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Residual Stress Prediction and Relaxation in Welded Tubular Joint
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.ORCID iD: 0000-0003-4180-4710
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.

Place, publisher, year, edition, pages
2007. Vol. 51, no 1/2, 23-30 p.
Keyword [en]
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: urn:nbn:se:kth:diva-8173Scopus ID: 2-s2.0-34247234147OAI: oai:DiVA.org:kth-8173DiVA: diva2:13425
Note
QC 20100702Available from: 2008-04-03 Created: 2008-04-03 Last updated: 2010-11-09Bibliographically approved
In thesis
1. Residual Stress Analysis and Fatigue Assessment of Welded Steel Structures
Open this publication in new window or tab >>Residual Stress Analysis and Fatigue Assessment of Welded Steel Structures
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This doctoral thesis is concerned with fatigue life 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 life.

The work that is reported in this doctoral thesis is part results of the Nordic R&D project QFAB (Quality and Cost of Fabricated Advanced Welded Structures) and the Swedish R&D project LOST (Light Optimized Welded Structures). One of the main objectives is to compare different welding processes for the fatigue performance, weld quality and gain understanding of the weld defects, their appearance in different welding processes and their effect 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 the weld 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.

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 were measured.

Further fatigue testing, weld defect assessment and residual stress and local weld geometry measurements were carried out on joints welded with flux cored and metal cored arc wires. Two-and three dimensional LEFM crack growth analysis were carried out in order to predict the influence of weld defects, local weld geometry and residual stresses.

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 multi-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.

A two dimensional finite element welding simulation procedure was developed in order to predict welding residual stress. The predicted residual stresses were used together with a developed 2D LEFM subroutine to predict the fatigue life, crack path and the effect of residual stresses on weld root defects. The developed simulation subroutines were validated with results found in the literature.

Residual stresses measurement, two-and three dimensional welding simulations were carried out in fillet welded joints in order to study the three dimensional effects of the welding process, boundary conditions and modelling technique on the formation of residual stresses.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. iv, 36 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2008:11
Keyword
fatigue failure, welding, weld defects, welded joints, stress concentration, residual stress, linear elastic fracture mechanics, welding simulation, finite element analysis, fatigue crack growth.
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-4687 (URN)
Public defence
2008-04-25, E1, E-huset, KTH, Lindstedtsvägen 3, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100706Available from: 2008-04-03 Created: 2008-04-03 Last updated: 2011-04-12Bibliographically approved
2. Residual Stress Analysis and Fatigue of Welded Structures
Open this publication in new window or tab >>Residual Stress Analysis and Fatigue of Welded Structures
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
welding, fatigue, finite element analysis, fracture mechanics, residual stresses
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-3872 (URN)91-7178-264-8 (ISBN)
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

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Barsoum, Zuheir

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