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Betriebsfeste Bemessung von Punktschweissverbindungen im Fahrzeugbau

Fatigue strength evaluation of spot-welded automotive structures
: Rupp, A.

Deutscher Verband für Schweißtechnik e.V. -DVS-, Düsseldorf:
Technologietransfer in der Schweisstechnik Universitätsforschung - Anwendung
Braunschweig, 1991
Braunschweig-Kolloquium <1991, Braunschweig>
Conference Paper
Fraunhofer LBF ()
Bemessung; crack initiation; design; Fahrzeugbau; finite element analysis; Finite-Elemente-Methode (FEM); Punktschweißverbindung; Rißentstehung; Schweißverbindung; spot welding; vehicle construction; welded joint

In order to obtain the fatigue strength of spot welded structures especially the determination of the local stress conditions at the welds, leading to the cracks is rather unknown. Here a calculation method using engineering formulas for these stresses is presented, which could be implemented in a design procedure. There are two different local stress conditions at the spot weld, the stresses in the sheets and the stresses in the weld, and depending on the ratio stress/strength for each condition the fatigue cracks propagate through one of the sheets or through the weld nugget. Both stress conditions, describing the fatigue strength are determined, according to the state of art in the German automotive industry, based on the cross-sectional forces and moments acchieved by Finite-Element-analyses on a loaded structure or component. The stresses are converted to a "simple" stress condition with the same damage, which can be realized on a specimen. On this specimen the endurable local str esses are obtained by fatigue tests. For the fatigue live evaluation as a matter of routine in the design stage now this procedure is being established as a Nastran-postprocessor for the German car producers.