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Residual Stress Analysis and Fatigue of Welded Structures
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.ORCID iD: 0000-0003-4180-4710
2006 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

This licentiate thesis is generally concerned with the fatigue of welded structures. Several topics related to fatigue of welded structures are treated such as; weld defects and their influence on fatigue performance of welded structures, fatigue life prediction using LEFM (Linear Elastic Fracture Mechanics), fatigue testing, welding simulation, residual stress prediction and measurement and their influence on fatigue. The work that is reported in this thesis is a part result of a Nordic research project QFAB (Quality and Cost of Fabricated Advanced Welded Structures). One of the main objectives is to compare different welding processes in fatigue performance, weld quality and gain understanding of the weld defects, their appearance in different welding processes and their influence on fatigue life. Another main objective is to study welding residual stresses and their effect on fatigue. The design rules are in some cases conservative and especially on root sides the knowledge about the residual stress field may improve the life prediction. The aim is to develop simplified procedures for analysis of residual stresses, their relaxation and influence on fatigue life. In one study fatigue testing of Hybrid Nd: YAG laser/MAG and MAG welded (tandem arc solid wire, flux cored wire, tandem flux cored wire) non-load carrying cruciform joints was carried out. Four batches were produced, tested and the results were compared. The local weld geometry of the cruciform welded joints was measured and analyzed. Residual stress measurement was carried out close to the toe region using X-ray diffraction. Weld defects, in most cases cold laps, in the cracked specimens was measured. Residual stresses in multi-pass welded tube-to-plates were studied for two different tubular joint configurations; a three-pass single-U weld groove for maximum weld penetration and a two-pass fillet (no groove) welded tube-to-plates for minimum weld penetration. Torsion fatigue tests were performed in order to study crack propagation from the weld root. Mode III propagation from the lower and upper weld toe on the same tubular joints was also studied. Some tubes were stress relieved (PWHT) and some were fatigue tested with internal static pressure. A three dimensional finite element welding simulation of the 3 pass welded tubular joint was carried out. The calculated temperatures in the transient thermal analysis were compared with measured temperatures. The FE predicted residual stresses in the as-welded conditions were verified with hole drilling strain gage measurements. The residual stresses were used as internal stresses in the finite element model for the torsion fatigue simulation in order to study the cycle by cycle relaxation of the residual stresses in constant amplitude torsion loading.

Place, publisher, year, edition, pages
Stockholm: Farkost och flyg , 2006. , iii, 21 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2006:02
Keyword [en]
welding, fatigue, finite element analysis, fracture mechanics, residual stresses
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-3872ISBN: 91-7178-264-8 (print)OAI: oai:DiVA.org:kth-3872DiVA: diva2:9820
Presentation
2006-03-01, S40, Farkost o Flyg, teknikringen 8, stockholm, 00:00
Opponent
Supervisors
Note
QC 20101109Available from: 2006-03-13 Created: 2006-03-13 Last updated: 2010-11-09Bibliographically approved
List of papers
1. Fatigue Assessment of Cruciform Joints Welded with Different Methods
Open this publication in new window or tab >>Fatigue Assessment of Cruciform Joints Welded with Different Methods
2006 (English)In: Steel Research International, ISSN 1611-3683, Vol. 77, no 12, 882-888 p.Article in journal (Refereed) Published
Abstract [en]

The advantages of the relatively new laser welding method are low welding distortions and high productivity, and it opens new opportunities for welding of steel structures in the automotive and heavy machinery industries. There is a need for understanding the fatigue strength and to develop fatigue design curves for laser welded joints. In this paper fatigue testing and weld quality of Hybrid Nd: YAG laser/MAG and MAG welded non-load carrying cruciform joints is examined. Four batches were produced, tested and the results were compared. The local weld geometry of the cruciform welded joints was measured and analysed. The measured parameters were used to calculate the stress concentration factors by implementing FE-models, in order to anticipate the influence of size of weld geometrical parameters on the stress concentrations. Residual stress measurement was carried out close to the toe region using the X-ray diffraction method and weld defects (cold laps) in the cracked specimens was measured.

Keyword
fatigue life; stress concentration; welds defects; residual stress; and laser welding
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-8170 (URN)000243162500006 ()2-s2.0-33846689914 (Scopus ID)
Note

QC 20100702. Original title "Assessment of Cruciform Joints Welded with Different Methods"

Available from: 2008-04-03 Created: 2008-04-03 Last updated: 2014-12-16Bibliographically approved
2. Residual Stress Analysis and Fatigue of Multi-pass Welded Tubular Structures
Open this publication in new window or tab >>Residual Stress Analysis and Fatigue of Multi-pass Welded Tubular Structures
2008 (English)In: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 15, no 7, 863-874 p.Article in journal (Refereed) Published
Abstract [en]

The purpose of this study is to investigate the residual stresses near the weld root and the weld toe for multi-pass welded tube-to-plates. Two different tubular joint configurations were studied; a three-pass single-U weld groove for maximum weld penetration and a two-pass fillet (no groove) welded tube-to-plates for minimum weld penetration. A 2D axi-symmetric finite element model was developed to calculate the temperature distribution, HAZ, penetration depth and the residual stress distribution for the sequentially coupled thermo-mechanical analysis. The calculated residual stresses was compared with experimental results and showed qualitatively good agreement. Torsion fatigue tests were performed in order to study crack propagation from the weld root, lower and upper weld toe in mode III. Some of the tube structures were loaded with a static internal pressure in order to separate the root crack and initiate the crack growth in mode III. Another batch was PWHT and fatigue tested, in order to study the influence of residual stresses.

Keyword
welding simulation; residual stresses; tubular joints; fatigue; fracture mechanics; CRACK-GROWTH; MODE; DEFORMATIONS; SIMULATION; DEFECTS; JOINT
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-8172 (URN)10.1016/j.engfailanal.2007.11.016 (DOI)000256631600007 ()2-s2.0-41849142003 (Scopus ID)
Note
QC 20100702Available from: 2008-04-03 Created: 2008-04-03 Last updated: 2017-12-14Bibliographically approved
3. Residual Stress Prediction and Relaxation in Welded Tubular Joint
Open this publication in new window or tab >>Residual Stress Prediction and Relaxation in Welded Tubular Joint
2007 (English)In: Welding in the World, ISSN 0043-2288, Vol. 51, no 1/2, 23-30 p.Article in journal (Refereed) Published
Abstract [en]

In this paper a three-dimensional welding simulation was carried out in the FE software ANSYS in order to predicttransient temperatures and the residual stresses in a three-pass welded tubular joint structure. The thermal analysisand the moving heat source were verified with temperature measurements, and the computed residual stresseswere verified with hole drilling measurements. The calculated and measured temperatures were in good agreement,and the computed residual stresses were in qualitatively good agreement with the experimental results. Residual stressrelaxation analyses were carried out with similar load as in earlier fatigue testing on the same tubular joint structure.The FE residual stress relaxation analysis showed a small amount of relaxation early in the fatigue life.

Keyword
Computation; Fatigue life; Finite element analysis; Measurement; Prediction; Reference lists; Residual stresses; Simulating; Stress distribution; Stress relaxation; Tubular constructions
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-8173 (URN)2-s2.0-34247234147 (Scopus ID)
Note
QC 20100702Available from: 2008-04-03 Created: 2008-04-03 Last updated: 2010-11-09Bibliographically approved

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