1. Deformation behaviour of optimised three-dimensional axisymmetric chiral auxetic structuresNejc Novak, Alen Grebo, Matej Borovinšek, Lovre Krstulović-Opara, Zoran Ren, Matej Vesenjak, 2025, izvirni znanstveni članek Opis: Background/Objectives: Developing functional tissue constructs via 3D bioprinting relies heavily on scaffold architecture, demanding precise mechanical tunability and highresolution feature fidelity. Methods: This paper presents a novel approach utilising photocurable resins and resin 3D printing to fabricate auxetic axisymmetric chiral structures (ACSs), which can be used for advanced scaffold engineering. Results: The experimental tests showed that the optimised ACS (optACS) possess superior mechanical properties compared to their non-optimised counterpart. Both analysed structures possess an auxetic behaviour up to 40% longitudinal strain, with a Poisson’s ratio of about −0.1. Conclusions: This auxetic capability is promising for biomedical applications, particularly in developing enhanced stents or tissue scaffolds.
Ključne besede: auxetic, axisymmetric chiral structures, 3D printing, mechanical testing, deformation behaviour, optimisation
Objavljeno v DKUM: 10.12.2025; Ogledov: 0; Prenosov: 4
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2. Integrated design, simulation, and experimental validation of advanced cellular metamaterialsNejc Novak, Zoran Ren, Matej Vesenjak, 2025, izvirni znanstveni članek Opis: Cellular metamaterials offer supreme properties for engineering, medicine, and defence, but their transition to industrial use faces design, fabrication, and characterisation challenges. This review provides an overview of 20 years of advancements in cellular structures, from open-cell foams to triply periodic minimal surfaces (TPMS), presenting novel fabrication techniques (e.g., explosive compaction for UniPore structures) and demonstrating validated computational models for optimising graded auxetic and hybrid TPMS lattices. The study indicates that porosity and base material primarily govern energy absorption, with closed-cell foams and TPMS outperforming other geometries. Additive manufacturing enables spatially graded designs with tailored mechanical properties. This work accelerates the development of next-generation metamaterials for crash absorption, blast protection, and biomedical devices.
Ključne besede: cellular structures, metamaterials, experimental testing, computational simulations, mechanical properties
Objavljeno v DKUM: 09.12.2025; Ogledov: 0; Prenosov: 2
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3. Fatigue and fracture characterisation of copper-brazed 316L stainless steelTonica Bončina, Franc Zupanič, Branko Nečemer, Roman Satošek, Erik Rihter, Srečko Glodež, 2026, izvirni znanstveni članek Opis: This study focuses on the mechanical, fatigue and metallographic characterisation of copper-brazed 316L stainless steel for the potential use in different plate heat exchangers (PHE) applications. The quasi-static and fatigue tests have been performed on the specially designed copper-brazed tensile specimens to obtain the engineering stress–strain diagram and the fatigue life curve of the analysed brazed joint. Furthermore, a comprehensive metallographic investigation has been done, focusing on (i) material characterisation of asreceived stainless steel 316L, (ii) characterisation of the brazed joint and (iii) fractographic analyses of fractured surfaces by quasi-static and fatigue loading. The obtained experimental results may be beneficial for designing copper-brazed plate heat exchangers in the future.
Ključne besede: brazed joint, fatigue, experimental testing, metallographic investigation
Objavljeno v DKUM: 28.11.2025; Ogledov: 0; Prenosov: 2
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4. Reducing scrap in long rolled round steel bars using Genetic Programming after ultrasonic testingMiha Kovačič, Anže Zupanc, Uroš Župerl, Miran Brezočnik, 2024, izvirni znanstveni članek Opis: At Štore Steel Ltd., continuously cast billets (180 mm × 180 mm) are reheated and rolled after cooling to room temperature. Hot-rolled bars are controlled as they cool to room temperature in specially designed cooling chambers, minimizing residual stresses and the development of pre-existing surface and internal defects. The bar ends can be additionally covered with insulating material. The cooled, rolled bars undergo examination using automated control lines to detect surface and internal defects, which primarily originate from the casting process. Internal defects are identified using ultrasonic testing. Between January 2022 and June 2023, 1550.0 tons of 61SiCr7 rolled bars, with diameters ranging from 53 mm to 72 mm and lengths from 7010 mm to 7955 mm, were examined using ultrasonic testing. The scrap was 109.6 tons (7.07 %). After collecting data on chemical composition (C, Si, Mn, Cr, Mo, Ni content), the casting process (casting temperature, cooling water pressure and flow in the first, second, and third zones of secondary cooling, as well as the temperature difference between input and output mould cooling water), and rolled bar geometry (diameter, length), scrap modelling after ultrasonic testing was carried using genetic programming. The genetic programming model suggested reducing the length of the rolled bar. Due to length multiplication, it was possible to reduce the rolled bar length from the initial lengths of 7010-7955 mm to the current lengths of 4558-6720 mm in June 2023. Based on this adjustment, a new production of rolled bars was established. By August 2024, 1251.9 tons of 61SiCr7 rolled bars were produced with the mentioned length adjustments. These rolled bars were subsequently examined using ultrasonic testing. The scrap was reduced by nearly 14 times, amounting to only 8.1 tons (0.64 %).
