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1.
Trdnostna analiza in konstrukcijske izboljšave pravokotnih vinskih posod
Patrik Šavli, 2024, master's thesis

Abstract: V magistrskem delu analiziramo in izvajamo trdnostne analize na družini pravokotnih vinskih posod s pomočjo programa SolidWorks. Za družino posod najprej izdelamo parametrični model, čemur sledijo prve trdnostne simulacije ter zajemanje realne geometrije primera posode s pomočjo tehnologije 3D skeniranja, kar lahko uporabimo za validacijo rezultatov dobljenih v omenjenih simulacijah. Tokom simuliranja bomo namenili največji poudarek zmanjšanju debelin komponent posode ter tipu postavitve ojačitev na dnu posode. Izboljšave, ki jih bomo uspeli narediti, bodo dale vpogled v to, kje in kaj točno bi lahko pri celotni družini posod izboljšali ter s tem zmanjšali proizvodne stroške.
Keywords: Pravokotne vinske posode, metoda končnih elementov, trdnostna analiza, računalniške simulacije, 3D skeniranje, validacija
Published in DKUM: 20.06.2024; Views: 25; Downloads: 0
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2.
High strain rate hardening of metallic cellular metamaterials
Nejc Novak, Matej Vesenjak, Zoran Ren, 2024, original scientific article

Abstract: Strain rate hardening caused by the changed deformation mode is a fascinating phenomenon in cellular metamaterials where the material’s stiffness and energy absorption capabilities increase as the strain rate increases. This unique behaviour is attributed to a combination of micro-inertia effects, base material’s strain rate hardening and inertia effects. At high strain rates, the metamaterial’s inertia influences its deformation response, which changes to shock mode. This work briefly presents the geometry and fabrication of different metallic metamaterials. Then, it evaluates their mechanical response at different strain rates, ranging from quasi-static to intermediate dynamic and shock, determined by experimental and computational investigation. The three deformation modes can be separated into two critical loading velocities, unique for each metamaterial, which are also presented and compared in this work for various metamaterials. The investigations show that the deformation mode change in metallic metamaterials depends on their porosity. The critical velocities separating the deformation modes decrease with increasing porosity, i.e., decreased density of the metamaterial results in reduced critical loading velocities. The shock deformation mode in cellular metamaterials is thus attainable at much lower loading velocities than in homogeneous (nonporous) materials.
Keywords: metamaterials, cellular structures, high strain rate, experimental testing, computational modelling, compression loading, mechanical properties
Published in DKUM: 22.05.2024; Views: 128; Downloads: 5
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3.
Mechanical behaviour of photopolymer cell-size graded triply periodic minimal surface structures at different deformation rates
Yunus Emre Yilmaz, Nejc Novak, Oraib Al-Ketan, Hacer Irem Erten, Ulas Yaman, Anja Mauko, Matej Borovinšek, Miran Ulbin, Matej Vesenjak, Zoran Ren, 2024, original scientific article

Abstract: This study investigates how varying cell size affects the mechanical behaviour of photopolymer Triply Periodic Minimal Surfaces (TPMS) under different deformation rates. Diamond, Gyroid, and Primitive TPMS structures with spatially graded cell sizes were tested. Quasi-static experiments measured boundary forces, representing material behaviour, inertia, and deformation mechanisms. Separate studies explored the base material’s behaviour and its response to strain rate, revealing a strength increase with rising strain rate. Ten compression tests identified a critical strain rate of 0.7 s−1 for “Grey Pro” material, indicating a shift in failure susceptibility. X-ray tomography, camera recording, and image correlation techniques observed cell connectivity and non-uniform deformation in TPMS structures. Regions exceeding the critical rate fractured earlier. In Primitive structures, stiffness differences caused collapse after densification of smaller cells at lower rates. The study found increasing collapse initiation stress, plateau stress, densification strain, and specific energy absorption with higher deformation rates below the critical rate for all TPMS structures. However, cell-size graded Primitive structures showed a significant reduction in plateau and specific energy absorption at a 500 mm/min rate.
Keywords: cellular materials, triply periodical minimal surface, photopolymer, mechanical properties, strain rate, experimental compressive testing, computer simulations
Published in DKUM: 22.05.2024; Views: 133; Downloads: 7
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4.
5.
Introducing auxetic behavior to syntactic foams
Nejc Novak, Miha Kolar, Nima Movahedi, Matej Vesenjak, Zoran Ren, Thomas Fiedler, 2020, original scientific article

