1. Corrosion behavior of nickel–titanium continuous-casted alloysMinja Miličić Lazić, Dijana Mitić, Katarina Radović, Igor Djordjević, Peter Majerič, Rebeka Rudolf, Branimir Grgur, 2024, original scientific article Abstract: 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.
Keywords: nickel–titanium, corosion behaviour, electrochemical testing, NiTi biocompatibility
Published in DKUM: 30.06.2025; Views: 0; Downloads: 4
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2. Design and implementation of soft robotic gripper using 3D printing technologyTone Lerher, Primož Bencak, Suhaib Ebrahim, Marko Motaln, Darko Hercog, 2025, published scientific conference contribution Abstract: 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.
Keywords: intralogistics, robotization, robotic order picking, robotic gripper, tensile strength testing, 3D printing
Published in DKUM: 18.06.2025; Views: 0; Downloads: 6
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3. Chemical analysis of thermally aged cables in nuclear power plantsMarko Pirc, Jurij Avsec, Dijana Vrsaljko, 2025, original scientific article Abstract: 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.
Keywords: cable, ageing, nuclear, diagnostic testing criteria, chemical condition monitoring
Published in DKUM: 16.06.2025; Views: 0; Downloads: 1
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4. The national assessment of mathematics in high schools in Italy with Slovene as the language of instructionDaniel Doz, 2019, original scientific article Abstract: 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.
Keywords: mathematics, Slovene education in Italy, national examinations, testing
Published in DKUM: 10.06.2025; Views: 0; Downloads: 2
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5. 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, original scientific article Abstract: 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.
Keywords: TPMS, interpenetrating phase composite, polymer filler, hybrid structure, experimental testing, mechanical properties, strain rate effect
Published in DKUM: 26.05.2025; Views: 0; Downloads: 8
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6. Fatigue behaviour of copper-brazed 316L stainless steelJernej Kralj, Blaž Hanželič, Srečko Glodež, Janez Kramberger, Roman Satošek, Branko Nečemer, 2024, original scientific article Abstract: 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.
Keywords: plate heat exchanger, brazed joint, fatigue, experimental testing
Published in DKUM: 10.04.2025; Views: 0; Downloads: 9
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7. A computational model for analysing the wear behaviour of polymer gearsAljaž Ignatijev, Srečko Glodež, Aleš Belšak, Matej Borovinšek, 2025, original scientific article Abstract: In the presented study, a computational model was developed to analyse the wear behaviour of contacting mechanical elements like gears, bearings, etc. The model was built in the framework of the PrePoMax open-source CalculiX FEM (Finite Element Method) solver and enables a detailed analysis of the meshing dynamics of contacting mechanical elements. The model also considers the hyperelastic behaviour of the material in contact and the impact of operating temperature. The developed computational model was evaluated on a spur gear pair, where the pinion made of POM (Polyoxymethylene) was meshed with a support gear made of case-hardened steel 16MnCr5. The computational results were compared with the analytical results according to the VDI 2736 guidelines and experimental results on the real gear pairs. Compared to the standardised procedure according to the VDI 2736 guidelines, the model's main advantage is the geometry updating after a chosen number of loading cycles, enabling a more accurate prediction of wear behaviour under rolling/sliding loading conditions.
Keywords: wear, polymer gears, computational modelling, experimental testing
Published in DKUM: 08.04.2025; Views: 0; Downloads: 9
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8. Structural integrity and life assessment of Ti-6Al-4V orthopaedic implantsKatarina Čolić, Svetlana M. Kostić, Simon Sedmak, Nenad Gubeljak, Aleksandar Grbović, 2024, original scientific article Abstract: This paper presents an experimental and numerical analysis of the mechanical behaviour of orthopaedic implants with crack-type defects, considering the principles and advantages of the modern X-FEM method, which was used due to limitations of traditional FEM in terms of crack growth simulation, especially for complex geometries. In X-FEM, the finite element space is enriched with discontinuity functions and asymptotic functions at the crack tip, which are integrated into the standard finite element approximation using the unity division property. Though rare, femoral component failures are well-documented complications that can occur after hip prosthetic implantation. Most stem fractures happen in the first third of the implant due to the loosening of the proximal stem and fixation of the distal stem, leading to bending and eventual fatigue failure. The main goal of this paper was to obtain accurate and representative models of such failures. Experimental analyses of the mechanical behaviour of implants subjected to physiological loads, according to relevant standards, using a new combined approach, including both experiments and numerical simulations was presented. The goal was to verify the numerical results and obtain a novel, effective methodology for assessing the remaining fatigue life of hip implants. For this purpose, the analysis of the influence of Paris coefficients on the total number of cycles was also considered. Hence, this simulation involved defining loads to closely mimic real-life scenarios, including a combination of activities such as ascending stairs, stumbling, and descending stairs. The tensile properties of the titanium alloy were experimentally determined, along with the Paris law coefficients C and m. The finite element software ANSYS 2022R2 version was used to develop and calculate the three-dimensional model with a crack, and the resulting stresses, stress intensity factors, and the number of cycles presented in the figures, tables, and diagrams. The results for the fatigue life of a partial hip implant subjected to various load cases indicated significant differences in behaviour, and this underscores the importance of analysing each case individually, as these loads are heavily influenced by each patient’s specific activities. It was concluded that the use of numerical methods enabled the preliminary analyses of the mechanical behaviour of implants under fatigue loading for several different load cases, and these findings can be effectively used to predict the possibility of Ti-6Al-4V implant failure under variable cyclic loads.
