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Computational weld mechanics: Towards simplified and cost effective FE simulations
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

It is the demand of the world’s ever increasing energy crisis to reduce fuel consumption wherever possible. One way of meeting this demand is by reducing the weight of a structure by replacing thick plates of low strength steel with thin plates of high strength steel in the structure. Fusion welding process is extensively used in the manufacturing industry, however, despite many advantages different problems such as weld defects, residual stresses and permanent distortions are associated with this process.

Finite element (FE) method has proved itself as an alternative and acceptable tool for prediction of welding residual stresses and distortions. However, the highly nonlinear and transient nature of the welding process makes the FE simulation computationally intensive and complex. Thus, simplified and efficient welding simulations are required so that they can be applied to industrial scale problems.

In this research work an alternative FE simulation approach for the assessment of welding residual stresses, called rapid dumping is developed. This approach proved to be efficient and predicted the residual stress with acceptable accuracy for different small scale welded joints. This approach was further implemented on a large scale welded structures along with other available approaches. It was found that the computational time involved in the welding simulations for large structures using rapid dumping approach can be reduced but at the cost of accuracy of the results.

Furthermore, influence of thermo-mechanical material properties of different steel grades (S355-S960) on welding residual stresses and angular distortion in T-fillet joints is investigated. It is observed that for assessment of residual stresses, except yield stress, all of the thermo-mechanical properties can be considered as constant. For the prediction of angular distortions with acceptable accuracy, heat capacity, yield stress and thermal expansion should be employed as temperature dependent in the welding simulations.

Finally, the influence of two different LTT (Low Transformation Temperature) weld filler material on residual stress state and fatigue strength was investigated. It was observed that a reduction in tensile residual stresses at the weld toe of the joint was observed. Furthermore, at higher R-ratio no significant increase in the fatigue strength was observed . However, at low R-ratio significant  increase in fatigue strength was observed.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , xii, 26 p.
Series
TRITA-AVE, ISSN 1651-7660 ; 2015:32
National Category
Manufacturing, Surface and Joining Technology Vehicle Engineering
Research subject
Vehicle and Maritime Engineering
Identifiers
URN: urn:nbn:se:kth:diva-168174ISBN: 978-91-7595-626-8 (print)OAI: oai:DiVA.org:kth-168174DiVA: diva2:814586
Public defence
2015-06-15, D3, Lindstedtsvägen 5, KTH, Stockholm, 09:00 (English)
Opponent
Supervisors
Note

QC 20150529

Available from: 2015-05-29 Created: 2015-05-27 Last updated: 2015-05-29Bibliographically approved
List of papers
1. Development of efficient three-dimensional welding simulation approach for residual stress estimation in different welded joints
Open this publication in new window or tab >>Development of efficient three-dimensional welding simulation approach for residual stress estimation in different welded joints
2012 (English)In: Journal of Strain Analysis for Engineering Design, ISSN 0309-3247, E-ISSN 2041-3130, Vol. 47, no 8, 539-552 p.Article in journal (Refereed) Published
Abstract [en]

Based on the available welding simulation approaches found in the literature, an alternative and simplified welding simulation approach is developed, called rapid dumping. It is a sequential thermomechanical approach, which makes use of the moving heat source in thermal analysis and the block-dumping approach in mechanical analysis for prediction of welding residual stresses in three dimensions. It is first developed for longitudinal stiffener joint and then validated by applying on a butt-welded, T-fillet, and multipass tube-flange joints. The temperature-dependent material properties were obtained using JMat Pro software, a java-based material property simulation software. The material properties were validated with experimentally determined material properties found in the literature. The predicted residual stresses were validated by X-ray diffraction measurements on the longitudinal stiffener fillet-welded joint. Using the rapid-dumping approach, the residual stresses obtained at the weld toe were in qualitatively good agreement with the measured residual stresses. The rapid-dumping approach showed to capture the effects of moving heat source and weld start/stop location. In addition, it has reduced the computational time significantly with a preserved accuracy of the estimated welding residual stresses.

