1. Topološka optimizacija nosilca elektromotorja dirkalnika formule student : magistrsko deloTadej Leskošek Zmagaj, 2025, magistrsko delo Opis: Magistrsko delo obravnava obstoječi nosilec elektromotorja Formule Student. V njem je natančno opisan preračun obremenitev, ki delujejo na nosilec med njegovim delovanjem, pri čemer so te obremenitve posledica delovanja drugih komponent v sistemu. Glavni cilj naloge je s pomočjo topološke optimizacije zmanjšati maso nosilca ob upoštevanju prej omenjenih obremenitev, ne da bi s tem bistveno povečali napetosti v materialu. Naloga se bo podrobneje osredotočila na izdelavo modela v programskem paketu SolidWorks 2024 za optimizacijo. Temu bo sledil podrobnejši opis same topološke optimizacije v programu CAESS ProTop ter predstavitev pridobljenih rezultatov optimizacije. V zadnjem delu naloge pa bodo zbrani rezultati še grafično prikazani in opisani.
Ključne besede: Topološka optimizacija, nosilec elektromotorja, MKE, Formula Student, CAESS ProTop, SolidWorks
Objavljeno v DKUM: 15.09.2025; Ogledov: 0; Prenosov: 23
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2. Time dependent load capacity of the press fitVinko Močilnik, Nenad Gubeljak, Jožef Predan, 2025, izvirni znanstveni članek Opis: 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.
Ključne besede: FEM analysis, interface oversize, hub, shafts, loading creep, press fit, roughness
Objavljeno v DKUM: 08.07.2025; Ogledov: 0; Prenosov: 15
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3. Experimental testing and numerical bite simulation of complete acrylic dentures in eugnathic and progenic occlusal relationshipsMartin Pavlin, Robert Ćelić, Nenad Gubeljak, Jožef Predan, 2025, izvirni znanstveni članek Opis: 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.
Ključne besede: bite force, finite element method, dental biomechanics, numerical simulations, complete acrylic dentures, occlusal force distribution, occlusal pressure distribution
Objavljeno v DKUM: 11.06.2025; Ogledov: 0; Prenosov: 8
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4. Materialni model kompozitne strukture in optimizacija topologije kompozitnega monokoka : magistrsko deloPatrik Gnus, 2025, magistrsko delo Opis: Magistrska naloga se osredotoča na razvoj materialnega modela kompozitne strukture in optimizacijo topologije karbonskega monokoka za dirkalnik ekipe Formula Student, UNI Maribor Grand Prix Engineering. Cilj naloge je pridobiti natančne podatke o mehanskih lastnostih kompozitne strukture, ki bodo uporabljeni v numeričnih simulacijah z metodo končnih elementov v programu Ansys. Na podlagi teh podatkov bo izvedena osnovna topološka optimizacija monokoka, pri čemer bo glavni poudarek na zmanjšanju mase ob ohranjanju strukturne trdnosti.
V okviru raziskave bo izvedena analiza obstoječih materialnih modelov, optimizacija geometrije in strukture monokoka ter validacija rezultatov s pomočjo eksperimentalnih podatkov. Glavne predpostavke vključujejo obravnavo karbonskih vlaken kot linearno elastičnega materiala v določenem območju obremenitev ter homogeno obravnavo monokoka, čeprav je sestavljen iz več slojev. Omejitve raziskave zajemajo osredotočenost na statične in dinamične obremenitve brez upoštevanja toplotnih vplivov ter prilagajanje optimizacije v skladu s tekmovalnimi predpisi.
Rezultati naloge bodo prispevali k izboljšanju procesov načrtovanja kompozitnih struktur ter omogočili nadaljnji razvoj lahkih in zmogljivih monokokov v okviru ekipe Formula Student.
Ključne besede: kompozitna struktura, karbonska vlakna, monokok, Formula Student, materialni model, optimizacija topologije, metoda končnih elementov, numerične simulacije, zmanjšanje mase, vzvojna togost, eksperimentalna validacija.
