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More Than a Shadow: Computed Tomography Method Development and Applications Concerning Complex Material Systems
Örebro University, School of Science and Technology.ORCID iD: 0000-0002-9362-8328
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The complexity of the components fabricated in today's industry is ever increasing. This is partly due to market pressure, but it is also a result from recent progress in fabrication technologies that open up new design 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 bring benets in many areas such as; mechanical properties, weight reduction, and multifunctions. However, the increased complexity also makes inspection and dimensional control more dicult. 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, industrial computed tomography is still not a fully mature method and there are many uncertainties associated with the investigation technique. In this work, a dual-energy computed tomography tool has been developed with the aim to increase the performance of computed tomography when investigating complex geometries and material combinations. This method has been applied to various phantoms and an industrial case. Also, in this work, complex lattice structures fabricated with additive manufacturing have been investigated and analysed using computed tomography. The results show that the new DECT method improves measurement results and can be utilized to inspect multi-material components. The results also show that computed tomography can be used successfully to gain knowledge about complex lattices.

Place, publisher, year, edition, pages
Örebro: Örebro University , 2019. , p. 139
Series
Örebro Studies in Technology, ISSN 1650-8580 ; 84
National Category
Other Mechanical Engineering
Identifiers
URN: urn:nbn:se:oru:diva-73739ISBN: 978-91-7529-286-1 (print)OAI: oai:DiVA.org:oru-73739DiVA, id: diva2:1305049
Public defence
2019-06-12, Örebro universitet, Teknikhuset, Hörsal T, Fakultetsgatan 1, Örebro, 13:15 (English)
Opponent
Supervisors
Available from: 2019-04-15 Created: 2019-04-15 Last updated: 2019-06-13Bibliographically approved
List of papers
1. 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)In: iCT 2016, NDT.net , 2016, p. 143-150Conference 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
NDT.net, 2016
Keywords
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: 2019-06-13Bibliographically approved
2. 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, article id 115013Article 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
Keywords
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: 2019-05-13Bibliographically approved
3. Non-linear dual-energy method development and evaluation for industrial computed tomography
Open this publication in new window or tab >>Non-linear dual-energy method development and evaluation for industrial computed tomography
2019 (English)In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 30, no 6, article id 065006Article in journal (Refereed) Published
Abstract [en]

Industrial computed tomography of multi-material objects can be problematic due to difficulties in optimising the x-ray spectra of the scan. A possible solution to the problem is to use two x-ray spectra when scanning objects. The results from such scans can be fused into a single data-set that contains enhanced information. This practice is known as dual-energy computed tomography (DECT). In this work, the aim was to investigate two DECT methods ability to improve measurements in multi-material phantoms. To determine the performance of the methods three different phantoms containing precision spheres as measurement objects were investigated. To improve measurements in this work was defined as improving the measurement consistency of diameter measurements. The phantoms were also scanned with a single setting for comparison. The fusion of the data-sets was done using two methods, a linear fusion, and a novel non-linear fusion. Both of the methods relies on pre-reconstruction fusion of data-sets. The results show that both of the DECT methods improved measurement results significantly compared to the reference method. Further, the results show that the novel non-linear DECT method produces more accurate measurement results compared to the linear method.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2019
Keywords
Industrial computed tomography, dual-energy, metrology, multi-material, measurement consistency
National Category
Engineering and Technology Mechanical Engineering
Research subject
Physics
Identifiers
urn:nbn:se:oru:diva-74031 (URN)10.1088/1361-6501/ab10cc (DOI)000466894300001 ()
Available from: 2019-05-03 Created: 2019-05-03 Last updated: 2019-06-19Bibliographically approved
4. Multi-material gap measurements using dual-energy computed tomography
Open this publication in new window or tab >>Multi-material gap measurements using dual-energy computed tomography
2018 (English)In: Precision engineering, ISSN 0141-6359, E-ISSN 1873-2372, Vol. 54, p. 420-426Article in journal (Refereed) Published
Abstract [en]

