| 1. |
- Hedegård, Joakim, et al.
(författare)
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Influence of internal microfissures on fatigue life
- 2009
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Ingår i: Welding in the World. - 0043-2288 .- 1878-6669. ; 53, s. R209-R220
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Tidskriftsartikel (refereegranskat)abstract
- The influence of microfissures on the fatigue strength of submerged arc weids in two high-alloyed, austenitic stainless steels has been studied. It was shown that internal microfissures in the weld metal can have a significant influence on the fatigue strength of the joint when the weld geometry is omitted (machined flat).. Still, all test series showed good fatigue performance and reached better results than expected. Three of the four fatigue series reached a loading capacity close to Rp0.2 for the base metal and one of the series reached levels close to Rp0.2 for the weld metal.
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| 2. |
- al-Karawi, Hassan, 1993, et al.
(författare)
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Crack behaviour after High Frequency Mechanical Impact treatment in welded S355 structural steel
- 2021
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Ingår i: Bridge Maintenance, Safety, Management, Life-Cycle Sustainability and Innovations Proceedings of the Tenth International Conference on Bridge Maintenance, Safety and Management (IABMAS 2020), June 28-July 2, 2020, Sapporo, Japan. - : CRC Press. - 9780367232788 ; , s. 3113-3119
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Konferensbidrag (refereegranskat)abstract
- High-Frequency Mechanical Impact (HFMI) is a rather new post-weld-treatment method that has shown interesting fatigue life enhancement capabilities. The influence on material behaviour needs, however, to be investigated more to reach a full understanding and fully optimize the treatment, not least when the method is applied to existing welded structures. In this study, an experimental investigation was conducted to examine the effect of HFMI-treatment on crack behaviour in pre-fatigued welded details. A substantial reduction in crack width and a change in crack orientation were observed, both are believed to have beneficial effects in extending the remaining fatigue life. However, these beneficial effects decreased as the crack length increased. In light of the observations, a simplified phenomenological model was proposed to determine the crack opening after HFMI-treatment. In addition to that, finite element (FE) simulations were used to conduct several parametric studies. The conclusions from the FE study could be used to extend some of the IIW recommendations regarding the indenter inclination and the depth of indentation to cracked welds. Moreover, The FE simulations indicated that optimum results could be obtained if the indenter is placed and directed more towards the base metal than towards the weld.
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| 3. |
- al-Karawi, Hassan, 1993, et al.
(författare)
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Fatigue crack repair by TIG-remelting
- 2021
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Ingår i: Bridge Maintenance, Safety, Management, Life-Cycle Sustainability and Innovations Proceedings of the Tenth International Conference on Bridge Maintenance, Safety and Management (IABMAS 2020), June 28-July 2, 2020, Sapporo, Japan. - : CRC Press. - 9780367232788 - 9780367232788 ; , s. 3120-3127
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Konferensbidrag (refereegranskat)abstract
- Fatigue is one of the most detrimental problems that often limit the service life of steel bridges. Because of that, different post-weld treatment methods have been studied to extend the fatigue life and repair any existing cracks resulted from the traffic loading. The aim of this paper is to study the fatigue life extension of cracked structures by means of Tungsten Inert Gas (TIG) remelting. Fatigue tests were conducted at a stress ratio of 0.29 on a transverse attachment of 16 mm, thick-walled specimens. The specimens were instrumented with multiple strain gauges along the weld to detect the strain drop caused by crack growth. The specimens were pre-fatigued until a crack of around 1 mm- deep was obtained at the weld toe. After crack detection, the weld toes were treated by TIG-remelting to remove any existing cracks and to reduce the local stress concentration. The weld parameters were controlled so that the fusion depth was always larger than the crack depth. A substantial fatigue life extension could be achieved and the testing led to ran-out after 10 million cycles, which was attributed to the improvement in geometry and residual stress. Weld toe radius was measured before and after treatment by a laser scanner. Hole drilling was used to measure the residual stresses in as-welded state and after TIG-remelting. In this paper, a fatigue damage model is also presented. It is shown that the model gives a good prediction of the effect of TIG-treatment in repairing fatigue loaded welded details.
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| 4. |
- Gåsvaer, Daniel, et al.
(författare)
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Att utveckla den smarta svetscellen : Lean, svetsteknik och automation
- 2013
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- En svetscell producerar och är produktiv när svetsning pågår och ljubågen brinner. Då skapas värde i en svetscell. För att nå teknisk och ekonomisk framgång, behöver svetscellen fungera "smart" med effektiva flöden, hög tillgänglighet, optimerad svetsteknik och ur flera aspekter goda miljöegenskaper. Skriften fungerar som hjälp när företag vill utveckla sin svetsverkstad och förbättra svetsproduktionen, utifrån lean, svetsteknik och automation.
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| 5. |
- Hedegård, Joakim, et al.
