Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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Nova Uredba o mašinama (EU) 2023/1230
No full textRad analizira evoluciju regulative EU koja se odnosi na bezbednost mašina, od prvih direktiva do najnovije Uredbe (EU) 2023/1230, koja zamenjuje trenutno aktuelnu Direktivu 2006/42/EC. Opisani su ključni zahtevi za proizvođače mašina, promene u zakonodavstvu, te izazovi koje donosi primena nove Uredbe. Cilj rada je da ukratko prikaže uticaj novih regulativa na proces konstruisanja mašina namenjenih EU tržištu, kao i na pripremne aktivnosti koje proizvođači moraju preduzeti pre početka zvanične primene Uredbe 2027. godine
SAMPLE PREPARATION FOR CAVITATION EROSION TESTING OF 3D-PRINTED METAL
No full textCavitation erosion is a common occurrence in machine parts and elements operating under cavitation conditions (presence of high-speed working liquid in contact with parts’ working surfaces). This paper describes the comprehensive preparation of samples for testing resistance to cavitation erosion. The samples are 3D-printed metal parts, which is significant considering the increasing use of additive manufacturing technologies in the production of machine parts. The test samples were obtained by recycling samples previously used in rotational bending tests. These samples were made from MS1 maraging steel powder, 3D printed using Direct Metal Laser Sintering (DMLS). The study follows ASTM standard G32-16 for cavitation erosion testing, using a vibrating apparatus with a water bath for immersing the test samples. Samples will be subjected to cavitation for 1, 2, and 4 hours, with periodic mass loss measurements. The obtained data will be used to determine the cavitation rate of the tested material. Additionally, optical and SEM structural and morphological analyses will be conducted before and after testing to characterize the erosion damage process
Atlas Roman Pot Heat Sink Development for Low Pressure Working Conditions
No full textThe development of a heat sink for Atlas Roman Pots for the purpose of ATLAS Forward Proton (AFP) detector upgrade in 2024, is presented in this paper. During proton collisions, the Roman Pots (RP) used in the Large Hadron Collider (LHC) move very close to the beam. Since beam intensity had been gradually increased over the years, the temperature increase was also observed on the RP wall and bottom. Eventually, it started raising concerns that it would compromise surrounding vacuum conditions. Hence, in order to reduce RP temperature,
a heat sink needed to be developed which would transfer the excessive heat from the RP wall and bottom to the flange, which remains roughly at room temperature even during beam conditions. The RP and the flange are made of stainless steel and due to their low thermal conductivity it is impossible to avoid overheating of the RP bottom. A few concept designs were developed and the temperature field change with time was simulated in ANSYS Fluent. Since the heat sink has no symmetry planes, the simulations was performed in 3D numerical domain. The influence of Roman Pot movement on heat transfer was analysed. Operating conditions are very close to vacuum, so natural convection can be disregarded. Heat transfer mechanisms that were taken into account are radiation and conduction. Experimental investigation of the prototype was done at CERN at atmospheric and low pressure conditions. Furthermore, the temperatures are continuously
being remotely monitored in LHC working conditions. Temperature distribution obtained by numerical simulations showed very good agreement with the experimental results
A procedural and technical experimental review on material tensile and impact properties under cryogenic temperatures
No full textIn this paper, research and comparison of tensile and impact properties were conducted on several materials broadly categorized as Steel and Alloys at cryogenic temperature of 77 K or -196°C. Tensile and impact properties exhibit an inverse relationship due to the nature of metals, where if a material has high strength, its ductility will decrease, and if it has high ductility, its strength will decrease. Generally, cryogenic treatment will result in periodic strength enhancement of materials, but a significant reduction in ductility occurs when the temperature surpasses the ductile to brittle transition temperature (DBTT). However, some materials can be processed to achieve desired property advantages, such as high toughness, high ductility, or a balanced combination of ductility and toughness without significant reduction in either property
Development of an Analogical Model for Strain Monitoring of Welded Joint Regions During Uniaxial Tensile Testing
No full textThe idea behind the idea of developing this method was to introduce reference points at
important locations, such as the fusion line and heat-affected zones, the displacement of which
would be monitored during the uniaxial testing, and then measured at key moments. The uniaxial
tensile test process was recorded with a high resolution camera so that changes could be observed during the test. The reason why this approach was chosen was that the crucial zones
could be adequately marked and thus allows the allocation of the appropriate frame in order to
monitor the strain of each welded joint zone individually
Three-dimensional Numerical Investigation of Fluidized Bed Gasification in a Pilot Plant Gasifier: Fluid Flow
No full textFluidized bed combustion offers key advantages such as high efficiency, environmental friendliness, fuel flexibility, and load adaptability, making it suitable for various applications such as power generation, biomass gasification, and petrochemical processing. This study presents a numerical investigation of the gasification processes in a pilot-scale fluidized bed gasifier using a 3D computational model. The model simulates the complex turbulent multiphase flow within the real gasifier geometry of the pilot plant and focuses on the interactions between air and sand, as well as the temperature distribution. Initial numerical results show good agreement of fluid flow structure with experimental data. Future work will include combustion modeling, with the numerical results to be validated by experiments in the pilot plant. After model validation, the model will be used for similarity analysis to optimize the process parameters
Internality of two-measure-based generalized Gauss quadrature rules for modified Chebyshev measures
No full textNumerical Investigation of Fatigue Behavior in Ti-6Al-4V Orthopedic Hip Implants Subjected to Different Environments
No full textIn this paper, hip implants made of Ti-6Al-4V titanium alloy are analyzed numerically using Extended Finite Element Method XFEM. The combined effect of corrosion and fatigue was considered here since this is a common cause of failure of hip implants. Experimental testing of Ti-6Al-4V alloy was performed to determine its mechanical properties under different working environments, including normal, salty, and humid conditions. The integrity and life of the hip implant were assessed using the Linear Elastic Fracture Mechanics (LEFM) approach. For this purpose, the conditional fracture toughness Kq using CT specimens from all three groups (normal, humid, salty conditions) were determined. This provided insight into how different aggressive environments affect the behavior of Ti-6Al-4V alloy; i.e., how much its resistance to crack growth would degrade depending on conditions corresponding to the real exploitation of hip implants. Next, analytical and XFEM analyses of fatigue behavior in terms of the number of cycles were performed for all three groups, and the obtained results showed good agreement, confirming the validity of the integrity assessment approach shown in this work, which also represented a novel approach since fatigue and corrosion effects were investigated simultaneously