Strojniški vestnik - Journal of Mechanical Engineering

Editorial: Special Issue of the Faculty of Mechanical Engineering, University of Maribor — 30 Years of Excellence in Engineering Research

Matej Vesenjak, Luka Lešnik, Matej Borovinšek, Simon Klančnik — Mon, 27 Oct 2025 00:00:00 +0000

This editorial introduces the Special Issue of the Strojniški vestnik - Journal of Mechanical Engineering dedicated to the 30th anniversary of the Faculty of Mechanical Engineering as an independent member of the University of Maribor, and the 50th anniversary of the University of Maribor. The Faculty of Mechanical Engineering is one of the most successful members at the University of Maribor and is recognised for its excellence in education, research and collaboration with industry. Its history of development, from its early beginnings in 1959 to becoming an internationally active and research-driven institution, reflects a continuous commitment to technological progress and societal impact. The Special Issue presents a selection of articles covering applied fluid mechanics, advanced materials and metamaterials, manufacturing science, and biomedical modelling. The collected works combine experimental, numerical, and review-based approaches to address contemporary challenges in mechanical engineering. This publication not only highlights the scientific excellence achieved at the Faculty of Mechanical Engineering, University of Maribor, but also celebrates its enduring mission to connect knowledge, innovation and human creativity in shaping a sustainable and technologically advanced future.

Numerical Solving of Dynamic Thermography Inverse Problem for Skin Cancer Diagnosis Based on non-Fourier Bioheat Model

Ivan Dominik Horvat, Jurij Iljaž — Mon, 27 Oct 2025 00:00:00 +0000

This paper presents numerical solving of the inverse bioheat problem to estimate four skin cancer parameters; diameter, thickness, blood perfusion rate and thermal relaxation time, based on the thermal response on the skin surface obtained by dynamic thermography and numerical skin cancer model, which can greatly enhance dynamic thermography diagnostics. To describe the heat transfer inside biological tissue and thermal behavior during the dynamic thermography process as realistic as possible, the non-Fourier dual-phase-lag bioheat model was used, as well as skin cancer model has been composed of multilayered healthy skin, embedded skin tumor and subcutaneous fat and muscle. Boundary element method has been used to solve a complex non-Fourier bioheat model to simulate dynamic thermography based on the skin cancer model and guessed searched parameters to obtain the thermal response on the skin surface during the cooling and rewarming phase using a cold air jet provocation, which is needed for the solution of the inverse bioheat problem. The inverse problem has been solved by optimization approach using the hybrid Levenberg-Marquardt optimization method, while the measurement data has been generated numerically with known exact tumor parameters and added noise, to evaluate the accuracy and sensitivity of the solution. Inverse problem solution has been tested for two different thermal responses; absolute temperature and temperature difference response, as well as for two different tumor stages; early stage or Clark II and later stage or Clark IV tumor. All important tumor parameters were successfully retrieved, especially the diameter and relaxation time, even for the high level of noise, while the accuracy of obtained parameters is slightly better using absolute temperature response. The results demonstrate the robustness of the method and a promising way for early diagnosis. The findings contribute to improving bioheat modeling in biological tissues, solving inverse bioheat problems and advancing dynamic thermography as a non-invasive tool for early skin cancer diagnosis.

Numerical Investigation of Erosion Due to Particles in a Cavitating Flow in Pelton Turbine

Luka Kevorkijan, Matjaž Hriberšek, Luka Lešnik, Aljaž Škerlavaj, Ignacijo Biluš — Mon, 27 Oct 2025 00:00:00 +0000

Erosion of Pelton turbine components due to cavitation and particle-laden flow is a major challenge in hydropower applications, particularly in sediment-rich river environments. This study presents a numerical investigation on how solid particles contribute to the erosion of a Pelton runner. Computational fluid dynamics (CFD) simulations were conducted using ANSYS CFX 2023 R2, incorporating a Lagrangian particle tracking approach and the Finnie abrasion model to predict erosion patterns under varying sediment concentrations. The results indicate that, under normal sediment conditions, particle erosion does not significantly contribute to blade tip damage. However, under extreme sediment loading, the predicted erosion patterns closely match real-world observations, particularly at the blade tip.

