Ukrainian Journal of Mechanical Engineering and Materials Science. – 2015. – Vol. 1, No. 2

Permanent URI for this collectionhttps://ena.lpnu.ua/handle/ntb/32786

Науковий журнал

Засновник і видавець Національний університет «Львівська політехніка». Виходить двічі на рік з 2015 року.

Ukrainian Journal of Mechanical Engineering and Materials Science = Український журнал із машинобудування і матеріалознавства : науковий журнал / Lviv Politechnic National University ; editor-in-chief Oleksiy Lanets. – Lviv, 2015. – Volume 1, number 2. – 90 p. : il. – Паралельна назва англійською.

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Analysis of structure and kinematics of four-bar crank-rocker walkingmechanism
(Publishing House of Lviv Polytechnic National University, 2015) Korendiy, Vitaliy
Problems and prospects of using the walking mode for producing motion of robotic systems are considered. Advantages and spheres of the use of mobile robotic systems equipped with walking movers are substantiated. Preferences of cyclic (lever) walking mechanisms are analyzed. The kinematic parameters of four-bar crank-rocker walking mechanism, constructed on the basis of Chebyshov-Umnov mechanism, are accepted as the subject of research. The process of motion of the supporting foot of the walking mechanism is accepted as the object of research. The main aim of the investigation consists in carrying out structure and kinematics analysis of the mentioned mechanism with further derivation of analytical dependencies for calculating kinematic parameters of the supporting foot motion. The special features of the structure of four-bar walking mechanism and theoretical foot loci (paths) are considered. The form of the most reasonable path for further research is established. As a result of carried out structure analysis, it is ascertained that the mechanism consists of two structural groups: that of the first class and that of the second class second order first type. As a result of kinematics analysis, the analytical expressions for calculation of coordinates of the supporting foot hinge of the walking mechanism depending on geometric parameters of the mechanism and the angle of the crank rotation are deduced. The prospects of further investigation under the themes of the paper are analyzed. In particular, the goal function, which may be used for further optimization of structural parameters of the mechanism, is considered and the use of applied software for solving optimization problem is suggested. The optimization problem consists in evaluating such geometric parameters of the walking mechanism which allow the motion of the supporting foot in accordance with the prescribed (specified) path.
Cutter force and influence of elastic deformation of technological system of gear-hobbing machine on precision of radial-circumferential method of gear cutting
(Publishing House of Lviv Polytechnic National University, 2015) Hromniuk, Serhii; Hrytsai, Ihor
The relevance of the problem which is solved in this article has been substantiated. In modern machines and equipment, rotary motions which cannot be implemented without gear wheels and gear trains are always present. Attainment of high performance of a machine – increase in loading with simultaneous increase in speed, increase in transmitted forces and moments, decrease in noise during operation, ensuring high indexes of failure-free performance and longevity of a machine – depends on precision in manufacturing the gear wheels and gear trains. These requirements to modern machines are put simultaneously with improvement of technology of their manufacturing and with creation of new effective methods of machine parts working. A new effective method of radial-circumferential (RC) gear cutting by disk-type cutting tool under the conditions of continuous generation (revolving) around is described; this way enables us to considerably reduce the expenditures for expensive and complicated cutting tools, to increase productivity of the process, and to increase precision of gear wheels. However, for application of this method in the course manufacturing, it is necessary to develop a technique of prediction of the precision of the gear cutting; such a technique being able to serve as a basis of substantiation of the choice of regimes of gear cutting. Principles of the mathematical model of cutting force of gear cutting, i.e. a model which is based on modelling of parameters of shearings made by a disk-type milling cutter, are presented in this article. This mathematical relation takes into account the intensity of deformation of the layer which is being removed and the strength of the material which is being machined; the model also enables us to determine the force on individual blades and its total value on all the active teeth in RC-method at any instant of time of milling as a function of the turn angle of the cutting tool. Analysis of cutting force has indicated that in one revolution of a milling cutter the cutting force varies according to aperiodic regularity, and its peak values are considerably less than the force of gear-tooth milling by a hobbing cutter under the same initial conditions. Since the disc-type gear milling cutter, as compared with the hobbing cutter, is considerably more sensitive to elastic deformations, the cutting force can essentially influence the error of gear cutting of ring gears. Proceedings from this, the influence of primary errors and that of elastic deformations which are caused by variable cutting force in the cycle of revolution of the milling cutter and formation of gears on the error of the working is investigated. Laws of the influence of radial, axial, and torque deformations of the elastic system of a machine on the deviations of parameters of the teeth from their rated ones and on the error of profiles in the process of gear milling according to radial-circumferential method are presented. The enhance of precision of tooth cutting and reduction of the total error becomes possible due to the choice of such regimes of cutting (first of all, axial feed) under which the necessary precision of the chosen parameter of precision, in particular, profile error, can be attained.
