o:1677 Istraživanje uticaja parametara zavarivanja trenjem sa mešanjem na dinamičku izdržljivost zavarenog spoja legure aluminijuma 2024 T351 A research on influence of the friction stir welding's parameters on welded joint's fatigue strength at AA 2024 T351 : doctoral dissertation sr In order to ensure a quality welded joint, and thus safe operation and high reliability of the welded part or structure achieved by friction stir welding, it is necessary to select the optimal welding parameters. The parameters of friction stir welding significantly affect the structure of the welded joint, and thus the mechanical properties of the welded joint. Investigation of the influence of friction welding parameters was performed on 6 mm thick plates of aluminum alloy AA 2024 T351. The quality of the welded joint is predominantly influenced by the number of tool revolutions speed n and the welding speed v. In this research, it was adopted that the number of tool revolutions be constant n=750 rpm, and the welding speed changed (v=73, 116 and 150 mm / min). Imperfections of the face and roots of the welded specimens were not determined on all welded work pieces by the visual method. Not a single welded sample, examined by radiographic examination, have not been founded welding defects. Experimental investigations of the macro and micro-structure of welded joints achieved by different welding parameters were performed, followed by tests of mechanical properties of welded joints: tensile testing, bending testing, Charpy impact testing, fracture mechanics parameters testing, fatigue crack growth rate and fatigue testing of welded joints. The efficiency of welded joints for welding parameter B-750/116 is almost 100%, that is the tensile strength of the welded joint is approximately equal to the tensile strength of the base metal. Welded joints are not suitable for bending stresses according to the results of bending tests under static and dynamic loading conditions. By Charpy impact testing of welded joints using an instrumented pendulum, fairly low values of impact energy were obtained for all welded joints with generated notch in different positions of the welded joint structure. By examining the parameters of fracture mechanics, for welded joints achieved by different welding parameters, the fracture toughness KIc is the highest on the retreating side of the welded joint, and the lowest in the middle of the joint. The highest fracture toughness was obtained for welding parameters B-750/116. Fatigue tests of welded joints were performed on a servo-hydraulic pulsator and on electrodynamic shaker. The best properties of fatigue strength were shown by welded joints achieved by welding parameters B-750/116. Based on extensive experimental research, in general, the best structural, and thus mechanical properties of butt welded joints of aluminum alloy AA 2024 T351 were achieved by welding parameters B-750/116, that is with the ratio of welding parameters n/v=6.47. Biografija autora: list 220;Bibliografija: listovi 189-200. Datum odbrane: 31.08.2020. Mechanical elements and constructions, welding 22989833 91552101 7866 91552100 22989833 2021-02-02T16:38:14.053Z 45 no 46 mentor Miodrag D. 1987- Milčić 2020 63 mentor Boban 1957- Anđelković 2020 63 član komisije Janez 1953- Kramberger 2020 63 član komisije Vencislav 1978- Grabulov 2020 63 član komisije Milan 1979- Banić 2020 63 član komisije Miroslav Mijajlović 2020 VII, 220 listova 15681677 http://phaidrabg.bg.ac.rs/o:1677 no yes 4 2021-02-02T16:38:14.320Z 70 Zavarivanje trenjem sa mešanjem, Legura aluminijuma 2024 T351, Parametrizavarivanja, Mehanička svojstva zavarenih spojeva, Visokociklični zamor,Elasto-plastična mehanika loma, Zamorna prslina Friction stir welding, Aluminum alloy 2024 T351, Welding parameters,Mechanical properties of welded joints, High-cycle fatigue, Elastic-plasticfracture mechanics, Fatigue crack 621.791.1::[620.178.3:669.71.055(043.3) T130; T210; T450 1738 18A04 18A0405 2020