Keyword
Finite element method, welding simulation, X-ray diffraction and residual stresses
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-107623 (URN)10.1177/0309324712463866 (DOI)000311037100001 ()2-s2.0-84872004659 (Scopus ID)
Funder
EU, European Research Council
Note

QC 20121214

Available from: 2012-12-14 Created: 2012-12-14 Last updated: 2017-12-06Bibliographically approved
2. Development of a finite element simulation framework for the prediction of residual stresses in large welded structures
Open this publication in new window or tab >>Development of a finite element simulation framework for the prediction of residual stresses in large welded structures
2014 (English)In: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 133, 1-11 p.Article in journal (Refereed) Published
Abstract [en]

In this study a framework for efficient prediction of residual stresses in large welded structure is proposed. For this purpose different finite element simulation approaches available in literature are implemented on a large bogie beam structure. Among all approaches rapid dumping approach used minimum computational time and also it showed qualitatively good agreement with X-ray diffraction measurements for welding residual stresses. Moreover, gradual weld bead deposition approach predicted more accurate results when compared with the experimental measurements and other approaches. Also, by using substructuring approach the computational time is significantly reduced with an acceptable accuracy of predicted welding residual stresses.

Keyword
FEM, Large structure, Residual stresses, Substructuring, Welding simulation, X-ray diffraction
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-140089 (URN)10.1016/j.compstruc.2013.11.011 (DOI)000330916900001 ()2-s2.0-84890525370 (Scopus ID)
Note

QC 20140120

Available from: 2014-01-20 Created: 2014-01-17 Last updated: 2017-12-06Bibliographically approved
3. Influence of thermo-mechanical material properties of different steel grades on welding residual stresses and angular distortion
Open this publication in new window or tab >>Influence of thermo-mechanical material properties of different steel grades on welding residual stresses and angular distortion
2015 (English)In: Materials & Design, ISSN 0261-3069, Vol. 65, 878-889 p.Article in journal (Refereed) Published
Abstract [en]

The present study investigates the influence of thermo-mechanical material properties of different steel grades (S355-S960) on welding residual stresses and angular distortion in T-fillet joints. Different cases in which temperature dependent thermo-mechanical material properties are considered as constant, linear, and as a function of temperature are simulated by using finite element (FE) method. Experiments are carried out to evaluate temperature dependent yield stress and Young's modulus for S700 and S960 steel grades. Furthermore, JMat Pro software is used to obtain the remaining thermo-mechanical material properties. The numerical predictions of angular distortion and transverse residual stresses are validated with experimental measurements. It is observed that for assessment of residual stresses, except yield stress, all of the thermo-mechanical properties can be considered as constant. For the prediction of angular distortions with acceptable accuracy, heat capacity, yield stress and thermal expansion should be employed as temperature dependent in the welding simulations.

Keyword
Angular distortion, Welding residual stress, Thermo-mechanical material properties, High strength steel
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-158375 (URN)10.1016/j.matdes.2014.10.019 (DOI)000345520000109 ()2-s2.0-84918768590 (Scopus ID)
Note

QC 20150115

Available from: 2015-01-15 Created: 2015-01-07 Last updated: 2017-12-05Bibliographically approved
4. Fatigue strength improvement of welded structures using new low transformation temperature filler materials
Open this publication in new window or tab >>Fatigue strength improvement of welded structures using new low transformation temperature filler materials
Show others...
2013 (English)In: Fatigue Design 2013, International Conference Proceedings, Elsevier, 2013, 192-201 p.Conference paper, Published paper (Refereed)
Abstract [en]

The results reported in this research study are part of a larger EU RFCS (Research Fund for Coal and Steel) project where the aim is to study the fatigue behavior of improved welds in high strength steels by utilizing different improvement techniques. In this particular study LTT (Low Transformation Temperature) weld filler material have been investigated and their possibility to improve the fatigue strength. The characteristic of these filler material is that they undergo phase transformation at temperature close to room temperature which will reduce the tensile residual stress in the weld and in some cases result in compressive residual stresses. Two different LTT alloy compositions have been developed, with different Ms (Martensite Start) temperatures in order to study the amount of tensile/compressive residual stresses produced by these wires. Welding residual stress measurements were carried out by X-ray diffraction technique. Plates with welded longitudinal attachments were fabricated in 700 MPa and 960 MPa steel grades using different LTT filler materials. These specimens were fatigue tested in constant and variable amplitude loading and the fatigue test results were compared with results from specimen welded with conventional weld filler material.

Place, publisher, year, edition, pages
Elsevier, 2013
Series
Procedia Engineering, ISSN 1877-7058 ; 66
Keyword
Fatigue testing, LTT, Residual stresses, Welded joints
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-147456 (URN)10.1016/j.proeng.2013.12.074 (DOI)000338327000019 ()2-s2.0-84894422734 (Scopus ID)
Conference
5th International Conference on Fatigue Design, Fatigue Design 2013, 27 November 2013 through 28 November 2013, Senlis, France
Note

QC 20140804

Available from: 2014-08-04 Created: 2014-06-27 Last updated: 2015-05-29Bibliographically approved

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