Determination of porosity of materials by means of metallographic method swith a help of application programs
(Publishing House of Lviv Polytechnic National University, 2015) Huliieva, Nataliia
Theoretical and experimental investigations of porous permeable materials of saponite-titanium and saponite-aluminium composites are presented in this work. their qualitative and quantitative indexes are determined in PhotoM and Smart-eye applied programs. Metallographic images are presented by combination of structural components with different proportions: phases, shape and color, grain boundaries. The limits of technological parameters and synthesis of porous permeable materials on the basis of saponite-titanium and saponite-aluminium composites with the necessary balance of the designed and functional indexes and their variation with changes in individual properties have been studied. On the basis of results of the investigations, regimes of shaping of saponite-titanium and saponite-aluminium composites are stated and substantiated. Dry radial-isostatic compaction and self-propagating high-temperature synthesis are applied. The porosity for these composites is determined. Recommendations on application of porous permeable materials are developed; and the branch of their application is determined: filtering porous permeable materials of saponite-titanium ensure the necessary purification and tertiary treatment of water for drink preserving their main natural characteristics: balance of chemical composition, organoleptic indexes, safety, physiological full value, and biological stability; and the filtering porous permeable materials of saponitealuminium composite ensure treatment of sewage, of service and process waters. The suggested and tested resource-saving technology has been introduced in enterprises of the municipal services “Lutsk Vodokanal” and PAT “SKF-Ukraina” of Lutsk city; this technology provides manufacture of saponite-titanium composites for purification of water for drinking and saponite-aluminium composites for treatment of sewage and service and process waters; and developed, manufactured and tested porous permeable materials satisfy the requirements of state in the field of water supply, as well as in the food and industrial sectors, that, in its turn, plays an important role in solving complicated problems of modern materials science.
Fundamentals of creation of newdevices for speed change management
(Publishing House of Lviv Polytechnic National University, 2015) Malashchenko, Volodymyr; Strilets, Oleh; Strilets, Volodymyr
The article deals with problem of speed change management in engineering, i.e., hoisting, building, road and land reclamation machines, cars and tractors, machine tools and other equipment. The review of the methods and devices for stepped, steppless and combined speed change process management have been performed. Their major disadvantages have been identified. Among others, main disadvantages of stepped speed management devices are the complexity of design, their large material consumption, the emergence of dynamic loads during the transition from one speed to another, even in case of synchromesh using. Continuously variable speed devices have intense components wear due to the use of friction connections like brakes or lock-up clutches. The authors lead to the conclusion about the need for new devices of speed change management to remove, or at least decrease, identified deficiencies. New devices suggested for speed changes management via epicyclic gear trains with a closed circuit hydrosystem. Those new constructions are supposed to remove abovementioned shortcomings and can be the basis and foundation for new devices creation and their further research.
Impactand particle buffered vibration absorbers optimization and design
(Publishing House of Lviv Polytechnic National University, 2015) Diveyev, Bohdan
Passive, broadband targeted energy transfer refers to the one-way directed transfer of energy from a primary subsystem to a nonlinear attachment; this phenomenon is realized in damped, coupled, essentially nonlinear impact or particle dynamic vibration absorber (DVA). An impact damper is a passive control device which takes the form of a freely moving mass, constrained by stops attached to the structure under control, i.e. the primary structure. The damping results from the exchange of momentum during impacts between the mass and the stops as the structure vibrates. A particle-based damping system can overcome some limitations of ordinary DVA by using particles as the damping medium and inter- particle interaction as the damping mechanism. Large damping at such family constructions of DVA’s does not bring to destruction an elastic DVA element over in critical cases, when working frequency approaches own frequency of DVA, or when the transitional process of acceleration of rotating machines is slow enough and DVA’s has time to collect large amplitudes of vibrations. The primary structure is modelled as a spring-mass system. In this paper, an efficient numerical approach based on the theoretical-experimental method is proposed to maximize the minimal damping of modes in a prescribed frequency range for general viscous tuned-mass systems. Methods of decomposition and numerical synthesis are considered on the basis of the adaptive schemes. The influence of dynamic vibration absorbers and basic design elastic and damping properties is under discussion. A technique is developed to give the optimal DVA’s for the elimination of excessive vibration in sinusoidal forced rotating system. It is found that the buffered impact damper not only significantly reduces the accelerations, contact force and the associated noise generated by a collision but also enhances the level of vibration control. The interaction of DVA’s and basic design elastic and damping properties is under discussion. One task of this work is to analyze parameters identification of the dynamic vibration absorber and the basic structure. The discrete-continue models of machines dynamics of such rotating machines as water pump with the attachment of particle DVA’s and elongated element with multi mass impact DVA’s are offered. A technique is developed to give the optimal DVA’s for the elimination of excessive vibration in harmonic stochastic and impact loaded systems.
