Machines. Technologies. Materials.
Vol. 19 (2025), Issue 1

Table of Contents

  • MACHINES

    • A validation approach for a FEA model of thermal distortion for CO-CR thin wall structures produced by LPBF process

      pg(s) 3-6

      Laser Powder Bed Fusion (LPBF) is a prominent additive manufacturing process used for fabricating complex metallic structures, but it often encounters challenges related to thermal distortions and residual stresses, particularly in thin-walled structures. These issues compromise the integrity and dimensional accuracy of the parts. Finite Element Analysis (FEA) has been essential in simulating and understanding the thermal and mechanical behaviors during the LPBF process. This study focuses on validating a refined FEA model developed using ANSYS Additive Print (AAP) to predict the thermal distortions in CoCr thin-wall structures. The validation involves comparing simulation results with experimental data to verify the model’s effectiveness. The study demonstrates the integration of advanced simulation techniques in predicting distortions and stresses, thereby enhancing the reliability and accuracy of the manufacturing process.

    • Exergy analysis of 160 MW three cylinder steam turbine segments

      pg(s) 7-10

      Exergy analysis of three cylinder steam turbine segments is performed in this research. The highest mechanical power of 47389.66 kW is developed in the first segment (Seg. I, which actually represents the entire HPC – High Pressure Cylinder). Intermediate Pressure Cylinder (IPC) is the dominant mechanical power producer of all cylinders and it develops 48.95% of cumulative mechanical power produced in the whole turbine. The outlet Low Pressure Cylinder (LPC) segments (Seg. VII and IX) have the highest exergy destructions and the lowest exergy efficiency (equal to 61.27%) of all turbine segments. The best exergy performance shows IPC segments – Seg. V has the lowest exergy destruction (equal to 363.84 kW), while Seg. II has the highest exergy efficiency (equal to 94.04%) of all turbine segments. Outlet LPC segments (Seg. VII and IX) are the most sensitive to the ambient temperature change – their exergy efficiency decreases for 3.19% when the ambient temperature increases from 5 °C to 45 °C.

    • A Novel Hybrid Iterative Approach for Defining Plane Stress and Strain States

      pg(s) 11-17

      The definition of plane stress and strain states plays a crucial role in engineering, as recognizing these states within a structure enables the optimization of its design. This article introduces a novel hybrid wave method for analysing a circular disc geometry, with potential extensions to other geometric configurations. The method involves applying wave forces corresponding to the external loads, which then propagate through the structure and reflect back at the contours to satisfy static equilibrium conditions. The process is conceptualized in two phases while the first phase involves the application of forces where the second phase accounts for the arrival and reflection of waves at the contour boundaries. In each case, the static equilibrium at the contours is maintained by considering the reflection of the stress waves, or return waves. By incorporating these return waves and ensuring the boundary conditions are met, this approach facilitates the determination of stress at any given point within the structure.

  • TECHNOLOGIES

    • The influence of vibrations on the friction of removable electrical connectors during operation, and the causes of malfunctions in electrical contacts

      pg(s) 18-20

      This paper discusses contact interaction under mechanical stress and how vibrations change the physical properties of conductor materials, which affects their ability to provide reliable contact. It also analyzes the causes of contact failures, which allows us to better understand the mechanisms that lead to problems in the operation of electrical connectors. These factors can lead to serious consequences, including breakage and reduced reliability of connectors, and also considers the possibilities of improving the characteristics of electrical contacts at the stage of their creation, using various technologies for applying and creating an approximately ideal molecular structure of the contact surface of detachable electrical connectors, with an increase in the surface layer of the contact and a decrease in the coefficient of friction.

    • Mooring system for fuel oil unloading

      pg(s) 20-21

      The aim of this paper is the calculation of the PLEM (Pipeline End Manifold) System of the 18″ dia. subsea pipeline, according to the International Codes and Standards. A Geotechnical survey was carried out to define soil – structure interaction, effect of scour, soil stratigraphy and susceptibility to liquefaction. Then were defined the acting forces on PLEM, pipeline and submarine hoses taking in consideration the total buoyancy as well. The calculation was carried out for filled pipeline (in service), as well as for empty pipeline. The ground conditions along the sealines and at the location of the PLEM have been investigated by a dedicated additional site investigation, consisting of 12 no. vibrocore samplings and the related laboratory testing. The stability of PLEM was checked for several load combination. This calculation it was very important for environmental reason and shows that the structure meet the requirements of the project.

