude de la structure et du comportement des alliages légers soudés par friction malaxage FSW
La course à l’allègement des aéronefs constitue aujourd’hui l’un des enjeux principaux de l’industrie aéronautique. L’utilisation de certains alliages d’aluminium couplés à de nouveaux procédés d’assemblages est une bonne réponse à cette problématique. Le procédé de soudage FSW permet notamment la réalisation d’assemblages multi-matériaux en s’affranchissant des problèmes de fusion. Dans le contexte industriel, cette étude constitue un élément de réponse à deux problématiques industrielles peu étudier dans le domaine du procédé FSW. Donc, la compréhension des relations entre le décalage de l’outil par rapport à l’interface originale de la soudure ainsi que la position de chacune des nuances utilisées (2024 « le moins résistant » ou 7075 « le plus résistant ») par rapport au sens de rotation et d’avance de l’outil, nous a permis de développer des tolérances de fabrications à imposer sur les bruts de soudage. Dans le contexte scientifique, l’objectif est d’étudier l’effet des hétérogénéités microstructurales induites par le soudage sur les hétérogénéités de comportement mécanique dans les joints soudés. La corrélation d’images numériques a été utilisée pour définir la réponse mécanique (σnominale – εvraie) dans chacune des zones constituant ces soudures. En complément, des essais sur des mini-éprouvettes prélevées dans l’épaisseur des joints ont permis d’établir le comportement local (σvraie – εvraie) dans chacune des zones du joint. La rupture des soudures FSW a été observée dans la zone située aux minima des profils de microdureté. Afin de mieux caractériser la soudure, il est nécessaire d’évaluer la répartition des contraintes résiduelles induites dans celle-ci. Ces dernières peuvent modifier la structure et les propriétés initiales du matériau. La méthode ultrasonore a été choisie en utilisant l’onde longitudinale subsurfacique (LS). Cette méthode a l’avantage d’être non destructive, rapide et applicable sur site. Voir les détails
Mots clés : FSW, d’aluminium, mécanique, microstructure, CIN, ultrason, contraintes résiduelles
A probabilistic approach to estimate the remaining life and reliability of corroded pipelines
Considering corrosion rate during the remaining life assessment of aging pipelines is fundamental to calculate the interval between two consecutive inspections. A total of 798 internal and external corrosion defects have been detected, using the Magnetic Flux Leakage intelligent inspection tool, over 48 km of a pipeline length located in the west region of Algeria. The statistical analysis has shown that there is a strong correlation between the corrosion defect length and the corrosion defect circumferential width, with a significant correlation coefficient equal to 82.87%. A probabilistic methodology is presented for the assessment of the remaining life of a corroded pipeline transporting gas, and a finite element method (FEM) was used to assess the pipeline failure pressure. The numerical FEM modeling results were compared with the commonly used codes-models for calculating limit pressure to establish a more realistic and accurate engineering model. The reliability analysis of an API 5L X60 steel made Algerian natural gas pipeline, in service for thirty years, and exposed to active corrosion attack, is presented. The sensitivity analysis of the basic random variables within the nonlinear limit state function was carried out to bring out the relative contribution of each variable affecting the remaining life of corroded pipelines. The reliability analysis is carried out by using Breitung’s formula, based on the second-order reliability method (SORM). The reliability assessment of the corroded pipeline is based on the usage of the notched failure assessment diagram (NFAD), different codes for the calculation of the failure pressure, and the numerical results using the finite element analyses (FEA) software ANSYS. Voir les détails
Mots clés : Corrosion defects, pipelines, Remaining life, Probability of failure, Reliability, Probabilistic approach
Experimental Study Of The Effect Of Shot Peening Parameters On The Surface Texture - Influence On The Adhesion Of A Paint Coating
The investigation presented in this paper focuses on the effect of surface texture on the adhesion of a paint coating as well as the influence of shot peening regime parameters on the surface isotropy indicator "Str" and on the fractal dimension "Df". The tests have been organized according to full factorial designs 23, where three parameters have been examined, at their two levels (min, max), namely the pressure (P), the angle of attack (θ) and the time (t). 3D roughness measurements have been carried out to characterize the different surfaces after a shot peening operation. A mathematical model linking the input parameters (P, θ, t) and the output parameter "Str", in the study area has been established, and the fractal dimension (Df) has been used for the surface characterization. Paint deposit has been applied to surfaces and adhesion tests have been carried out. The results show the significant effect of the impact angle on "Str", and the interaction between the different parameters in the studied area. Furthermore, the greatest bond strength has been obtained with the sample 3 (F = 4.25 N / mm2), whose the isotropy indicator "Str" is equal to 0.6438 and the fractal dimension Df = is about 1.768. Voir les détails
