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Fatigue strength improvement of welded structures using new low transformation temperature filler materials
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.ORCID iD: 0000-0003-4180-4710
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2013 (English)In: Fatigue Design 2013, International Conference Proceedings, Elsevier, 2013, 192-201 p.Conference paper (Refereed)
Abstract [en]

The results reported in this research study are part of a larger EU RFCS (Research Fund for Coal and Steel) project where the aim is to study the fatigue behavior of improved welds in high strength steels by utilizing different improvement techniques. In this particular study LTT (Low Transformation Temperature) weld filler material have been investigated and their possibility to improve the fatigue strength. The characteristic of these filler material is that they undergo phase transformation at temperature close to room temperature which will reduce the tensile residual stress in the weld and in some cases result in compressive residual stresses. Two different LTT alloy compositions have been developed, with different Ms (Martensite Start) temperatures in order to study the amount of tensile/compressive residual stresses produced by these wires. Welding residual stress measurements were carried out by X-ray diffraction technique. Plates with welded longitudinal attachments were fabricated in 700 MPa and 960 MPa steel grades using different LTT filler materials. These specimens were fatigue tested in constant and variable amplitude loading and the fatigue test results were compared with results from specimen welded with conventional weld filler material.

Place, publisher, year, edition, pages
Elsevier, 2013. 192-201 p.
, Procedia Engineering, ISSN 1877-7058 ; 66
Keyword [en]
Fatigue testing, LTT, Residual stresses, Welded joints
National Category
Vehicle Engineering
URN: urn:nbn:se:kth:diva-147456DOI: 10.1016/j.proeng.2013.12.074ISI: 000338327000019ScopusID: 2-s2.0-84894422734OAI: diva2:735925
5th International Conference on Fatigue Design, Fatigue Design 2013, 27 November 2013 through 28 November 2013, Senlis, France

QC 20140804

Available from: 2014-08-04 Created: 2014-06-27 Last updated: 2015-05-29Bibliographically approved
In thesis
1. Computational weld mechanics: Towards simplified and cost effective FE simulations
Open this publication in new window or tab >>Computational weld mechanics: Towards simplified and cost effective FE simulations
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

It is the demand of the world’s ever increasing energy crisis to reduce fuel consumption wherever possible. One way of meeting this demand is by reducing the weight of a structure by replacing thick plates of low strength steel with thin plates of high strength steel in the structure. Fusion welding process is extensively used in the manufacturing industry, however, despite many advantages different problems such as weld defects, residual stresses and permanent distortions are associated with this process.

Finite element (FE) method has proved itself as an alternative and acceptable tool for prediction of welding residual stresses and distortions. However, the highly nonlinear and transient nature of the welding process makes the FE simulation computationally intensive and complex. Thus, simplified and efficient welding simulations are required so that they can be applied to industrial scale problems.

In this research work an alternative FE simulation approach for the assessment of welding residual stresses, called rapid dumping is developed. This approach proved to be efficient and predicted the residual stress with acceptable accuracy for different small scale welded joints. This approach was further implemented on a large scale welded structures along with other available approaches. It was found that the computational time involved in the welding simulations for large structures using rapid dumping approach can be reduced but at the cost of accuracy of the results.

Furthermore, influence of thermo-mechanical material properties of different steel grades (S355-S960) on welding residual stresses and angular distortion in T-fillet joints is investigated. It is observed that for assessment of residual stresses, except yield stress, all of the thermo-mechanical properties can be considered as constant. For the prediction of angular distortions with acceptable accuracy, heat capacity, yield stress and thermal expansion should be employed as temperature dependent in the welding simulations.

Finally, the influence of two different LTT (Low Transformation Temperature) weld filler material on residual stress state and fatigue strength was investigated. It was observed that a reduction in tensile residual stresses at the weld toe of the joint was observed. Furthermore, at higher R-ratio no significant increase in the fatigue strength was observed . However, at low R-ratio significant  increase in fatigue strength was observed.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. xii, 26 p.
TRITA-AVE, ISSN 1651-7660 ; 2015:32
National Category
Manufacturing, Surface and Joining Technology Vehicle Engineering
Research subject
Vehicle and Maritime Engineering
urn:nbn:se:kth:diva-168174 (URN)978-91-7595-626-8 (ISBN)
Public defence
2015-06-15, D3, Lindstedtsvägen 5, KTH, Stockholm, 09:00 (English)

QC 20150529

Available from: 2015-05-29 Created: 2015-05-27 Last updated: 2015-05-29Bibliographically approved

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Bhatti, Ayjwat AwaisBarsoum, Zuheir
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