Факультет електроніки та інформаційних технологій (ЕлІТ)
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Item Description of the Stationary Structural States of a Boundary Lubricant Making Use of the Relation between the Density-Modulation and Excess-Volume Order Parameters(Bogolyubov Institute for Theoretical Physics, 2021) Ляшенко, Яків Олександрович; Ляшенко, Яков Александрович; Liashenko, Yakiv OleksandrovychA second-order phase transition between the structural states of a boundary lubricant sandwiched between atomically smooth solid surfaces has been described in the framework of theLandau theory of phase transitions, by using the density modulation and the excess volumeas the order parameters. A relation between those order parameters is found. The stationarystates of a lubricant and their dependences on such control parameters as the lubricant tem-perature, the elastic strain in the lubricant layer, and the external load on the friction surfacesare studied. The melting kinetics was simulated in the framework of a mechanical analog ofthe tribological system with elasticity.Item Influence of Chemical Heterogeneity and Third Body on Adhesive Strength: Experiment and Simulation(Technical University of Berlin, 2021) Ляшенко, Яків Олександрович; Ляшенко, Яков Александрович; Liashenko, Yakiv Oleksandrovych; Li, Q.; Popov, V.L.We investigate experimentally and numerically the influence of chemical heterogeneity and of third-body particles on adhesive contact. Chemical heterogeneity is generated by chemical treatment of the contacting bodies changing locally the surface energy. For studying the influence of the third body, two types of particles are used: sand particles with various geometrical shapes and sizes, and steel spheres of equal radius. Dependencies of the normal force on the indentation depth at both indenting and pull-off as well as the evolution of the contact configuration are investigated. Corresponding numerical simulations are carried out using the boundary element method (BEM).Item Shape of a sliding capillary contact due to the hysteresis of contact angle: theory and experiment(University of Niš, Serbia, 2021) Popov, V.L.; Ляшенко, Яків Олександрович; Ляшенко, Яков Александрович; Liashenko, Yakiv Oleksandrovych; Starcevic, J.We consider a classical problem of a capillary neck between a parabolic body and a plane with a small amount of liquid in between. In the state of thermodynamic equilibrium, the contact area between the bodies and the liquid layer has a circular shape. However, if the bodies are forced to slowly move in the tangential direction, the shape will change due to the hysteresis of the contact angle. We discuss the form of the contact area under two limiting assumptions about the friction law in the boundary line. We also present a detailed experimental study of the shape of sliding capillary contact in dependence on the roughness of the contacting surfaces.Item Influence of spatial inhomogeneity on the formation of chaotic modes at the self-organization process(Bogolyubov Institute for Theoretical Physics, 2020) Ляшенко, Зінаїда Миколаївна; Ляшенко, Зинаида Николаевна; Liashenko, Zinaida Mykolaivna; Ляшенко, Яків Олександрович; Ляшенко, Яков Александрович; Liashenko, Yakiv OleksandrovychThe Lorentz system of equations, in which gradient terms are taken into account, has beensolved numerically. Three fundamentally different modes of evolution are considered. In thefirst mode, the spatial distribution of the order parameter permanently changes in time, anddomains of two types with positive and negative order parameter values are formed. In thesecond mode, the order parameter distribution is close to the stationary one. Finally, in thethird mode, the order parameter is identical over the whole space. The dependences of theaverage area of domains, their number, and their total area on the time are calculated in thefirst two cases. In the third case, the contribution of gradient terms completely vanishes, anda classical Lorenz attractor is realized.Item Influence of Tangential Displacement on the Adhesion Force Between Gradient Materials(Bogolyubov Institute for Theoretical Physics, 2020) Ляшенко, Яків Олександрович; Ляшенко, Яков Александрович; Liashenko, Yakiv Oleksandrovych; Ляшенко, Зінаїда Миколаївна; Ляшенко, Зинаида Николаевна; Liashenko, Zinaida MykolaivnaThe influence of a tangential displacement on the strength of the adhesive contacts betweengradient materials with different gradings of their properties has been studied. Variants witha controlled force (fixed load) and a controlled displacement (fixed grips) are considered. Arelationship between the normal and tangential critical force components at which the contact isdestroyed is obtained. It is valid within the whole interval of the gradient parameters, where thedetachment criterium is obeyed. The