1. Izbira ustreznega tipa kovice za aplikacijo na izpušnem sistemuMaj Pinter, 2025, undergraduate thesis Abstract: Diplomska naloga se osredotoča na primerjavo rezultatov analitičnih preračunov, praktičnih preizkusov ter numeričnih analiz za izbiro najustreznejšega tipa kovice za aplikacijo na izpušnem sistemu. Z uporabo programa Solidworks sta bila izdela na geometrijska modela kovic na katerih je kasneje bila izvedena numerična analiza v programu PrePoMax, katerih rezultati so bili nato primerjani. Oba tipa kovic sta bila tudi testirana na trgalnem stroju in sicer na nateg in strig, ter vibracijskem testu, saj je to značilnejša obremenitev zanje kot pa doseganje maksimalnih obremenitev. Rezultati so ustrezno analizirani, na podlagi katerih je bila izbrana ustrezna kovica.
Keywords: Kovica, metoda končnih elementov, nateg in strig, CAD modeliranje, vibracije
Published in DKUM: 22.09.2025; Views: 0; Downloads: 16
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2. Dimenzioniranje pogona rezalnika : diplomsko deloJan Bric, 2025, undergraduate thesis Abstract: V diplomskem delu smo predstavili podjetje Eurel, d.o.o. in zgodovino rezalnikov. Zaradi
prostorske stiske pri novi generaciji rezalnikov smo na novo dimenzionirali polžasto gred
in zobniški prenos. Pri tem smo upoštevali, da ob petminutnem neprekinjenem delovanju
ne pride do pregrevanja plastičnih komponent. Uporabili smo analitične in numerične
metode (preračun trdnosti, CREO Simulate, termično-strukturna analiza) ter
eksperimentalni preizkus 3D-tiskanega prototipa. Rezultati so podali optimalne
dimenzije gredi, dovoljene temperaturne režime in vpliv materialov na zanesljivost
prenosa. Sklep ponuja stroškovno ugodno in kompaktno rešitev, ki ohranja
funkcionalnost obstoječega rezalnika.
Keywords: rezalnik, polžna gonila, toplotna analiza zobniškega prenosa, sile v
zobniškem prenosu, izbira pogonskega elektromotorja
Published in DKUM: 19.09.2025; Views: 0; Downloads: 6
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3. Structural integrity of pressure vessel heads made by incremental sheet forming from high-quality steel P460 NL1 : elektronski virNedeljko Vukojević, Zlatan Ištvanić, Fuad Hadžikadunić, Nenad Gubeljak, Amna Bajtarević-Jeleč, 2025, original scientific article Abstract: The fabrication of pressure vessel heads with large diameters necessitates the production from a starting sheet composed of two sections with weld joint. Subsequent plastic deformation may influence changes in the mechanical properties of the sheet, particularly the welded joint. The subject of this research is the effect of incremental plastic deformation (known as Incremental sheet forming) and post weld heat treatment on the mechanical properties of the heat-affected zone in the welded joint, as well as an assessment of the structural integrity. One of the goals of the work is to show that in certain circumstances heat treatment is not necessary. The researches focus on destructive and semi destructive testing of samples extracted from an actual pressure vessel head structure. The material of the vessel head is steel grade P460 NL1, and the heads are manufactured in two thicknesses: 6 mm and 14 mm. The results of the structural integrity assessment are presented in the form of a FAD diagram.
Keywords: incremental sheet forming, post weld heat treatment, residual stress, steel grade P460 NL1, structural integrity, welded vessel heads
Published in DKUM: 19.08.2025; Views: 0; Downloads: 4
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4. Comparative analysis of fracture mechanics parameters for wrought and SLM-produced Ti-6Al-7Nb alloyIvan Gelo, Dražan Kozak, Nenad Gubeljak, Tomaž Vuherer, Pejo Konjatić, Marko Katinić, 2025, original scientific article Abstract: The research presented in this paper is based on the need for personalized medical implants, whose serial production is impossible, so the need for production process adjustments is inevitable. Conventional production technologies usually set geometrical limitations and generate a lot of waste material, which leads to great expenses, especially when the material used for production is an expensive Ti alloy. Additive technologies offer the possibility to produce a product almost without waste material and geometrical limitations. Nevertheless, the methods developed for additive production using metal powder are not significantly used in biomedicine because there is insufficient data published regarding the properties of additively produced parts, especially from the fatigue and fracture standpoint. The aim of this research is the experimental determination of fracture mechanics properties of additively produced parts and their comparison with the properties of parts produced by conventional technologies. Drawing is the first production process in the comparison, and the second one is selective laser melting (SLM). The Ti-alloy Ti-6Al-7Nb, used for medical implants, was selected for this research. Experimental testing was performed in order to determine ∆Kth fracture mechanics parameters and resistance curves according to ASTM E1820. Test specimen dimensioning and the experiments were carried out according to the respective standards. For the drawn test specimen, the value obtained was ∆Kth = 3.84 MPam0.5 , and the fracture toughness was Kc = 84 MPam0.5, while for SLM produced test specimens the values were ∆Kth = 4.53 MPam0.5, and Kc = 21.9 MPam0.5.
