“Naukovi Notatki” is a peer-reviewed, open-access journal (Category B) that publishes review articles and the results of original fundamental and applied research in the field of “Mechanical Engineering and Machine Building.” Scientific papers are published in the following specialties: G8 Materials Science; G9 Applied Mechanics; G11 Mechanical Engineering (by specialization)
Луцький національний технічний університет
EIGENFUNCTIONS OF THE LAPLACE/HELMHOLTZ EQUATION FOR WEDGE-SHAPED DOMAIN
The Laplace/Helmholtz equation for wedge-shaped regions (wedge-shaped sector of finite width, wedge-shaped sector of finite length) in a cylindrical coordinate system is solved. The solutions are obtained in the form of series in an orthonormal system of modified Bessel and McDonald functions. Formulas for estimating the required number of first terms of the corresponding series to ensure the given accuracy of calculations are derived.
DEVELOPMENT AND STRUCTURAL-PHASE EVOLUTION OF THE BIODEGRADABLE HIGH-ENTROPY Fe-Zn-Mn-Cu ALLOY
The synthesis and investigation of the structural and phase evolution patterns of an equiatomic high-entropy Fe-Zn-Mn-Cu alloy were carried out. The alloy was obtained by powder metallurgy methods: high-energy mechanical alloying (20 hours in "Kalosha" petroleum ether) followed by liquid-phase sintering at a temperature of 900 ℃ in a pure nitrogen atmosphere. It is shown that this technological approach overcomes the thermodynamic immiscibility of the elements (specifically the Fe–Cu pair) and forms a supersaturated solid solution without a critical accumulation of oxide phases. It was established that after sintering, the alloy forms a specific microporous structure (scaffold), which reduces the elastic modulus of the material and promotes the free circulation of physiological fluids. The prospects of the developed system for creating new-generation biodegradable orthopedic implants with a controlled corrosion rate and potential antibacterial properties are proven.
FORWARD-ACCELERATED SIMP FOR TOPOLOGY OPTIMIZATION OF LOAD-BEARING MACHINE PARTS
A modification of the SIMP method for topology optimization of load-bearing elements of mechanical engineering structures is proposed – the FA-SIMP (Forward-Accelerated SIMP) algorithm, which combines an adaptive lookahead step governed by a FISTA-type momentum coefficient with a double box/volume projection of the lookahead point. The sensitivity is evaluated at a physically admissible lookahead point shifted along the previous descent direction, and an adaptive momentum restart reduces the risk of divergence in the non-convex problem. This approach makes it possible to assess not only the final stiffness of the optimized structure but also the stability of the iterative process under changes in geometry and discretization. The method is studied on compliance minimization of a cantilever beam for three configurations differing in physical size and finite-element mesh density. At the same volume fraction and iteration budget, FA-SIMP consistently reduces compliance (up to 3.95 %), grayness index (up to 10.90 %) and maximum displacement while preserving the prescribed mass and keeping the computation time practically unchanged, providing a mesh-stable acceleration of SIMP.
DETERMINATION OF THE STRENGTH CHARACTERISTICS OF TRAPEZOIDAL MULTIFRACTALS
The article presents the results of an experimental study of the strength of trapezoidal multifractals manufactured from PETG by FDM (Fused Deposition Modeling) 3D printing. The investigated specimens were regular discrete structures with a trapezoidal outer contour and a multifractal system of internal triangular cells, whose geometry was defined by the anisotropy parameter ε. The specimens were subjected to uniaxial compression tests with continuous recording of the load–displacement curves and determination of the maximum failure load. The relationship between the ultimate load-bearing capacity of the multifractals and the anisotropy parameter ε was established, and their fracture behavior was investigated. It was found that an increase in the anisotropy parameter leads to a higher maximum failure load, while the deformation process is accompanied by the formation of inclined shear planes and the localization of residual deformation mainly in the edge regions of the specimens. The obtained results can be used in the design of lightweight structures with controlled mechanical properties for applications in mechanical engineering, transportation engineering, civil engineering, and additive manufacturing.
RESEARCH ON INDIVIDUAL REHABILITATION VEHICLES: MAINTENANCE AND REPAIR
Providing mobility for people with disabilities is a critically important challenge for modern engineering. Individual rehabilitation vehicles (IRVs), including manually and electrically powered wheelchairs, operate under demanding and often unpredictable conditions. As a result, they are subject to accelerated wear, as well as mechanical and electronic failures, which reduce operational safety and increase maintenance and repair costs. Therefore, investigating the operational performance of IRVs, analyzing the mechanisms of their failures, and developing scientifically grounded strategies for preventive maintenance and repair constitute important scientific and practical tasks in the field of rehabilitation engineering.
