Ukrainian Journal of Mechanical Engineering and Materials Science
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Item A brief overview of stationary two-dimensional thermoelastic state models in homogeneous and piecewise-homogeneous bodies with cracks(Видавництво Львівської політехніки, 2023-02-28) Zelenyak, Volodymyr; Kolyasa, Liubov; Klapchuk, Myroslava; Lviv Polytechnic National UniversityPurpose. A two-dimensional mathematical model of the problem of thermo-elasticity for piecewise-homogeneous component plate containing a crack has been built. The stress intensity coefficients in the vertices of the crack increase affecting strength of the body significantly. This leads to the growth of a crack and, as a result, to further local destruction of a material. Therefore, such a model reflects, to some extent, the destruction mechanism of the elements of engineering structures with cracks. Methodology. Based on the method of the function of a complex variable we have studied the two-dimensional thermoelastic state for the body with crack as stress concentrators. As result, the problem of thermoelasticity was reduced to a system of two singular integral equations (SIE) of the first and second kind, a numerical solution of which was found by the method of mechanical quadratures. Findings. The two-dimensional mathematical model of the thermoelastic state has been built in order to determine the stress intensity factors at the top of the crack and inclusion. The systems of singular integral equations of the first and second kinds of the specified problem on closed (contour of inclusion) and open (crack) contours are constructed. The influence of thermophysical and mechanical properties of inclusion on the SIF sat the crack types was investigated. The dependences of the stress intensity factor which characterizes the distribution of the intensity of stresses at the vertices of a crack have been built, as well as its elastic and thermoelastic characteristics of inclusion. This would make it possible to analyze the intensity of stresses in the neighborhoods of crack vertices depending on the geometrical and mechanical factors. As a result, this allows to determine the critical values of temperature in the three-component plate containing a crack in order to prevent the growth of the crack, as well as to prevent the local destruction of the body. It was found that the appropriate selection of mechanical and thermophysical characteristics of the components of a three-component plate containing a crack can be useful to achieve an improvement in body strength in terms of the mechanics of destruction by reducing stress intensity factors at the crack’s vertices. Originality. The solutions of the new two-dimensional problem of thermoelasticity for a specified region due to the action of constant temperature as well as due to local heating by a heat flux were obtained. The studied model is the generalization of the previous models to determine the two-dimensional thermoelastic state in a piecewise homogeneous plate weakened by internal cracks. Practical value. The practical application of this model is a more complete description of the stress-strain state in piecewise homogeneous structural elements with cracks operating under temperature loads. The results of numerical calculations obtained from the solution of systems of equations and presented in the form of graphs can be used in the design of rational modes of operation of structural elements. This takes into account the possibility of preventing the growth of cracks by the appropriate selection of composite components with appropriate mechanical characteristics.Item Contents(Видавництво Львівської політехніки, 2023-02-28)Item Applicability assessment of the vickers indentation for determining the fracture toughness of yttria-stabilized zirconia(Видавництво Львівської політехніки, 2023-02-28) Vavrukh, Valentyna; Klimczyk, Piotr; Priakhin, Volodymyr; Petryk, Vitalii; Momot, Kinga; Lviv Polytechnic National University; Krakow Institute of TechnologyCrack growth resistance of ZrO2-(3-8) mol% Y2O3 ceramics was investigated. Young's modulus by the ultrasonic flaw detection method were determined. Vickers hardness and parameters of cracks after Vickers indentation were obtained. Based on the Young's modulus values, Vickers hardness, and parameters of cracks, the fracture toughness of the investigated ceramics was calculated using 9 different equations of the Vickers indentation method. A comparative analysis of the calculated fracture toughness values with those obtained by the single-edge notch beam method was carried out. It was found that choosing the optimal equation for calculating fracture toughness by the Vickers indentation method is quite difficult and requires comparison with the results of standardized tests. It was shown that to determine crack resistance characteristics of the yttria-stabilized zirconia ceramics, the use of only the Vickers indentation method without comparison with other methods of fracture mechanics is incorrect.Item Optimization of oligonucleotides characteristics with topsis(Видавництво Львівської політехніки, 2023-02-28) Javanbakht, Taraneh; Concordia UniversityThis paper focused on a new application of the TOPSIS method for the prediction and optimization of the oligonucleotides characteristics. This method has been used for these purposes as it has shown its efficacy for these analyses. This is the first time that it has been applied to the investigation of these biomolecules. The hypothesis in this paper was that the characteristics of these biomaterials would be optimized according to their structural differences. The obtained results showed that the stabilization of oligonucleotides would affect their ranking with TOPSIS when the stability of these biomolecules increased against enzymes in their structure. In other words, the oligonucleotides with less enzymatic degradation were ranked better with this method. This study showed the first