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In design codes for the dimensioning of welded joints, no distinction is made between low-, medium- and high-strength steels. The investigation should emphasize the advantages of high-strength steels S690Q and S960Q compared with the S355N and S355M in the welded state, particularly under cyclic variable amplitude loading and overloads.

The fatigue investigations with butt welds and transverse stiffeners were accompanied by determining the notch factors, microstructural investigations, hardness measurements, residual stress measurements, strain controlled tests, fracture mechanical investigations, calculation of real damage sums and the evaluation of the fatigue tests using the standard procedure from Eurocode 3.

The results of the investigation showed that there is, a priori, no clear advantage for the investigated states of the high-strength steels, butt welds and transverse stiffeners under constant amplitude loading. But fatigue tests with un-notched specimens pointed out that, in the case of good (machined) weld surface quality, about 30% higher endurance limits are reachable for the high-strength steels. Hence, when cracks are avoided, the 960Q can take advantage of its approximately 50% higher threshold stress-intensity-range Delta-K(th)-value of the heat affected zone. In the case of variable amplitude loading, a large part of fatigue life is crack propagation. Due to its highest yield strength, the S960Q was able to build up the highest compressive residual stresses at the crack front. Therefore, butt welds of this steel bear 30% higher local stresses than the lower grades and under pulsating loading, when overloads occur, 100% are reached.hed.

Additional information

Authors: WEGMANN H G, Thyssen Krupp Stahl AG, Duisburg (DE);HANUS F, Dillinger Hütte GTS, Dillingen/Saar (DE);MÜLLER C, IEHK-RWTH Aachen (DE);SEDLACEK G, IEHK-RWTH Aachen (DE);KAUFMANN H, Fraunhofer-Institut für Betriebsfestigkeit LBF, Darmstadt (DE);SONSINO C M, Fraunhofer-Institut für Betriebsfestigkeit LBF, Darmstadt (DE);RISCIFULI S, CSM, Rome (IT);DEMOFONTI G, CSM, Rome (IT)
Bibliographic Reference: EUR 19989 EN (2001), pp. 337. Euro: 50.00
Availability: Available from EUR-OP sales agent URL:
ISBN: ISBN 92-894-1588-6
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