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Einfluß hoher Zugeigenspannungen auf das Langzeitschwingfestigkeitsverhalten N größer 10 hoch 7 von geschweißten Strukturen unter veränderlicher Amplitudenbelastung. Gebrauchseigenschaften und Betriebsverhalten

Influence of high tensile residual stresses on the high cycle fatigue behaviour N bigger 10 high 7 of welded structures under variable amplitude loading
: Müller, A.; Grubisic, V.; Theobalt, -
: European Commission, Directorate-General for Science, Research and Development

Luxemburg, 1994, 130 pp.
EUR, 14652/DE
ISBN: 92-826-4066-3
Fraunhofer LBF ()
Betriebsfestigkeitsversuch; crack propagation; Eigenspannung; fatigue strength; Langzeitbeanspruchung; long-time loading; residual stress; Rißfortschritt; Schweißverbindung; Schwingfestigkeit; Spannungsanalyse; Stahl; steel random fatigue test; stress analysis; welded joint

Aim of the research project was to investigate the influence of tensile residual stresses on the high cycle fatigue behaviour of welded structures (in this case St 52-3 and St 37-2) under variable (blocked) amplitude loading. Fatigue tests on specimens of material St 52-3 as well as residual stresses using strain gage technic were carried out at the Fraunhofer-Institut für Betriebsfestigkeit (LBF). Tests on St 37-2 as well as x-ray residual stress measurements were carried out at UNIREC, F-Firminy. The results of these investigations will be presented in a seperate final report. The measurement of residual stresses at St 52-3 specimens show remarkable differences between the "as welded" and "stress relieved" specimens. However each material state had a typical strain distribution via the depth. On the specimens made from St 37-2 no reproducible characteristic strain distribution via the depth was found for the "as welded" state. The tests with Gaussian type load spectra showed distinct smaller differences in the endurance limit of both material states, than it was the case for tests with constant amplitude loading. The tests with a "p-value" load spectra (more fully shaped than the Gaussian type spectra) showed also smaller differences in the fatigue strength of both material states (as welded and stress relieved) than it was the case for tests with constant amplitude loading. However, the differences in the fatigue strength for this spectra now again were greater than for the tests with Gaussian type spectra. The lifetime to fracture for both material states is described sufficiently good with the use of the modified damage accumulation theory in the area of less than 2 x 10 high 7 cycles, above this value, the fatigue strength is underestimated for both material states. By detecting the initial crack and controlling the crack propagation life it was found in most cases that the position of the crack propagation life for the "as welded specimens" was larger compare