| 1. |
- Kahlin, Magnus, 1982-
(författare)
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3D-printing for Aerospace : Fatigue Behaviour of Additively Manufactured Titanium
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Laser powder bed fusion (L-PBF) and electron beam powder bed fusion (E-PBF) are two of the most common additive manufacturing (AM) methods which both provide the engineer with a great freedom of design.This means that parts with light weight, multifunctional applications and improved performance could be achieved through innovative design solutions which have attracted a lot of interest from the aerospace industry.This PhD project has focused on the following fatigue related areas forL-PBF and E-PBF Ti6Al4V material which all need to be addressed before AM can be fully introduced to critical aerospace applications: effect of geometry, roughness and loading on fatigue life, improved fatigue life through post processing, fatigue crack growth behaviour and fatigue prediction methods.The results show that the rough as-built surface is the single most severe factor for fatigue but that the fatigue strength of at least L-PBF material can be improved to levels similar to conventionally manufactured material using surface post processing. Furthermore, the results verify that acumulative damage approach gives good accuracy in predicting fatigue life for variable amplitude loading and that fatigue crack growth rates using material data from standard specimens can be used for damage tolerancean alysis independent of part geometry and stress level.The conclusion is therefore that the fatigue properties can be improved to acceptable levels and predicted using conventional methods. There are still some challenges to solve, however, especially within non-destructive testing before AM can be introduced to critical aerospace applications.
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| 2. |
- Kahlin, Magnus, et al.
(författare)
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Fatigue behaviour of additive manufactured Ti6Al4V, with as-built surfaces, exposed to variable amplitude loading
- 2017
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Ingår i: International Journal of Fatigue. - : ELSEVIER SCI LTD. - 0142-1123 .- 1879-3452. ; 103, s. 353-362
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Tidskriftsartikel (refereegranskat)abstract
- Additive Manufacturing (AM) allows for great design freedom compared to conventional manufacturing. This is very attractive for the aerospace industry in which AM could contribute to lightweight designs and thereby reduce fuel consumption, increase payload and extend flight range. The fatigue behaviour for rough as-built AM surfaces has previously been characterized with constant amplitude testing but in aerospace applications, most parts are exposed to variable amplitude loading. The fatigue behaviour for variable amplitude is not always consistent with the behaviour for constant amplitude due to effects of overloads and local plastic deformations. Therefore, variable amplitude loading behaviour of laser sintered and electron beam melted Ti6Al4V, with rough as-built surfaces have been investigated in this study using the Short-FALSTAFF (Fighter Aircraft Loading STAndard For Fatigue) load sequence. The predicted and the experimental fatigue life was overall consistent even though most experimental results exceeded the predicted life, especially for the laser sintered material. These findings show that conventional cumulative damage fatigue life predictions give reliable predictions for AM materials with rough as-built surfaces for the type of tension dominated load sequence used. (C) 2017 Elsevier Ltd. All rights reserved.
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| 3. |
- Kahlin, Magnus, et al.
(författare)
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Fatigue Behaviour of Notched Additive Manufactured Ti6Al4V with As-built Surfaces
- 2017
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Ingår i: International Journal of Fatigue. - : Elsevier. - 0142-1123 .- 1879-3452. ; :101, s. 51-60
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Tidskriftsartikel (refereegranskat)abstract
- Additive manufacturing (AM) allows the manufacturer to produce parts with complex geometries that are difficult to produce with conventional production methods. Generally, AM is considered to have great potential for the aerospace industry by contributing to reduced weight and lower costs. There are a number of challenges to be solved before AM can be fully utilized in the aerospace industry, and the understanding of fatigue behaviour is one of the major challenges. Although the fatigue properties of flat additive manufactured specimens with rough as-built surfaces already have been widely studied, in practice, few aerospace components have a simple flat geometry with no corners or radii that would act as stress concentrations. Therefore, the combined effect on fatigue life of a rough as-built surface and a geometrical notch needs to be established. In this study, the fatigue properties of both laser sintered and electron beam melted Ti6Al4V have been investigated and a combined effect of a rough as-built surface and a geometrical notch has been determined. In addition, hot isostatic pressing was found to have no impact on fatigue life for rough as-built surfaces. These findings can be directly applied to predict fatigue behaviour of an AM industrial component.
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| 4. |
- Kahlin, Magnus, 1982-, et al.
(författare)
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Fatigue crack growth for through and part-through cracks in additively manufactured Ti6Al4V
- 2022
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Ingår i: International Journal of Fatigue. - : Elsevier. - 0142-1123 .- 1879-3452. ; 155
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Tidskriftsartikel (refereegranskat)abstract
- Critical aerospace parts require damage tolerance analysis to determine the inspection intervals in-service. Such analyses, based on linear fracture mechanics, require that the fatigue crack growth (FCG) rate relation to the stress intensity factor range is applicable independent of geometry and stress. FCG rates for laser powder bed fusion Ti6Al4V material for conventional compact tension (CT) specimens have therefore been compared to FCG rates for specimens with a crack configuration more technically relevant from an industrial and engineering perspective. The FCG rates corresponded very well and data obtained with CT-specimens can therefore be considered relevant for general damage tolerance predictions.
