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Fatigue Assessment and LEFM Analysis of Cruciform Joints Fabricated with Different Welding Processes
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.ORCID iD: 0000-0003-4180-4710
Volvo CE HL Divisions.
2008 (English)In: Welding in the World, ISSN 0043-2288, Vol. 52, no 7-8, 93-105 p.Article in journal (Refereed) Published
Abstract [en]

In this study fatigue testing and defect assessment were carried out on specimens welded with robotic and manualwelding using fl ux cored (FCAW) and metal cored (MCAW) fi ller materials in order to study the effect of the weldingmethod on the fatigue strength and weld quality. Thirteen different batches were investigated of which two wasshot peened before fatigue testing. The local weld geometry was measured for all the specimens before testing.The specimens welded with fl ux cored weld wire showed the best fatigue strength, small defects and low residualstresses. Large scatter in the fatigue data is observed, especially when manual welding is employed. The few largestdefects were removed by the shot peening process, although small defects survived. This led to a smaller scatterin fatigue live for the shot peened specimens. Linear elastic fracture mechanics, LEFM, was employed for analysisof the fatigue test results. The fatigue life predictions using a 2D LEFM FE-model for simulating a continuous coldlap defect along the weld toe showed a qualitative agreement with the fatigue test results. The 2D analysis showedthat a continuous cold lap defect should be no more than 0.5 mm deep in order to comply with the requirement offatigue lives for normal weld quality according to the IIW design rules. For larger defects (> 0.8 mm) an increased toeradius will have a small effect on the fatigue strength. A 3D LEFM analysis of crack growth from a spatter-inducedcold lap defect was also carried out. This showed similar trends in crack growth compared to the 2D analysis ofa continuous cold lap, although the spatter-induced cold lap defect (semi-elliptical) had a longer fatigue life (x2.7),and hence is less dangerous from a fatigue point of view.

Place, publisher, year, edition, pages
2008. Vol. 52, no 7-8, 93-105 p.
Keyword [en]
Arc welding; Defects; Fatigue tests; Fracture mechanics; Mechanical tests; Reference lists; Residual stresses; Stress distribution
National Category
Engineering and Technology
URN: urn:nbn:se:kth:diva-8171ScopusID: 2-s2.0-47149110006OAI: diva2:13423
QC 20100702 Uppdaterad från accepted till published i DiVA 20100702Available from: 2008-04-03 Created: 2008-04-03 Last updated: 2010-07-02Bibliographically 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.
Trita-AVE, ISSN 1651-7660 ; 2008:11
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
urn:nbn:se:kth:diva-4687 (URN)
Public defence
2008-04-25, E1, E-huset, KTH, Lindstedtsvägen 3, Stockholm, 10:00
QC 20100706Available from: 2008-04-03 Created: 2008-04-03 Last updated: 2011-04-12Bibliographically approved

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