DEVELOPEMENT OF BIOMPOSITE MATERIALS BASED ON GLUTIN AND FLAX FIBER
The article presents a study on the compressive strength of biocomposite materials based on an aqueous solution of glutin and chopped technical flax fibers with a length of 5 mm. Biocomposite materials were developed with various component ratios: 50% glutin solution and 50% flax fibers; 46% glutin solution and 54% flax fibers; 43% glutin solution and 57% flax fibers; 40% glutin solution and 60% flax fibers Under compressive load, the destruction of biocomposite materials with various component ratios at lower pre-drying degrees (5–15%) is accompanied by plastic deformation and shear cracking. The maximum compressive strength value of 71.7 MPa was obtained for biocomposite materials containing 43% glutin solution and 57% chopped flax fibers at a composition pre-drying degree of 20%. A further increase in the filler content or excessive pre-drying of the composition impairs the wettability of the fibers by the binder, leading to brittle fracture and splitting of the material.
INTELLIGENT SYSTEM FOR MONITORING THE TECHNICAL CONDITION OF AN ABOVEGROUND PIPELINE
The paper considers modern approaches to monitoring the technical condition of main aboveground pipelines using intelligent diagnostic systems. An analysis of the main types of pipeline defects was carried out, including corrosion damage, cracks, mechanical deformations, weld defects, and damage to the insulation layer. It was established that the development of such defects leads to pipeline leakage and emergency situations with significant environmental and operational consequences. Modern methods of non-destructive pipeline testing are considered, including electromagnetic, ultrasonic, radiographic, acoustic, and surface diagnostic methods. Special attention is paid to the Smart Maintenance concept, which involves the integration of unmanned aerial vehicles (UAVs), IoT technologies, sensor systems, and machine learning algorithms for continuous monitoring of the technical condition of pipeline infrastructure. The prospects of applying computer vision methods, convolutional neural networks, and semantic segmentation systems for automated defect detection and classification are demonstrated. The main advantages of intelligent monitoring systems are identified, including improved diagnostic accuracy, reduced human factor influence, and optimization of pipeline maintenance processes.
PROSPECTS OF USING COMPOSITES BASED ON THE ZrB₂–HEASYSTEM FOR THE AEROSPACE INDUSTRY
This paper summarizes the current state of research on ZrB₂-based ceramics and their modification using high-entropy systems. The influence of composition and fabrication technologies on densification processes, microstructure formation, and mechanical properties of the materials is analyzed. The main problems of ZrB₂ are assessed, in particular its low fracture toughness and sintering difficulties, and the effectiveness of using high-entropy alloy (HEA) additives to address these issues is demonstrated. Promising directions for further development are proposed, focusing on composition optimization, phase state control, and the improvement of manufacturing technologies for high-density composite materials designed for use in extreme conditions.
STRAINED n-SI CRYSTAL LATTICE IN THE PRESENCE OF PHOSPHORUS IMPURITY
The successful application of heterojunctions in various devices is due to the ability of epitaxy technology to grow semiconductor materials with a well-matched lattice structure on top of each other practically without traps at the interface. Therefore, it is relevant to study (investigate) the characteristics (parameters, behavior) of semiconductor materials caused by deformations of the crystal lattice and deformation changes in their properties in the presence of impurities. This can provide important information in modeling heterostructures and successful application of heterojunctions (strained heteroepitaxy) in creating various devices with predicted properties. In the development of electronic devices, the main attention is paid to the three most-important semiconductors: silicon (Si), germanium (Ge) and gallium arsenide (GaAs). Silicon has been studied extensively and widely used in commercial electronics products. The paper presents the results of research for undeformed and uniaxially deformed (Х ≤ 1.2 GPa) along [100] Si n-type crystals with a concentration of NP donor phosphorus (Р) impurity of 2.4 · 1013 cm-3 and 2.3 · 1015 cm-3. We studied the longitudinal (Х || j [100]) and transverse (Х ⊥ j [100]) piezoresistance in the temperature range 78 ÷ 300 K. When the crystal lattice of n-Ge and n-Si crystals is deformed, the mobility anisotropy parameter K is an important characteristic. For sufficiently pure n-Ge crystals, the set of curves ρX/ρ0 = f(Х) for different temperatures in the case of Х || j || [111] is characterized in the temperature range T > 120 K by essentially a single plateau ρ∞/ρ0 value, which determines the value of the mobility anisotropy parameter. For the correct determination of the parameter K in n-Si in such cases, the experimental data on the longitudinal