Mots clés : surface texture, fractal dimension, shot peening, Adhesion
Microstructural and Mechanical Properties of Welding and Thermal Spraying Coatings on Ductile Cast Iron
The subject of this work is to evaluate the influence and adhesion degree of different coating layers deposited on a ductile cast iron substrate by two different methods, thermal spraying and welding with and without use of an interlayer. Microstructures of different zones and interfaces of coated specimens are investigated using optical microscope and scanning electron microscope SEM. Also, the mechanical behavior was evaluated by tensile test. It is found that when stainless steel thermal spraying coating onto the ductile cast iron substrate, the use of the nickel-based interlayer Ni allowed us to mitigate the disadvantages of cracking at the interface. This is due to the mechanical effect of nickel plasticity. In the case of coating by welding, the use of nickel-based buttering ENi-CI allowed us to reduce the diffusion of graphite to stainless steel, resulting in a reduction in the formation of harder alloy carbides. Finally, the mechanicals tests in particular the tensile test shows that the coating by welding is effective but causes a structural hardening; on the other hand the coating realized by thermal spraying does not really present sufficient adhesion. Voir les détails
Mots clés : Ductile Cast Iron, mechanical properties, microstructure, Thermal Spraying, Welding Coating
Effect of Heat Treatment on the Structure, Wear and Corrosionof AISI L6 Tool Steel
This work is a contribution in analyzing structure, tribological behavior and corrosion ofAISI L6 hardened tool steel. Structural characterization and tribological behavior of steel wereinvestigated using Optical Microscopy (OM), Scanning electron microscopy (SEM), wear testing byfriction on a pin-on-disc Tribometer and corrosion by potentiodynamic polarization. Comparing tothe as-received steel, hardening has generated a fine martensitic microstructure causing a 1.5 timeshardness increase. Hardening has contributed to improvement of wear resistance as the coefficient offriction has decreased from 0.86 to 0.67μ. An increase in corrosion resistance was observed afterhardening treatment. Voir les détails
Mots clés : tool steel, AISI L6, friction, hardening, corrosion, heat treatment, wear
Reliability Estimation of Cracked API 5L X70 Pipeline Steel
The aim of this paper is to estimate the reliability of cracked pipeline steel grade API5L X70 used for hydrocarbon transportation, by coupling a developed mechanical model, basedin one hand on the simulation of cracked specimen, and an experimental result of tensile and Charpy test, and in the other hand, based on a reliability model by using a first-order reliability method (FORM). These pipes are produced by the Algerian company of manufacture of welded pipes (ALFAPIPE Annaba). The experimental task such as resilience and tensile test were carried out on specimens taken from a pipe in the longitudinal and the transversal directions. The resilience tests are carried out at different temperatures in order to estimate the fracture toughness of the material, basing on a global correlation. Besides, tensile tests are performed to bring out the mechanical characteristics of the material. After, the stress intensity factor is assessed using the analytical model of IRWIN. In the reliability analysis, the limit state function is attributed to the moment when the stress intensity factor estimated by Irwin mechanical model, is equal tothe fracture toughness of the steel pipe. The basic random variables within the limit state function are assumed to follow a normal distribution in order to simplify the assessment. Then, the evaluation of the reliability index and the parameters sensitivities of the cracked pipelines steel are assessed. Voir les détails
Mots clés : Reliability, Cracked API 5L X70, Pipeline Steel
Effect of ball burnishing process on mechanical propertiesand impact behavior of S355JR steel
