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Behavior of compressive residual stresses in high strength steel welds induced by high frequency mechanical impact treatment
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
Department of Applied Mechanics, Aalto University, Finland.
2014 (English)In: Journal of Pressure Vessel Technology-Transactions of the ASME, ISSN 0094-9930, E-ISSN 1528-8978, Vol. 136, no 4, 041404- p.Article in journal (Refereed) Published
Abstract [en]

Residual stress state plays an important role in the fatigue life of welded structures. The effect can be beneficial or detrimental, depending on the nature of residual stresses. High frequency mechanical impact (HFMI) treatment is a postweld fatigue improvement technique for welded joints. In this research work the behavior of compressive residual stresses induced in welded joints in high strength steels (HSS) by HFMI treatment has been investigated. Longitudinal nonload carrying attachments in HSS are tested with constant amplitude (CA) and variable amplitude (VA) fatigue loading. Stress concentration factors have been calculated using finite element analysis (FEA). Residual stresses have been measured at different cycles during fatigue testing using X-ray diffraction technique. It is observed that the induced residual stresses are quite stable with some relaxation in CA and VA loading. The overloads in VA loading seem to be more detrimental. Relaxation of residual stresses is more obvious in VA tests.

Place, publisher, year, edition, pages
2014. Vol. 136, no 4, 041404- p.
Keyword [en]
Compressive residual stress, Fatigue improvement, Mechanical impacts, Relaxation of residual stress, Residual stress state, Stress concentration factors, Variable amplitudes, X-ray diffraction techniques
National Category
Other Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-145381DOI: 10.1115/1.4026651ISI: 000338507600009Scopus ID: 2-s2.0-84898064883OAI: oai:DiVA.org:kth-145381DiVA: diva2:718210
Note

QC 20140520

Available from: 2014-05-20 Created: 2014-05-19 Last updated: 2017-12-05Bibliographically 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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