1. 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: 5
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2. The influence of the ratio of circumference to cross-sectional area of tensile bars on the fatigue life of additive manufactured AISI 316L steelLuka Ferlič, Filip Jerenec, Mario Šercer, Igor Drstvenšek, Nenad Gubeljak, 2024, izvirni znanstveni članek Opis: The static and dynamic loading capacities of components depend on the stress level to which the material is exposed. The fatigue behavior of materials manufactured using additive technology is accompanied by a pronounced scatter between the number of cycles at the same stress level, which is significantly greater than the scatter from a material with the same chemical composition, e.g., AISI 316L, but produced by rolling or forging. An important reason lies in the fact that fatigue cracks are initiated almost always below the material surface of the loaded specimen. Thus, in the article, assuming that a crack will always initiate below the surface, we analyzed the fatigue behavior of specimens with the same bearing cross section but with a different number of bearing rods. With a larger number of rods, the circumference around the supporting part of the rods was 1.73 times larger. Thus, experimental fatigue of specimens with different sizes showed that the dynamic loading capacity of components with a smaller number of bars is significantly greater and can be monitored by individual stress levels. Although there are no significant differences in loading capacity under static and low-cycle loading of materials manufactured with additive technologies, in high-cycle fatigue it has been shown that the ratio between the circumference and the loading cross section of tensile-loaded rods plays an important role in the lifetime. This finding is important for setting a strategy for manufacturing components with additive technologies. It shows that a better dynamic loading capacity can be obtained with a larger loading cross section. Ključne besede: AISI 316L stainless steel, additive manufacturing, FEM, high-cycle fatigue, fractography analysis Objavljeno v DKUM: 25.11.2024; Ogledov: 0; Prenosov: 18
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3. Experimental and numerical analysis of fracture mechanics behavior of heterogeneous zones in S690QL1 grade high strength steel (HSS) welded jointDamir Tomerlin, Dražan Kozak, Luka Ferlič, Nenad Gubeljak, 2023, izvirni znanstveni članek Opis: The heterogeneity of welded joints’ microstructure affects their mechanical properties, which can vary significantly in relation to specific weld zones. Given the dimensional limitations of the available test volumes of such material zones, the determination of mechanical properties presents a certain challenge. The paper investigates X welded joint of S690QL1 grade high strength steel (HSS), welded with slightly overmatching filler metal. The experimental work is focused on tensile testing to obtain stress-strain properties, as well as fracture mechanics testing. Considering the aforementioned limitations of the material test volume, tensile testing is carried out with mini tensile specimens (MTS), determining stress-strain curves for each characteristic weld zone. Fracture mechanical testing is carried out to determine the fracture toughness using the characteristic parameters. The experimental investigation is carried out using the single edge notch bend (SENB) specimens located in several characteristic welded joint zones: base metal (BM), heat affected zone (HAZ), and weld metal (WM). Fractographic analysis provides deeper insight into crack behavior in relation to specific weld zones. The numerical simulations are carried out in order to describe the fracture behavior of SENB specimens. Damage initiation and evolution is simulated using the ductile damage material behavior. This paper demonstrates the possibility of experimental and numerical determination of fracture mechanics behavior of characteristic heterogeneous welded joint zones and their influence on crack path growth. Ključne besede: heterogeneous welded joint, high strength steel, mechanical testing, damage, fracture, mechanical properties, finite element analysis Objavljeno v DKUM: 30.11.2023; Ogledov: 405; Prenosov: 36
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4. Zasnova in izdelava merilne priprave za kontrolo nastavne mere bovden potega za podiranje avtomobilskih sedežev : diplomsko deloŽan Smej, 2023, diplomsko delo Opis: V diplomskem delu je na kratko predstavljeno podjetje TBP d.d., v sodelovanju s katerim sem opravljal diplomsko nalogo. Predstavljene so različne izvedbe bovden potegov, ki se izdelujejo v podjetju, kateri se uporabljajo v avto industriji. Opisali smo bovden potege, za katere smo konstruirali merilno pripravo, katera omogoča kontrolo nastavne mere direktno ob proizvodni liniji. V nalogi smo modelirali sestavne dele merilne priprave ter izdelali delavniške risbe ter kosovnico, sestavili pripravo v strojegradnji in izvedli preskus meritev ter izdelali Gage R&R analizo. Ključne besede: kontrola, nastavna mera, bovden, bovden poteg, ležišče, končnik, žica, meritev, nosilec, sklop, testiranje, modeliranje, merilna priprava, variacija, merjenje Objavljeno v DKUM: 05.10.2023; Ogledov: 254; Prenosov: 24
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6. Konstruiranje naprave za tritočkovno in štiritočkovno upogibno testiranje : magistrsko deloLuka Ferlič, 2021, magistrsko delo Opis: Meritve lomno mehanskih lastnosti preizkušancev se izvajajo v skladu s standardi, ki zajemajo tudi napravo za tritočkovno in štiritočkovno upogibno preizkušanje in jih moramo pri konstruiranju takšne naprave upoštevati. Upoštevati je potrebno tudi omejitve, ki jih imamo zaradi komore, v kateri se izvajajo testiranja ter zagotavljati prilagodljivost naprave glede na vrsto in velikost preizkušancev, ki se testirajo. Zaradi spreminjanja razdalj med vpetji valjčkov je numerično določena največja natezna trdnost preizkušancev, ki se lahko testirajo pri posameznih razdaljah. Da se med testiranjem izognemo dodanim merilnim napravam moramo poznati karakteristiko pomika uporabljenih izvedb naprave, s katerimi lahko določimo dejansko karakteristiko preizkušanca. Ključne besede: Upogibno testiranje, Tritočkovno vpetje, Štiritočkovno vpetje Objavljeno v DKUM: 13.09.2021; Ogledov: 798; Prenosov: 92
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