Druckmittelspannungen
-
Jörg Rörup
Kurzfassung
Zur Untersuchung des Einflusses der Mittelspannungen auf das Schwingfestigkeitsverhalten wurden Proben einer axial beanspruchten Platte mit aufgeschweißter Längssteife untersucht. Es zeigte sich, dass das Niveau der schweißinduzierten Eigenspannungen einen entscheidenden Einfluss auf die erreichte Lebensdauer hat. Ein Zugeigenspannungsfeld, welches die Rissspitze vor sich her schiebt und mit zunehmender Risslänge an Größe und Intensität verliert, ermöglicht ein Fortschreiten des Risses in Bereiche, in denen Druckeigenspannungen aus dem Schweißprozess vorliegen. Mittels nicht-linearer Strukturanalysen mit der Methode der Finiten Elemente wurden Schließeffekte für einen Durchriss erfasst. Dabei konnte die in den Versuchen ermittelte Rissverzögerung durch die berechnete Rissfortschrittskurve in zufrieden stellender Weise abgebildet werden.
Abstract
It is widely accepted that due to high residual tensile stresses the fatigue strength of welded joints is essentially independent of the mean load-induced stress. On the other hand, theoretical considerations of the stable crack growth as well as experience from ship operation indicate a positive effect of mean compressive stresses on the fatigue life. In order to further investigate this effect, fatigue tests with specimens of longitudinal stiffener-type have been carried out under constant amplitude load with mean compressive stress. The level of the residual stresses was shown to have a great influence on the fatigue life under compressive cyclic load. The fatigue life determined for a series of tests with high residual stress level was around the factor 2 below that of a series of tests with a residual stress level obtained from usual welding conditions. The shift of the mean stress into the compression range caused an increase of the fatigue life. With a constant crack initiation life for different stress ratios, the increase in total fatigue life is caused by the crack propagation phase. The welding-induced residual stresses and the load-induced residual stresses at the crack tip were measured. Due to the tensile residual stresses measured at the weld toe, the crack initiation under compressive cyclic loads can be explained. The tensile residual stresses determined at the crack tip are the reason for the fact that the crack can propagate into areas of the specimen where compressive residual stresses from the welding process are present. The crack moves thereby a field of tensile residual stresses in front of itself, which loses its size and intensity with increasing crack length. With the finite element method and consideration of the residual stresses computed before, a nonlinear structural analysis was performed for the assessment of the closure effects of a through-thickness crack. The determination of the effective stress intensity factor for crack lengths from 30 to 90 mm allowed an estimation of the fatigue life under constant amplitude loads with a stress ratio of R=—∞. Two differently high load levels and different residual stress conditions were considered with the model using plane strain condition. The crack deceleration determined in fatigue tests was estimated in all cases by the computed crack propagation curve in satisfactory way.
Literatur
1 Rörup, J.; Petershagen, H.: The effect of compression mean stresses on the fatigue strength of welded structures. In: Welding in the world, Vol. 44, n° 5, International Institute of Welding, Pergamon Press, Oxford2000Suche in Google Scholar
2 Elber, W.: The Significance of Fatigue Crack Closure. In: Damage Tolerance in Aircraft Structures, ASTM STP 468, American Society for Testing and Materials, Philadelphia1970Suche in Google Scholar
3 Schwalbe, K.-H.: Bruchmechanik metallischer Werkstoffe, Carl Hanser Verlag, München1980Suche in Google Scholar
4 Lombera, G.; Sendrai, A.; de Vedia, L. A.: Computational and experimental determination of temperature distribution in arc welding, in: Recent trends in welding science and technology TWR’89, S. 55–58, ASM-International, OhioSuche in Google Scholar
5 Guidance on methods for assessing the acceptability of flaws in fusion welded structures, BSI PD 6493, British Standards Institution, London 1991Suche in Google Scholar
6 Mikkola, T. P. J.: Numerical analysis methods of surface cracks, VTT Publications 119, Technical Research Centre of Finnland, Espoo1989Suche in Google Scholar
7 Rörup, J.: Einfluss von Druckmittelspannungen auf die Betriebsfestigkeit von geschweißten Schiffskonstruktionen, Technische Universität Hamburg-Harburg Schriftenreihe Schiffbau, Bericht619, Hamburg 2003Suche in Google Scholar
© 2004, Carl Hanser Verlag, München
Artikel in diesem Heft
- Inhalt/Contents
- Inhalt
- Kurzbeiträge
- Erfolgreiches Networking
- Fachbeiträge/Technical Contributions
- Druckmittelspannungen
- Laserstrahl-Auftragsschweißen
- Niedrigspannungsbrüche
- Characterisation of highly porous glass ceramic scaffolds
- Physical features of pure metals
- Neuere Schwingfestigkeitsartikel
- Kurzbeiträge
- Europäisches Forschungsprojekt für die effektivere Nutzung von Eisenbahnbrücken
- Vorschau/Preview
- Vorschau
Artikel in diesem Heft
- Inhalt/Contents
- Inhalt
- Kurzbeiträge
- Erfolgreiches Networking
- Fachbeiträge/Technical Contributions
- Druckmittelspannungen
- Laserstrahl-Auftragsschweißen
- Niedrigspannungsbrüche
- Characterisation of highly porous glass ceramic scaffolds
- Physical features of pure metals
- Neuere Schwingfestigkeitsartikel
- Kurzbeiträge
- Europäisches Forschungsprojekt für die effektivere Nutzung von Eisenbahnbrücken
- Vorschau/Preview
- Vorschau