Nonlinear analysis in synthesis of the resonant vibro-impact systems
(Publishing House of Lviv Polytechnic National University, 2015) Gursky, Volodymyr; Kuzio, Ihor
The paper considers differential equation of the vibro-impact resonance system with an asymmetric piecewise linear elastic characteristic. The time-instant of switching of elastic characteristic is determined on the basis of equality of oscillation period to average value of the corresponding eigenfrequencies. Then, expansion of the asymmetric piecewise linear elastic characteristic into Fourier series was made. The initial differential equation was reduced to a kind of parametric equations of Hill’s andMathieu’s type with taking into account the time of elastic characteristic change. Stability analysis of parametric Mathieu equation is shown for the analysis of natural oscillations. For stability analysis of the synthesized by various stiffness coefficients of vibro-impact system, dependencies of Mathieu equations coefficients on the parameter of synthesis are used. The solution of the initial equation with forced oscillations in the form of asymmetric two-frequency vibrations has been obtained by means of Bubnov-Galerkin and Levenberg-Marquardt methods for nonlinear algebraic systems of equations, also amplitude and phase frequency dependence was graphically drawn. The basic equation with an asymmetric elastic response characteristic feature is determined by the fixed natural frequency of oscillations independently of amplitude. Numerical solution of differential equations by means of Runge–Kutta method are presented for comparison. Comparison of the vibro-impact resonance system kinematics characteristics, synthesized by the elastic parameters and solved by the listed methods, is conducted. The feasibility of using nonlinear analysis presented in two harmonics in Fourier series asymmetric elastic characteristic is justified in the article. The suggested approach with Bubnov-Galerkin method for general Hill’s equation and correlation analysis of time kinematic characteristics was used. Acceleration frequency spectrum and harmonics are obtained on the basis of Runge–Kutta numerical method simulation of the initial nonlinear differential equation.
Propagation of elastic-tough-plastic wave in a rod of ideally plastic materialwhich possesses the property of yield delay
(Publishing House of Lviv Polytechnic National University, 2015) Andrusyk, Yaroslav
The great number of theoretical and experimental investigations indicate that it is necessary to consider plastic deformation of metals as a process which proceeds in certain time interval. However, in such approaches, contradictive points of view emerge concerning investigation of wave processes in materials which possess peculiar properties. In order to describe different mechanical effects, new models of plastic medium are being improved. The phenomenon of emergence of a tooth yield in the strain diagram belongs to such properties of materials. In this article, investigation of propagation of elastic-tough-plastic wave is conducted in a semi-infinite rod; it is conducted on the basis of the electromechanical model of ideal elastic-plastic material with yield delay. The dynamic criterion of plasticity, which is stated by the author is used here. The solving of the problem is conducted according to the statement where constant force is abruptly exerted on a bult of an unloaded rod. the main solution is obtained in stresses, both for elastic and plastic domains of the rod. It is established that characteristic curves which separate an elastic domain from a plastic one and vice versa are frontal lines of weak rupture. On the basis of calculations, fields of stresses? strains, rates of displacements of cross-sections of the rod in a plastic domain are determined. for a fixed instant of time, graphs of changes of stresses and displacements of points on the whole segment of a disturbed rod are plotted. The obtained results have been verified as to exactness of satisfaction to the boundary condition.
Ways of improvement of technological process of copper wire rod production
(Publishing House of Lviv Polytechnic National University, 2015) Dvoryanyn, Hrystyna; Shvachco, Sergiy
Copper is a unique chemical element which is used since ancient times due to its universal chemical properties. By means of the method of continuous founding, hundreds of items of rod-like billets of different cross-section shapes are manufactured from copper. The problem of production of defectfree copper wire rods is important nowadays, because the market of cable products still increases. As the deposits of cooper ore in the nature are being exhausted, the processing of copper scrap becomes of still growing interest for non-ferrous metallurgy. There emerged the necessity of further study and improvement of the technology of production of copper wire for electrical engineering and that of copper wire rods. In manufacturing of copper wire rods according to the method of continuous founding, there emerge violations of technological process because of formation of hot cracks in a cast billet. Just for this reason, in this article, such problems are described, and ways of their solving are considered. The character of their structure formation during crystallization of copper wire rods is analyzed. Advantages and drawbacks of the method of continuous founding of copper wire rods are described. The possibility of the use of ultrasonic oscillations for improvement of the quality of finished products is shown.
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