piezoresistance must be supplemented with the results of measurements of the transverse piezoresistance. The work aims to comprehensively investigate the features of changes in electrophysical parameters during crystal lattice deformation, which distinguish germanium and n-type silicon, associated with the inadequacy of scattering mechanisms in these crystals for strained heteroepitaxy. The values of K determined by different methods for a crystal with a donor impurity concentration of 2.3 · 1015 cm-3 differ significantly. This is due to the fact that at a donor impurity concentration NP > 1015 cm-3 in silicon crystals, due to the expansion of the spectrum of impurity states, the phosphorus impurity is not completely ionized at T = 78 K. In the case of undeformed n-Si crystals with NP = 2.4 · 1013 cm-3 up to 100 K ρ ~ T1.66. With increasing temperature due to the appearance of intervalley scattering ρ ~ T2.3. In the case of deformed crystals with complete exclusion of f-transitions (Х = 1.2 GPa) no breaks are observed on the ()Tρρ=∞|| and ()Tρρ=⊥∞ curves and at the same time ρ ~ T1.66. Based on the ||∞ρ and ⊥∞ρ values, we obtained the value of the carrier mobility anisotropy parameter K = 5.1 ± 0.1. In the case of undeformed n-Si crystals with an impurity concentration NP = 2.3 · 1015 cm-3, the temperature dependence of ρ has a complex character. At low temperatures (T > 78 K), its form is determined not only by intervalley scattering of electrons on acoustic lattice vibrations, but also by their scattering on ionized impurities with an increase in the concentration of charge carriers n in the conduction band due to thermal ionization of impurity states (which manifest themselves in n-Si at NP > 1015 cm-3). Only in the high temperature region (T > 230 K) does the slope of the ρ(T) dependence approach 2.3. In the case of deformed crystals with NP = 2.3 · 1015 cm-3 at X = 1.2 GPa, the last factor affecting the value of ρ disappears due to the deformation reduction of the ionization energy of the impurity when the deformation axis is oriented along the [100] direction (n = const) in the temperature range 78 ÷ 300 K. Based on the ||∞ρ and ⊥∞ρ values, it is possible to reliably determine the parameter K, and accordingly, Kτ at any temperature. In the case of NP = 2.3 · 1015 cm-3 at 78 K, Kτ = 1.2 ± 0.1. From a comparison of the scattering anisotropy parameters for n-Si crystals with impurity concentrations of 2.4 · 1013 cm-3 and 2.3 · 1015 cm-3, it is seen that when scattering on impurity ions, the parameter Kτ is significantly larger than in intervalley acoustic scattering. Analysis of the Kτ = Kτ(Т) dependence indicates a decrease in the contribution to the anisotropy of impurity scattering and an increase in the relative contribution of scattering on acoustic lattice vibrations with increasing temperature. It was found that in n-Si crystals at 78 K, the values of the parameters of the anisotropy of electron mobility and scattering at low concentrations of the donor impurity (2.4 · 1013 cm-3), i.e. under conditions of dominance of scattering on acoustic phonons, as in n-Ge, can be reliably determined from the data of the longitudinal piezoresistance only. At concentrations of the doping impurity that provide mixed scattering (2.3 · 1015 cm-3), as well as with increasing temperature, for the correct determination of the parameter K in n-Si, measurements of both the longitudinal and transverse piezoresistance in the saturation region of the ρ = ρ(X) curves are necessary.
OPERATING CONDITIONS FOR MULTI-DEGREE-OF-FREEDOM ACTUATORS IN MULTIMODAL COMBAT SUPPORT ROBOTS
The paper investigates the operating conditions of a multi-degree-of-freedom drive intended for multimodal robotic platforms used in military support operations. The growing demand for robotic systems capable of performing reconnaissance, logistics, engineering, and rescue missions in hazardous environments requires the development of adaptive locomotion mechanisms. A review of existing multimodal robots demonstrates the advantages of combining different locomotion modes, including wheeled, legged, aerial, and amphibious movement. A concept of a reconfigurable robotic platform with a variable-geometry chassis is proposed. The platform is based on wheel modules capable of changing their spatial orientation through a drive system incorporating spherical joints and harmonic gear transmissions. The developed architecture enables multiple operational modes, including high-speed wheeled motion, enhanced obstacle-crossing capability, vertical observation, and potential aerial mobility. The study identifies the kinematic, geometric, stability, and power requirements necessary for reliable operation of the drive system. Particular attention is paid to the integration of harmonic drives within spherical joints, providing compact dimensions, high positioning accuracy, and increased torque transmission. The obtained results confirm the feasibility of using multi-degree-of-freedom drives for the development of adaptive multimodal robots capable of effective operation under the challenging conditions of the modern battlefield.
