1. Mechanical uniaxial compression of 3D-printed non-periodic ASA lattice structures using semi-controlled design modelsNebojša Rašović, Inga Krešić, Jasmin Kaljun, 2025, original scientific article Abstract: This work examines the mechanical behaviour of 3D-printed stochastic lattice structures fabricated using a semi-controlled design. A primary goal is to predict and optimize the mechanical response of these Acrylic Styrene Acrylonitrile (ASA) filament structures when subjected to compressive stress. By transitioning from a purely stochastic method to a semi-controlled tessellation approach within Rhinoceros 7 software, we effectively generated the proposed design models. This methodology results in mechanical responses that are both predictable and reliable. The design parameters, including nodal formation, strut thickness, and lattice generation based on a predefined geometric routine, are associated with the regulation of the relative density. This approach aims to minimize the effect of relative density on the actual stiffness and strength evaluation. Our findings are cantered on the compressive testing of structures, which were generated using a Voronoi population distributed along a parabolic curve. We analyzed their mechanical response to the point of failure by examining stress–strain fluctuations. Three distinct behaviour stages are observed: elastic range, plastic range, and collapse without densification. The influence of crosslink geometry on the elastic responses was highlighted, with parabolic configurations affecting the peak stresses and elastic line slopes. The structures exhibited purely brittle behaviour, characterized by abrupt local cracking and oscillatory plateau formation in the plastic stage.
Keywords: semi-controlled Voronoi tessellation, stress–strain curve, mechanical response
Published in DKUM: 03.11.2025; Views: 0; Downloads: 5
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2. Environmental pollution and economic activity : estimating the environmental Kuznets curve for a panel of countries worldwideDarja Boršič, Petar Todorčević, Nejc Fir, 2025, original scientific article Abstract: This paper aims to assess the impact of certain economic factors on pollution for selected 112 countries worldwide. Due to data availability, carbon dioxide emissions in tonnes per capita were chosen as the dependent variable measuring pollution. Based on panel data and generalized moments method, the relationship between economic activity and environmental pollution was estimated. The results show that in the whole sample, as well as for two subsamples of developed and undeveloped countries, carbon dioxide emissions are statistically significantly affected by gross domestic product per capita, energy intensity and renewable energy consumption. The linear effect of economic activity positively effects the pollution, while the quadratic relationship is negative. Thus, the validity of inverted-U curve of the environmental Kuznets curve has been demonstrated. The estimated effect of economic activity measured by gross domestic product per capita on pollution does not differ in developed and undeveloped countries.
Keywords: environmental Kuznets curve, carbon dioxide emissions, renewable energy, industrialisation, urbanisation, economic development, cross-section analysis
Published in DKUM: 21.10.2025; Views: 0; Downloads: 4
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3. Comparative analysis of fracture mechanics parameters for wrought and SLM-produced Ti-6Al-7Nb alloyIvan Gelo, Dražan Kozak, Nenad Gubeljak, Tomaž Vuherer, Pejo Konjatić, Marko Katinić, 2025, original scientific article Abstract: The research presented in this paper is based on the need for personalized medical implants, whose serial production is impossible, so the need for production process adjustments is inevitable. Conventional production technologies usually set geometrical limitations and generate a lot of waste material, which leads to great expenses, especially when the material used for production is an expensive Ti alloy. Additive technologies offer the possibility to produce a product almost without waste material and geometrical limitations. Nevertheless, the methods developed for additive production using metal powder are not significantly used in biomedicine because there is insufficient data published regarding the properties of additively produced parts, especially from the fatigue and fracture standpoint. The aim of this research is the experimental determination of fracture mechanics properties of additively produced parts and their comparison with the properties of parts produced by conventional technologies. Drawing is the first production process in the comparison, and the second one is selective laser melting (SLM). The Ti-alloy Ti-6Al-7Nb, used for medical implants, was selected for this research. Experimental testing was performed in order to determine ∆Kth fracture mechanics parameters and resistance curves according to ASTM E1820. Test specimen dimensioning and the experiments were carried out according to the respective standards. For the drawn test specimen, the value obtained was ∆Kth = 3.84 MPam0.5 , and the fracture toughness was Kc = 84 MPam0.5, while for SLM produced test specimens the values were ∆Kth = 4.53 MPam0.5, and Kc = 21.9 MPam0.5.
