Machines. Technologies. Materials.
Vol. 20 (2026), Issue 3

Table of Contents

  • MACHINES

    • Wear Performance of Agricultural Harrow Discs Coated by Plasma-Jet Thermal Deposition

      pg(s) 81-84

      A comparative analysis of wear performance of coated harrow discs by plasma-jet thermal deposition was evaluated under agricultural conditions to assess the performance of atmospheric plasma spraying systems. This paper presents a long-term comparative field evaluation under identical operating conditions on a quartz-rich argic luvisol soil. Disc wear was quantified by periodic measurements of mass loss and diameter of the studied discs.
      The uncoated disc showed the most severe degradation, with a total mass loss of approximately 700 g and a rapid acceleration of wear after the first 5-10 ha of harrowing. The results obtained under field conditions demonstrate that the microstructural integrity of the coating is more critical than the nominal hardness and highlight the superior effectiveness of APS ceramic coatings for extending disc life in abrasive agricultural soils.

    • Experimental determination of the limit values of longitudinal accelerations of a motorcycle leading to loss of stability

      pg(s) 85-88

      Road experiments were conducted – when accelerating the motorcycle to the limit values of longitudinal geometric stability and the loss of contact of the front wheel with the road or reaching the “wheelie” phenomenon. From the theory of the motorcycle it follows that the critical accelerations depends on the height of the center of mass and its horizontal coordinate. In the presence of a passenger, the center of gravity is moved back and up, which leads to a decrease in the theoretical value of these accelerations. Therefore, the experiments were conducted on a motorcycle equipped with a suitcase and a passenger located on the back seat. The received information is recorded and visualized on a portable computer, and then processed in the Matlab and Excel environment. The results obtained from the experiments and the accumulation of databases can be used to create models for determining the influence of the driver’s behavior, the passenger’s influence, models for determining the behavior of the motorcycle and the comfort of the trip. During the measurements, the change in position of the driver and passenger is not taken into account.

    • Two-stroke low-speed engines and maritime transition to net-zero

      pg(s) 89-91

      The world’s maritime industry is currently undergoing an unprecedented transformation, driven by the climate crisis and the strict regulations imposed by the International Maritime Organization (IMO). The IMO’s Greenhouse Gas (GHG) Strategy for 2023 has fundamentally redefined the industry’s goals, from gradually reducing carbon intensity to comprehensively phasing out greenhouse gas emissions by 2050. At the heart of this transition is the low-speed, two-stroke engine, which serves as the main source of propulsion for most deep-sea merchant ships. Contrary to being considered a legacy of the limitations of the fossil fuel-dependent era, these engines are being transformed into highly efficient and adaptable platforms capable of using the next generation of carbon-neutral and zero-carbon energy carriers. This analysis examines the technical, operational and regulatory mechanisms that enable the maritime sector to meet its net-zero emission commitments, with a particular focus on dual-fuel engine architectures, advanced combustion control, and the holistic integration of ship energy systems.

    • Тheoretical investigation into the influence of a teeth fault to gear train vibrations

      pg(s) 92-93

      The vibration behavior of a healthy gear train is modelled as a sum of sinusoidal accelerations of a pinion, a gear, and a gear-mesh. A while noise is added trough waveform of normally distributed random numbers. The corresponding time-diagram and spectrogram are obtained. After that, an impulse acceleration waveform is added to simulate a teeth fault. The time-diagram and spectrogram are obtained again and compared. Conclusions are made.

  • TECHNOLOGIES

    • Implementation of slow stress rating test method (SSRT) in determination susceptability to hydrogen embritlement of P460NL1 steel