COLD STAMPING WITH SELF-REGULATING COUNTERPRESSURE USING LIQUID AISI 52100 STEEL PUNCHES FOR COIN MINTING
In the context of mass production of products using cold deep-drawing processes, the challenge is to improve the durability of punches and ejectors, which can be addressed by replacing machining with cold extrusion in the manufacture of such tools.This work employs FEM modeling using an elastic-plastic metal model to determine the parameters for cold extrusion with self-regulating counterpressure of AISI 52100 steel punches for coin minting, and experiments were conducted to produce the punches. For two geometric shapes of punches, the simulation established maximum fluid counterpressure values of 200 and 300 MPa, which ensured the extrusion of punches with deformation rates of 40.8% and 50.6%, respectively. The relationship between the extrusion force and the displacement of the forming tool, the force required to eject the formed blanks from the containers, and the distribution of specific forces on the surfaces of the blank in contact with the tool have been determined. The shape and dimensions of the punches after extrusion, as well as the distributions of temperature and the components of stresses and strains in the deformed metal, were identified. The work hardening of the metal structure due to cold plastic deformation was analyzed based on the distribution of strain intensity. The greatest work hardening occurs at the transition from the cylindrical deforming surface of the punches to the conical support surface, which is necessary to increase the stability of the punches during stamping. Experimental studies were conducted and confirmed the results of the calculations. The results of the modeling and experiments on extrusion with counterpressure for AISI 52100 steel are novel. Extrusion with self-regulating counterpressure can be used in the manufacture of forming tools from low-ductility die and tool steels for metal forming processes.
AUXETIC LATTICE STRUCTURES FABRICATED BY 3D PRINTING USING FUSED DEPOSITION MODELING AND LCD-SLA PHOTOPOLYMERIZATION
The paper presents a study of auxetic lattice structures fabricated by additive manufacturing using fused deposition modeling (FDM) and liquid crystal display stereolithography (LCD-SLA). The investigated samples were produced from TPU filament and ABS-like photopolymer resin. Particular attention was paid to the influence of printing technology on the accuracy of reproducing thin ribs, nodes, and repeating auxetic cells. It was shown that LCD-SLA provides higher geometric accuracy, better surface quality, and more precise reproduction of small structural elements, which is especially important for research and demonstration samples. At the same time, FDM printing with flexible thermoplastics, particularly TPU, may be more suitable for functional auxetic structures subjected to repeated deformation or impact loading. The main technological difficulties of both methods are discussed, including shrinkage and increased stiffness of photopolymer samples, as well as first-layer adhesion problems, layer shifting, and stringing during FDM printing. The results confirm that the choice of 3D printing technology and material is critical for obtaining auxetic lattice structures with the required geometry and deformation behavior.
UTILIZATION OF ULTRASONIC SENSORS ON DRONES AND ANALYSIS OF THEIR ACCURACY
Unmanned aerial vehicles (UAVs), commonly referred to as drones, have become an increasingly important part of modern technological systems. Over the last decade, their development has accelerated significantly, mainly due to advances in electronics, embedded systems, sensor technologies, and autonomous control algorithms. Today, drones are no longer limited to recreational use; they are widely applied in industrial inspection, agriculture, environmental monitoring, rescue operations, terrain mapping, logistics, and security applications. One of the key aspects influencing drone performance is the implementation of sensor systems. Sensors provide essential information about the surrounding environment and the current state of the aircraft. Without reliable sensor data, autonomous flight, stabilization, and obstacle detection would not be possible. Modern UAV platforms typically integrate multiple sensing technologies such as gyroscopes, accelerometers, GPS modules, optical cameras, LiDAR systems, infrared sensors, and ultrasonic sensors. Among these technologies, ultrasonic sensors represent one of the simplest and most affordable solutions for short-range distance measurement. Their low weight, compact dimensions, and relatively low power consumption make them suitable for integration into lightweight drone platforms. Ultrasonic sensors are most commonly used for altitude stabilization, automatic landing, obstacle avoidance, and indoor navigation, where GPS signals may not be sufficiently accurate or available. The operating principle of ultrasonic sensors is based on the transmission and reception of high-frequency sound waves. After the emitted acoustic signal reflects from an obstacle, the sensor evaluates the return time of the reflected wave and calculates the distance between the sensor and the object. Although the principle itself is relatively simple, measurement accuracy may be influenced by several environmental factors, including temperature, air humidity, wind, surface material, and the geometry of the measured obstacle. Despite certain limitations, ultrasonic sensors continue to be widely used in educational, experimental, and low-cost UAV systems. Their advantages are particularly evident in applications that require reliable short-range measurements without the need for expensive hardware. The main objective of this paper is to analyze the use of ultrasonic sensors in drone systems and experimentally evaluate their accuracy in practical distance measurements. The experimental part of the study focuses on the HC-SR04 ultrasonic sensor connected to an Arduino Uno microcontroller. Measurements were performed under controlled indoor conditions at various distances in order to compare measured values with actual distances and assess the suitability of the sensor for drone applications.
