| 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, 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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| 3. |
- Segersäll, Mikael, 1982-, et al.
(författare)
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Fatigue Response Dependence of Thickness Measurement Methods for Additively Manufactured E-PBF Ti-6Al-4 V
- 2021
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Ingår i: Fatigue & Fracture of Engineering Materials & Structures. - : John Wiley & Sons. - 8756-758X .- 1460-2695. ; 44:7, s. 1931-1943
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Tidskriftsartikel (refereegranskat)abstract
- Light weight metal parts produced with additive manufacturing have gained increasing interest from the aerospace industry in recent years. However, light weight parts often require thin walls which can have different material properties compared to thick bulk material. In this work, the fatigue properties of Ti-6Al-4 V produced by electron beam powder bed fusion have been investigated for samples with three different wall thicknesses ranging from 1.3 to 2.7 mm and in three different directions; 0°, 45°, and 90° relative to the build plate. Generally, the 90° specimens show worse fatigue life compared to both 0° and 45°. It was found that the fatigue strength is lower for thin samples compared to thicker samples when the stress is calculated from nominal thickness or calliper measurements. However, since materials produced by electron beam powder bed fusion often have a rough as-built surface, the load bearing area is not easy to determine. In this paper, four different methods for determining the load bearing area are presented. It is shown that if the surface roughness is considered when calculating the stress levels, the influence from specimen thickness decreases or even disappears.
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