Objavljeno v DKUM: 28.05.2025; Ogledov: 0; Prenosov: 57
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5. Estimate of the driving force for creep crack growthOtmar Kolednik, Marko Kegl, Nenad Gubeljak, Jožef Predan, 2025, izvirni znanstveni članek Opis: A discussion on the conventional creep crack growth parameters, e.g. the experimental C*-integral, C*exp, or the experimental Ct-integral, Ct,ssc, shows that the physical meaning of these parameters for growing cracks in elastic–plastic, creeping materials is not fully clear. Therefore, a comparison is presented in this paper between the conventional creep crack growth parameters, several J-integral related parameters and the crack driving force (CDF), which has been used in linear elastic and elastic–plastic fracture mechanics. The CDF for elastic–plastic, creeping materials is derived from basic thermodynamic principles and by applying the concept of configurational forces (CFs). A comprehensive numerical study is performed where crack propagation is modelled by alternating creep and crack extension steps at constant loads in a compact tension specimen made of the nickel-base superalloy Waspaloy at a temperature of 700 °C. The CDF is evaluated by a CF-based post-processing procedure after a conventional finite element computation. This procedure is applicable for small-scale creep (ssc-), transition creep (tc-) and “moderate” extensive creep (ec-) conditions. For more pronounced ec-conditions, the procedure might have to be adapted. It is shown that C*exp and Ct,ssc reflect the time derivative of the CDF during the creep stages. In contrast, the variations of the CDF coincide well with that of J-values estimated from the crack-tip opening displacement.
Ključne besede: fracture mechanics, creep crack growth, crack driving force, C*-integral, J-integral, configurational force concept, finite element method
Objavljeno v DKUM: 20.03.2025; Ogledov: 0; Prenosov: 6
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6. Total Knee replacement with an uncemented porous tantalum tibia component: A failure analysisSamo K. Fokter, Nenad Gubeljak, Esther Punzón Quijorna, Primož Pelicon, Mitja Kelemen, Primož Vavpetič, Jožef Predan, Luka Ferlič, Igor Novak, 2022, izvirni znanstveni članek Opis: Porous tantalum has been extensively used in orthopaedic surgery, including uncemented
total knee arthroplasty (TKA). Favourable results were reported with earlier monobloc tibial components and the design evolved to modular implants. We aimed to analyse possible causes for extensive
medial tibia bone loss, resulting in modular porous tantalum tibia baseplate fracture after primary
TKA. Retrieved tissue samples were scanned with 3 MeV focused proton beam for Proton-Induced
X-ray Emission (micro-PIXE) elemental analysis. Fractographic and microstructural analysis were
performed by stereomicroscopy. A full 3D finite-element model was made for numerical analysis
of stress–strain conditions of the tibial baseplate. Histological examination of tissue underneath
the broken part of the tibial baseplate revealed dark-stained metal debris, which was confirmed by
micro-PIXE to consist of tantalum and titanium. Fractographic analysis and tensile testing showed
that the failure of the tibial baseplate fulfilled the criteria of a typical fatigue fracture. Microstructural
analysis of the contact surface revealed signs of bone ingrowth in 22.5% of the surface only and
was even less pronounced in the medial half of the tibial baseplate. Further studies are needed to
confirm the responsibility of metal debris for an increased bone absorption leading to catastrophic
tibial tray failure.
Ključne besede: total knee arthroplasty, uncemented, cementless, trabecular metal, porous tantalum, tibial component, cementless baseplate fracture
Objavljeno v DKUM: 20.03.2025; Ogledov: 0; Prenosov: 11
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7. Monitoring surface state of AA7075-T6 during dynamic loading with FBG sensorMarijana Milković, Matej Njegovec, Jožef Predan, Jure Javornik, Denis Đonlagić, Nenad Gubeljak, 2023, izvirni znanstveni članek Opis: The AA7075-T6 material is widely used in aerospace applications due to its favourable strength-to-weight ratio and cost-effectiveness. The material undergoes a process of cold rolling and subsequent stretching to form metal sheets. This process generates residual compressive stresses on the surface of the material. Surface changes in the material are observed at low stress levels, resulting in variations in residual stresses and surface roughness. This article presents an approach to monitor the surface state changes of AA7075-T6 material during dynamic loading using Fiber Bragg Grating (FBG) sensor. Numerical Finite Element Method (FEM) simulations analyse the transfer of deformations from the damaged surface through the adhesive layer to FBG with different cladding thicknesses. Loading induces microcrack-related intensity changes in the FBG optical spectrum and deformation response. The magnitude of the response is greater, when the cladding thickness of the optical fibre is thinner. Experimental results show that the FBG optical spectrum response varies with cumulative number of dynamic cycles.