Ključne besede: steel industry, rolling, long bars, ultrasonic testing, scarp, defects, modelling, genetic programming
Objavljeno v DKUM: 27.08.2025; Ogledov: 0; Prenosov: 3
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5. Corrosion behavior of nickel–titanium continuous-casted alloysMinja Miličić Lazić, Dijana Mitić, Katarina Radović, Igor Djordjević, Peter Majerič, Rebeka Rudolf, Branimir Grgur, 2024, izvirni znanstveni članek Opis: Variations in the corrosion behavior of biomedical NiTi alloys in Cl− containing and acidic
environments present a problem with their biological implantation. The objective of this research
was to evaluate the synergy of the microstructure, the corrosion behavior, and the biocompatibility of
novel continuous-cast NiTi alloys and to compare them with commercial NiTi alloys. The two alloys
have a practically identical nominal chemical composition, but they differ in production technology.
The continuous casting technology involved vacuum induction melting of the basic components
and vertical continuous casting, while the commercial NiTi alloy was produced through a process of
casting, hot rolling, and forming into square shapes. The microstructure was revealed to determine
the surface area and size of grains. The corrosion of a commercial nickel–titanium alloy and one
prepared by a novel continuous casting method in acidic and chloride-containing solutions was
studied via analytical and electrochemical tests. Localized corrosion characteristics related to oxide
properties, when exposed to 9 g L−1 NaCl solution, were examined with focused ion beam analysis
and subsequent microchemical analysis of the formed corrosive products. Corrosion potential over
time and the oxide film resistance were analyzed using linear polarization measurements. To obtain
a preliminary estimate of biocompatibility, human fibroblast cells were used in indirect contact,
i.e., alloy conditioning medium. The continuous casting method resulted in a reduction in the
average grain size in comparison to the commercial sample and better corrosion stability of the
sample in an acidic environment. Also, in a solution of 9 g L−1 NaCl the commercial sample showed
high values for the corrosion current density (jcorr = 6 µA cm−2), which indicated low corrosion
resistance, while the continuous casting sample possessed much better corrosion stability and lower
values for the corrosion current density (jcorr = 0.2 µA cm−2). In line with that, elemental analysis of
the corroded surfaces showed higher Cl− ion deposition over the surface layer of the commercial
sample, suggesting local oxide breakdown. Moreover, NiTicc reached a value three times higher
for polarization resistance (Rp = 270 kΩ cm2) over time in comparison to the commercial sample
(Rp~100 kΩ cm2). Biocompatibility evaluation showed that human fibroblast cells exhibited altered
metabolic activity. An MTT assay showed that cells’ mitochondrial activity dropped below that of
control cells in the presence of both materials’ supernatants.
Ključne besede: nickel–titanium, corosion behaviour, electrochemical testing, NiTi biocompatibility
Objavljeno v DKUM: 30.06.2025; Ogledov: 0; Prenosov: 6
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6. Design and implementation of soft robotic gripper using 3D printing technologyTone Lerher, Primož Bencak, Suhaib Ebrahim, Marko Motaln, Darko Hercog, 2025, objavljeni znanstveni prispevek na konferenci Opis: Automated warehouses rely on robotic systems for efficient order picking, yet object manipulation remains challenging due to variations in object shape, size, and material properties. This study focuses on the material selection for the holder of flexible robotic grippers using fused deposition modelling. The holder plays a crucial role in ensuring a secure fit of the gripper’s fingers, which is essential for stable and precise object handling in bin picking applications. Testing specimens were fabricated following the ASTM D638-22 standard with a grid infill pattern at full density. Two different variants of Polyethylene Terephthalate Glycol and Acrylonitrile Styrene Acrylate were tested. Mechanical properties, including ultimate tensile strength, elongation at break, and Young’s modulus, were estimated using a universal testing machine. Results indicate that one variant of Polyethylene Terephthalate Glycol exhibited the highest tensile strength (40.54 MPa), making it suitable for applications requiring high mechanical strength and resistance to tensile loads, while Acrylonitrile Styrene Acrylate provided a balance between strength and flexibility. These results illustrate the comparison of materials and how material selection and infill density impact the mechanical performance of the holder, which contributes to a better choice of material. Future research will explore the influence of 3D printing temperatures, layer height and testing other infill patterns to further enhance the efficiency and reliability of materials used for robotic grippers in robotic manipulation.
