Bemessung zyklisch beanspruchter Schweißverbindungen aus höchst- und ultrahochfesten Stählen

Fatigue assessment of welded high-strength steels.

The design of highly loaded crane structures is linked to the fatigue life assessment of welded structures in the low cycle fatigue (LCF) regime. In the FOSTA research project P900 MAG welded butt joints and transverse stiffeners made of 8 mm thick sheets as well as tube- clevis-components were investigated using the nominal stress, the notch stress and the notch strain concept. Constant amplitude loading fatigue tests up to the LCF regime result in Wöhler curves, which fulfill FAT class 80 (butt joints) and FAT 71 (transverse stiffeners) according to the recommendations and can be estimated with a slope of k = 3. A fatigue life increase can be achieved by post weld treatment methods, even in the LCF regime.
In addition to knowledge about the cyclic material behavior, the effect of a Gaussian spectrum on the fatigue life has to be considered. A fatigue life increase under variable amplitude loading is shown by Gaßner curves and characteristic damage sums resulting from a linear damage accumulation. The results have been extended to sample component investigations of tube-clevis connections. A fatigue assessment using local approaches confirms FAT225 for the effective notch stress approach up to N ≥ 103 cycles. In addition an assessment is concluded considering the elastic-plastic material behavior and using damage parameters.