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The multiaxial weld root fatigue of butt welded joints subjected to uniaxial loading
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
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
2016 (English)In: Fatigue & Fracture of Engineering Materials & Structures, ISSN 8756-758X, E-ISSN 1460-2695, Vol. 39, no 10, 1281-1298 p.Article in journal (Refereed) Published
Resource type
Text
Abstract [en]

In this study, the fatigue strength of inclined butt welds subjected to a proportional multiaxial stress state generated by uniaxial loading is studied in nominal and local stress concepts. The local methodologies studied included principal stress hypothesis, von Mises stress hypothesis and modified Wöhler curve method. Nominal methodologies included modified Gough-Pollard interaction equation, the design equation in Eurocode3 and the interaction equation in DNV standard. Results are evaluated along with data published in relevant literature. It is observed that both local and nominal stress assessment methods are able to estimate multiaxial fatigue strength. No obvious difference in fatigue strength is observed in the nominal stress concept, but the notch stress concept is able to capture a decrease in fatigue strength in shear-dominated joints. It is concluded that modified Wöhler curve method is a suitable tool for the evaluation of fatigue strength in joints dominated by both normal and shear stresses.

Place, publisher, year, edition, pages
Blackwell Publishing, 2016. Vol. 39, no 10, 1281-1298 p.
Keyword [en]
Fatigue strength, Multiaxial stress ratio, Multiaxial stress state, Weld inclination, Welded joints, Butt welding, Shear stress, Welding, Welds, Interaction equations, Local stress concept, Multi-axial fatigue, Multiaxial stress, Nominal stress concept, Normal and shear stress, Stress analysis
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-186757DOI: 10.1111/ffe.12444ISI: 000383726900009Scopus ID: 2-s2.0-84962688225OAI: oai:DiVA.org:kth-186757DiVA: diva2:931630
Note

QC 20160530

Available from: 2016-05-30 Created: 2016-05-13 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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