    • Assessment of the risk of electromagnetic emissions through monitoring for an object on the territory of the Metropolitan municipality

      pg(s) 22-24

      In many cases, the importance of electromagnetic fields or the so-called “electromagnetic smog” on human health, living organisms, and the environment is ignored or at least minimized. The electromagnetic field (EMF) is a combination of invisible electric and magnetic fields with charge that occur in nature. Today, the impact of electromagnetic fields on the environment is increasing from human activities with the development and application of telecommunication technologies. Measurement, continuous monitoring, database creation, and evaluation of electromagnetic field parameters in urban environments are important aspects of optimizing EMF levels to achieve a healthy living environment. The paper presents an analysis and evaluation of electromagnetic radiation measurements from base stations of mobile operators, at one site, in a lightly urbanized urban environment over a certain time interval. Initial measurements showed exceeding the levels of electromagnetic emissions according to national legislation. During the repeated measurements, it was found that mobile operators, after correcting the radiation from base station antennas, have brought the radiation levels within the permissible limits. This underscores the necessity of ongoing monitoring.

    • Large-scale distortion analysis of the welding and thermal straightening process chain

      pg(s) 25-29

      An coupled analytic-numerical model for calculation of distortions arising by welding fabrication is introduced. Target of the analytical model is the calculation of the inherent strains after the local thermal-mechanical influence of the welding or thermal straightening process. Following the fabrication processing chart the strains are loaded on an elastic FE-model of the structure and the residual stresses and distortions of the whole structure are calculated. The consideration of welding and thermal straightening scenarios, inclusively the assembling stages, is done by taking into consideration the intermediate variation of the strain state in the FE-model of the structure at every processing step. The important physical relations are demonstrated. The model is intended to be used for solving industrial tasks, i.e. intending acceptable precision and calculation time as well as low simulation costs.

    • Investigation of extruded polyethylene blend films tensile creep elongation with different open holes configurations

      pg(s) 30-32

      In this article,tensile creep elongation of PE plastic films with two configurations of open holes stressed at the incremental temperatures of 23,30,37,43,51,58 degrees and a constant dead weight of 50 kg will be analyzed. The aim of the article is to analyze influence of the two configurations of open holes on the relative elongation. The test was conducted with the same blend, under the same test conditions. The test was conducted entirely according to the conditions established in the ASTM D6992 standard.

    • Methods of Temperature Measurement in Heat Affected Zone during Welding

      pg(s) 33-37

      The metal materials are subject to severe temperature variation during the application of the welding process. The heat input and thermal shock during arc welding cause change of the base material properties in the heat affected zone. Temperature measurements and destructive tests of sample pieces, subjected to different process parameters and conditions, enable identification of minimum and maximum cooling rates, at which the material properties remain in pre-defined limits. Temperature measurements on the surface of the material in proximity to the weld seam enables cooling rate monitoring and material properties evaluation at manufacturing or site installation conditions, when the products could not be subjected to destructive tests. The requirements to the surface temperature measurement during welding and the characteristics of the different measuring devices were investigated for fitness to the purpose of cooling rate calculations, material properties evaluation, as well as for calibration of welding process simulations in volumes in close proximity to the arc welding seams.

  • MATERIALS

    • Effect of technological parameters on the structure and physico-mechanical properties of Fe-FeCr800 system composite

      pg(s) 38-41

      The article investigates the influence of technology and technological parameters of manufacturing on the structure, phase composition and physical and mechanical properties of the Fe-FeCr800 composite system. It was established that the determining factor in phase and structure formation is the manufacturing technology, while vacuum sintering and hot forging have their own optimal technological parameters. At the same time, hot forging makes it possible to obtain a composite with a higher microhardness of structural components due to a change in the content of component components. The results of the research also showed that the preheating time (for 20 min.), as well as thermomechanical treatment, is sufficient for the phase formation process, in particular, with the release of carboboride phases of the type Me3CB and Me3(CB)2, while the densification processes are intensified, which makes it possible to obtain a material with lower residual porosity. Analysis of mechanical tests showed that vacuum sintering makes it possible to obtain composites with higher mechanical properties due to the active interaction between the components of the composite. However, high-temperature annealing after hot deformation will allow for a composite with high mechanical properties.