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Fatigue Strength of Friction Stir WeldedAluminium Profile for Train Car Application
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
2008 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Friction stir welded aluminium alloys are used for many applications in transportation. In theseapplications the material is frequently subject to varying load conditions, making fatigue failure acritical issue. In the scope of this paper, the fatigue performance of friction stir welded profiles ofAl-alloy 6005A has been investigated. A profile that is used for railway car wall side panels waschosen. The profiles were joined together with the friction stir welding method at both sides ofthe profile. 3-point fatigue bending tests were performed for the profiles. Stress ranges givingfailure after 105 to 106 cycles with the stress ratio R=0.1 were used.With FEM simulations critical positions for crack initiation and failure were identified in the parentmetal. These positions were all at narrow radii in the profiles. In fact, the fatigue failures alwaysoccurred at these positions. The maximum stress varied somewhat between the positions. Inspite of this, the cracking and failure took place at six different positions indicating that the profilehad a balanced design.The maximum von Mises stress at the failure positions as determined with FEM was about 50%higher than the corresponding uniaxial fatigue data for the same number of cycles. Thissuggests that the cracks initiate at places with high stresses but propagate into areas with lowerstresses.The FSW joint was a lap-butt joint with a sharp notch (interface between the work pieces) next tothe weld nugget. Since both sides of the profile were welded, such sharp notches appeared onboth sides. In most profiles cracks initiated and propagated form the notch where the centre loadwas placed. However, failure never took place there, i.e. complete fracture was not observed.The direction in which the cracks propagated was perpendicular to the plane of the profiles andperpendicular to the maximum stress direction. On the opposite side to the load position nocracking was observed

Place, publisher, year, edition, pages
TWI , 2008.
Keyword [en]
friction stir welding, aluminium alloy, profile, fatigue, railway car wall side panel
National Category
Manufacturing, Surface and Joining Technology Other Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-49556ISBN: 978-1-903761-06-9 (print)OAI: oai:DiVA.org:kth-49556DiVA: diva2:459823
Conference
7th Int. Symp. on Friction Stir Welding, Awaji Island, Japan,
Note

QC 20120109

Available from: 2012-01-09 Created: 2011-11-28 Last updated: 2017-02-22Bibliographically 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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