X-ray computed tomography is a highly versatile investigation method with applications in a wide range ofareas. One of the areas where the technique has seen an increased usage, and an increased interest from industry,is in dimensional metrology. X-ray computed tomography enables the measurement of features and dimensionsthat are difficult to inspect using other methods. However, there are issues with the method when it comes tomeasurements of objects that consist of several materials. In particular, it is difficult to obtain accurate computedtomography results for all materials when the attenuation of materials differs significantly. The aim of this workwas to measure small air gaps between different materials using dual-energy X-ray computed tomography. Thedual-energy method employed in this work uses two energy spectra and fuses the data in the projections spaceusing non-linear fusion. The results from this study show that the dual-energy method used in this work was ableto capture more measurements than regular absorption computed tomography in the case of specimens withhighly different attenuation, enabling, in particular, the measurement of smaller gaps. The contrast-to-noise ratiowas also increased significantly with the use of dual-energy.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Metrology, Computed tomography, Dual-energy, Multi-material measurements
National Category
Mechanical Engineering
Research subject
Mechanical Engineering
Identifiers
urn:nbn:se:oru:diva-68991 (URN)10.1016/j.precisioneng.2018.07.012 (DOI)000452579900046 ()2-s2.0-85051065309 (Scopus ID)
Funder
EU, FP7, Seventh Framework Programme, 607817
Available from: 2018-09-21 Created: 2018-09-21 Last updated: 2019-05-13Bibliographically approved
5. Characterisation of additive manufacturing metal: carbon-fibre composite bond by dual-energy computed tomography
Open this publication in new window or tab >>Characterisation of additive manufacturing metal: carbon-fibre composite bond by dual-energy computed tomography
2017 (English)In: EUSPEN, Conference Proceedings, Special Interest Group: Dimensional Accuracy and Surface Finish in Additive Manufacturing, Octrober 2017, KU Leuven, Belgium: EUSPEN , 2017, p. 189-192Conference paper, Published paper (Refereed)
Abstract [en]

Joining of dissimilar materials is a topic of high interest for the industry. The ability to seamlessly join materials with significant differences in properties would advance the development of efficient designs and concepts within many fields. In this work, bonds between aluminium and carbon-fibre reinforced plastic have been studied. The aluminium side of the bonds were fabricated using classical methods (milling) and additive manufacturing. Two types of bonds were fabricated using additive manufacturing, one flat, relying on the rough surface for adhesion in the bond, and the other with surface features designed to hook into the carbon-fibre plies. All the bonds were fabricated using wet layup of carbon-fibre, the idea was that the aluminium parts would bond to the plastic composite in one step. The bonds were characterised using dual-energy computed tomography. The method used in this work was non-linear and based around fusing of projections acquired with different energy spectra. The mechanical strength of the bonds was also evaluated, both through tensile tests and four-point bending.It was found that the bonds including additive manufactured aluminium was stronger than the milled samples in general. In the computed tomography data, it could be seen that the adhesion in those bonds were better, most likely due to the rough surface. The strongest bonds were those with additive manufacturing surface features. However, the computed tomography data revealed that these bonds have difficulties with integration between the surface features and the carbon-fibre plies.

Place, publisher, year, edition, pages
KU Leuven, Belgium: EUSPEN, 2017
Keywords
Additive manufacturing, Dual-energy computed tomography, carbon-fibre composite, joining
National Category
Mechanical Engineering
Research subject
Mechanical Engineering
Identifiers
urn:nbn:se:oru:diva-61550 (URN)978-0-9957751-1-4 (ISBN)
Conference
EUSPEN, Conference Proceedings, Special Interest Group: Dimensional Accuracy and Surface Finish in Additive Manufacturing, Katholieke Universiteit Leuven, October 2017
Available from: 2017-10-16 Created: 2017-10-16 Last updated: 2019-05-13Bibliographically approved
6. Dual-energy computed tomography investigation of additive manufacturing aluminium: carbon-fibre composite joints
Open this publication in new window or tab >>Dual-energy computed tomography investigation of additive manufacturing aluminium: carbon-fibre composite joints
2019 (English)In: Heliyon, ISSN 2405-8440, Vol. 5, no 2, article id e01200Article in journal (Refereed) Published
Abstract [en]

