Title: Relaxation of welding residual stresses – Part II: under cyclic loading

Authors: Majid Farajian; Thomas Nitschke-Pagel; Klaus Dilger

Addresses: Institute of Joining and Welding, University of Braunschweig, Langer Kamp 8, D-38106 Braunschweig, Germany. ' Institute of Joining and Welding, University of Braunschweig, Langer Kamp 8, D-38106 Braunschweig, Germany. ' Institute of Joining and Welding, University of Braunschweig, Langer Kamp 8, D-38106 Braunschweig, Germany

Abstract: In this paper the variation of the initial residual stresses at the surface of butt-welded specimens made out of S690QL under cyclic loading was investigated. In low cycle fatigue and within the finite life, relaxation takes place during the very first loadings. The major portion of the relaxation occurs in the first half of the first loading cycle and could be treated as relaxation under quasi-static loading. The von Mises failure criterion with the local yield strength as the material resistance against plastic deformation is able to describe this behaviour. In high cycle fatigue loading, with or without mean stresses, except for a small reduction at the beginning, no considerable residual stress relaxation as a function of number of cycles was observed. That is, in the range of high cycle fatigue, high tensile residual stresses in butt welds with low stress concentration at the weld toe, accompany the weld until the failure initiation. Hereafter, the relaxation because of the crack initiation and propagation begins.

Keywords: fatigue strength; butt welding; residual stress; welded joints; relaxation; crack propagation; crack initiation; cyclic loading.

DOI: 10.1504/IJMMP.2012.045799

International Journal of Microstructure and Materials Properties, 2012 Vol.7 No.1, pp.16 - 26

Published online: 12 Mar 2012 *

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