Often, surface mechanical treatment (SMT) or heat (quenching, tempering) is used to improve the surface condition andmechanical characteristics such as impact resistance and tensile strength. Hence the objective of this experimental work, whereball burnishing (BB) as well as quenching and tempering were applied on S355 JR steel specimens, is to evaluate the surfacehardness Hv, the rupture strength Rm, the energy absorbed W during the impact test, and the work-hardened thickness e after theburnishing operation. Factorial designs were used for the test organization and mathematical models were established for theprediction of Hv, Rm, W, and “e” in function on treatment parameters considered: number of tool passes (i) and the pressure force(Py). The results show that the surface hardness increases by 30.46%. The high levels of Py and i were allowed to improve Rm by30.8% as well as an increase in tenacity of only 3.6%. Increasing the force to 20kgf promotes mixed rupture under the effect ofimpact to shock. The quenching and tempering improve the Rupture strength Rm by 183% and 119%, respectively, while theeffect of burnishing was limited to a rate of increase of this property of 28% compared to machining. Voir les détails
Mots clés : Tensile resistance . Burnishing . Heat treatment . Superficial hardness . Absorbed energy . Penetration depth . Ruptures facies
DETERMINATION DES PROPRIETES ELASTIQUES PAR LES ESSAISDE TRACTION ET D’ULTRASON DE L’ALLIAGE EUTECTIQE AlSi13
Aluminum has very low mechanical properties. To significantly increase them, we actedon three main modifying factors of the microstructure. Addition to aluminum of a very lowdensity element including 13% silicon which facilitates the flowability of the metal, gravitysand molding and structural hardening treatments.Al-Si alloys are highly indicated by their lightness, their high tensile and corrosionresistance. The study focuses on the influence of maturation on the evolution of the elasticproperties determined by the tensile and ultrasound tests of the Al-13% mass eutectic alloy. Iffor six states: raw casting noted - F and maturation in 6h steps noted - M0h, M6h, M12h,M18h and M24h. The parts produced from this alloy are part of the components used invarious projects by SNVI Rouïba and Electro-Industries de Fréha (covers, pump casing,motor pistons, etc.).All the results of the mechanical and structural properties gathered in Part III of our thesisshow us that we should recommend for the molding of parts whatever the series: the grossreference state designated - F. Voir les détails
Mots clés : Al-Si, sand, ripening, mechanical properties
Caractérisation et modélisation numérique d’un composite époxy/Alfa.
Nowdays, natural fiber composites are increasingly getting great interest on an industrial scale. This undeniable success is linked to the intrinsic properties of natural fibers reinforcements and to their ecological character. Our study consists in characterizing the mechanical properties in tensile, bending and ultrasonic as well as morphological characterization by optical and scanning electron microscopy in order to evaluate their aptitude to replace synthetic fiber composites. The material to be characterized is composed of an epoxy matrix reinforced with 20% in weight Alfa short fibers. Numerical modeling using the finite element method allowed us to predict the Young's modulus of our randomly reinforced biocomposites. The ANSYS modeling software was used to generate the 3D representative elementary volume and to calculate the Young's modulus of the composite. The experimental results recorded are close to those obtained by numerical modeling. The latter remains therefore the goal to reach. Voir les détails
Mots clés : natural fibers, Alfa fibers, biocomposites, mechanical characterization, numerical modeling, ecology
Caractérisation des paramètres de fissuration en mode d'ouverture par corrélation d'images et éléments finis d’un alliage d’aluminium 2xxx
In this work, a problem of fracture and crack resistance is studied, the 2000 aluminum alloy series available in market is chosen, in this context of fracture mechanics the structural durability and integrity of materials is investigated. Couple techniques are used, an experimental characterization assisted by the digital image correlation technique and finite elements based numerical simulations, the aim is to study the mechanical behavior in presence of cracks and determine the fracture toughness. Making use of theoretical notions, analytical formulas, experimental tests coupled by the recent digital image correlation technique and numerical simulations constitute an efficient protocol to characterize materials to resist against cracks. At the end of our work, the study was done to know the crack propagation in opening mode (mode I) and the stress evolution on the crack paths by the X-FEM extended finite element method. Voir les détails
Mots clés : failure in mode 1, stress intensity factor (SIF), Cracking, Correlation of digital images (CDI), FEM finite elements, Abaqus, Integral J, Extended finite element method (XFEM)