Keywords: fracture toughness, crack growth curve, resistance curve, additive technologies, powder metallurgy, selective laser melting, Ti-6Al-7Nb
Published in DKUM: 19.08.2025; Views: 0; Downloads: 10
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5. The effects of ozone sterilization on the chemical and mechanical properties of 3D-printed biocompatible PMMAIvan Morosavljević, Dražan Kozak, Tihomir Kosor, Janko Morosavljević, Luka Ferlič, Nenad Gubeljak, 2024, original scientific article Abstract: Since ozone is highly corrosive, it can substantially affect the mechanical and chemical properties of the materials; consequently, it could affect the applicability of those materials in medical applications. The effect of ozone sterilization on the chemical and mechanical properties of additively manufactured specimens of biocompatible poly(methyl-methacrylate) was observed. FDM 3D-printed specimens of biocompatible PMMA in groups of five were exposed to high concentrations of ozone generated by corona discharge for different durations and at different ozone concentrations inside an enclosed chamber with embedded and calibrated ozone, temperature, and humidity sensors. A novel approach using laser-induced fluorescence (LIF) and spark-discharge optical emission spectrometry (SD-OES) was used to determine an eventual change in the chemical composition of specimens. Mechanical properties were determined by testing the tensile strength and Young’s modulus. A calibrated digital microscope was used to observe the eventual degradation of material on the surface of the specimens. SD-OES and LIF analysis results do not show any detectable sterilizationcaused chemical degradation, and no substantial difference in mechanical properties was detected. There was no detectable surface degradation observed under the digital microscope. The results obtained suggest that ozone sterilization appears to be a suitable technique for sterilizing PMMA medical devices.
Keywords: ozone sterilization, poly(methyl-methacrylate) (PMMA), polymer oxidation, personalized medical device, environmentally friendly, fused deposition modeling (FDM)
Published in DKUM: 30.07.2025; Views: 0; Downloads: 1
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6. Numerical investigation of imperfection-induced secondary bending stresses in box girdersJernej Kralj, Nenad Gubeljak, Srečko Glodež, Janez Kramberger, 2025, original scientific article Abstract: Numerous studies have demonstrated that the initial out-of-plane deflection can significantly affect stress distribution along the web boundaries of steel plate girders, potentially leading to the initiation of fatigue cracks and eventual structural failure over time. Fatigue cracks in thin-walled structures commonly initiate at locations of maximum secondary bending stress, arising from the web imperfections introduced during the complex manufacturing process and further amplified by the interaction of global and local stresses. The secondary bending stress of box girders web plate has been numerically investigated in this article. Several nonlinear static analyses have been performed, using the hybrid parametric FE model, consisting of shell and beam finite elements. Vertical normal stress in the upper web boundary below rail was evaluated under different boundary conditions and geometric modifications. Considering the deflection shape of critical buckling mode 1, the directional effects of initial web imperfection and eccentric moment have been evaluated. Also, a comparison in terms of secondary bending stress at different girder spans, intermediate plate spacing and load positions are discussed. The results of this study offer valuable insights into the most and least favorable scenarios related to geometric modifications and varying loading conditions, while also highlighting existing research gaps in current design codes.
Keywords: box girder, initial web imperfection, out of plane deflection, secondary bending stress, wheel loading
Published in DKUM: 09.07.2025; Views: 0; Downloads: 14
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7. Time dependent load capacity of the press fitVinko Močilnik, Nenad Gubeljak, Jožef Predan, 2025, original scientific article Abstract: This study investigates the loading capacity of a press fit using experimental, numerical and theoretical methods. Tests on specimens with different interferences showed that the loading capacity increases over time as long as the plasticity remains at the micro level. At larger interferences, the plasticity extends to the macro level, which in the long term means a reduction in the loading capacity of the press fit due to creep. Numerical simulations using finite element modelling showed the influence of surface roughness and time-dependent effect on contact pressure and friction. Models in text books do not take in account plasticity and creep of the material in press fit. The phenomenon can lead to a weakening of the press fit over time. The results highlight the importance of optimizing the interference and surface preparation to improve the loading capacity and joint performance. The article presents an approach for calculating the press fit taking in to account the Bowden Tabor friction model and the visco-plasticity of the material used.
