Abstract
The high cycle fatigue strengths at the toe of the cruciform welded joints of SM41A and HT60 were investigated experimentally under tensile and bending fatigue loading. The effects of welding process (toe treatment), mean stress and welding residual stress on fatigue strength were studied.
The main results obtained are as follows.
(1) The fatigue limit of SM41A welded joint under tensile loading was increased up to 64% by the toe treatment of CO2 soft plasma welding. Similarly, in the case of HT60 welded joint the fatigue limits under bending loading were increased to 77%, 43% and 25% by the toe treatment of CO2 soft plasma welding, TIG welding and grinding, respectively. These improvements can be attributed to the change of the toe part geometry; lowering the elastic stress concentration factor at the toe.
(2) The relation between fatigue limit of welded joint and mean stress can be expressed by the straight line intercepted at the true rupture stress on the axis of mean stress in fatigue limit diagram.
(3) The fatigue limit of welded joint was decreased by tensile welding residual stress. This decrease can be well estimated by regarding the welding residual stress as the static stress.