Removal of Inclusions and Trace Elements from Al-Mg-Si Alloys Using Refining Fluxes

Uroš Kovačec, Franc Zupanič — Mon, 27 Oct 2025 00:00:00 +0000

The cleanliness of aluminium alloys has a decisive effect on their properties and performance. In this work, the melts of several Al-Mg-Si alloys (6xxx series) were refined using rotary flux injection (RFI) of the salt fluxes in the industrial environment. A typical charge consisted of 25 % to 30 % external scrap, 45 % to 50 % internal scrap, and 20 % to 30 % primary aluminium. During injection, the entire melt volume was mixed uniformly. The melt was filtered using a porous ring filtration apparatus. The fraction and type of non-metallic inclusions were determined using light and scanning electron microscopy. The contents of alkali and alkaline-earth metals were determined using optical emission spectroscopy. The reduction of alkali and alkaline earth metals and the fraction of non-metallic inclusions were used to evaluate the process efficiency and the flux selection for the regular production. An analysis of more than 100 industry charges confirmed that the flux selected after the experimental trials, consisting of a mixture of MgCl2, KCl, NaCl and CaF2, was effective in regular production.

Effect of Presetting and Deep Rolling on Creep of Torsion Spring Bars

Vinko Močilnik, Nenad Gubeljak, Jožef Predan — Mon, 27 Oct 2025 00:00:00 +0000

This study investigates the creep behavior of torsion spring bars by combining experimental testing and numerical modeling. Experimental investigations were performed on torsional specimens subjected to different presetting levels and deep rolling surface treatments, showing different effects on stress relaxation at a constant torsion angle. Finite element method (FEM) simulations incorporating elasto-visco-plastic material behavior successfully reproduced the time-dependent deformation observed experimentally. Material parameters for the FEM model were derived from experimental data. The findings show that a two-stage presetting process combined with intermediate deep rolling results in higher residual compressive stresses in the surface layers compared to a single-stage presetting process. Although this method aims to mitigate creep under constant loading conditions, its effectiveness is limited. A reduction in creep strains is only observed up to a presetting level of approximately 4.3 %; above this threshold, creep strains increase significantly and loading capacity decreases.

Integrated Design, Simulation, and Experimental Validation of Advanced Cellular Metamaterials

Nejc Novak, Zoran Ren, Matej Vesenjak — Mon, 27 Oct 2025 00:00:00 +0000

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.

Fusion Behavior of Pure Magnesium During Selective Laser Melting

Mon, 27 Oct 2025 00:00:00 +0000

This study examined the melting behavior and flowability of pure magnesium during selective laser melting. The potential to increase product density was also investigated. Various combinations of manufacturing parameters were considered. The laser power was gradually increased in different machine runs, with different scanning speeds for each run to vary the energy density (ED). The laser power ranged from 10 W to 75 W, and the scanning speed ranged from 100 mm/s to 800 mm/s. Lower laser powers resulted in poor melting, while higher laser powers produced better melting, with significant differences even when the ED was the same. High EDs between 3.50 J/mm² and 4.30 J/mm² led to a lack of melting at low laser power and to an unstable melt pool with significant spattering at high laser power. In contrast, moderate EDs in the range of 1.40 J/mm² to 2.90 J/mm² resulted in better density at high laser power. Higher scanning speeds helped to avoid the formation of a dense smog cloud and provided sufficient energy in a short time with the aid of higher laser power. Therefore, increasing both laser power and scanning speed improved melting performance and increased product density. The relative product density ranged from 80 % to 96.5 %. Reducing the layer thickness from 50 µm to 25 µm at a laser power of 40 W resulted in the formation of a well-formed melt pool in some areas and significant melt spattering in others, which led to a deterioration in density.

Advancing Intelligent Toolpath Generation: A Systematic Review of CAD–CAM Integration in Industry 4.0 and 5.0