CURRENT STATE AND PROSPECTIVE DIRECTIONS OF RESEARCH ON THE TECHNOLOGICAL ACCURACY OF WOODWORKING MACHINES
This article presents an analytical review of the current state and prospective directions of research on the technological accuracy of woodworking machines. Four main research directions have been identified: structural provision of machining accuracy, experimental investigation of actual accuracy and dynamics of its changes, mathematical modelling, and automatic in-process control of part dimensions. It is established that the moving workpiece-feeding system of conventional four-side plano-milling machines contributes up to 60% of the total machining error, while at critical cutting tool wear the actual errors exceed permissible tolerances by up to 3.7 times. The distribution of machining errors is most accurately described by the Weibull law with shape parameter b = 1.89–3.11. The most promising direction is the integration of in-process workpiece measurement and machine learning algorithms (Random Forest, CNN, LSTM) for predictive maintenance with prediction accuracy above 99%. Prospective directions for further research are outlined.
APPLICATION OF THE MODULAR DESIGN PRINCIPLE FOR CNC MACHINE TOOLS
The development of the machine tool industry, driven by the implementation of cutting-edge technologies, equipment, and production management methods, is a crucial factor for industrial growth. Continuous and stringent requirements for higher productivity and quality in the manufacturing of machine parts and structures necessitate the improvement of methods for developing new machine tool models. The objective is to minimize design and manufacturing time while optimizing resource consumption. The application of the aggregate-modular principle enables the rapid creation of manufacturing equipment from a relatively limited set of unified units within the framework of modern automated production. This study analyzes the conditions, limitations, and specific features of applying the modular principle to the creation of new CNC machine tools. The structural units of machines designed using the modular approach are systematized, alongside the conditions for implementing unified modules. Furthermore, the general principles of modular configuration for metal-cutting CNC machine tools are examined, and a refined algorithm for the design synthesis of new machine tools is proposed.
STUDY OF THE FORCE CHARACTERISTICS OF SOIL-WORKING IMPLEMENTS
This paper presents a methodology and apparatus for testing, as well as the results of statistical analysis of the dynamic performance of a plow body, using the PLN 3-35 as an example. The authors conducted a comparative assessment of the energy and force parameters of the interaction between the working surface of the plow body and the soil, which makes it possible to identify the three components of the resultant resistance force during soil cultivation and allows for their more accurate consideration when designing new surfaces for soil-working implements.
INNOVATIVE TRANSPORT AND LOGISTICS TECHNOLOGIES AND MATERIALS SCIENCE SOLUTIONS IN THE POST-WAR RECOVERY OF THE KHERSON REGION
The article explores the challenges and prospects for restoring the transport infrastructure of the Kherson region following large-scale destruction. The research analyzes the damage to industrial and engineering facilities and identifies critical challenges for the region’s logistics and economic activity. Drawing on international experience (Europe, Asia), the study substantiates the necessity of combining financial support with innovative technological solutions. The system-forming role of logistical systems is demonstrated, and alternative short-term solutions are proposed, specifically the development of inland water transport. Particular attention is paid to the implementation of materials science innovations – polymer and composite coatings – to enhance the durability of infrastructure. Strategic directions for post-war recovery are proposed based on the principles of "Industry 4.0."
EFFICIENCY ASSESSMENT OF A ROBOTIC WELDING SYSTEM CONSIDERING STABILIZATION OF THERMOPHYSICAL PARAMETERS OF THE TECHNOLOGICAL PROCESS
The article examines the evaluation of the efficiency of a robotic welding system with consideration of the stabilization of the thermophysical parameters of the technological process. It is substantiated that the efficiency of welding robotization should be determined not only by productivity, labor intensity, and payback period, but also by the stability of current, voltage, torch travel speed, arc energy, and linear heat input. A calculation framework is proposed that relates the stabilization of the tool trajectory to the conditions of weld pool formation, weld geometry, defect rate, and production performance.For a standard welding operation, it is shown that reducing the primary welding time from 5 to 3 minutes while maintaining constant values of current at 150 A and voltage at 18 V increases the torch travel speed from 3.33 to 5.56 mm/s. Under these conditions, the arc energy per unit length decreases from 0.810 to 0.486 kJ/mm, i.e., by 40.0%. This confirms the necessity of coordinated control of current, voltage, and speed in order to stabilize heat input in the robotic process.It was established that robotization reduces the average deviation of weld geometry from 2.5 to 0.8 mm, the standard deviation from 1.2 to 0.3 mm, and the probability of defects from 0.10 to 0.03. For a standard operation duration of 10 minutes, the productivity of manual welding amounts to 48 units per 8-hour shift, whereas a robotic operation with a duration of 6 minutes ensures 80 units per shift. Taking into account the reduction in defects, the output of acceptable products increases from 43.2 to 77.6 units per shift, i.e., by 79.6%.The obtained results demonstrate that the production and economic effect of robotization is achieved through the combination of reduced operation time, stabilization of the thermophysical conditions of the process, and improved repeatability of welded joint quality.
