Abstract: The influence of welding parameters of butt joints, made by three processes (MMA, MAGand T.I.M.E), on their geometric characteristics has been evaluated, which in turn caused a change of the fatigue strength. That fore the statistic analysis and FEM were used and a method developed in the Institute of Welding, which consist in a direct connection of parameters used during welding with the fatigue strength of joints welded by various processes. It has been proven, among others.which by using more advanced welding processes (TLM.E) the fatigue strength of welded joints can be increased in comparison to joints welded by MMA and MAG.

Key words: fatigue strength, fatigue class (FAT), structural stress