Articles de périodique
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Item Experimental Study of Thermal Ageing and Hydrogen Embrittlement Effect on the Equipments of a Rocket Engine(International Journal of Engineering Journal Homepage: www.ije.ir, 2024-01-01) REZALA, Aicha; JABBAR, HassanIn the present study employed disc pressure tests to assess the effects of hydrogen embrittlement and thermal ageing on the fatigue life of a thin-wall circular part within a rocket engine. The technique compared the pressure resistance of membranes tested under helium and hydrogen, offering a simple, sensitive, and reliable method. Disc tests were selected to mimic natural operating conditions, as they align with those of a thin-wall circular part within a rocket engine. The originality of these tests appears to lie in their enhanced performance in terms of sensitivity and reproducibility. To achieve this, tests were conducted across various conditions, including sample thicknesses of 0.75 mm, a broad range of strain rates from 10-6 s-1 to 100 s-1, temperatures spanning from 20°C to 900°C, and pressure rates from 10-2 to 2.104 MPa/min. Furthermore, a variety of materials were investigated, including copper, nickel alloy, and stainless steel. The results demonstrated that thermal aging leads to precipitation, particularly intergranular precipitation. These precipitates diminish the material's ductility, particularly when they are nearly continuous. Additionally, the material's sensitivity to hydrogen becomes significant when hydrogen, supersaturated due to rapid cooling, becomes trapped on precipitates formed at high temperatures. Furthermore, the results indicated that thermal and hydrogen-induced damage mutually reinforces each other, resulting in reduced fatigue life under high deformation.Item Contribution to analysis and friction exploitation as part of the improvement in terms of industrial robot repeatability(Université des Sciences et technologie Houari Boumediene, 2023-02-01) REZALA, AichaThe imperfections at the origin of the lack of repeatability are of random nature, caused by the adjustments of the servo-control and especially by non-geometric phenomena such as the play and friction existing at the joints level. The occurring friction constitutes one of the main causes of performance loss. The friction modeling isn’t an easy task, and therefore, its correction in advance remains difficult. The adopted method consisted of employing mechanical approaches in order to theoretically identify the contribution of friction on the pose repeatability. The tribological experimental study was carried out on the alternative tribometer and is based on the steel grade 42CD4 with a steel pin 100C6 used on the robot joints. Due to the variability of the friction values coefficient, the main asperities on isotropic surfaces were analyzed by considering their characteristics, namely the top altitude of each asperity, the distance between two consecutive views, and its radius. Each of these geometric characteristics is described using statistical analysis with probability density functions such as Gaussian laws. Finally, these developments resulted in a model that was applied by using measurements of three different types of microgeometry, ranging from quasi-periodic to quasi-random. The obtained results are interesting because they served to improve the analysis of repeatability by taking into accountItem REPAIR OF AIRCRAFT STRUCTURES(2022-11-22) REZALA, AichaComposite materials are only one of the types of materials used in the aeronautical field, but their use has progressed dramatically over the last decades. Knowing that an aeronautical program is developed over an average of ten years, and a time necessary to study, test, and launch the industrialization of an aircraft, improving its aerodynamic quality, while increasing the performance of engines and especially reducing the weight of structures. On the other hand, non-destructive testing (NDT) plays a very important role in detecting or characterizing the defects existing in the composite structure, estimating the importance of damage as well as determining the quality of a repair. However, the purpose of this study is to characterize some existing defects in the composite structure commonly used in aeronautical manufacturing, by representing the less expensive repair methods, to reduce the overweight of the final repair.Item Contribution à l’amélioration de la précision de robots parallèles par les ellipsoïdes stochastiques(2022-10-22) REZALA, AichaLa conception mécanique des robots exige de très haute précision des éléments du système mécanique qui le compose afin que leur organe terminal puisse réaliser des précisions élevées. Ces robots doivent, aussi présenter une bonne répétabilité lors de leur utilisation. Notre travail traite de la modélisation de robots parallèles afin de permettre le positionnement d’une façon précise dans les applications mécaniques. Pour l’analyse de la répétabilité, une méthode probabiliste basée sur les ellipsoïdes stochastiques est utilisée dans tout l’espace de travail d'un robot au voisinage d’un point de cet espace.Item Introduction of plug-in hybrid electric vehicles in an isolated island system(2018-05) Loakimidis, Christos S.; Genikomsakis, Konstantinos N.Item Autonomous lighting assessments in buildings : part 2 – light identification and energy analysis(2017) Terrill, Trevor J.; Bay, Christopher J.; Rasmussen, Bryan P.Item Autonomous lighting assessments in buildings : part 1 – robotic navigation and mapping(2017) Bay, Christopher J.; Terrill, Trevor J.; Rasmussen, Bryan P.Item Procedure for evaluating and refurbishing envelopes of obsolete buildings in warm regions(2017) Garcia-Esparza, Juan A.; Roig, Carolina CaballeroItem Application of building-dynamics-based control strategies to improve air-conditioning performance in educational buildings(2017) Ben-Nakhi, Abdullatif E.; Mahmoud, M. A.Item Flexural response to impulsive loads of a fluid-saturated thin poroelastic circular plate(2017) Tsay, Huoy-Shyi; Yeh, Fung-Huei