Experiment and modeling on fatigue of the DP780GI spot welded joint

Abstract Fatigue life prediction of advanced high strength steels (AHSS) spot welded joints is of great importance for autobody design with AHSS being increasingly used. In the present work, the fatigue failure behaviors of the DP780GI spot welded joints under the tensile shear (TS) and coach peel (CP) loading conditions are experimentally investigated and numerically modelled. Two failure modes, eyebrow failure and weld button pull out occur in the tests of TS joints, while only interfacial fracture exists in CP joints. A fatigue life prediction method based the crack growth approach is proposed. The TS/CP specimens are simplified to the neural line models, by which the reaction forces and moments directly acting on the spot welds are calculated. Then the stress intensity factor is obtained by using the finite element method and analytical equations fitted to the FE results. Finally, the fatigue life of a spot weld is evaluated by applying the Paris law to the crack front and including the plastic zone in crack path update. The calculated fatigue lives show good agreement with experiment results for DP780GI, within five times error band.