Generalized Formulation for Fatigue Assessment of Laser Stake-welded T-joints Varying Thicknesses and Loading Conditions

The present work considers the evolution of the crack tip plasticity ahead of the crack-like notches with varying the loading condition and the thickness of laser stake-welded T-joints. A general procedure is described for the fatigue assessment of the joints under different loading conditions and made of different thicknesses. The new method is based on the analyses of the first order plastic radius (according to Irwin) for pure mode I, and it is generalized to mixed mode (I+II) by using the Minimum Plastic Zone Radius (MPZR) criterion. The method is validated, in the end, with a case study and explains why the fatigue slope m varies for joints loaded under bending/tension and when the thickness is reduced. The results prove that the procedure gives an excellent estimation of the fatigue life.