Fatigue damage of weld seams with and without postweld treatment under multiaxial loading*: Simulations based on a fracture mechanics approach

Klemens Rother; Tomas Nicak; Eckart Weiß; Jürgen Rudolph; Benedikt Postberg

doi:10.3139/120.100715

Article

Fatigue damage of weld seams with and without postweld treatment under multiaxial loading*

Simulations based on a fracture mechanics approach

Klemens Rother , Tomas Nicak , Eckart Weiß , Jürgen Rudolph and Benedikt Postberg

Published/Copyright: May 28, 2013

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From the journal Materials Testing Volume 48 Issue 3

Abstract

The service durability of weld seams is one of the most challenging problems of component fatigue. Hereby, the complexity is due to several peculiarities of welded structures: the detailed weld seam geometry with macroscopic and microscopic notch effects and/or defects, the properties of the welded material, residual stresses and multiaxial proportional or non-proportional loading conditions. Non-experimental approaches to design against fatigue have to account for the difference between weld seams with and without post-weld treatment as well as proportional and non-proportional loading. The application of fracture mechanics parameters allows for a more realistic description of damage progression. This paper is intended to explain possible design approaches based on numerical fracture mechanics and their combination with stress and strain based approaches using clear and classified damage criteria (engineering crack size, fracture). All numerical approaches are presented with special regard to complexity and modeling requirements from the point of view of the practicing design engineer. Non-proportional loading is considered by the identification of a damage critical plane which requires special post-processing routines within the numerical analysis. Again, the question of practicability is raised.

Kurzfassung

Die Betriebsfestigkeit von Schweißverbindungen stellt eine der größten Herausforderungen innerhalb des Nachweises der Ermüdungsfestigkeit von technischen Komponenten dar. Die Komplexität des Problems ist dabei auf einige Besonderheiten geschweißter Strukturen zurückzuführen: die Schweißnahtfeingeometrie mit makroskopischen und mikroskopischen Kerb- und Risseffekten, die Eigenschaften des geschweißten Materials im versagenskritischen Bereich, Schweißeigenspannungen und mehrachsig proportionale und nichtproportionale Beanspruchungsverhältnisse. Nichtexperimentelle Konzepte des Ermüdungsfestigkeitsnachweises müssen den Unterschieden zwischen nicht nachbearbeiteten und nachbearbeiteten Schweißnähten sowie zwischen proportionalen und nichtproportionalen Beanspruchungsverhältnissen in methodisch adäquater Art und Weise Rechnung tragen. Die Anwendung bruchmechanischer Parameter erlaubt eine realistischere Beschreibung des Schädigungsfortschrittes. Im Rahmen des Beitrages werden mögliche bruchmechanische Ansätze und ihre Kombination mit spannungs- und dehnungsbasierten Methoden diskutiert, wobei klare und klassifizierte Schädigungskriterien (Technischer Anriss, Bruch) zu Grunde liegen. Sämtliche numerischen Ansätze werden unter spezieller Berücksichtigung ihrer Komplexität und modellierungstechnischer Anforderungen vom Standpunkt des in der Berechnungspraxis tätigen Ingenieurs betrachtet und bewertet. Nichtproportionale Beanspruchungsverhältnisse werden durch die Identifikation einer versagenskritischen Ebene berücksichtigt, wofür spezielle Postprozessorroutinen innerhalb der numerischen Analyse erforderlich sind. Hierbei wird wiederum die Frage der Praxistauglichkeit aufgeworfen.

Dr.-Ing. Klemens Rother, born 1962, studied from 1981 to 1985 mechanical engineering at the University of Applied Sciences in Munich. From 1985 to 1986 he was Fulbrigth grant at Michigan State University East Lansing (Mechanics). 2005, he got PhD from Dortmund University on multiaxial fatigue under nonproportional loading. From 1986 to 1993 he was head of structural integrity group at Thyssen Industry AG Henschel Transrapid. 1993 he changed to Münchner Medizin Mechanik GmbH, where he led the design department. Since 1995 he is head of Consulting Division at CADFEM GmbH, Grafing.

Dipl.-Ing. Tomas Nicak, born 1977 studied mechanical engineering at the University of Technology Brno. 2000 he became scientific assistant at the University of Technology Brno, where he worked on explicit dynamic problems. From 2002 to 2004 he was scientific assistant at Dortmund University where he investigated at fatigue and fracture mechanic. Since 2004 he is at Framatome ANP GmbH in the department material engineering and testing and failure analysis.

Prof. Dr.-Ing. habil. Eckart Weiß habilitat ed at the Magdeburg University “Otto von Guericke”. Since 1991 he is Professor at the Dortmund University and Head of the working group Pressure Vessel Technology.

Dr.-Ing. habil. Jürgen Rudolph, born 1966 studied from 1987–1992 chemical engineering at the Technical University of Magdeburg. From 1992 to 2005 he worked at the University of Dortmund, Department of Biochemical and Chemical Engineering. 1997 he got PhD from Dortmund University on fatigue of pressure vessel components. 2004 Postdoctorate (German Habilitation) on fatigue of welded joints. 2001, International Internship at Lehigh University, Bethlehem, USA (Mechanical Engineering Department). From 1992 to 2005 he was assistent and senior engineer at Dortmund University. Since 2005 he is specialist of strength analysis at TÜV Nord EnSys Hannover GmbH & Co. KG.

Dr.-Ing. Benedikt Postberg, born 1971 studied chemical engineering at the University of Dortmund. From 1997 to 2000 he did his PhD at the Dortmund University on ratcheting. Since 2000 he is manager at Wacker Chemie AG, Munich.

Contribution to the 7th International Conference on Biaxial/Multiaxial Fatigue and Fracture (7ICBMFF)

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Published Online: 2013-05-28

Published in Print: 2006-03-01

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https://doi.org/10.3139/120.100715