Keywords: structural integrity, fatigue fracture, extended finite element method (XFEM), experimental testing, DIC, numerical simulations, stress intensity factor, orthopaedic implants, crack-type defect
Published in DKUM: 21.03.2025; Views: 0; Downloads: 8
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9. Fatigue behaviour of PA66 GF30 at different temperaturesMarko Zadravec, Janez Kramberger, Branko Nečemer, Srečko Glodež, 2024, original scientific article Abstract: A comprehensive experimental investigation to understand the mechanical properties and fatigue behaviour of glass-reinforced polyamide (PA66 GF30) at different temperatures is presented in this paper. The specimens for quasi-static and fatigue testing were machined from previously extruded plates, where two orientations were considered: (i) the extrusion direction (ED) and (ii) the direction perpendicular to extrusion (PED). Both the quasi-static and fatigue tests were performed under different temperatures (22 ◦C and 100 ◦C). The fatigue tests were performed in a load control regime under pulsating loading (R = 0.1) to create S–N curves for all the temperatures and loading directions. The experimental results of the quasi-static tests showed that the test specimens manufactured in the extrusion direction have better mechanical properties when compared to those of the specimens manufactured perpendicular to the extrusion direction. Furthermore, the analysis of the quasi-static tensile test results showed that tensile strength, yield strength, and the modulus of elasticity are significantly dependent on the temperature and deteriorate when the temperature is increased from 22 ◦C to 100 ◦C. The results of the fatigue tests showed that at both the temperatures (22 ◦C and 100 ◦C), the samples produced in the direction of extrusion exhibited higher fatigue strength than those produced perpendicular to the direction of extrusion. For all the sample orientations, the fatigue strength decreased significantly with increasing temperature. The obtained experimental results could be very useful when designing and dimensioning different dynamically loaded engineering components made of PA66 GF30 subjected to high temperatures.
Keywords: PA66 GF30, increased temperatures, fatigue, experimental testing
Published in DKUM: 10.03.2025; Views: 0; Downloads: 8
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10. Development of novel hybrid TPMS cellular lattices and their mechanical characterisationNejc Novak, Oraib Al-Ketan, Matej Borovinšek, Lovre Krstulović-Opara, Reza Rowshan, Matej Vesenjak, Zoran Ren, 2021, original scientific article Abstract: Uniform lattices composed of one type of lattice structure repeated periodically have been extensively investigated in literature for their mechanical and physical properties. Their promising properties, which include a desirable combination of high strength, stiffness and toughness, suggest that hybrid structures made of two or more lattice types can exhibit even more advantageous and desired properties. In this work, the mechanical properties of hybrid cellular structures designed using implicit functions are investigated both experimentally and numerically. Two proposed samples are investigated comprised of a Gyroid and a Diamond unit cells hybridised linearly and radially. First, a finite element computational model was utilised in LS-DYNA to capture the mechanical properties of the additively manufactured constituent lattices (i.e., Gyroid and Diamond) made of stainless steel 316L and tested under dynamic and quasi-static loading conditions. The model was validated for three different relative densities. Then, the validated computational model was then tested to predict the mechanical behaviour of the proposed hybrid lattices. Finally, the proposed hybrid lattices were fabricated and mechanically tested to obtain their mechanical properties. A good agreement between experimental and computational results was achieved. The validated computational models will be used to evaluate other designs of TPMS lattices and their crashworthiness performance for protective equipment applications.
Keywords: cellular materials, triply periodical minimal surface, hybrid lattices, experimental testing, computational modelling, multi-morphology
Published in DKUM: 27.11.2024; Views: 3; Downloads: 13
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