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Residual stresses in welded components following post-weld treatment methods
Stresstech Oy.
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
Stresstech Oy.
2013 (English)In: Procedia Engineering, Elsevier, 2013, 181-191 p.Conference paper, Published paper (Refereed)
Abstract [en]

Weld seam is the weakest point of the structure. Weld defects, weld geometry such as toe radius, and residual stresses, which are typically tensile in the critical area, weaken the fatigue strength of the weld seam. These factors become more important with the welding of high strength steels (HSS) because structures containing welded seams loose the benefit from the strength of the steel. The weld seam fatigue strength can be improved locally with several different methods. In this paper residual stresses of the weld area and their modifications for improving the fatigue strength are discussed. The residual stresses of the toe area are changed from tensile up to compressive stresses, which are known to improve fatigue strength, with several methods. High tensile stresses can be relaxed mechanically or thermally as postweld heat treatment. Mechanical treatments are more common especially in large structures. Typical mechanical methods are burr grinding, TIG remelting, hammer peening and needle peeing. A new method is laser re-melting method. All these methods also change the geometry of the weld toe by improving it. This paper concentrates to needle peening (high frequency mechanical impact, HFMI), and presents some results from laser remelting tests. Both surface measurements and depth distributions of stress measured by X-ray diffraction (XRD) method are presented.

Place, publisher, year, edition, pages
Elsevier, 2013. 181-191 p.
Series
Procedia Engineering, ISSN 1877-7058 ; 66
Keyword [en]
Fatigue strenght improvement, HFMI, High stregnth steel, Residual stress, Welding
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-137313DOI: 10.1016/j.proeng.2013.12.073ISI: 000338327000018Scopus ID: 2-s2.0-84894490402OAI: oai:DiVA.org:kth-137313DiVA: diva2:678709
Conference
5th International Conference on Fatigue Design, Fatigue Design 2013; Senlis; France; 27 November 2013 through 28 November 2013
Note

QC 20140107

Available from: 2013-12-12 Created: 2013-12-12 Last updated: 2017-02-03Bibliographically approved
In thesis
1. Static and fatigue analyses of welded steel structures: some aspects towards lightweight design
Open this publication in new window or tab >>Static and fatigue analyses of welded steel structures: some aspects towards lightweight design
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The objectives of this thesis comprise of overcoming the challenges in designing lightweight welded structures such as material selection, choice of fatigue design methods, and increased performance by using improvement techniques. Material selection of welded joints is dependent on the filler and base material strengths. Partially and fully penetrated cruciform and butt welded joints were designed in under-matching, matching, and over-matching filler materials. Base material steel grades were S600MC, S700MC, and S960. Current design rules are developed for welds in steel up to yield strength of 700MPa. Therefore, design rules in Eurocode3, AWS d1.1, and BSK 07 were verified and recommendations for developing design rules for designing welded joints in S960 were concluded. Numerical methodology for estimating static strength of welded joints by simulating heat affected zone was also developed.

Another objective of the thesis work was to overcome the challenges in selection of fatigue design methods. The available design curves in standards are developed for uniaxial stress states, however, in real life the welds in mechanical structures are subjected to complex multiaxial stress states. Furthermore; weld toe failures are frequently investigated, weld root failures are seldom investigated. Therefore, in this work the multiaxial fatigue strength of welded joints failing at the weld root was assessed using experiments and various nominal and local stress based approaches. Butt welded joints with different weld seam inclinations with respect to applied uniaxial loading were designed to assess the root fatigue strength in higher multiaxial stress ratio regime. The fatigue strength of multi-pass tube-to-plate welded joints subjected to internal pressure only and combined internal pressure and torsion in and 90° out of phase loading was also investigated. Test data generated in this thesis was evaluated together with the test data collected from literature.

Last objective of the thesis included investigation of the increased performance in fatigue strength by post weld treatment methods such as HFMI. The behavior of residual stresses induced due to HFMI treatment during fatigue loading is studied. Numerical residual stress estimations and residual stress relaxation models are developed and the effect of various HFMI treatment process parameters and steel grade on the induced residual stress state is investigated. Specimens studied were non load carrying longitudinal attachments and simple plates. Residual stresses in both test specimens were measured using X-ray diffraction technique.

Place, publisher, year, edition, pages
Stockholm: KTH School of engineering sciences, 2017. 33 p.
Series
TRITA-AVE, ISSN 1651-7660 ; 2017:04
Keyword
Fatigue strength, welded joints, static strength, high strength steel
National Category
Vehicle Engineering Aerospace Engineering
Research subject
Vehicle and Maritime Engineering; Aerospace Engineering
Identifiers
urn:nbn:se:kth:diva-200829 (URN)978-91-7729-270-8 (ISBN)
Public defence
2017-04-07, Sal F3, Lindstedsvägen 26, Stockholm, 09:00 (English)
Opponent
Supervisors
Note

QC 20170206

Available from: 2017-02-06 Created: 2017-02-03 Last updated: 2017-02-06Bibliographically approved

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