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Ultimate strength and failure modes for fillet welds in high strength steels
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.ORCID iD: 0000-0003-4180-4710
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
2012 (English)In: Materials and Design, ISSN 0261-3069, Vol. 40, 36-42 p.Article in journal (Refereed) Published
Abstract [en]

A study has been carried out on the effect of strength mismatch in weld metal and penetration ratio on the ultimate strength capacity of fillet welds and their failure modes. The ultimate strength capacity evaluated with nonlinear Finite Element Analysis (FEA) and testing is compared with the ultimate strength capacity predicted by standards: Eurocode3, BSK 07 (Boverkets handbok om StalKonstruktioner) and AWS (American Welding Society) D1.1 Structural welding code-Steel. Test results are used to establish correct material properties, to be input into the finite element model. A criterion for selection of consumables has been developed, when two different grades of high strength steels are to be joined. The results show that fully penetrated joint with under-matched filler material is more ductile and the ultimate strength capacity of base plate can be achieved. It is observed that joints with under-matched filler material are more sensitive to penetration ratio. The test data correlates reasonably well to the results predicted by FEA software and design codes. It is also concluded that joint preparation has an effect on the ultimate strength capacity of the joint.

Place, publisher, year, edition, pages
2012. Vol. 40, 36-42 p.
Keyword [en]
fillers, finite element method, high strength steel, standards, steel testing
National Category
Vehicle Engineering
Identifiers
URN: urn:nbn:se:kth:diva-98313DOI: 10.1016/j.matdes.2012.03.048ISI: 000304545000004Scopus ID: 2-s2.0-84859648579OAI: oai:DiVA.org:kth-98313DiVA: diva2:536922
Note
QC 20120625Available from: 2012-06-25 Created: 2012-06-25 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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Barsoum, Zuheir

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