Видання зареєстровані авторами шляхом самоархівування
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Item Adhesion and friction in hard and soft contacts: theory and experiment(Tsinghua University Press, 2021) Popov, V.L.; Li, Q.; Ляшенко, Яків Олександрович; Liashenko, Yakiv Oleksandrovych; Pohrt, R.This paper is devoted to an analytical, numerical, and experimental analysis of adhesive contacts subjected to tangential motion. In particular, it addresses the phenomenon of instable, jerky movement of the boundary of the adhesive contact zone and its dependence on the surface roughness. We argue that the "adhesion instabilities" with instable movements of the contact boundary cause energy dissipation similarly to the elastic instabilities mechanism. This leads to different effective works of adhesion when the contact area expands and contracts. This effect is interpreted in terms of “friction” to the movement of the contact boundary. We consider two main contributions to friction: (a) boundary line contribution and (b) area contribution. In normal and rolling contacts, the only contribution is due to the boundary friction, while in sliding both contributions may be present. The boundary contribution prevails in very small, smooth, and hard contacts (as e.g., diamond-like-carbon (DLC) coatings), while the area contribution is prevailing in large soft contacts. Simulations suggest that the friction due to adhesion instabilities is governed by "Johnson parameter". Experiments suggest that for soft bodies like rubber, the stresses in the contact area can be characterized by a constant critical value. Experiments were carried out using a setup allowing for observing the contact area with a camera placed under a soft transparent rubber layer. Soft contacts show a great variety of instabilities when sliding with low velocity – depending on the indentation depth and the shape of the contacting bodies. These instabilities can be classified as "microscopic" caused by the roughness or chemical inhomogeneity of the surfaces and "macroscopic" which appear also in smooth contacts. The latter may be related to interface waves which are observed in large contacts or at small indentation depths. Numerical simulations were performed using the Boundary Element Method (BEM).Item An experimental study on third-body particle transport in sliding contact(University of Nis, 2021) Li, Q.; Ляшенко, Яків Олександрович; Liashenko, Yakiv Oleksandrovych; Starcevic, J.An experiment is designed to study the third-body particle transport in a rough contact. To study the influence of particles in a pure form, it is assured that the first bodies have no contact and the sliding is very slow, so that the process can be considered as quasistatic. An example of sliding contact of a 3D printed “rough body” on small spheres artificially located on a rubber layer is presented. The trajectory of particles during the sliding is captured for studying their movement and the correlation to the fluctuation of normal and tangential force.Item Adhesion Between Rigid Indenter and Soft Rubber Layer: Influence of Roughness(Frontiers in Mechanical Engineering, 2020) Ляшенко, Яків Олександрович; Liashenko, Yakiv Oleksandrovych; Pohrt, R.We report a series of experiments on the indentation of steel indenters into a soft layer of transparent rubber with relatively high adhesion. The roughness properties of the steel indenters are varied by undergoing preparation using sandpaper with different grain sizes. Starting from a smooth surface, additional roughness increases the adhesive strength up to a critical roughness value, after which it significantly decreases. Furthermore, we look at the evolution of the contact area during slow indentation and detachment. It was found that, during indentation, the contact area changes more sharply compared to detachment (pull-off).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 Динамическое моделирование развития экономических систем на основе самосогласованной эволюционной модели спрос/предложение(Придніпровська державна академія будівництва та архітектури, 2013) Чорток, Юлія Володимирівна; Чорток, Юлия Владимировна; Chortok, Yuliia Volodymyrivna; Люльов, Олексій Валентинович; Люлев, Алексей Валентинович; Liulov, Oleksii Valentynovych; Ляшенко, Яків Олександрович; Ляшенко, Яков Александрович; Liashenko, Yakiv Oleksandrovych; Моргуненко, Р.М.В роботі наведено та проаналізовано різні підходи до трактування категорії «розвиток». Виділено основні характеристики і особливості досліджуваної дефініції. Запропоновано модель, що дозволяє на якісному рівні описати самоузгоджену еволюційну поведінку попиту і пропозиції в економічних системах в залежності від ціни, яка встановлюється на товар. У стаціонарному випадку модель показує стандартний вигляд кривої попиту-пропозиції.