application of this algorithm for the prediction and optimization of the oligonucleotides’ characteristics. The results in this work revealed that the ranks of candidates depended on their distances from their ideal solutions. This showed that TOPSIS could be used as an appropriate method in the optimization of oligonucleotides as the rankings with this method would coincide with the data that concern the stability of these biomolecules against enzymatic degradation. The results of this work could be applied for the preparation of novel materials with applications in science and engineering.Item Reducing the kinetic power of the crank press machine(Видавництво Львівської політехніки, 2023-02-28) Pasika, Viacheslav; Augousti, Andy; Lanets, Olena; Parashchyn, Oleh; Lviv Polytechnic National University; Kingston UniversityCrank presses belong to the class of machines in which the payload (stamping force) acts for a short period of time at the end of the working stroke. Since the power of a force is the product of the force times the speed, it is possible to reduce the power of a specific force only by reducing the speed of the point of action of the force. The kinematic characteristics of slider-crank mechanisms (SCMs), which are the main mechanism of crank presses, are qualitatively the same and cannot be changed. The speed of the slider, as a working body, is the most influenced by the rotation frequency and the crank's length. However, reducing the frequency of rotation leads to a decrease in the productivity of the press, and a decrease in the length of the crank is limited by the design possibilities and technological process of stamping. The purpose of this work is to reduce the kinetic power of the main working mechanism of crank presses by redistributing the start-up and run-out phases of the working body and designing the corresponding structural diagram of the SCM. Research methodology. A non-standard approach to reducing the kinetic power of crank presses is proposed. It is suggested to change the distribution of the run-up and run-out phases of the slider (punch) in order to reduce its speed in the range of the punching force to achieve this. To change the run-up and run-out time, a slider-crank mechanism with a programmable change in the length of the crank with a fixed cam is proposed. As a result of this research, an asymmetric cosine law of the movement of the slide was analyzed and it was synthesized into a variable crank length that ensures the movement of the slider according to the determined law. As far as we aware this is the first research that has been carried out on crank presses with the aim of reducing the kinetic power without reducing the value of the stamping force and press productivity. For a given punching force and an asymmetric cosine law for the punch motion, the kinetic power of the press is reduced by 31.4%. This will reduce the mass and/or radius of the flywheel. A list of planned further studies is: the influence of different functions for punch motion, functions for changing the punching force, and an investigation of the value and position of the force interval on the kinetic power of the press.Item Research on the characteristics of gear-cutting processes for external and internal meshing using the power skiving method(Видавництво Львівської політехніки, 2023-02-28) Hrytsay, Ihor; Slipchuk, Andrii; Bembenek, Michal; Lviv Polytechnic National University; AGH University of KrakowThe results of modelling and investigation of external and internal gear-cutting processes using the power skiving method are presented. The principles of constructing a geometric model of undistorted chip formation are described, based on parameters from which cutting forces are calculated. It is found that, under identical conditions, the cutting force is three times greater when internal gears are cut than when external gears are cut. The influence of this force on the machining error is determined by the gear pitch parameter. It is shown that the most rational way to reduce the machining error is to reduce the cutting force by reducing the axial feed rather than by increasing the number of passes.Item Simulation of the stress-strain state and determination of the natural frequency of the laboratory centrifuge shaft vibration using ansys and kisssoft(Видавництво Львівської політехніки, 2023-02-28) Lavrenko, Iaroslav; Sydora, Tetiana; Sushchenko, Maksym; Chaikovska, Olena; National Technical University of Ukraine "Ihor Sikorsky Kyiv Polytechnic Institute"The rotor is a key element of high-speed mechanisms that are widely used in various industries, such as laboratory centrifuges used to separate mixtures of different fractions, gas turbines, industrial compressors, engines, and others. The main requirement for such mechanisms is reliability and safety during operation. To ensure the above requirements, it is necessary to determine the stress-strain state of the most loaded structural elements of the system and the dynamic characteristics. This paper presents an analysis of the stress-strain state of a rotor system using the example of a Pico21 laboratory centrifuge. The Ansys and KISSsoft software packages were used for 3D modelling of the finite element model. The system consists of a flexible shaft with a rotor, the rotor mass was changed during the simulation and supports, the role of which is performed by bearings. A comparative analysis of the obtained results of the stress-strain state is presented, which further makes it possible to carry out appropriate calculations taking into account stress concentrators to determine the durability and lifetime of high-speed mechanisms. The stresses are determined according to the von Mises and Tresca criteria. The paper also presents the results of the calculation and analyses the natural frequencies of the rotor system. Further studies, it is planned to determine the natural frequencies of vibration, taking into account gyroscopic effects, which are necessary to