      pg(s) 94-99

      The hydrogen embrittlement susceptibility of P460NL1 pressure-vessel steel was assessed by slow strain rate testing (SSRT) with in situ electrochemical hydrogen charging. An electrochemical cell integrated with a tensile testing machine was used to generate hydrogen in a 3.5 wt.% NaCl solution containing 1 g/L thiourea. Cathodic charging was applied at a constant current of −20 mA (approximately −1.4 V). SSRT was performed at a strain rate of 10⁻ ⁵ s⁻ ¹ in accordance with ASTM G129-21. Tensile specimens extracted from the base material and welded joints were tested in air and under hydrogen-charging conditions. The methodology enabled controlled hydrogen introduction during deformation of tensile probes and allowed comparison of hydrogen-assisted cracking susceptibility between base metal and welded material. Tested brocken tensile probes were subjected to determination of dissolved hydrogen. Tensile probes were first tested in the air and after that in prepared solution.
      To analyse hydrogen embritlement of investigated steel hydrogen embritlement index was determined through determination of fracture elongation and reduction of Area (RA) of the brocken specimen. Light and SEM microscopy was used to analyse possible location of the present defects in material i.e. hot rolled steel. Types of non-metallic inclusions were determined too.

    • A methodological framework for achieving sustainable hydrogen supply chain produced via biogas-based steam methane reforming

      pg(s) 99-102

      Growing energy and environmental challenges highlight the need for a transition to sustainable supply chains. This paper presents a methodology for assessing a hydrogen supply chain based on steam reforming of biogas (SMR), as a low-carbon alternative to conventional natural gas. The framework covers the entire life cycle, from feedstock to end use. The proposed framework supports strategic planning and provides a basis for future modeling, optimization, and assessment of environmental and socio-economic benefits.

    • Modeling of Densification Kinetics during Electro-Pulse Consolidation of Titanium Powder

      pg(s) 103-107

      This study presents a theoretical investigation of the densification kinetics of titanium powder during electro-pulse consolidation. A mathematical model was developed to analyze the influence of electrical current parameters in different sintering regimes – direct current (DC), alternating current (AC), pulsed current, and their superposition – on the thermophysical processes governing sintering.
      The heating rates and the evolution of relative density were calculated for different applied pressing pressures. The results show that the superposition of currents is the most energy-efficient regime. This regime enables the material to reach a relative density above 99% within a minimal processing time. The effect is attributed to the combined action of intense Joule heating and the electroplastic effect.

    • Cathodic Protection Modeling of Steels in Corrosive Chemical Environments Using COMSOL Multiphysics

      pg(s) 108-110

      This study investigates the electrochemical performance of Sacrificial Anode Cathodic Protection (SACP) systems for offshore steel structures using Finite Element Analysis (FEA). Two structural substrates, S235JR carbon steel and S550QL high-strength steel, were modelled in a 3 wt.% NaCl electrolyte. A comparative analysis was performed between two sacrificial anode materials: a conventional Al- 5Mg alloy and a quaternary Al-6Zn-0.2In-1Mg-0.03Ti alloy. The simulations evaluate the influence of anode placement errors by comparing an ideal symmetric distribution (90°) with a clustered configuration (10°). The results show that geometric clustering significantly alters the potential distribution along the structure. For S235JR steel, the clustered configuration produces localized underprotection with potentials reaching −0.78 V (vs. Ag/AgCl). In contrast, for S550QL steel, the same configuration results in localized over-polarization (≈ −0.96 V), thereby increasing the risk of hydrogen-induced stress cracking (HISC). The study demonstrates that improper anode placement may compromise cathodic protection efficiency even when high-performance anode alloys are used. These findings highlight the importance of accurate anode distribution and support the use of numerical simulations in digital twin approaches for offshore corrosion management.

    • Machine Learning Prediction of Mechanical Properties for Al-Cu Alloys Using Monte Carlo Data Augmentation

      pg(s) 111-113

      This study presents a machine learning framework for predicting the mechanical properties of 2xxx series Al-Cu alloys (2024, 2219, 2524) across 11 temper conditions. Monte Carlo augmentation generated 8,800 synthetic samples from compositional specification ranges of a literature-mined dataset. Three regression models, Random Forest, Gradient Boosting, and SVR-RBF were evaluated via 5-fold cross-validation (CV) to predict ultimate tensile strength (UTS), yield strength (YS), and elongation. All models achieved coefficient of determination R² > 0.991, with Mean Absolute Error MAE ≤ 7.4 MPa for UTS, ≤ 5.4 MPa for YS, and ≤ 0.51% for elongation. Feature importance analysis revealed that temper condition encoding dominated predictions (>75% importance), while individual compositional features contributed <5% each. The high predictive accuracy reflects the effectiveness of the augmentation scheme in capturing withingroup property–composition–temper relationships, though generalization to unseen alloy–temper conditions remains to be validated. The results illustrate the potential of combining corpus-mined data with Monte Carlo augmentation for rapid alloy property screening.