In this work, aluminium–carbon-fibre reinforced plastic joints have been studied. Three types of samples were designed as double lap joints where the aluminium inserts were fabricated using both classical methods (milling) and additive manufacturing. Two versions of the joint were fabricated using additive manufacturing, one flat, and the other with small teeth designed to hook into the carbon-fibre plies. The joints were characterised using a non-linear, dual-energy computed tomography method to evaluate the bond between the composite and the metal inserts. The mechanical strength of the bonds was evaluated, both through tensile tests and four-point bending. A simple finite element model was used to discuss the joints behaviour. It was found that the joints fabricated using additive manufactured inserts were more resistant to peel stress than the milled inserts. In four-point bending tests the moment that the joint could withstand was increased by roughly 300% with the use of additive manufacturing and 400% with the use of additive manufacturing and small teeth. However, in tensile tests it was found that the teeth design reduced the maximum load capacity of the joints by roughly 30% due to porosity. Further, it was found that the additive manufactured samples did not add to the capability of withstanding shearstress. The information gained with the dual-energy computed tomography method was highly valuable as the behaviour of the joints would have been difficult to explain without the porosity information.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Mechanical engineering, Materials science
National Category
Mechanical Engineering
Research subject
Mechanical Engineering
Identifiers
urn:nbn:se:oru:diva-72142 (URN)10.1016/j.heliyon.2019.e01200 (DOI)000460082200023 ()30839940 (PubMedID)2-s2.0-85061013958 (Scopus ID)
Available from: 2019-02-05 Created: 2019-02-05 Last updated: 2019-06-19Bibliographically approved
7. Surface vs Truss lattice networks, benefits and limitations
Open this publication in new window or tab >>Surface vs Truss lattice networks, benefits and limitations
2018 (English)In: NAFEMS nordic: Exploring the Design Freedom of Additive Manufacturing through Simulation, NAFEMS , 2018, p. 217-218Conference paper, Published paper (Refereed)
Abstract [en]

The use of additive manufacturing is growing rapidly among industries within many different fields of fabrication. The benefits of applying additive manufacturing can be many and an application that have received special interest is the ability to design lightweight components. Lightweight components can be fabricated with additive manufacturing with the use of lattices that have a high stiffness to weight ratio and topology optimised, complex, designs. The most commonly used lattices today are based on trusses, however, there is also the possibility to generate lattices based around continuous surfaces. In this study, the properties of the popular body-centred-cubic lattice are compared the properties of the lesser known Schwartz diamond surface lattice. The mechanical compression properties, the fabrication processes, and the possibilities of the lattices are discussed and analysed.

Place, publisher, year, edition, pages
NAFEMS, 2018
National Category
Engineering and Technology Composite Science and Engineering
Research subject
Mechanical Engineering
Identifiers
urn:nbn:se:oru:diva-70704 (URN)
Conference
NAFEMS Nordic 2018, Göteborg, Sweden, 24-25 April, 2018
Available from: 2018-12-12 Created: 2018-12-12 Last updated: 2019-06-13Bibliographically approved
8. In-situ computed tomography investigation of the compression behaviour of strut, and periodic surface lattices
Open this publication in new window or tab >>In-situ computed tomography investigation of the compression behaviour of strut, and periodic surface lattices
2019 (English)In: iCT 2019 / [ed] Rolf Diederichs, NDT.net , 2019, p. 221-227Conference paper, Published paper (Refereed)
Abstract [en]

In this work the effects of fabrication errors in the Body Centered Cubic strut lattice, and the periodic surface lattice Schwarz Diamond has been investigated. The lattices were both fabricated as-is and with induced errors to evaluate the lattices response to fabrication errors. The behaviour of the lattices were studied using compression test and in-situ computed tomography investigation. The results show that the Schwarz Diamond lattices in general are stronger than the Body Centered Cubic lattices in all of the measured aspects. Often up to five times stronger. It was also found that the elastic behaviour of the Schwarz Diamond lattices were mainly unaffected by fabrication errors while the Body Centered Cubic lattices experienced severe losses in performance. The behaviour of the lattices under compression could be followed using computed tomography which aided in the understanding of their behaviour.

Place, publisher, year, edition, pages
NDT.net, 2019
Keywords
Additive manufacturing, computed tomography, periodic surface lattices, in-situ compression, fabrication error
National Category
Engineering and Technology Mechanical Engineering
Research subject
Mechanical Engineering
Identifiers
urn:nbn:se:oru:diva-72514 (URN)
Conference
9th Conference on Industrial Computed Tomography (iCT) 2019, 13-15 Feb, 2019, Padova, Italy
Available from: 2019-02-18 Created: 2019-02-18 Last updated: 2019-06-13

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