determine the resonant frequencies and zones of stable operation of the system.Item Optimization of the shape and dimensions of the continuous section of the discrete-continuous inter-resonance vibrating table(Видавництво Львівської політехніки, 2023-02-28) Maistruk, Pavlo; Lviv Polytechnic National UniversityEnergy-efficient technologies are an important aspect of the development of mechanical engineering. Therefore, the creation of highly efficient vibration technological equipment is an urgent task. There are discrete-continuous inter-resonance vibration machines that have high values of dynamic amplification of oscillations. Rectangular plates or rods are used as the reactive mass of such vibrating machines. However, the rectangular shape of the plate may not be the optimal shape for achieving maximum energy efficiency. To conduct experimental studies of alternative plates with a variable cross-section to determine the optimal shape of the reactive mass of the vibration machine. Methodology. The selection of alternative options of plates with a variable cross-section, which would satisfy the necessary conditions of fastening and the value of the natural frequency of oscillations, was carried out. Experimental studies were carried out on a sample of an inter-resonance vibrating table. The value of the power supply voltage at which loads of different masses were separated from the working body of the vibrating table for each of the plate samples was compared. Findings (results) and originality (novelty). For the first time, experimental studies of the energy efficiency of inter-resonance vibration machines with plates with a variable cross-section installed as a reactive mass were conducted. It was found that the rhomboid shape of the plate is optimal when using it as a continuous section in a vibration machine with an electromagnetic drive. It was determined that the use of diamond-shaped plates as the reactive mass of the vibrating machine can improve the energy efficiency of the inter-resonance vibrating equipment. For further analysis of plates with a variable cross-section as a reactive mass of an inter-resonance vibration machine, it is necessary to calculate and compare their lumped inertia-stiffness parameters.Item The dependence of thermal processes in non-metallic heterogeneous materials on mechanical vibration loads(Видавництво Львівської політехніки, 2023-02-28) Tonkonogyi, Volodymyr; Holofieieva, Maryna; Levynskyi, Oleksandr; Klimov, Sergii; Dasic, Predrag; Odesa Polytechnic National University; Academy of Professional Studies SumadijaOne of the promising directions in the development of mechanical engineering is using of new non-metallic heterogeneous materials with high physical and mechanical properties. Such materials consist of two or more components (reinforcing filler and polymer matrix) and have specific physical and mechanical properties that are different from the properties of the constituent components. This is achieved by forming a complex developed structure. Reliable control methods play an important role in ensuring the quality of such structures. The paper considers an acoustic infrared thermometric method of control, which is based on the interaction of structural defects with acoustic waves. At the same time, thermal energy is generated at their boundaries, which is an indicator not only of the presence of cracks but also of their direction and development. a mathematical model has been developed that describes the transformation of the energy of mechanical vibrations into thermal energy, which occurs in non-metallic heterogeneous materials.Item Study of durability in the connection “cone-tungsten carbide insert” for tension dependence(Видавництво Львівської політехніки, 2023-02-28) Slipchuk, Andrii; Jakym, Roman; Bembenek, Michal; Lviv Polytechnic National University; Drohobych State Pedagogical University by name I. Franko; AGH University of Science and Technology in KrakówDuring and after the technological operation of pressing these factors significantly determine the residual stress states of tungsten carbide inserts, as well as in the areas near the holes of the cones’ crowns of the cone. The stressed state of the inserts and the magnitude of the stress concentration determine their fatigue strength of them and the durability of the inserted carbide rockblasting equipment of the cones in the area where the inserts the cone. Dimensional analysis was done for the inserts and holes in the cones of bit and it was established that size errors of component links of dimensional chains are distributed according to laws that are similar to the normal law of distribution of random variables. The test was carried out according to the criteria of Pearson and Kolmogorov. The influence of various random and systematic factors results to the dispersion of dimensions on the dimensional processing of conjugated surfaces. The amount of tension is a function of the dimensions for mating surfaces during assembly operations. Dispersion of dimensions for the component links of the dimensional chain of a press connection causes the formation of a practical field of dispersion of the closing link. Accuracy control for the closing link in the dimensional chain is impossible if there are no direct measurements of the constituent links. A mathematical model of the process of assembling “cone-tungsten carbide insert” joints was created. For this, the methods of mathematical statistics were applied in the study. It was established that the tension values have a greater influence on the force of pressing inserts into the holes of drill steels 14 NiCrMo1, when its hardness value is HRC 59–60 compared to HRC 48-50. This dependence has a linear character within the limits of the studied tension values. The established relationships make it possible to reasonably and most accurately form selective groups of inserts and mark holes for them. This method significantly reduces losses in the production of drilling tools.