Ključne besede: intralogistics, robotization, robotic order picking, robotic gripper, tensile strength testing, 3D printing
Objavljeno v DKUM: 18.06.2025; Ogledov: 0; Prenosov: 13
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7. Chemical analysis of thermally aged cables in nuclear power plantsMarko Pirc, Jurij Avsec, Dijana Vrsaljko, 2025, izvirni znanstveni članek Opis: The paper presents findings on the implementation of various mechanical and chemical diagnostic procedures aimed at enhancing the monitoring of cable insulation conditions in Krško Nuclear Power Plant (NEK). This article introduces the advancement of four novel diagnostic testing methodologies for evaluating the mechanical and chemical properties of cable insulation: Indenter Modulus (IM), Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric analysis (TGA) and X-Ray Fluorescence Spectral Analysis (XRF). Experiments were performed on diverse samples of widely used nuclear-qualified cable polymer materials, including Ethylene Propylene Rubber (EPR) and Crosslinked Polyethylene (XLPE), all with a Chlorosulphonated Polyethylene (CSPE) jacket. Samples from various vintages were subjected to additional temperature ageing in many stages, to establish field testing acceptability requirements and assess the remaining lifespan of the polymer insulation. Diagnostic tests were performed and some preliminary results are reported.
Ključne besede: cable, ageing, nuclear, diagnostic testing criteria, chemical condition monitoring
Objavljeno v DKUM: 16.06.2025; Ogledov: 0; Prenosov: 4
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8. The national assessment of mathematics in high schools in Italy with Slovene as the language of instructionDaniel Doz, 2019, izvirni znanstveni članek Opis: In the following paper, we analyzed the question types in the INVALSI national mathematics assessments in Italian high schools with Slovene as the language of instruction. Through a statistical analysis, we found that closed-type questions were more frequent than open-type questions. A greater presence of closed-type questions could lead to the issue of guessing and cheating. Moreover, a greater quantity of closed-type questions could lead to a partial evaluation of knowledge, since procedures and other mathematical competences are not considered. In our research, we also considered the topics of the questions that were presented in national assessments.
Ključne besede: mathematics, Slovene education in Italy, national examinations, testing
Objavljeno v DKUM: 10.06.2025; Ogledov: 0; Prenosov: 2
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9. Quasi-static and impact behaviour of polymer-metal interpenetrating phase TPMS compositesNejc Novak, Oraib Al-Ketan, Anja Mauko, Lovre Krstulović-Opara, Shigeru Tanaka, Matej Borovinšek, Boštjan Vihar, Uroš Maver, Kazuyuki Hokamoto, Matej Vesenjak, Zoran Ren, 2025, izvirni znanstveni članek Opis: Interpenetrating phase composites (IPC) are materials with two or more mutually continuous, interconnected phases. This structure allows each phase to retain its properties, while together they exhibit enhanced synergistic properties. In this work, polymer-metal IPCs with Triply Periodical Minimal Surface (TPMS) structures were fabricated and tested for their mechanical properties at different impact velocities (ranging from 0.1 mm/s to 250 m/s). Samples. The samples comprise a stainless steel reinforcement phase and two polymeric matrices (silicone and epoxy). Computed tomography was used to evaluate the internal structure and the fabrication quality. The results showed that the samples were thoroughly infiltrated with polymeric filler, achieving a high degree of homogeneity in the composite. The compression tests of silicone-filled IPCs showed an increase in stiffness. Still, the Specific Energy Absorption (SEA) was not improved due to the non-optimal stiffness ratio between the polymeric matrix and the metallic reinforcement phase. However, using epoxy as the matrix resulted in the SEA enhancement of 38 %. This is attributed to the interlocking mechanism between the two phases, which improved the macroscopic mechanical properties. The compression tests showed significant strain rate hardening due to the base material’s strain rate sensitivity and the inertia effects.
Ključne besede: TPMS, interpenetrating phase composite, polymer filler, hybrid structure, experimental testing, mechanical properties, strain rate effect
Objavljeno v DKUM: 26.05.2025; Ogledov: 0; Prenosov: 14
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10. Fatigue behaviour of copper-brazed 316L stainless steelJernej Kralj, Blaž Hanželič, Srečko Glodež, Janez Kramberger, Roman Satošek, Branko Nečemer, 2024, izvirni znanstveni članek Opis: The plate heat exchanger (PHE) is a component that provides heat to be transferred from hot water to domestic cold water with-out mixing them with high efficiency. Over the lifetime of the PHE, cyclic pressure acts on the brazing points and the plates, andthis can lead to fatigue failure. The fatigue behaviour of the PHE, designed by using copper-brazed 316L (also known as 1.4404) stainless steel, was investigated by performing fatigue tests to obtain the S-N curve of the analysed brazed joint. The fatigue tests were performed on a Vibrophore 100 testing machine under the load ratio R= 0.1 for different values of calculated ampli-tude stress. Based on the obtained experimental results, an appropriate material model of the analysed brazed joint was created, which was validated with a numerical calculation in the framework of a program code Ansys. A validated material model canthen be used for the subsequent numerical analysis of the PHE.
Ključne besede: plate heat exchanger, brazed joint, fatigue, experimental testing
Objavljeno v DKUM: 10.04.2025; Ogledov: 0; Prenosov: 24
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