Marko Simonič, Iztok Palčič, Simon Klančnik — Mon, 27 Oct 2025 00:00:00 +0000

This systematic literature review investigates advancements in intelligent computer-aided design and computer-aided manufacturing (CAD–CAM) integration and toolpath generation, analyzing their evolution across Industry 4.0 and emerging Industry 5.0 (I5.0) paradigms. Using the theory–context–characteristics–methodology framework, the study synthesizes 51 peer-reviewed studies (from 2000 to 2025) to map theoretical foundations, industrial applications, technical innovations, and methodological trends. Findings reveal that artificial intelligence (AI) and machine learning dominate research, driving breakthroughs in feature recognition, adaptive toolpath optimization, and predictive maintenance. However, human-centric frameworks central to I5.0, such as socio-technical collaboration, remain underexplored. High-precision sectors (aerospace, biomedical) lead adoption, while small and medium enterprises (SMEs) lag due to resource constraints. Technologically, AI-driven automation and STEP-NC standards show promise, yet interoperability gaps persist due to fragmented data models and legacy systems. Methodologically, AI-based modeling prevails (49 % of studies), but experimental validation and socio-technical frameworks are sparse. Key gaps include limited real-time adaptability, insufficient AI training datasets, and slow adoption of sustainable practices. The review highlights the urgent need for standardized data exchange protocols, scalable solutions for SMEs, and human-AI collaboration models to align CAD–CAM integration with I5.0’s sustainability and resilience goals. By bridging these gaps, this work provides a roadmap for advancing intelligent, human-centered manufacturing ecosystems.

Comparison of 1D Euler Equation Based and 3D Navier-Stokes Simulation Methods for Water Hammer Phenomena

Nejc Vovk, Jure Ravnik — Mon, 27 Oct 2025 00:00:00 +0000

Water hammer phenomena in pipelines can induce significant transient pressure surges, leading to structural failures and operational inefficiencies. This study presents a comparative analyzis of two numerical approaches for simulating water hammer: a one-dimensional (1D) inviscid model with added friction based on the Euler equations and the method of characteristics, and a three-dimensional (3D) viscous model utilizing the Navier-Stokes equations in OpenFOAM. Benchmarking problems are solved first, then both methods are used to study a 3.4 km long DN400 pipeline subject to sudden pump failure by analyzing pressure surges, cavitation, and water column separation. The 1D model effectively predicts transient pressure waves and cavitation conditions with minimal computational cost, while the 3D model provides a detailed representation of multiphase flow dynamics, including cavitation bubble growth and collapse via the volume of fluid method. To mitigate adverse effects, a dynamic combination air valve is introduced, and its effectiveness in reducing pressure surges and cavitation is demonstrated. The results highlight the trade-offs between computational efficiency and accuracy in modelling water hammer events and underscore the importance of protective measures in pipeline systems.

Analysis of Gas Flow Distribution in a Fluidized Bed Using Two-Fluid Model with Kinetic Theory of Granular Flow and Coupled CFD-DEM: A Numerical Study

Matija Založnik, Matej Zadravec — Mon, 27 Oct 2025 00:00:00 +0000

Fluidized bed systems are widely used in chemical and process engineering due to their excellent heat and mass transfer properties. Numerical modeling plays a crucial role in understanding and optimizing these systems, with the two-fluid model enhanced by the kinetic theory of granular flow (TFM-KTGF) and the coupled computational fluid dynamics-discrete element method (CFD-DEM) emerging as leading techniques. This study employs both models to simulate gas-solid interactions and evaluates their performance using a benchmark single-spout fluidized bed case validated against experimental data. Subsequently, the influence of particle presence on gas flow distribution through a non-uniform distribution plate is analyzed. The results show that the common assumption of proportional flow distribution based on the opening area fraction is inaccurate, particularly in the presence of particles. Both numerical models capture this behavior, with TFM-KTGF showing trends comparable to the coupled CFD-DEM approach but at significantly reduced computational cost. The findings highlight the importance of accounting for particle dynamics in distribution plate design and promote the TFM-KTGF approach as a promising alternative for large-scale simulations.

Fatigue of Triply Periodic Minimal Surface (TPMS) Metamaterials – a Review

Žiga Žnidarič, Branko Nečemer, Nejc Novak, Matej Vesenjak, Srečko Glodež — Mon, 27 Oct 2025 00:00:00 +0000

A review of the fatigue behavior of triply periodic minimal surface (TPMS) metamaterials with consideration for their fabrication is presented in this paper. The review analyses the most common TPMS geometries used due to their mechanical characteristics. Production methods and the base materials used are presented with the key advantages and drawbacks. Furthermore, the mechanical characteristics of cellular structures with emphasis on TPMS geometries are described. Lastly, the state-of-the-art findings of their fatigue behavior are analyzed and explained. Based on the findings in this article, cellular geometries based on TPMS are superior to conventional cellular structures when comparing their fatigue life. Because of the smooth transitions between struts or surfaces, the stress distribution is much more uniform without stress concentration zones.