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Effective notch stress and critical distance method to estimate the fatigue life of T and overlap friction stir welded joints
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.ORCID iD: 0000-0002-8494-3983
2012 (English)In: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 25, 250-260 p.Article in journal (Refereed) Published
Abstract [en]

The interface notch is a general characteristic of friction stir welded joints and appears in many types of the welds. Indeed interface notch most likely is a location that fatigue failure can occur there. This paper is concerned with the fatigue of friction stir welded joints. In the present paper fatigue of T and over lap joints were modelled base on critical distance method. Two material properties Delta K-th, the fatigue threshold stress intensity factor and Delta sigma(0), the fatigue limit were used in order for estimating the fatigue life at interface location. This is shown that assuming homogeneous material throughout the weld and the base material in FE analysis still can provide a reasonable fatigue prediction for friction stir joints when using critical distance method. This suggests the same procedure can be used for complex component when failure appears in the interface notch. In order to verify it the critical distance prediction method was also used for actual component where the failure occurred in the weld. The predicted fatigue limit deviated only 15% from the experimental result.

Place, publisher, year, edition, pages
2012. Vol. 25, 250-260 p.
Keyword [en]
Fatigue failure, Interface notch, Friction stir welding, Critical distance method
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-92224DOI: 10.1016/j.engfailanal.2012.05.019ISI: 000308770000026Scopus ID: 2-s2.0-84862681128OAI: oai:DiVA.org:kth-92224DiVA: diva2:512804
Note

QC 20121130

Available from: 2012-03-29 Created: 2012-03-29 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Fatigue Assessment of Friction Stir Welded Joints in Aluminium Profiles
Open this publication in new window or tab >>Fatigue Assessment of Friction Stir Welded Joints in Aluminium Profiles
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Friction stir welding (FSW) is a low heat input solid state welding technology. It is often used for fabrication of aluminium alloys in transportation applications including railway, shipbuilding, bridge structures and automotive components. In these applications the material is frequently subject to varying load conditions and fatigue failure is a critical issue. In most cases standard codes and fatigue guidelines for aluminium welded joints address only welded structures with conventional welding methods but not those with FSW procedure. In the scope of this thesis fatigue life assessment of friction stir welded components was performed using theoretical approaches along with finite element method (FEM). The further aim of this study was to generate a basis for standardization of fatigue assessment of friction stir welded joints.

Friction stir welded hollow aluminium panels of alloy 6005A are investigated. The panels are used for train wall sides, train floors, deck and bridges. Each panel is made of several profiles that are joined with the friction stir welding method. Fatigue bending tests were performed for profiles in these panels. Fatigue cracks and failure appeared at notches in the profiles. With FEM simulations critical positions for crack initiation and failure were identified. The method of critical distance was used to analyse and estimate the fatigue life. It was shown that the failure location and fatigue limit could be predicted for both base metal and weld location. Choice of welding procedure (clamping condition) can significantly influence the fatigue life. It was shown that for some panels the critical distance method was not able to explain the failure in the weld. In this case fracture mechanics together with residual stress analysis were used successfully to predict the failure.

Assuming homogeneous material properties throughout the weld and the base material, FEM analysis for T and overlap joints as well can provide a reasonable fatigue prediction. This suggests that the same assumption can be extended to complex components for failure analysis of the friction stir welded joints when using the critical distance method.

Fatigue assessment of friction stir welded joints was also performed using standard codes Eurocode 9 and IIW. Fatigue curves of traditional fusion welded joints were used. The results are in reasonable agreement with experimental data and FEM predictions.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. vii, 45 p.
Keyword
Friction stir welding, Fatigue, Aluminium alloys, Critical distance, Finite element method, Standard codes
National Category
Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:kth:diva-92157 (URN)978-91-7501-291-9 (ISBN)
Public defence
2012-04-26, Sal F3, Lindstedsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20120330Available from: 2012-03-30 Created: 2012-03-27 Last updated: 2012-04-02Bibliographically approved

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Sandström, Rolf

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