Machines. Technologies. Materials.
Vol. 20 (2026), Issue 6

Table of Contents

  • MACHINES

    • Rapid prototyping of a friction coupling for joining rebar

      pg(s) 210-213

      Friction couplings for joining rebar are widely used in civil engineering and mechanical structures, including the construction of high-rise buildings, towers, bridges, overpasses, tunnels, dams, and other infrastructure. These friction couplings are mechanical elements that provide a strong and reliable connection between the components being joined by transferring loads through the friction force generated between the contact surfaces. This force is applied by the geometry of the friction coupling and the installation-induced clamping force. The primary factor governing the proper selection and application of a friction coupling is the cross-sectional diameter of the rebar, as the friction coupling must be designed to withstand the loads encountered under service conditions. In addition, environmental influences, particularly the difference in the coefficients of thermal expansion of the joined materials, represent an important consideration. Another critical factor is the installation process itself, as the performance of the friction coupling depends directly on proper installation. Therefore, comprehensive testing of the installed friction coupling is essential to ensure its reliable performance throughout its service life. This paper presents an original design solution for the development of a friction coupling for joining Ø25 mm rebar, developed through three successive design iterations. The proposed friction coupling is intended to ensure structural integrity under static and dynamic loading, including seismic loading and vibration. An initial prototype design was developed in accordance with the applicable technical standards and validated using the Finite Element Method (FEM) to evaluate its load-bearing capacity under static loading conditions and identify potential stress concentrations. The prototype models were manufactured using the Fused Filament Fabrication (FFF) additive manufacturing process with the support of CAD/CAE systems. The friction coupling was ergonomically designed through mass and shape optimization.

  • TECHNOLOGIES

    • Complex-composition ceramics based on Al2O3 and basalt glass

      pg(s) 214-216

      To reduce the sintering temperature in the microstructural design of α-Al2O3-based ceramics, a mixture of basalt glass and yttria-stabilized zirconia (YSZ) was used. The effect of isothermal holding time during liquid-phase sintering of a composite containing 85 wt.% α-Al2O3 and 15 wt.% (basalt glass + YSZ) on its mechanical properties was investigated. The samples were sintered at temperatures of 1450 and 1500 °C for 2–6 hours. It was established that sintering occurs in the presence of a liquid phase that persists throughout the entire holding period, and the densification of the material is determined by the rearrangement and Ostwald ripening processes of Al2O3 grains. The maximum hardness reached 7.73 GPa, while the fracture toughness reached 7.95 MPa•m¹ᐟ². The effect of microstructural evolution on the hardness and fracture toughness of the composite was demonstrated.

    • Tolerance treatment of sliding pairs and repeatability in assembly

      pg(s) 217-219

      The basic prerequisite for trouble-free assembly of moving structures is that the assembled structure has as many degrees of freedom as its function requires. In practice, we often encounter cases of statically overdetermined pairs. Designers often use them to increase the rigidity of products. This article describes a way to mitigate the consequences of problematic assembly in sliding pairs, which are often statically overdetermined. The article also addresses an important problem in assembly, which is repeated assembly accuracy, especially when designing assembly lines and automated and robotic systems.

    • Influence of thermodynamic properties of metallic materials on the efficiency of hydro-vacuum atomization and hydriding processes

      pg(s) 220-228

      In this study, we present the key results of computer modeling and experimental series of a combined technological process that integrates hydro-vacuum atomization and hydrogenation of metallic melts. The simulations considered several representative cases in which lead, aluminum, magnesium, Armco iron, and magnesium–aluminum alloys were used as initial materials. A comparative analysis of the obtained data revealed that, during hydro-vacuum atomization, the cooling, solidification, and hydrogenation kinetics of atomized droplets are strongly governed by the specific thermodynamic characteristics of the metals, such as the solidification interval, latent heat of fusion/solidification, and specific heat capacity. It was established that the relationship between the melt overheating temperature and the width of its solidification interval constitutes a key controlling factor in the combined processes of atomization and hydrogenation. This factor is critical because it determines both the duration and the nature of the residence of atomized metallic droplets in the transitional liquid–crystalline state, thereby defining the temporal window and the depth of highly effective physico-technological influences that promote hydrogen uptake. These influences arise during the entrainment and breakup of the melt jet in the water stream and include hydromechanical activation, structural metastabilization, and interstitial hydrogen incorporation released from collapsing cavitation cavities in water due to the thermobaric energy generated during their directed cumulative implosion.

    • Study of the influence of the cross-linker on the modification of cotton fabric with chitosan for controlled release of diclofenac and preparation of antimicrobial textiles

      pg(s) 229-231

      Composite materials with potential application in medical textiles were developed by modifying cotton fabric with chitosan containing diclofenac. The influence of the concentration of citric acid as a crosslinking agent on the properties of the materials was studied. The resulting composite materials were characterized by gravimetric analysis, optical microscopy, contact angle measurement and thermogravimetric analysis. The antimicrobial activity of the cotton samples was evaluated against Gram-positive and Gram-negative model bacterial strains. A synergistic antimicrobial effect of chitosan and diclofenac and a uniform release of diclofenac in vitro under physiological conditions were established.

