Bruchmechanisches Modell zur Ermittlung der Schwingfestigkeit von geschweißten und nichtgeschweißten Proben∗

Uwe Zerbst; M. Madia; J. Eufinger; Thomas Bruder

doi:10.3139/120.110465

Article

Bruchmechanisches Modell zur Ermittlung der Schwingfestigkeit von geschweißten und nichtgeschweißten Proben∗

Uwe Zerbst , M. Madia , J. Eufinger and Thomas Bruder

Published/Copyright: August 22, 2013

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From the journal Materials Testing Volume 55 Issue 7-8

Abstract

Ermüdungsrisse gehen in technischen Materialien in der Regel von Werkstoffdefekten auf oder nahe der Oberfläche aus. Bei Schweißverbindungen können Schweißnahtdefekte, z. B. oberflächennahe Schlackeneinschlüsse die Risseinleitungsphase erheblich verkürzen, so dass der Hauptteil der Lebensdauer auf die Phase der Kurzriss- und zu geringerem Anteil auf die Langrissausbreitung entfällt. Bei nichtgeschweißten Bauteilen aus technischen Werkstoffen starten Ermüdungsrisse häufig an Einschlüssen, oberflächennahen Poren oder anderen Ungänzen. Einerseits ermöglicht dies prinzipiell die Anwendung bruchmechanischer Methoden zur Ermittlung der Schwingfestigkeit, andererseits müssen die Methoden in der Lage sein, spezielle Aspekte des Kurzrisswachstums wie den graduellen Aufbau des Rissschließeffekts und die lokale Rissspitzenplastizität zu erfassen. Im Beitrag werden ein geeignetes analytisches Modell sowie erste Validierungen an Proben aus verschiedenen Aluminiumlegierungen vorgestellt. Der abschließende Teil des Beitrags geht auf Besonderheiten von Schweißverbindungen (Schweißnahtdefekte, Eigenspannungen etc.) im Kontext des vorgestellten Modells ein. Eine Erweiterung des Modells für Schweißverbindungen aus Stahl wird im Rahmen eines kürzlich gestarteten DFG-AiF-Clusterprojekts erfolgen.

Abstract

Fatigue cracks commonly start in technical materials from defects at or near the surface. At welded joints, welding defects, as for instance slag inclusions near the surface, can significantly reduce the crack incubation period in such way the main part of the fatigue life is falling into short crack growth and not into long term crack growth. At non-welded components made of technical materials, fatigue cracks frequently start at inclusions, near-surface pores or other discontinuities. On one hand this entails the application of fracture mechanics procedures in principal. On the other hand, such procedures should enable consideration of specific short crack growth aspects, as for instance the gradual build-up of the crack stop effect and the local crack tip plasticity. In the present contribution, a suitable analytical model as well as first validations at specimens from various aluminium alloys are highlighted. In the final part, specialties associated to welds (weld defects, residual stresses, ….) are presented in the context of the established model. An extension of the model for steel welds will be developed within the briefly started DFG-AiF Cluster Project.

∗

Dieser Beitrag erschien bereits im DVM-Bericht Betriebsfestigkeit 2012

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Online erschienen: 2013-08-22

Erschienen im Druck: 2013-07-15

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https://doi.org/10.3139/120.110465