Betriebsfestigkeit von Punktschweißverbindungen

In order to obtain an adequate procedure to determine the fatigue strength of spotwelded structures, based on calculated forces and moments in the cross section, tests on hat profile specimens under constant and random loading and finite-element analyses were carried out. There are two different stress conditions at the spot-welds and depending on the ratio stress/stength for each condition the fatigue cracks propagate through the sheet or the weld nugget. Depending on these failure modes the procedures are worked out to evaluate the fatigue strength of spot-welds. These are the maximum radial stress on the inside of the welded sheet where the cracks start in the metal sheet, and an equivalent normal stress at the spot weld for cracks through the welding nugget. A spot welded structure should be investigated for both types of failure and the prevailing stress state should be compared to the allowable one which was found in tests