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| 5. |
- Kahlin, Magnus
(författare)
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Fatigue Performance of Additive Manufactured Ti6Al4V in Aerospace Applications
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Additive Manufacturing (AM) for metals includes is a group of production methodst hat use a layer-by-layer approach to directly manufacture final parts. In recent years, the production rate and material quality of additive manufactured materials have improved rapidly which has gained increased interest from the industry to use AM not only for prototyping, but for serial production. AM offers a greater design freedom, compared to conventional production methods, which allows for parts with new innovative design. This is very attractive to the aerospace industry, in which parts could be designed to have reduced weight and improved performance contributing to reduced fuel consumption, increased payload and extended flight range. There are, however, challenges yet to solve before the potential of AM could be fully utilized in aerospace applications. One of the major challenges is how to deal with the poor fatigue behaviour of AM material with rough as-built surface.The aim of this thesis is to increase the knowledge of how AM can be used for high performance industrial parts by investigating the fatigue behaviour of the titanium alloy Ti6Al4V produced with different AM processes. Foremost, the intention is to improve the understanding of how rough as-built AM surfaces in combination with AM built geometrical notches affects the fatigue properties.This was done by performing constant amplitude fatigue testing to compare different combinations of AM material produced by Electron Beam Melting(EBM) and Laser Sintering (LS) with machined or rough as-built surfaces with or without geometrical notches and Hot Isostatic Pressing (HIP) treatment. Furthermore, the material response can be different between constant amplitude and variable amplitude fatigue loading due to effects of overloads and local plastic deformations. The results from constant amplitude testing were used to predict the fatigue life for variable amplitude loading by cumulative damage approach and these predictions were then verified by experimental variable amplitude testing.The constant amplitude fatigue strength of material with rough as-built surfaces was found to be 65-75 % lower, compared to conventional wrought bar, in which HIP treatments had neglectable influence on the fatigue strength. Furthermore, the fatigue life predictions with cumulative damage calculations showed good agreement with the experimental results which indicates that a cumulative damage approach can be used, at least for a tensile dominated load sequences, to predict the fatigue behaviour of additive manufactured Ti6Al4V.
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| 6. |
- Kahlin, Magnus, et al.
(författare)
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Improved fatigue strength of additively manufactured Ti6Al4V by surface post processing
- 2020
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Ingår i: International Journal of Fatigue. - : ELSEVIER SCI LTD. - 0142-1123 .- 1879-3452. ; 134
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Tidskriftsartikel (refereegranskat)abstract
- A major challenge for additively manufactured structural parts is the low fatigue strength connected to rough as-built surfaces. In this study, Ti6Al4V manufactured with laser powder bed fusion (L-PBF) and electron beam powder bed fusion (E-PBF) have been subjected to five surface processing methods, shot peening, laser shock peening, centrifugal finishing, laser polishing and linishing, in order to increase the fatigue strength. Shot peened and centrifugal finished L-PBF material achieved comparable fatigue strength to machined material. Moreover, the surface roughness alone was found to be an insufficient indicator on the fatigue strength since subsurface defects were hidden below smooth surfaces.
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| 7. |
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| 8. |
- Kahlin, Magnus, et al.
(författare)
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Variable Amplitude Loading of Additively Manufactured Ti6Al4V Subjected to Surface Post Processes
- 2021
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Ingår i: International Journal of Fatigue. - : Elsevier. - 0142-1123 .- 1879-3452. ; 142
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Tidskriftsartikel (refereegranskat)abstract
- The fatigue life of additively manufactured metals need to be improved before they can be introduced to flight critical aerospace structural applications. In this study, laser powder bed fusion (L-PBF) and electron beam powder bed fusion (E-PBF) Ti6Al4V material were therefore subjected to four different surface post processes. Furthermore, variable amplitude fatigue testing were performed and compared to fatigue life predictions based on constant amplitude fatigue tests using a cumulative damage approach. The predictions were in good accordance with the experimental results and post processed L-PBF and E-PBF material showed an increase in fatigue life with >5 times.
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| 9. |
- Knutsson, Johan, et al.
(författare)
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Clinical and audiological short-term and long-term outcomes of fat graft myringoplasty
- 2017
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Ingår i: Acta Oto-Laryngologica. - : Informa UK Limited. - 0001-6489 .- 1651-2251. ; 137:9, s. 940-944
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: Results of fat graft myringoplasty are often reported with only short-term follow-up. Audiological results are less commonly reported, as well as long-term follow-up results. Materials and methods: One hundred consecutive patients scheduled for fat graft myringoplasty were included in a prospective cohort study. Clinical and audiological outcomes were assessed at six weeks and one year postoperatively. Results: Perforation sizes ranged from 0.5 to 4 mm. The six-week follow-up showed a total perforation closure rate of 72.9% with a statistically significant (p = .03) higher rate for the pediatric age group (83.0%). 64.4% of all patients were healed at one-year follow-up. Statistical analyses for background factors did not reveal any significant difference in healing rates with regard to patient sex or location or cause of the perforation. The mean preoperative air-conduction (AC) threshold was 25dB with an air-bone gap of 12 dB. At the one-year follow-up the mean air conduction threshold for healed ears was improved to 16.6 dB, still 54.2% of them had a type B tympanogram. Conclusions: Children had a higher perforation closure rate at six-week follow-up than adult patients. Recurrent tympanic membrane perforations were common after initially successful fat graft myringoplasties. Long-term hearing was improved after successful fat graft myringoplasty, resulting in a mean AC threshold of 16.6 dB.
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| 10. |
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