Browsing by Author "Kulyk, Volodymyr"
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Item Experimental determination of critical strain energy density of ductile materials(Видавництво Львівської політехніки, 2019-03-20) Molkov, Yuriy; Ivanyts’kyi, Yaroslav; Lenkovs’kyi, Taras; Trostianchyn, Andriy; Kulyk, Volodymyr; Shyshkovskyy, Roman; Karpenko Physico-mechanical Institute of the NAS of Ukraine; Lviv Polytechnic National UniversityThe method of experimental determination of strain energy density of plastic materials is developed. The technique for complete true stress-strain curves plotting is formulated. The standard hydraulic testing machine is equipped with specially designed experimental setup for Bridgman specimens testing at strain controlled tension loading with digital camera and light source for using digital image correlation method – a non-contact technique for strain and displacement measurement. The digital image correlation method was used to determine the local strain at the onset of fracture in the neck of Bridgman specimen. The technique takes into account the change of crosssection area in the neck of specimen due to internal crack propagation when calculating the true stresses. The complete true stressstress-curve of 40Kh alloyed steel is plotted end criticalstrain energy density of steel is determined from it. It is shown that the critical strain energy density of material, determined from the curve obtained by developed technique is 1.8 times higher than determined from the classical true stress-strain curve and is close to the value of the specific heat of fusion of steel. The curves built using the proposed technique can be used for setting material properties in stress-strain state calculations by finite element method at large scale yielding conditions, for instance at pressure vessels critical pressure calculation. The critical strain energy density value can be considered as a material property at fatigue life-time calculation using energy approach.Item Influence of heat treatment modes on the performance characteristics of resistive cermet coatings(Lviv Politechnic Publishing House, 2020) Kovbasiuk, Taras; Duriagina, Zoia; Kulyk, Volodymyr; Pleshakov, Eduard; Kushpir, Vasyl; Lviv Polytechnic National UniversityDielectric and resistive coatings based on glass ceramics with nickel boride additives have been synthesized. It was found that the microstructure of the resistive coating consists of a large number of phases. X-ray fluorescence analysis revealed the presence of Ni and Cr borides in the structure of the resistive layer. It was found that the change in the structure and specific surface resistance of resistive pastes practically does not affect the temperature coefficient of resistance of the synthesized resistive tracks.