METHODOLOGY FOR COMPUTATIONAL EVALUATION OF THE ACCURACY AND STIFFNESS OF ROBOTIC TECHNOLOGICAL COMPLEXES
The article addresses the problem of computational and information-based evaluation of the accuracy and stiffness of robotic technological complexes performing operations involving force interaction between the tool and the workpiece or manipulated object. The relevance of the study is обусловлена by the fact that the nominal specifications of an industrial robot do not provide sufficient grounds for determining the suitability of the complex for a specific technological operation, since the actual TCP error is formed under the influence of configuration-dependent compliance, technological loading, tool parameters, dynamic effects, calibration, measurement data, and the technical condition of the system. The aim of the study is to develop an integrated evaluation methodology combining a kinematic-static model of the tool center point position, a stiffness and compliance model, a dynamic error component, and a digital information data layer. A structural representation of the robotic technological complex is proposed as a system including an industrial robot, a control system, a technological tool, an interaction object, a technological operation, a sensor subsystem, and a digital information layer. A sequential evaluation procedure has been developed, within which the position of the tool center point, wrench loading, generalized joint torques, deformation error, dynamic component, and total working-point error are determined. In addition, an information data structure is proposed for storing robot, tool, operation, loading, calibration, measurement, diagnostics, and evaluation-result parameters. Unlike approaches in which accuracy, stiffness, dynamics, and digital representation are considered separately, the proposed methodology provides a formalized transition from input data and computational models to an engineering decision regarding the suitability, conditional suitability, or unsuitability of the robotic complex for a specified operation.
INFLUENCE OF THE BILLET GEOMETRIC SHAPE ON THE PROCESS OF HOT BACKWARD EXTRUSION OF HOLLOW PRODUCTS FROM HIGH-CARBON STEEL
Mathematical models were developed using the finite element method to investigate the hot reverse extrusion of high-carbon steel hollow products from round and square billets. A plastic metal model was employed. The deformation rates were determined to maintain the required thermal conditions for hot deformation throughout the forming process. For both billet shapes, the relationships between extrusion force and punch displacement were established, along with the distribution of specific forces on the contact surfaces between the deformed billets and the tooling. The distribution of temperature, stress components, and strains for the final stages of extrusion are presented. The refinement of the metal structure through plastic deformation was evaluated based on train intensity distributions. The final shapes and dimensions of the products were identified. A comparative analysis of the simulation results for the extrusion processes was performed.
FRACTOGRAPHIC FEATURES OF FRACTURE OF A STEAM TURBINE CONTROL VALVE STEM
Fractographic analysis of the fracture surface of a steam turbine control valve stem was performed, and its fracture mechanism was examined. Damage inside the nitrided layer and the base metal of a stem was investigated. Microanalysis revealed secondary cracks along the entire perimeter of a stem, a sign of weak adhesion between the base metal and the nitrided layer, and associated with internal oxidation. The classical failure mechanism by fatigue striation formation dominated practically the majority of a stem fracture, which is typical of high-cycle fatigue. Only at the final stage of stem failure were signs of low-cycle fatigue visualized.
JUSTIFICATION OF THE NUMBER OF HARVESTING AND TRANSPORT UNITS FOR FLOW FRUIT HARVESTING
The study focuses on improving the flow process of “harvesting – transportation – post-harvest handling” of fruit in horticulture, which is important for food security and the export potential of the industry. The impact of on-farm logistics organization on product quality preservation and loss reduction is examined. Queue formation at the reception channel and conditions ensuring continuous technological flow are analyzed. A queuing system model is proposed, enabling an analytical description of crop arrival, optimization of the number of transport units, and coordination of processing capacities. The results contribute to reducing crop losses and increasing production efficiency.
