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International Journal of Fracture

, Volume 11, Issue 2, pp 221–243 | Cite as

An analysis of fatigue cracks in fillet welded joints

  • S. J. Maddox
Article

Abstract

In most of the lower fatigue strength welded joints failure occurs by the propagation of a semi-elliptical surface crack which initiates at the weld toe. In order to analyse the progress of these cracks using fracture mechanics techniques, the solution for the stress intensity factor, K, is required. Fatigue cracks in most welded joints adopt shapes which give low a/2c values (up to approximately 0.3) while solutions in the literature are more applicable to a/2c values close to 0.5. Therefore, results in the literature were used to estimate the stress intensity factor for cracks with low a/2c values. Furthermore, the effect of the weld stress concentration factor was incorporated in the solution. The accuracy of the resulting solution was confirmed by using it to determine ΔK values of weld toe cracks for which crack propagation data were available. The results agreed with the expected da/dN vs. ΔK scatterband obtained from centre-notched specimens.

Keywords

Fatigue Fatigue Crack Stress Intensity Factor Fatigue Strength Stress Concentration Factor 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Résumé

Dans la plupart des soudures ayant une résistance à la fatigue moins élevée, la défaillance survient à cause de la propagation d'une fissure de surface semi-elliptique commençant à l'endroit de transition de la soudure. Pour l'analyse de la progression de telles fissures à l'aide de méthodes de la mécanique de la rupture, on a besoin de la solution pour le facteur de l'effort de tension, K. Dans presque toutes les soudures, les fissures de fatigue prennent des formes qui donnent de basses valeurs a/2c (jusqu'à près de 0,3), alors que les solutions figurant dans les ouvrages de métier s'appliquent plutôt à des valeurs a/2c de près de 0,5. Pour cette raison, on a utilisé de résultats figurant dans les ouvrages de métier pour évaluer le facteur de l'effort de tension pour des fissures ayant de basses valeurs a/2c. De plus, tenant compte de l'effet du facteur de la concentration des tensions, ce facteur a été incorporé dans la solution. On a confirmé l'exactitude de la solution résultante, en l'utilisant pour la détermination des valeurs ΔK de fissures situées à l'endroit de transition pour lesquelles on possédait des données de propagation. Les résultats s'accordaient avec la bande de dispersion prévue, da/dN vs. ΔK, obtenue à partir des éprouvettes entaillées au centre.

Zusammenfassung

In den meisten der Schweißverbindungen von niedrigerer Dauerfestigkeit stellt sich Versagen durch die Ausbreitung eines halbelliptischen, am Nahtübergang entstandenen, Oberflächenrisses ein. Um den Verlauf solcher Risse unter Anwendung von bruchmechanischen Methoden analysieren zu können, ist die Lösung des Spannungsgrößenfaktors, K, notwendig. Ermüdungsrisse nehmen in den meisten Schweißverbindungen Formen an, die zu niedrigen a/2c-Werten (von bis zu etwa 0,3) führen, während die in der Schweißliteratur angegebenen Lösungen mehr auf a/2c-Werte nahe bei 0,5 zu beziehen sind. Daher wurden Resultate aus der Schweißliteratur dazu benutzt, um den Spannungsgrößenfaktor für Risse mit niedrigen a/2c-Werten zu errechnen. Sodann wurde die Wirkung des Schweißspannungskonzentrations-faktors in die Lösung miteingeschlossen. Die Genauigkeit der erzielten Lösung bestätigte man, indem man sie zur Bestimmung von ΔK-Werten von Nahtübergangsrissen, für welche Rißausbreitungsdaten vorhanden waren, benutzte. Die Resultate stimmten mit dem erwarteten da/dN vs. ΔK-Streuungsband der mittegekerbten Versuchsproben überein.

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Copyright information

© Noordhoff International Publishing 1975

Authors and Affiliations

  • S. J. Maddox

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