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

The fatigue failure of friction stir (FS) welded aluminium panels of alloy 6005A has been analysed. Thesepanels are produced with two main joint geometries: namely half overlap and hourglass. Presence ofcrack like notches (interface between the welded work pieces) and blunt notches (corners and bendsin the base metal) have been studied with finite element method (FEM) stress analysis combined withthe critical distance method. It was shown that the failure location and fatigue limit could be predictedfor 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 procedurewas used the weld failure was not reproduced by model and failure location was not predictedcorrectly. In this case fracture mechanics approach along with residual stress analysis has been used toanalyse the failure. It is also shown that local plastic deformation on the crack tip is induced by clampingresulting in tensile residual stresses at the crack tip. Taking stress intensity factor of the residual stressinto account, the position of the failure can be explained