    • Analysis of workover operations over a ten-year period in an oil and gas field with sucker rod pump production

      pg(s) 114-117

      At the start of exploitation of any hydrocarbon or geothermal water reservoir, production of reservoir fluids is driven by natural energy in the form of reservoir pressure. Therefore, the primary task for production engineers is to maintain this reservoir pressure for as long as possible, ensuring long-term economic production. Unfortunately, sooner or later it becomes necessary to introduce mechanical methods of fluid lifting. Today, there are numerous solutions on the market for mechanical lifting of reservoir fluids (progressing cavity pumps-PCP, electric submersible pumps-ESP), and one of the oldest mechanical methods for producing reservoir fluids is the sucker rod pump. In the Republic of Croatia, sucker rod pumps are among the most commonly used mechanical methods for lifting reservoir fluids. Although Croatian production engineers have significant experience working with sucker rod pumps, operational problems are common and are accompanied by additional expenses related to workover operations. This paper presents an analysis of workover operations over a tenyear period (from 2011 to 2022) in an oil and gas field in the Republic of Croatia. Based on the collected data, an analysis was conducted to determine the volume of fluid not produced during equipment maintenance and repair, the waiting time for repairs, the duration of equipment maintenance as well as the cost-effectiveness of the repairs. Special attention is given to the analysis of the causes of problems in using sucker rod pumps and the identification of problematic wells.

    • A MES Application for OEE Improvement in Plastic Injection Facilities

      pg(s) 118-122

      In plastic injection and plastic welding processes, the inability to accurately classify machine downtimes, the lack of visibility regarding performance discrepancies between shifts, and the reliance on largely manual methods for operator tracking hinder the sustainable improvement of Overall Equipment Effectiveness (OEE). Furthermore, the retention of pro- duction and energy consumption data in isolated systems complicates integrated performance evaluation.
      In this study, the HBS MES system, developed by the in-house engineering team of Pleksan A.S. and fully integrated with HBS ERP, is examined within the scope of a field application aimed at real-time production tracking, performance analysis, and energy consumption reporting in plastic injection lines. As of 2025, HBS MES is actively used in its V1 version across three different plastic manufacturing enterprises; this paper exemplifies a facility predominantly focused on plastic injection.
      The paper presents the system architecture, data collection logic, modeling of production and downtime events, the approach to calculating OEE and its sub-metrics, and user interface components in detail. As a result of the implementation in the studied facility, an improvement of approximately 25% in production quantities was reported, particularly during night shifts, and the mechanisms underlying this improvement are discussed. The findings demonstrate that MES solutions integrated with machine-embedded data collection modules can provide measurable productivity gains even in small and medium-sized enterprises.

  • MATERIALS

    • Photoluminescence properties of Sm3+-doped ZrO2–TiO2–Al2O3 coatings

      pg(s) 123-126

      The emission spectrum of the ZrO2–TiO2–Al2O3–Sm2O3 coating was recorded at different excitation wavelengths. Under UV excitation (λₑₓ = 354 nm), broad band with a maximum around 420–440 nm was observed and can be associated with oxygen vacancies in ZrO2 together with Ti³⁺ centers. Weakly intense and narrower emission bands at 600 nm and 647 nm are assigned to the 5G5/2  7H7/2 and 5G5/2  7H9/2 transitions of Sm3+ ions. Under excitation with 404 nm the emission is dominated by defect levels in the oxide coating. The values of the chromaticity coordinates of the coating excited under 354 nm correspond to the pale pink color of emission (0.252, 0.272) and under 404 nm has orange color of emission (0.353, 0.370).