Abstract: This paper proposes an innovative multi-material approach for introducing auxetic behaviour to syntactic foams (SFs). By carefully designing the size, shape, and orientation of the SFs, auxetic deformation behaviour was induced. Re-entrant hexagon-shaped SF elements were fabricated using expanded perlite (EP) particles and a plaster of Paris slurry first. Then, an auxetic pattern of these SF elements was arranged within a stainless-steel casting box. The empty spaces between the SF elements were filled with molten aluminium alloy (A356) using the counter-gravity infiltration casting technique. The cast auxetic composite had a bulk density of 1.52 g/cm3. The cast composite was then compressed under quasi-static loading to characterise its deformation behaviour and to determine the mechanical properties, especially the Poisson’s ratio. The cast composite deformation was auxetic with a Poisson’s ratio of −1.04. Finite Element (FE) simulations were conducted to understand the deformation mechanism better and provide means for further optimisation of the geometry.
Keywords: auxetic cellular structure, syntactic foams, experimental tests, mechanical properties, Poisson’s ratio
Published in DKUM: 28.03.2024; Views: 150; Downloads: 14
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6.
Introduction to the Computer Simulations : Script
Nejc Novak, Matej Borovinšek, Matej Vesenjak, Zoran Ren, 2024

Abstract: The script entitled „Introduction to the computer simulations“ in the field of Engineering Computer Simulations is intended as a study aid in the lectures of the courses Engineering Computer Simulations for foreign students at the University of Maribor and for students at Kumamoto University, Japan. It explains all the material that students must master in these subjects, and is consistent with the subject curriculum. The basics of computational simulations, based on the Finite Element Method, are given from the theoretical basics to step-by-step preparation of simple computational models and their analysis in PrePoMax software.
Keywords: computational simulations, solid mechanics, Finite Element Method, designing, numerical methods
Published in DKUM: 12.03.2024; Views: 283; Downloads: 17
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7.
Rekonstrukcija ogrodja za potiskala kompozitne križno lepljene plošče : diplomsko delo
Domen Širovnik, 2023, undergraduate thesis

Abstract: Cilj diplomske naloge je rekonstrukcija jeklenega ogrodja, ki se uporablja za odstranjevanje CLT (angl.: cross-laminated timber) plošč z aluminijaste mize. Predstavljene so tri različne konstrukcijske variante. Za izdelavo modelov je bil uporabljen programski paket Autodesk Inventor Professional 2023. Za izdelavo računalniških statičnih preračunov sta bili uporabljeni funkciji Frame Analysis in Stress Analysis. S funkcijo Stress Analysis je bila izdelana simulacija z uporabo metode končnih elementov, s katero se je potem potrdila pravilnost rezultatov funkcije Frame Analysis. Nato so pri vsaki konstrukcijski varianti predstavljene prednosti in slabosti. Izdelana je bila tudi medsebojna primerjava. Na koncu so nastale dve uspešni alternativi in ena alternativa, ki ni zadovoljivo izpolnjevala vseh kriterijev. Pokazali sta se tudi pomembnost geometrije podpornih elementov in upoštevanje usmerjenosti obremenitev.
Keywords: jeklene konstrukcije, kompozitne lesene plošče, rekonstrukcija, trdnostna analiza, računalniške simulacije
Published in DKUM: 28.02.2024; Views: 226; Downloads: 13
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8.
Dynamic characterisation of novel three-dimensional axisymmetric chiral auxetic structure
Anja Mauko, Yunus Emre Yilmaz, Nejc Novak, Tomáš Doktor, Matej Vesenjak, Zoran Ren, 2024, original scientific article