Keywords: fracture toughness, crack growth curve, resistance curve, additive technologies, powder metallurgy, selective laser melting, Ti-6Al-7Nb
Published in DKUM: 19.08.2025; Views: 0; Downloads: 10
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4. The learning curve of laparoscopic liver resection utilising a difficulty scoreArpad Ivanecz, Irena Plahuta, Matej Mencinger, Iztok Peruš, Tomislav Magdalenić, Špela Turk, Stojan Potrč, 2022, original scientific article Abstract: Background: This study aimed to quantitatively evaluate the learning curve of laparoscopic liver resection (LLR) of a single surgeon.
Patients and methods: A retrospective review of a prospectively maintained database of liver resections was conducted. 171 patients undergoing pure LLRs between April 2008 and April 2021 were analysed. The Halls difficulty score (HDS) for theoretical predictions of intraoperative complications (IOC) during LLR was applied. IOC was defined as blood loss over 775 mL, unintentional damage to the surrounding structures, and conversion to an open approach. Theoretical association between HDS and the predicted probability of IOC was utilised to objectify the shape of the learning curve.
Results: The obtained learning curve has resulted from thirteen years of surgical effort of a single surgeon. It consists of an absolute and a relative part in the mathematical description of the additive function described by the logarithmic function (absolute complexity) and fifth-degree regression curve (relative complexity). The obtained learning curve determines the functional dependency of the learning outcome versus time and indicates several local extreme values (peaks and valleys) in the learning process until proficiency is achieved.
Conclusions: This learning curve indicates an ongoing learning process for LLR. The proposed mathematical model can be applied for any surgical procedure with an existing difficulty score and a known theoretically predicted association between the difficulty score and given outcome (for example, IOC).
Keywords: difficulty score, learning curve, laparoscopy, hepatectomy, intraoperative complications, surgical procedures
Published in DKUM: 07.04.2025; Views: 0; Downloads: 258
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5. Effects of fixture configurations and weld strength mismatch on J-integral calculation procedure for SE(B) specimensPrimož Štefane, Stijn Hertelé, Sameera Naib, Wim de Waele, Nenad Gubeljak, 2022, original scientific article Abstract: This work presents the development of a J-integral estimation procedure for deep and
shallow cracked bend specimens based upon plastic ηpl factors for a butt weld made in an S690 QL
high strength low alloyed steel. Experimental procedures include the characterization of average
material properties by tensile testing and evaluation of base and weld metal resistance to stable tearing
by fracture testing of square SE(B) specimens containing a weld centerline notch. J-integral has been
estimated from plastic work using a single specimen approach and the normalization data reduction
technique. A comprehensive parametric finite element study has been conducted to calibrate plastic
factor ηpl and geometry factor λ for various fixture and weld configurations, while a corresponding
plastic factor γpl was computed on the basis of the former two. The modified ηpl and γpl factors were
then incorporated in the J computation procedure given by the ASTM E1820 standard, for evaluation
of the plastic component of J and its corresponding correction due to crack growth, respectively. Two
kinds of J-R curves were computed on the basis of modified and standard ηpl and γpl factors, where
the latter are given by ASTM E1820. A comparison of produced J-R curves for the base material
revealed that variations in specimen fixtures can lead to ≈10% overestimation of computed fracture
toughness JIc. Furthermore, a comparison of J-R curves for overmatched single-material idealized
welds revealed that the application of standard ηpl and γpl factors can lead to the overestimation of
computed fracture toughness JIc by more than 10%. Similar observations are made for undermatched
single material idealized welds, where fracture toughness JIc is overestimated by ≈5%.
Keywords: metal weld, strength mismatch, fracture, plastic correction factors, fixture rollers, J-R resistance curve
Published in DKUM: 20.03.2025; Views: 0; Downloads: 9
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6. Security enhanced CLS and CL-AS scheme without pairings for VANETsAnjali Bansal, Saru Kumari, Nishant Doshi, Mohammed Amoon, Marko Hölbl, 2025, original scientific article Abstract: While vehicle ad-hoc networks (VANETs) have many advantages, they also present privacy and security concerns. Certificate management issue has been seen in traditional public key infrastructure based privacy preserving authentication schemes while key escrow problem exists in identity based privacy preserving authentication techniques. Also existing cryptographic techniques rely heavily on assumptions about tamper-proof equipment to ensure their security. A proposal has been made for a certificateless aggregate signature system for VANETs addressing these issue and was proved provably unforgeable against collusion attack. However we found that the proposed technique was insecure and cannot withstand collusion assault. Therefore, this paper presents an improved and secure certificateless aggregate signature technique for VANETs. We also illustrate the security & performance evaluation of our presented technique and based upon the hardness assumption of the elliptic curve discrete logarithm problem we have shown that the technique is safe against existential forgery on adaptive chosen message attack in the random oracle model. Also the presented technique has better efficiency compared to some recent existing authentication techniques.
