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Only a Shadow: Industrial computed tomography investigation, and method development, concerning complex material systems
Örebro University, School of Science and Technology, Örebro University, Sweden.ORCID iD: 0000-0002-9362-8328
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The complexity of components fabricated in today's industry is ever increasing. This increase is partly due to market pressure but it is also a result from progress in fabrication technologies that opens up new possibilities. The increased use of additive manufacturing and multi-material systems, especially, has driven the complexity of parts to new heights. The new complex material systems brings benefits in many areas such as; mechanical properties, weight optimisation, and sustainability. However, the increased complexity also makes material integrity investigations and dimensional control more difficult. In additive manufacturing, for example, internal features can be fabricated which cannot be seen or measured with conventional tools. There is thus a need for non-destructive inspection methods that can measure these geometries. Such a method is X-ray computed tomography. Computed tomography utilizes the X-rays ability to penetrate material to create 3D digital volumes of components. Measurements and material investigations can be performed in these volumes without any damage to the investigated component. However, computed tomography in material science is still not a fully mature method and there are many uncertainties associated with the investigation technique. In the work presented in this thesis geometries fabricated by various additive manufacturing processes have been investigated using computed tomography. Also in this work, a dual-energy computed tomography tool has been developed with the aim to increase the measurement consistency of computed tomography when investigating complex geometries and material combinations.

Place, publisher, year, edition, pages
Örebro: Örebro University , 2016. , 61 p.
Series
Örebro Studies in Technology, ISSN 1650-8580 ; 73
Keyword [en]
Computed tomography, Dual-energy, Material investigation, Additive manufacturing, Measurement consistency
National Category
Other Mechanical Engineering
Research subject
Mechanical Engineering
Identifiers
URN: urn:nbn:se:oru:diva-54880ISBN: 978-91-87789-10-6 (print)OAI: oai:DiVA.org:oru-54880DiVA: diva2:1067365
Presentation
2017-01-19, HSM, Örebro universitet, Örebro, 13:15 (English)
Opponent
Supervisors
Projects
MultiMatCT
Available from: 2017-02-03 Created: 2017-01-20 Last updated: 2017-02-03Bibliographically approved
List of papers
1. Characterisation of carbon fibre-reinforced polyamide manufactured by selective laser sintering
Open this publication in new window or tab >>Characterisation of carbon fibre-reinforced polyamide manufactured by selective laser sintering
2016 (English)In: Additive Manufacturing, ISSN 2214-8604, Vol. 9, 7-13 p.Article in journal (Refereed) Published
Abstract [en]

Polymers and reinforced plastics are employed in various load-bearing applications, from household objects to aerospace products. These materials are light, strong, and relatively cheap but can be difficult to form into complex geometries. However, the development of additive manufacturing processes has made it easier to manufacture reinforced plastics in complex shapes. The aim of this work was to study the internal features and mechanical properties of carbon fibre-reinforced polyamide (CF/PA12) fabricated with the additive manufacturing technique of selective laser sintering. The test specimens were studied using computed tomography to analyse the internal geometry, and the material proved to be highly porous. Moreover, the test specimens revealed an internal layered structure, which was found to have a great effect on the tensile properties of the material. The results highlight that there is room for further optimisation of the manufacturing parameters for CF/PA12, because the layered structure makes it challenging to design end user parts with acceptable mechanical properties.

Place, publisher, year, edition, pages
Amsterdam, Netherlands: Elsevier, 2016
Keyword
Computed tomography, carbon fibre–reinforced polymer, selective laser sintering, additive manufacturing
National Category
Materials Engineering
Research subject
Mechanical Engineering
Identifiers
urn:nbn:se:oru:diva-47800 (URN)10.1016/j.addma.2015.12.003 (DOI)2-s2.0-84952789063 (Scopus ID)
Available from: 2016-01-27 Created: 2016-01-27 Last updated: 2017-01-20Bibliographically approved
2. Measurement of internal features in additive manufactured components by the use of computed tomography
Open this publication in new window or tab >>Measurement of internal features in additive manufactured components by the use of computed tomography
2015 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Additive manufacturing (AM) is a set of manufacturing processes currently in rapid development providing designersnew freedoms in their designs. One distinct difference from other manufacturing methods is the ability to makecomplex internal features which can be of great benefit for applications in many industries. These features can bechannels, cavities, filled or not filled with powder, parts in parts etc. In order for these advantages to be industriallyapplicable there is a need for robust verification methods for these internal features. X-ray computed tomography (CT)holds the promise of being one of the few powerful tools for non-destructive imaging of internal features. In this work,selective laser sintering (SLS) has been used to manufacture parts of a complex geometry containing internal cavities.The test specimens were manufactured in two different materials; Polyamide12 and Titanium (Ti6Al4V). In order toinvestigate the limitations and controllability of the process, the dimensions of the internal cavities were determinedby a correlation of tactile measurements on external features and CT-data. The results were also compared to computeraided design (CAD) data. This work provides some insight concerning part accuracy of today’s frontier of AM systemsand the ability to measure and characterize internal features using CT.

