The dissertation „Research of improvement of non-alloy steel surface hardness and stiffness by laser treatment“ („Nelegiruotojo plieno paviršiaus kietumo ir standumo didinimo lazerinio apdorojimo metodu tyrimai“) prepared by VILNIUS TECH, Oleksandr Kapustynskyi. The dissertation was prepared in 2018–2023, supervisor Assoc. Prof. Dr Nikolaj Višniakov.
The dissertation was defended at the public meeting of the Dissertation Defense Council of the Scientific Field of Materials Engineering in the Senate Hall of Vilnius Gediminas Technical University at 10 a. m. on 15 June 2023.
The dissertation deals with the development of new metal processing technologies that enable to control and improve the microstructure and properties of the metals. Laser treatment is one such modern technique. The dissertation aims to determine the laser processing effect on the surface of a thin sheet of non-alloy structural steel. The research aims to solve one of the critical problems in diversifying the use of thin-sheet steel products in the industry by developing laser-processing technology for the creation of structural strengthening ribs, which can significantly affect the overall strength and stiffness of metal parts. The proposed solutions will help solve the problems of using thin-sheet metal products in the industry by increasing the stiffness with preserving the original design parameters (e.g., the product’s size, shape, and weight). This will save production time and resources due to the reduced number of technological and maintenance operations compared to traditional methods of increasing the stiffness of thin-sheet metals, where designing methods are based on the relationship between a construction geometry and its stiffness. The introductory chapter discusses the research aim and objectives. It also describes the research methodology, its scientific novelty, and the practical significance of the results. The introduction closes by presenting the author’s publications and conference papers on the dissertation’s topic and structure. The first chapter reviews the existing methods of increasing the hardness and stiffness of thin-sheet steel products. It also overviews the microstructure and the possibility of increasing the mechanical strength and hardness of the non-alloy steel. At the end of the chapter, the conclusions of the literature review are formulated, and the essential tasks of the dissertation are specified. The second chapter describes the materials and laboratory equipment used in the research work. This includes the methodology of microstructure analysis, mechanical properties testing, surface laser processing technology, calculating laser processing parameters, and modeling bending and tensile cases. The third chapter presents the results of the analysis of surface layer microstructure and phase composition, mechanical properties, calculation and selection of laser processing parameters, modeling of bending and tensile of treated thin-sheet samples, analysis of the importance of laser processing depth, and direction of processing, geometry, and direction of processing, and location of reinforcement areas. Six articles on the topic of the dissertation have been published, and the research results have been presented at nine scientific conferences in Lithuania and abroad.
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The dissertation was defended at the public meeting of the Dissertation Defence Council of the Scientific Field of Electrical and Electronic Engineering in the Senate Hall of Vilnius Gediminas Technical University at 2 p. m. on 15 June 2023.
The dissertation deals with permanent magnet synchronous motors (PMSM) classical control theory and also by applying magnetic field theory approach. The purpose of the thesis is to create the mathematical model of the PMSM based on analytical equations of magnetic field accounting torque ripple, inductance distributions and back electromotive force, to develop the measurement system for direct measurement of magnetic flux density and to propose PMSM parameter estimation method. In order to solve the stated problem and reach the goal following main tasks of the thesis are formulated: create PMSM model based on the analytical equations of magnetic flux density; develop vector control method of PMSM and investigate it experimentally; develop PMSM parameter estimation method; develop and implement a magnetic flux density measurement system; perform experimental measurement of magnetic flux density of PMSM using the developed system. The dissertation consists of the introduction, three chapters, general conclusions, references, and the list of scientific publications of the author on the topic of the dissertation. The introduction discusses the research problem, the relevance of the dissertation, the object of the research, formulates the aim and tasks, de- scribes the research methodology, the scientific novelty of the dissertation, de- fended statements and the practical value of the research findings. At the end of the introduction, the dissertation and the structure of the dissertation are provided. The first chapter reviews the PMSM design, rotor and stator types, magnetic field analytical solutions for predicting magnetic flux in the PMSM and magnetic field measurement systems. The second chapter presents an analysis of the following topics of PMSM’s magnetic field distribution: the field created only by the rotor (open-circuit) and the field created only by the stator (armature reaction). Next, the effect of the stator slot on the magnetic field distribution is analysed. Finally, the enhanced PMSM model concept is stated based on magnetic field analysis. The third chapter presents the magnetic flux density measurement systems and compares the experimental results with the simulation results obtained using the proposed enhanced PMSM model. The main results of the dissertation were published in seven scientific publications: four in the Clarivate Analytics Web of Science database with an impact factor and three in other databases. The results were presented at eight scientific conferences.
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