METODS OF CALCULATION OF OPTIMAL PARAMETERS OF ROLLING
Enterprises in various industries are still using machines with different designs of roller working bodies, which, depending on the technological process, perform various operations. Such machines need to be improved, especially small-sized machines with controlled processes in which the main process takes place in the working area. A preliminary analysis of the operation of a certain class of machines showed insufficient productivity and quality of finished products. This problem has shown modern trends in the improvement of roller working bodies in machines of different classes where different work processes are carried out with their help. The aim of the study is to develop a method for determining and distributing the amount of compression of the dough piece in the gap between the roller working bodies, improving product quality and describing these processes using a mathematical model. The paper analyzes the complexity of the injection process, insufficient stability and reliability of operation; with uneven feeding of components into the working chamber. In addition, a number of other factors affect the quality of rolls feeding: physical and mechanical properties of raw materials, operating mode, insufficient impulse of external forces during axial movement, and an excessive number of working bodies. Determining the movement of the medium between the rolls is one of the most difficult tasks. The solution to these problems is possible on the basis of a thorough study of the essence of the process occurring during rolling. This approach will make it possible to determine the nature of the stage distribution of dough sticking together in the gap between the rolls, taking into account the contact angle. Thus, the surface design of the new roll made it possible to reduce the impact on the dough and thus improve the quality of forming with the same technological parameters. At the same time, dry matter losses and process rejects are reduced. The developed model makes it possible to determine the compressibility of the dough at the initial and final viscosity values at given technological and design parameters, and the analysis can be the basis for the development of engineering methods for designing working bodies to regulate the stability of the process.
EXPERIMENTAL STUDY OF THE LIGHT CHARACTERISTICS OF A PHOTOVOLTAIC MODULE
The article presents the results of an investigation of the light current–voltage characteristics of a photovoltaic module 615 W Longi Solar LR8-66HGD-615M under different levels of irradiance. The influence of solar radiation on the key electrical parameters of the module, including open-circuit voltage, short-circuit current, and output power, is analyzed. The features of changes in the photovoltaic module characteristics depending on its operating modes are studied. The obtained results can be used to improve the operating regimes of photovoltaic systems and to increase the efficiency of solar energy conversion.
TO DETERMINATION OF DEFORMATION CHARACTERISTICS OF GLUE-LAIMED PINE AND SPRUCE WOOD AT DIFFERENT HUMIDITIES IN THE PRECRITICAL AND POSTCRITICAL STAGES OF WORK: EXPERIMENTAL STAGE
Solid and glued wood is often operated in environments with different humidity levels. Current regulatory documents limit such operation to the Kmod coefficient. In some cases, it is unclear how to determine certain mechanical characteristics with increased moisture content, including deformable ones. For example, the operation of elements in bridge structures, hydraulic structures, sea piers, shore protection structures, and others. Very often, materials, elements, and structures based on wood operate in a post-critical stage of operation (seismic vibrations, dynamic loads, progressive destruction, floods, changes in water levels, and others). The purpose of our research is to conduct experimental studies of structural glued laminated wood of pine and spruce with different moisture content under a strict regime of axial compression tests along the fibers during operation in river and marine aquatic environments. As well as to establish the main deformation parameters in the pre-critical and post-critical stages of operation under such operating conditions. Experimental studies of structural glued pine and spruce wood of different humidity after immersion in river and sea water environments by axial compression along the fibers under a rigid test regime were carried out. The main mechanical characteristics of glued pine and spruce wood in the pre-critical and post-critical stages of operation were experimentally established, including the temporary ultimate strength of wood, the modulus of elasticity, relative critical, limiting and residual deformations, under such operating conditions. Formulas were proposed for determining the relative limiting deformations of structural glued wood at different humidity. The main deformation characteristics of glued pine and spruce wood, both in river and sea water environments, relative critical, limiting and residual deformations were established. At humidity levels of 21% and 30%, they increase in comparison with the characteristics determined at a standard humidity of 12%.
INVESTIGATION OF HYDRODYNAMIC AND GAS DYNAMIC PROCESSES IN A CLOSED BYPASS CHANNEL WITH A RECTANGULAR CROSS-SECTION OF VARYING ASPECT RATIOS
The article addresses a scientific and applied problem of determining the hydrodynamic and gas dynamic characteristics of flow in closed channels with a rectangular cross-section. It is substantiated that classical analytical relations based on the Hagen-Poiseuille law are valid exclusively for channels with a circular cross-section, whereas in real engineering systems, rectangular or more complex geometries are predominant. The study presents an analytical investigation of laminar flow of liquids and gases in a rectangular channel based on the Navier-Stokes equations. For the rectangular channel, the solution was constructed using the method of expansion in trigonometric series, which allows proper consideration of boundary conditions and the geometric characteristics of the flow domain. It was established that the flow capacity of the channel depends on the aspect ratio of its sides, with the extreme value of the corresponding coefficient being achieved for a square cross-section. The analytical results were verified through numerical simulations using MATLAB and SOLIDWORKS Flow Simulation. Functional dependencies of velocity and flow characteristics on the geometric parameters of the channel were constructed.