    • Integrated comparative assessment of material, energy and construction-time efficiency of prefabricated and conventional reinforced concrete systems

      pg(s) 232-238

      The selection of an appropriate structural and construction system significantly influences material consumption, energy demand, construction duration and overall project efficiency. This study presents an integrated parametric methodology for comparing prefabricated and conventional cast-in-situ reinforced concrete systems under equivalent functional and structural requirements. A representative five-storey building with a gross floor area of approximately 5,000 m² is analysed using two construction scenarios: CIS (conventional cast-in-situ reinforced concrete) and PRE (prefabricated reinforced concrete). The assessment incorporates concrete and reinforcement consumption, material losses, structural construction duration, embodied energy of principal materials, additional production energy, transportation and site energy. The analysed performance dimensions are integrated into a dimensionless Construction Efficiency Index (CEI), while sensitivity analysis evaluates the influence of decision priorities. At a reference factory-to-site distance of 50 km, the parametric scenario indicates a reduction of approximately 7.8% in total structural-material input, 25% in structural construction duration and 6.2% in total energy demand for PRE relative to CIS. The baseline CEI increases from 1.000 for CIS to 1.153 for PRE. The study additionally introduces a project-specific break-even transportation-distance model. Under the adopted assumptions, the energy advantage of prefabrication disappears at approximately 185 km, whereas the integrated CEI advantage persists to a substantially larger theoretical distance because material and time benefits remain. The proposed framework demonstrates that prefabrication should not be evaluated through a single indicator. Its relative advantage depends on the combined effects of materials, energy, time and logistics. The methodology is intended as an early-stage engineering decision-support approach and requires project-specific inventory data for application to real construction projects.

  • MATERIALS

    • Intelligent Brazing Materials

      pg(s) 239-241

      The paper presents the research carried out for the development of brazing materials which, in a single pass, deposit two layers in the brazing joints: a buffer layer with high diffusion potential and increased silver content, and a filling layer with high strength and reduced silver content. The brazing performance of Ag20-type coated rods was improved by introducing a percentage of Ag40-type powder into the deoxidizing coating. The research was completed by establishing and patenting both the product formulation and the manufacturing process. The new product was successfully tested for producing brazed joints in copper pipes, copper-to-steel joints, and steel-to-tungsten carbide joints. The results of the mechanical tests met the required specifications, while the metallographic analysis of the joints showed an increase in diffusion of approximately 18.5% compared with the diffusion obtained using Ag20-type rods. The advantages of the brazing process using the new products consist of increased brazing productivity, improved quality of the brazed joints, and reduced environmental emissions from the resulting slag.

    • Innovative Nanomaterials for the Conservation and Sustainable Protectionof Cultural Heritage

      pg(s) 242-244

      Cultural heritage objects represent an essential component of human identity, history, and collective memory. However, monuments, artworks, manuscripts, archaeological artefacts, and historical buildings are continuously exposed to environmental deterioration processes, including humidity fluctuations, pollution, biological colonization, salt crystallization, and mechanical degradation. Conventional conservation methods often provide effective protection but may involve invasive procedures, limited durability, or the use of environmentally harmful chemicals. In recent decades, nanotechnology has emerged as a promising approach for sustainable conservation due to the unique physicochemical properties of nanomaterials, including high surface area, enhanced reactivity, photocatalytic activity, and the possibility of designing multifunctional protective coatings. This review discusses innovative nanomaterials used in cultural heritage conservation, including silica nanoparticles, titanium dioxide, zinc oxide, calcium hydroxide nanoparticles, graphene-based materials, and nanocomposites. Their applications in consolidation, cleaning, protection against pollutants, antimicrobial treatments, and sustainable preservation strategies are examined.
      The report is under project No. KП-06-H90/6 dated 10.12.2024 on the topic: “Ecologically sustainable conservation strategy for written heritage” from the Scientific Research Fund, Competition for funding of fundamental scientific research – 2024. Supervised by Chief Associate Professor, PhD, MSc Eng. Iskra Tsvetanska.

    • Thermodynamic Properties and Phase Equilibria in the Fe–W–C System

      pg(s) 245-246

      By utilizing the tools of the PyCALPHAD library and a thermodynamic database, Python-based software components were developed to calculate the energetic characteristics of phase transitions, enabling the prediction of Fe–W–C system behavior under varying composition and temperature. According to the CALPHAD calculation, it was established that within the temperature range of 500–2000 K for the composition of 43 at.% Fe, 43 at.% W, and 14 at.% C, an intermediate Fe3W3C phase is formed, which melts incongruently at 1770K.