Keywords: FEM analysis, interface oversize, hub, shafts, loading creep, press fit, roughness
Published in DKUM: 08.07.2025; Views: 0; Downloads: 15
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8. Analyzing site-specific tractor draft force in different passes during plowingMateja Ortopan, Vojislav Simonović, Nevena Tasić, Emil Veg, Ivan Zlatanović, Nenad Gubeljak, 2024, original scientific article Abstract: The difference in draft force is analyzed for six different passes during longitudinal plowing of the plot. The force is measured indirectly using four strain transducers. Values of the force are obtained by calculation after previous calibration and then measurements in the experimental field. The strain readings on the sensors installed on the outside of the tractor lower links are used. Similar values are obtained on the other two sensors installed on the inside of the links. The biggest difference is observed between the first and second pass, respectively, the second and third one for which the value of effect size amounts to 0,824 and 0,835 respectively. The study highlights draft force in the function of soil resistance as an exceptionally important parameter in the analysis of agricultural soil and suggests the expansion of current routine in precision agriculture mapping.
Keywords: draft force, lower links, pass, strain transducer
Published in DKUM: 02.07.2025; Views: 0; Downloads: 4
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9. Comparison of three methods of measuring residual stresses in welded joints of high-strength steel S960QLMirza Manjgo, Gorazd Lojen, Nenad Gubeljak, Blaž Karpe, Tomaž Vuherer, 2025, original scientific article Abstract: The influence of residual stresses as a result of the welding process in the overall stress state of the weld joint is of great importance because they significantly affect the creation and growth of cracks, the occurrence of brittle fracture, and material fatigue. Previous experiences indicate that it would be necessary to provide an assessment of the deformation and stress state in the critical zones of the weld joints using a suitable test method, which will not endanger the structural integrity of the tested places. There are different methods for measurement of residual stress in welded constructions: destructive, semi-destructive and non-destructive. To choose one method over another, it is necessary to take into account the advantages and limitations of these techniques for practical application. This paper considers and analyzes the residual stresses in the welded joint of high-strength steel S960QL. MAG welding was performed by a robot. Three methods were used to measure the residual stresses: the magnetic method (MAS), the X-ray diffraction method (XRD), and the hole drilling method (HD). By all three methods, the highest residual stresses were measured in the weld metal and in the heat-affected zones. Nevertheless, the measured values differed considerably. The differences can be contributed to (a) the kind of stress that the individual method measures, (b) to the volume of material from which each method captures the signal and averages it, and (c) to the different sensitivities of the applied methods to coarse-grained microstructure and microstructural gradients.
Keywords: welded joints, high-strength steel, residual stress, magnetic method, X-ray diffraction method, hole drilling method
Published in DKUM: 11.06.2025; Views: 0; Downloads: 5
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10. Experimental testing and numerical bite simulation of complete acrylic dentures in eugnathic and progenic occlusal relationshipsMartin Pavlin, Robert Ćelić, Nenad Gubeljak, Jožef Predan, 2025, original scientific article Abstract: Complete dentures are exposed to complex masticatory forces that may lead to material fatigue and eventual structural failure. Occlusal relationships, such as eugnathic and progenic, influence the distribution of these forces significantly. Understanding their biomechanical impact is essential for improving denture design and longevity. The aim of this study was to evaluate the mechanical behaviour of complete dentures under bite loads in eugnathic and progenic occlusal relationships, using both experimental testing and numerical simulations. The focus was placed on identifying the conditions that lead to initial damage and the patterns of stress distribution. The material properties of the denture base and artificial teeth were determined through experimental tensile and compressive testing on cylindrical PMMA specimens. The denture geometry was acquired via 3D tomography based on impressions of an edentulous patient. Experimental testing of the denture bite was conducted to determine the force thresholds at which the initial cracks occur. Numerical simulations were carried out using finite element analysis at bite loads of 100 N and 200 N in both occlusal types, incorporating the obtained material parameters. The experimental results showed that the first signs of denture damage occurred at 6400 N in eugnathic occlusion and 7010 N in progenic occlusion. The numerical simulations confirmed that, during occlusion, the pressure is redistributed across multiple contact points, with a broader distribution reducing the localised stress. This redistribution was more efficient in eugnathic occlusion, which reduced the risk of longitudinal cracking in acrylic teeth. In contrast, progenic occlusion showed higher susceptibility to fractures within the acrylic denture base, particularly between adjacent teeth. Both the experimental and numerical approaches demonstrated that occlusal relationships affect the mechanical resilience of complete dentures directly. The findings highlight that eugnathic occlusion offers biomechanical advantages in stress distribution, potentially reducing the risk of fracture. Incorporating occlusal analysis into denture design protocols can enhance clinical outcomes and improve prosthetic longevity.
Keywords: bite force, finite element method, dental biomechanics, numerical simulations, complete acrylic dentures, occlusal force distribution, occlusal pressure distribution
Published in DKUM: 11.06.2025; Views: 0; Downloads: 8
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