ULTRASONIC NON-DESTRUCTIVE STUDY OF REACTION-SINTERED SILICON CARBIDE MODIFIED WITH TUNGSTEN CARBIDE
Using the technology of reactive sintering of nanosized powders, composite materials based on silicon carbide, containing in the charge from 1 to 8% (wt.) of tungsten carbide powder particles were fabricated. The influence of the WC content in the charge on the regularities of changes in the electrical resistivity and elastic characteristics of composites, determined from the results of ultrasonic measurements of the propagation velocities of elastic waves of various types using pulse methods, was investigated.
PREREQUISITES FOR TAKING INTO ACCOUNT MODIFICATIONS OF CONIFERS OF WOOD SPECIES IN CALCULATIONS OF TIMBER ELEMENTS AND STRUCTURES
The study highlights the methodology for considering the impact of softwood modification in the design of timber structures. Although timber is a widely used building material due to its environmental friendliness, low weight, ease of processing, high longitudinal strength and cost-effectiveness, it has limitations such as moisture sensitivity, anisotropy and natural defects that limit its structural application. Modification of timber with various composite materials improves the physical and mechanical properties of timber, improves moisture resistance and increases durability. Such types of modifications change the behaviour of timber structures and their stress-strain state, which is not taken into account in current design standards, which highlights the need to update design approaches. The study focuses on structural elements, including beams, columns and cross-laminated panels, where longitudinal strength largely determines the load-bearing capacity and stiffness. Traditional design includes characteristic and design values of compressive, tensile, and flexural strengths, as well as elastic and shear moduli modified by reliability factors. This paper presents the possibility of using experimental data when taking into account the modification of coniferous wood species. In this case, experimental values are used to determine modification factors that correct the design resistance to bending, compression, tensile, and elastic moduli. Formulas are given to illustrate the application of these factors under uniaxial bending and combined loading conditions. A methodology is proposed that allows for accurate consideration of changes in mechanical behavior due to processing with composite materials, providing an accurate assessment of the strength and improved serviceability of wooden structures. The introduction of these factors into structural calculations demonstrates that modification can significantly improve the performance and service life of wooden structures. This approach lays the foundation for incorporating modified wood properties into future design standards and provides engineers with practical tools for more reliable and durable wood construction designs.
CURRENT ISSUES OF STRUCTURAL TRANSFORMATIONS IN POLYMER COMPOSITE MATERIALS UNDER THE INFLUENCE OF PHYSICAL FIELDS: A REVIEW
The article analyzes the literature in the aspect of the formation of polymer composites under the influence of physical fields, which provide intensive structuring of the composition based on thermosets. The characteristics of physical fields and the features of structural transformations at the level of fine structure and supramolecular formations, which occur as a result of external energy influence, are presented. The positive influence of physical fields on the processes of structuring of polymer composite materials based on reactive polymers is proven, which is determined by the processes of ordering structural components and the formation of polymer composites with a low stress state and a high degree of structuring of the polymer matrix.
SPECTROPHOTOMETRIC METHODS FOR QUALITY ASSESSMENT OF BIOFUEL MATERIALS DERIVED FROM OIL FLAX STEMS: IMPLICATIONS FOR SUSTAINABLE DEVELOPMENT
The study is devoted to the development of a spectrophotometric methodology for evaluating biofuel materials produced from non-conditioned oil flax (Linum usitatissimum L.) stems. Solid biofuel briquettes with different ratios of flax biomass and sapropel binder (L70/S30, L50/S50, L100) and a control wood sample were investigated. Aqueous extracts of combustion residues were analyzed using spectrophotometry in the wavelength range of 200–1100 nm. The obtained transmission spectra demonstrated similar overall patterns for all samples, indicating comparable structural features of combustion residues. A pronounced minimum at a wavelength of 975 nm was identified for all investigated samples. This spectral feature is attributed to the second overtone of O–H stretching vibrations and reflects the presence of hydroxyl-containing compounds and bound water in the analyzed systems. Comparative analysis showed that the differences in transmission values between flax-based biofuels and the control wood sample do not exceed 3–4%, indicating a high degree of similarity in the chemical composition of their combustion residues. The use of sapropel as a binder does not significantly affect the overall spectral characteristics, although it increases absorption intensity due to higher mineral content. The results confirm the feasibility of using oil flax stem biomass for the production of solid biofuels and demonstrate that spectrophotometric analysis can be applied as a rapid diagnostic tool for assessing their quality and environmental safety.