Keywords: aggregate signature, certificateless public key cryptography, elliptic curve cryptosystem, vehicular ad hoc networks
Published in DKUM: 13.03.2025; Views: 0; Downloads: 4
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8. Experimental characterization and phase-field damage modeling of ductile fracture in AISI 316lVladimir Dunić, Nenad Gubeljak, Miroslav Živković, Vladimir Milovanović, Darko Jagarinec, Nenad Djordjevic, 2024, original scientific article Abstract: ) Modeling and characterization of ductile fracture in metals is still a challenging task in
the field of computational mechanics. Experimental testing offers specific responses in the form of
crack-mouth (CMOD) and crack-tip (CTOD) opening displacement related to applied force or crack
growth. The main aim of this paper is to develop a phase-field-based Finite Element Method (FEM)
implementation for modeling of ductile fracture in stainless steel. (2) A Phase-Field Damage Model
(PFDM) was coupled with von Mises plasticity and a work-densities-based criterion was employed,
with a threshold to propose a new relationship between critical fracture energy and critical total
strain value. In addition, the threshold value of potential internal energy—which controls damage
evolution—is defined from the critical fracture energy. (3) The material properties of AISI 316L steel
are determined by a uniaxial tensile test and the Compact Tension (CT) specimen crack growth test.
The PFDM model is validated against the experimental results obtained in the fracture toughness
characterization test, with the simulation results being within 8% of the experimental measurements.
Keywords: phase-field damage modeling, ductile fracture, crack-tip opening displacement, crack growth, resistance curve, finite element method, simulations
Published in DKUM: 19.09.2024; Views: 0; Downloads: 12
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9. A new transformation technique for reducing information entropy : a case study on greyscale raster imagesBorut Žalik, Damjan Strnad, David Podgorelec, Ivana Kolingerová, Luka Lukač, Niko Lukač, Simon Kolmanič, Krista Rizman Žalik, Štefan Kohek, 2023, original scientific article Abstract: This paper proposes a new string transformation technique called Move with Interleaving (MwI). Four possible ways of rearranging 2D raster images into 1D sequences of values are applied, including scan-line, left-right, strip-based, and Hilbert arrangements. Experiments on 32 benchmark greyscale raster images of various resolutions demonstrated that the proposed transformation reduces information entropy to a similar extent as the combination of the Burrows–Wheeler transform followed by the Move-To-Front or the Inversion Frequencies. The proposed transformation MwI yields the best result among all the considered transformations when the Hilbert arrangement is applied.
Keywords: computer science, algorithm, string transformation, information entropy, Hilbert space filling curve
Published in DKUM: 22.05.2024; Views: 160; Downloads: 19
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10. Analysis of higher-order bézier curves for approximation of the static magnetic properties of NO electrical steelsErmin Rahmanović, Martin Petrun, 2024, original scientific article Abstract: Adequate mathematical description of magnetization curves is indispensable in engineering. The accuracy of the description has a significant impact on the design of electric machines and devices. The aim of this paper was to analyze the capability of Bézier curves systematically, to describe the nonlinear static magnetic properties of non-oriented electrical steels, and to compare this approach versus the established mathematical descriptions. First, analytic functions versus measurements were analyzed. The Bézier curves were then compared systematically with the most adequate analytic functions. Next, the most suitable orders of Bézier curves were determined for the approximation of nonlinear magnetic properties, where the influence of the range of the input measurement dataset on the approximation process was analyzed. Last, the extrapolation capabilities of the Bézier curves and analytic functions were evaluated. The general conclusion is that Bézier curves have adequate flexibility and significant potential for the approximation and extrapolation of nonlinear properties of non-oriented electrical steels.
Keywords: analytical modeling, anhysteretic curve, applied mathematics, Bézier curve, curve fitting, first magnetization curve, major loop, mathematical modeling, non-oriented electrical steel
Published in DKUM: 01.02.2024; Views: 382; Downloads: 50
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