Abstract: The study presents an extensive mechanical and computational characterisation of novel cellular metamaterial with axisymmetric chiral structure (ACS) at different strain rates. The Direct Impact Hopkinson Bar (DIHB) testing device was used for impact testing up to 21 m/s striker speed, which was insufficient to reach the shock deformation regime. Thus, using computational simulations to estimate the structure behaviour at high strain rates was necessary. Experimental and computational results showed that all ACS structures exhibit a nominal stress–strain relationship typical for cellular materials. As the loading conditions shifted to a dynamic regime, the micro–inertia effect became increasingly pronounced, leading to a corresponding rise in structure stiffness. The Poisson's ratio in all ACS increases gradually, making them superior to traditional cellular materials, which experience a sudden increase in Poisson's ratio during loading. Additionally, the study found that the structures exhibited a rise in the auxetic effect with an increase in strain rate, highlighting the benefits of axisymmetric structures in high-loading regimes. Overall, the obtained results provide valuable insights into the mechanical properties of ACS under different loading regimes and will contribute to further design improvements and the fabrication of novel ACS metamaterials.
Keywords: axisymmetric chiral structure, auxetic, chiral unit cell, impact testing, dynamic characterisation, finite element simulations
Published in DKUM: 15.02.2024; Views: 264; Downloads: 20
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9.
High strain-rate deformation analysis of open-cell aluminium foam
Anja Mauko, Mustafa Sarıkaya, Mustafa Güden, Isabel Duarte, Matej Borovinšek, Matej Vesenjak, Zoran Ren, 2023, original scientific article

Abstract: This study investigated the high-strain rate mechanical properties of open-cell aluminium foam M-pore®. While previous research has examined the response of this type of foam under quasi-static and transitional dynamic loading conditions, there is a lack of knowledge about its behaviour under higher strain rates (transitional and shock loading regimes). To address this gap in understanding, cylindrical open-cell foam specimens were tested using a modified Direct Impact Hopkinson Bar (DIHB) apparatus over a wide range of strain rates, up to 93 m/s. The results showed a strong dependency of the foam's behaviour on the loading rate, with increased plateau stress and changes in deformation front formation and propagation at higher strain rates. The internal structure of the specimens was examined using X-ray micro-computed tomography (mCT). The mCT images were used to build simplified 3D numerical models of analysed aluminium foam specimens that were used in computational simulations of their behaviour under all experimentally tested loading regimes using LS-DYNA software. The overall agreement between the experimental and computational results was good enough to validate the built numerical models capable of correctly simulating the mechanical response of analysed aluminium foam at different loading rates.
Keywords: Open-cell aluminium foam, Micro-computed tomography, High-strain rate, Direct impact hopkinson bar, Digital image correlation, Computer simulation
Published in DKUM: 06.12.2023; Views: 364; Downloads: 28
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10.
Konstruiranje in trdnostna analiza povezovalnega elementa motorja in menjalnika v športnih avtomobilih : magistrsko delo
Nejc Pesek, 2023, master's thesis

Abstract: Podjetja, katera konstruirajo športne avtomobile morajo biti v stiku z novo tehnologijo, slediti razvoju novih materialov ter iskati vedno nove in boljše rešitve. Pri konstruiranju morajo želje kupcev, vozne lastnosti in varnost postaviti na prvo mesto. Uspešnost trženja in prodaje se začne z vlaganjem v kadre, ki so potrebni za nastanek novega boljšega športnega avtomobila od konkurence. Pri razvoju in nadaljnjem konstruiranju je pomemben vsak del elementa v končni sestavi. Najmanjša malenkost pripomore k izboljšavi in upravičevanju cene avtomobila. V magistrskem delu smo spoznali in konstruirali ohišje zvona, ki je eden izmed pomembnih delov pogonskega sklopa. S pomočjo programskega paketa SolidWorks smo skonstruirali tri različne oblike ohišje zvona. V nadaljevanju smo s pomočjo programskem paketa PrePoMax izvedli trdnostno analizo za vse tri primere. Dobljene rezultate smo med seboj primerjali in izbrali najprimernejšo obliko. Podali smo ugotovitve in smernice za nadaljnji razvoj izdelka.
Keywords: ohišje zvona, konstruiranje, trdnostna analiza, športni avtomobil
Published in DKUM: 27.10.2023; Views: 221; Downloads: 35
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