optimal parameters at which the adhesive contact strengthis maximum are determined. A case of detachment under the action of only the tangentialforce, i.e. when the normal force equals zero, is analyzed separately.Item Dynamical model of the asymmetric actuator of directional motion based on power-law graded materials(University of Niš (Republic of Serbia), 2020) Ляшенко, Яків Олександрович; Ляшенко, Яков Александрович; Liashenko, Yakiv Oleksandrovych; Борисюк, Вадим Миколайович; Борисюк, Вадим Николаевич; Borysiuk, Vadym Mykolaiovych; Popov, V.L.We consider an actuator whose driving bodies are made of Power-Law graded materials. The directional motion is generated by an asymmetric mechanism producing simultaneously vertical and horizontal oscillations of the indenter. The dynamic contact of gradient materials is described and the equation of motion for the drive is written down and analyzed. It is shown that the exponent of the elastic inhomogeneity significantly affects the average velocity of motion of the cargo, which can be dragged by the drive.Item The Viscosity Temperature Dependence in the Boundary Friction Model under a Periodic External Action(Sumy State University, 2014) Заскока, Антон Миколайович; Заскока, Антон Николаевич; Zaskoka, Anton Mykolaiovych; Ляшенко, Яків Олександрович; Ляшенко, Яков Александрович; Liashenko, Yakiv OleksandrovychThe effective viscosity temperature dependence of the lubricant is taken into consideration within the thermodynamic model of boundary friction. Transitions between the friction kinetic modes are described as the second-order phase transitions. For the system kinetic investigation the mechanical analogue of the simple tribological system has been considered. The time dependences of block coordinate, velocity, friction force and shear stress have been build. Therefore, the stick-slip motion has been described for a wide range of the system parameters. A comparison of simulation results with experimental data in sequence increasing shear rate has been made.Item Hysteresis Behavior in the Stick–Slip Mode at the Boundary Friction(Taylor & Francis, 2013) Хоменко, Олексій Віталійович; Хоменко, Алексей Витальевич; Khomenko, Oleksii Vitaliiovych; Ляшенко, Яків Олександрович; Ляшенко, Яков Александрович; Liashenko, Yakiv Oleksandrovych; Заскока, Антон Миколайович; Заскока, Антон Николаевич; Zaskoka, Anton MykholayevichРозглядається трибологічна система, що складається із атомарно-гладких твердих поверхонь, які розділені ультратонкою плівкою мастила. На основі теорії фазових переходів Ландау побудована термодинамічна модель, що описує поведінку цієї системи в режимі межового тертя. Густина вільної енергії для ультратонкої плівки мастила представлена у вигляді розвинення в ряд за степенями параметра порядку, що зводиться до модуля зсуву мастила. На основі моделі, що описує фазові переходи першого роду між кінетичними режимами тертя, досліджено кінетику системи. Показано, що за наявності пружини між зовнішнім приводом і блоком у порівнянні із жорстким з'єднанням зростає ширина гістерезису за температурою. При цитуванні документа, використовуйте посилання http://essuir.sumdu.edu.ua/handle/123456789/33977Item Thermodynamic theory of two rough surfaces friction in the boundary lubrication mode(Tribology Letters, 2012) Хоменко, Олексій Віталійович; Хоменко, Алексей Витальевич; Khomenko, Oleksii Vitaliiovych; Ляшенко, Яків Олександрович; Ляшенко, Яков Александрович; Liashenko, Yakiv OleksandrovychThe thermodynamic theory of thin lubricant film melting, confined between two hard rough solid surfaces, is built using the Landau phase transition approach. For the description of a melting condition the order parameter is introduced which is a periodical part of microscopic medium density function. The shear modulus of lubricant is proportional to the order parameter squared. The thermodynamic and shear melting are described consistently. A mechanical analogue of a tribological system in the boundary friction mode is studied. The time dependencies of the friction force, the relative velocity of the interacting surfaces, and the elastic component of the shear stresses appearing in the lubricant are obtained. It is shown that the shear modulus of the lubricant and the elastic stresses become zero in the liquid-like state. The irregular stick-slip mode of melting is described, which is observed in experiments. It is shown that the frequency of stiction spikes in the irregular mode increases with growth of the shear velocity. Comparison of the obtained results with experimental data is carried out. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/30623Item Friction force for boundary lubrication(Видавництво СумДУ, 2011) Ляшенко, Яків Олександрович; Ляшенко, Яков Александрович; Liashenko, Yakiv Oleksandrovych
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