Ključne besede: AA7075-T6, dynamic loading, Fiber Bragg Grating (FBG) sensor, surface condition
Objavljeno v DKUM: 10.03.2025; Ogledov: 0; Prenosov: 120
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8. Dimenzioniranje premične čeljusti primeža za stiskalnico "Rotopress" : diplomsko deloNejc Lazar, 2024, diplomsko delo Opis: V diplomskem delu je predstavljen postopek dimenzioniranja premične čeljusti primeža stiskalnice »Rotopress« za podjetje Ledinek Engineering d.o.o. Pri samem dimenzioniranju smo upoštevali, da je potrebno ohraniti vse pritrdilne površine, čeljust se ne sme plastično deformirati pri maksimalni delovni sili, ki znaša 200 kN, in pa sama konstrukcija mora biti enostavna za varjenje. Predstavili smo tri variante premične čeljusti in jih primerjali s staro verzijo, katere maksimalna delovna sila je bila 140 kN. Cilj je bil, da je na novi verziji premične čeljusti napram stari verziji zmanjšana masa konstrukcije, zmanjšana maksimalna napetost in pa pomik ne sme biti večji od 1 mm. Za potrebe varjenja smo določili tehnologijo varjenja in katere pozicije na konstrukciji je potrebno predhodno predgrevati. Izdelali smo tudi tehnično dokumentacijo.
Ključne besede: dimenzioniranje, premična čeljust, lameliran lepljen les, MKE, varjenje
Objavljeno v DKUM: 09.10.2024; Ogledov: 0; Prenosov: 34
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9. Določanje faktorja intenzitete napetosti na razpoki, ki obdaja praznine v materialu : magistrsko deloMarcel Prosen, 2024, magistrsko delo Opis: V magistrski nalogi smo obravnavali problematiko votline, ki je posledica nekovinskega vključka ali pore in razpoke v elementu. Obravnavali smo več različnih primerov, ki so imeli različne geometrijske kombinacije velikosti in lokacije votline, okrog katere je nastala razpoka. S pomočjo numeričnih simulacij smo ugotavljali, kakšna je razlika v enako veliki razpoki, ki je nastala iz votline, od ravninske do v materialu zajete razpoke. Razliko smo ugotavljali na osnovi numeričnih simulacij modela iz končnih elementov, na osnovi izračuna faktorja intenzitete napetosti vzdolž konture razpoke.
Ugotovili smo, da pri kratkih razpokah, ki so nastale iz votline v materialu, so vrednosti faktorja intenzitete napetosti manjše, kot to velja za enako veliko ravninsko razpoko v notranjosti materiala. Rezultati so pomembni zaradi določanja relevantne vrednosti faktorja intenzitete napetosti po konturi razpoke, ki je nastala iz vključka, za določitev trajne dinamične trdnosti materiala.
Ključne besede: faktor intenzitete napetosti, razpoke, nekovinski vključki, pore, numerične simulacije, analitični preračuni
Objavljeno v DKUM: 04.09.2024; Ogledov: 69; Prenosov: 61
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10. Load-bearing capacity of hybrid riv-bonded aluminum-magnesium joints at quasi-static and cyclic loadingsJosef Domitner, Zahra Silvayeh, Jožef Predan, Peter Auer, Jennifer Stippich, Norbert Enzinger, Nenad Gubeljak, 2023, izvirni znanstveni članek Ključne besede: lightweight design, car body manufacturing, body-in-white, aluminum alloys, magnesium alloys, riv-bonding, adhesive, self-piercing riveting, SPR, static strength, fatigue performance
Objavljeno v DKUM: 02.04.2024; Ogledov: 489; Prenosov: 388
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