(författare)
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Avoiding porosity and spatter in hot-dip galvanized C-Mn steels by laser twin-spot welding
- 2010
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Ingår i: Proc. of the Int. Conf. on Advances in Welding Science and Technology for Construction, Energy and Transportation, AWST 2010, held in Conj. with the 63rd Annual Assembly of IIW 2010. - Istanbul : Ridgeview Publishing Company. - 9786056141911 ; , s. 325-329
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Konferensbidrag (refereegranskat)abstract
- During welding of zinc-coated materials, zinc trapped in the overlap of a lap joint expands violently because of vaporization, and therefore disturbs the laser keyhole. Laser twin-spot welding is a new approach for welding of thin sheet C-Mn steel. The dual beam principle creates a larger and more stabilized weld pool. Therefore welding of galvanized zero gap lap joints becomes possible. This opens a new joining approach for automotive and other industries to perform high speed laser welding. The possibility to laser weld steels with 20 μm zinc coating thickness with high speed and high quality is a technical breakthrough.
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| 6. |
- Hedegård, Joakim, et al.
(författare)
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LifeExt -Prolonged life for existing steel bridges -Livslängdsförlängning av befintliga stålbroar Open report / Publik rapport
- 2020
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Many bridges in the world have reached, or exceeded, their design fatigue life. It is a challenge for society to wisely manage this huge asset of old bridges. Replacing bridges because their theoretical life span is reached is not a sustainable solution, neither from societal nor economical point of view. Therefore, methods for accurate assessment and techniques for extending the service life of existing infrastructures are on top of priorities of all industrial countries. The LifeExt project reported here was created to address these issues, to enable substantial life extension for existing bridges by applying weld improvement techniques locally on selected (most critical) positions on a bridge. These areas receive faster damage accumulation and by improving these areas, the whole bridge life can be prolonged.
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| 7. |
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| 8. |
- Kaplan, Alexander, et al.
(författare)
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Controlled metal transfer from a wire by a laser-induced boiling front
- 2016
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Konferensbidrag (refereegranskat)abstract
- The addition of wire is an option during laser welding, laser cladding or laser additive manufacturing. By high speedimaging of leading wire addition during fibre laser keyhole welding it was observed that for the 40 experiments underconsideration the wire tip always established a concave boiling front. The front appears similar to a keyhole front and issort of a continuation of the keyhole, owing to the leading wire employment. For most of the parameters the melt istransferred downwards from the wire tip into the melt pool surrounding the keyhole front. In other words, hardly anyuncontrolled spatter to the sides was observed. A trailing wire would normally tend to a completely different behaviour.Typical as well as limiting phenomena of the wire melt transfer mechanism are presented and discussed. Controlledvertical melt transfer of the wire through the ablation pressure from a laser-induced boiling front, either in contact withthe workpiece surface or positioned higher above, can be a desirable mechanism of metal deposition for the differenttechniques, namely welding, surface treatment or LAM. By suitable choice of the laser power density above the boilingthreshold, the here observed mechanism can be applied in a controllable manner. An interesting technique option islateral beam oscillation for example by a galvanometer optics which shears off the melt in a manner similar to remotefusion cutting. The process limits become different to the static technique. The wire melt transfer technique has thepotential to be developed further towards a highly controllable remote drop transfer, e.g. in terms of direction.
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| 9. |
- Manai, Asma, 1990, et al.
(författare)
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A methodology for assessment and retrofitting by TIG dressing of existing pre-fatigued welded steel joints
- 2021
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Ingår i: Bridge Maintenance, Safety, Management, Life-Cycle Sustainability and Innovations - Proceedings of the 10th International Conference on Bridge Maintenaince, Safety and Management, IABMAS 2020. - : CRC Press. ; , s. 592-597
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Konferensbidrag (refereegranskat)abstract
- Several fatigue life extension methods of a welded structure are coveted in the industry such as Tungsten-Inert-Gas Dressing (TIG dressing). This paper presents a framework for a fatigue assessment and retrofitting of welded structures by TIG dressing. The proposed framework provides in detail the parameters that have an influence on fatigue life which can be divided into two groups, the first is related to the structure prior to treatment such (e.g: crack dimension, toe radius, and residual stresses) while the second is related to the state of the structure following the treatment (e.g: treatment depth, residual stresses and resulted toe radius). Experimental results, from the current work, were complemented with tests from literature to verify the proposed framework. An analysis between our predictions and reported values of fatigue life from literature show an absolute error of 20%.
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| 10. |
- Nilsson, Peter, 1982, et al.
(författare)
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The impact of production-dependent geometric properties on fatigue-relevant stresses in laser-welded corrugated core steel sandwich panels
- 2019
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Ingår i: Welding in the World. - : Springer Verlag. - 0043-2288 .- 1878-6669. ; 62:6, s. 1801-1818
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Tidskriftsartikel (refereegranskat)abstract
- For bridge deck applications, laser-welded corrugated core steel sandwich panels with dual weld lines per crest and trough have been shown to be highly material- and economically efficient. The nature of welding induces a variation in the geometric properties of the joint that connects the core to the faces. The geometric properties of the joint are the weld width, weld misalignment, and plate gap between the core and the faces. This paper aims to investigate the impact of the variation of the production-dependent geometric properties of the joint on the fatigue-relevant stresses. A secondary aim of this paper is to investigate the impact of contact between the core and the faces on the weld region stresses. Within this paper, the production of four sandwich panels is documented and the manufacturing-dependent geometric properties of their joints are quantified. In order to investigate the impact of the natural variation of the parameters, a parametric study based on finite element analyses is executed. The result of the parametric study shows, among several other findings, that misalignment of the weld line in relation to the core direction can lead to considerable increases in stresses, determinant for the fatigue life of the panel.
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