Motrunich S. Influence of welding methods and variable amplitude loading on fatigue resistance of heat strengthened aluminum alloys

The thesis is dedicated to determination of the influence of various welding methods (friction stir welding (FSW), electron-beam welding (EBW), tungsten inert gas (TIG) and metal inert gas (MIG) welding technologies) and variable amplitude loading on fatigue resistance of heat strengthened aluminum alloy joints. The work investigates the main factors that determine cyclic loading fracture strength of aluminum alloys D16T1, 1420T1, 1460T1 and 7056-T351 welded joints. Nature distribution of residual stresses, degree of softening and structural peculiarities of the joints of investigated alloys made by MIG, TIG, FSW and EBW were determined. The engineering methods was proposed for determination of the coefficient of stress concentration in the zones of geometry inhomogeneity of butt welds, in tension and bending for sheet joints with two-side symmetric and one-side reinforcement. The basic S-N curves under constant amplitude loading were experimentally obtained for welded joints of sheet aluminum alloys D16T1, 1420T1, 1460T1 (t = 1,8...2,0 mm) and 7056-T351 alloy (t = 12 and 30 mm) produced by MIG, TIG, FSW and EBW technologies. The algorithm and software were proposed for S-N curves plotting. They are used for estimation of welded joints cycle fatigue under narrow band variable amplitude loading in contrast to constant amplitude loading.