Fatigue Strength of Welded Lap Joints

ABSTRACT. The most advanced structural frames of cars and motorcycles are made of aluminium alloys welded box beams. A recent technological solution for the beams consists of press-formed metal sheets joined by welded lap-joints. Because the frames undergo relevant fatigue loads, the evaluation of fatigue endurance of this kind of connections plays a crucial role during the development of frame. The present research deals with the evaluation of fatigue behaviour of welded lap joints, subjected to tensile and bending loads. Fractographic evidences and numerical analyses showed that fatigue strength is controlled by the presence of defects ad inhomogeneities at the tip of the weld root. In particular these defects, which appear to lie onto the maximum Kqq path, increase SIF at weld singularity. Such an analysis, together with the statistical description of defects population, allowed to develop a methodology able to predict the fatigue strength of lap-joints. A simple method for SIF based on FEM analyses and structural stresses at the lap-joint is then presented