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Fatigue strength of welds in 800 MPa yield strength steels: Effects of weld toe geometry and residual stress
University West, Department of Engineering Science, Division of Manufacturing Processes. (PTW)ORCID iD: 0000-0003-4978-390X
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Nowadays there is a strong demand for lighter vehicles in order to increase the pay load. Through this the specific fuel consumption is decreased, the amount of greenhouse gases is lowered and the transport economy improved. One possibility to optimize the weight is to make the components from high strength steels and join them by welding. Welding is the main joining method for fabrication of a large proportion of all engineering structures. Many components experience fatigue loading during all or part of their life time and welded connections are often the prime location of fatigue failure.Fatigue fracture in welded structures often initiates at the weld toe as aconsequence of large residual stresses and changes in geometry acting as stress concentrators. The objective of this research is to increase the understanding of the factors that control fatigue life in welded components made from very high strength steels with a yield strength of more than 800 MPa. In particular the influences of the local weld toe geometry (weld toe radius and angle) and residual stress on fatigue life have been studied. Residual stresses have been varied by welding with conventional as well as Low Transformation Temperature (LTT) filler materials. The three non-destructive techniques Weld Impression Analysis (WIA), Laser Scanning Profiling (LSP) and Structured Light Projection (SLP) have been applied to evaluate the weld toe geometry.Results suggest that all three methods could be used successfully to measure the weld toe radius and angle, but the obtained data are dependent on the evaluation procedure. WIA seems to be a suitable and economical choice when the aim is just finding the radius. However, SLP is a good method to fast obtain a threedimensional image of the weld profile, which also makes it more suitable for quality control in production. It was also found that the use of LTTconsumables increased fatigue life and that residual stress has a relatively larger influence than the weld toe geometry on fatigue strength of welded parts.

Place, publisher, year, edition, pages
Trollhättan: University West , 2015. , 71 p.
Series
Licentiate Thesis: University West, 3
Keyword [en]
Fatigue strength; Residual stress; Welds; Weld toe geometry; High strength steel; Weld Impression Analysis; Laser Scanning Profiling; Structured Light Projection
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-8009ISBN: 978-91-87531-12-5 (print)ISBN: 978-91-87531-11-8 (print)OAI: oai:DiVA.org:hv-8009DiVA: diva2:849239
Supervisors
Available from: 2015-08-27 Created: 2015-08-27 Last updated: 2016-02-09Bibliographically approved
List of papers
1. The measurement of weld toe radius using three non-destructive techniques
Open this publication in new window or tab >>The measurement of weld toe radius using three non-destructive techniques
2014 (English)In: Proceedings of The 6th International Swedish Production Symposium 201416-18 September 2014 / [ed] Johan Stahre, Björn Johansson,Mats Björkman, 2014, 1-8 p.Conference paper, (Refereed)
Abstract [en]

The three non-destructive methods Weld Impression Analysis, Laser Scanning Profiling and Structured Light Projection were employed to measure the weld toe radius of fillet welds. All three methods could be used succesfully but results are dependent on evaluation procedure. The results show that the weld toe geometry cannot be considered uniform and varies along the weld. It was also found that the measured weld toe radii do not vary significantly with minor variations ofthe surface profile orientation.

Keyword
Weld toe radius, Weld Impression Analysis, Laser Scanning Profiling, Structured Light Projection.
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-6703 (URN)978-91-980974-1-2 (ISBN)
Conference
6th International Swedish Production Symposium 2014
Available from: 2014-09-19 Created: 2014-09-19 Last updated: 2016-02-09Bibliographically approved
2. Non-destructive measurement of weld toe radius using Weld Impression Analysis, Laser Scanning Profiling and Structured Light Projection methods
Open this publication in new window or tab >>Non-destructive measurement of weld toe radius using Weld Impression Analysis, Laser Scanning Profiling and Structured Light Projection methods
2014 (English)In: Proceedings of First International Conference on Welding and Non Destructive Testing (ICWNDT2014), 2014, 1-8 p.Conference paper, (Refereed)
Keyword
Weld toe, Non-destructive methods, Weld Impression Analysis, Laser Scanning Profiling, Structured Light Projection
National Category
Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:hv:diva-6497 (URN)
Conference
First International Conference on Welding and Non Destructive Testing (ICWNDT2014)February 25-26, 2014, Islamic Azad University, Karaj Branch-Karaj-Alborz, Iran
Available from: 2014-08-20 Created: 2014-08-14 Last updated: 2016-02-09Bibliographically approved
3. The relative effects of residual stresses and weld toe geometry on fatigue life of weldments
Open this publication in new window or tab >>The relative effects of residual stresses and weld toe geometry on fatigue life of weldments
2015 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 77, 160-165 p.Article in journal (Refereed) Published
Abstract [en]

The weld toe is one of the most probable fatigue crack initiation sites in welded components. In this paper, the relative influences of residual stresses and weld toe geometry on the fatigue life of cruciform welds was studied. Fatigue strength of cruciform welds produced using Low Transformation Temperature (LTT) filler material has been compared to that of welds produced with a conventional filler material. LTT welds had higher fatigue strength than conventional welds. A moderate decrease in residual stress of about 15% at the 300 MPa stress level had the same effect on fatigue strength as increasing the weld toe radius by approximately 85% from 1.4 mm to 2.6 mm. It was concluded that residual stress had a relatively larger influence than the weld toe geometry on fatigue strength.

Keyword
Weld toe geometry, residual stress, fatigue strength, Low Transformation Temperature filler material
National Category
Engineering and Technology Manufacturing, Surface and Joining Technology Other Materials Engineering
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-7503 (URN)10.1016/j.ijfatigue.2015.03.023 (DOI)000354147300015 ()2-s2.0-84927128911 (Scopus ID)
Note

Available online 2 April 2015

Available from: 2015-04-07 Created: 2015-04-07 Last updated: 2016-02-09Bibliographically approved

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