Place, publisher, year, edition, pages
Non destructive testing, 2015
Keyword
Computed tomography, additive manufacturing, internal features, selective laser melting
National Category
Mechanical Engineering
Research subject
Mechanical Engineering
Identifiers
urn:nbn:se:oru:diva-47801 (URN)
Conference
Digital Industrial Radiology and Computed Tomography (DIR 2015), Ghent, Belgium, June 22-25, 2015
Available from: 2016-01-27 Created: 2016-01-27 Last updated: 2017-01-20Bibliographically approved
3. Effects of X-ray Penetration Depth on Multi Material Computed Tomography Measurements
Open this publication in new window or tab >>Effects of X-ray Penetration Depth on Multi Material Computed Tomography Measurements
2016 (English)Conference paper, Published paper (Refereed)
Abstract [en]

The complexity of today’s products and materials is ever increasing. There is a demand on the industry to produce lighter, stronger, and more precise products. A common practice to achieve such products is to combine different materials to enhance strengths and reduce weaknesses; multi material products. Fabricating complex parts using multi materials does, however, lead to an increased difficulty in metrological verification and material characterisation. The use of computed tomography is today widespread within the industry, providing new possibilities for internal measurements, but there are still many uncertainties associated with the method. It is well known that large variations in density of multi materials greatly affects the contrast obtained by computed tomography, resulting in difficulties to scan and acquire reliable data from certain material setups.In this work the effects on internal measurements as a consequence of differences in X-ray penetration depth have been studied with regards to multi material setups. The main interest was the ability to acquire measurements from internal features of material compositions that are commonly used in the industry. In the result, difficulties and uncertainties associated with computed tomography of multi materials are highlighted and suggestions on how to reduce problems and obtain a more reliable test method are discussed.

Place, publisher, year, edition, pages
Non destructive testing, 2016
Keyword
Multi-materials, computed tomography, X-ray penetration depth, dual-energy computed tomography
National Category
Mechanical Engineering
Research subject
Mechanical Engineering
Identifiers
urn:nbn:se:oru:diva-47802 (URN)
Conference
6th Conference on Industrial Computed Tomography (iCT 2016), Wels, Austria, February 9-12, 2016
Available from: 2016-01-27 Created: 2016-01-27 Last updated: 2017-01-20Bibliographically approved
4. A dual-energy approach for improvement of the measurement consistency in computed tomography
Open this publication in new window or tab >>A dual-energy approach for improvement of the measurement consistency in computed tomography
2016 (English)In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 27, no 11, 1-9 p.Article in journal (Refereed) Published
Abstract [en]

Computed tomography is increasingly adopted by industries for metrological and material evaluation. The technology enables new measurement possibilities, while also challenging old measurement methods in their established territories. There are, however, uncertainties related with the computed tomography method. Investigation of multi-material components with, in particular, varying material thickness can result in unreliable measurements. In this paper the effects of multi-materials, and differing material thickness, on computed tomography measurement consistency has been studied. The aim of the study was to identify measurement inconsistencies and attempt to correct these with a dual-energy computed tomography approach. In this pursuit, a multi-material phantom was developed, containing reliable measurement points and custom-ability with regards to material combinations. A dual-energy method was developed and implemented using sequential acquisition and pre-reconstruction fusing of projections. It was found that measurements made on the multi-material phantom with a single computed tomography scan were highly inconsistent. It was also found that the dual-energy approach was able to reduce the measurement inconsistencies. However, more work is required with the automation of the dual-energy approach presented in this paper since it is highly operator dependant.

Place, publisher, year, edition, pages
Bristol, United Kingdom: Institute of Physics (IOP), 2016
Keyword
Multi-materials, computed tomography, dual-energy, metrology, measurement consistency, varying material thickness
National Category
Mechanical Engineering
Research subject
Mechanical Engineering
Identifiers
urn:nbn:se:oru:diva-52976 (URN)10.1088/0957-0233/27/11/115013 (DOI)000385929400008 ()2-s2.0-84992365816 (Scopus ID)
Available from: 2016-10-14 Created: 2016-10-14 Last updated: 2017-01-20Bibliographically approved

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