Critical distance method to estimate the fatigue life time of friction stir welded profiles

The fatigue failure of friction stir (FS) welded aluminium panels of alloy 6005A has been analysed. These panels are produced with two main joint geometries: namely half overlap and hourglass. Presence of crack like notches (interface between the welded work pieces) and blunt notches (corners and bends in the base metal) have been studied with finite element method (FEM) stress analysis combined with the critical distance method. It was shown that the failure location and fatigue limit could be predicted for three of the four types of profiles considered. Choice of the welding procedure (clamping condition), however, can significantly influence the fatigue life and prediction accuracy. When different welding procedure was used the weld failure was not reproduced by model and failure location was not predicted correctly. In this case fracture mechanics approach along with residual stress analysis has been used to analyse the failure. It is also shown that local plastic deformation on the crack tip is induced by clamping resulting in tensile residual stresses at the crack tip. Taking stress intensity factor of the residual stress into account, the position of the failure can be explained.

► Fatigue properties of friction stir welded hollow aluminium panels were investigated.
► Fatigue limit of the base metal and the weld location could be predicted using theory of critical distance.
► Clamping and welding procedure can significantly alter the fatigue life.
► It was found presence of tensile residual stresses was not incorporated into the stress analysis of critical distance method.