| 1. |
- Farjana, Sadia, 1983, et al.
(författare)
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Realizing a 140 GHz Gap Waveguide–Based Array Antenna by Low-Cost Injection Molding and Micromachining
- 2021
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Ingår i: Journal of Infrared, Millimeter and Terahertz Waves. - : Springer. - 1866-6892 .- 1866-6906. ; 42:8, s. 893-914
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a novel micromachining process to fabricate a 140 GHz planar antenna based on gap waveguide technology to be used in the next-generation backhauling links. The 140 GHz planar array antenna consists of three layers, all of which have been fabricated using polymer-based microfabrication and injection molding. The 140 GHz antenna has the potential to be used as an element in a bigger 3D array in a line-of-sight (LOS) multiple input multiple output (MIMO) configuration to boost the network capacity. In this work, we focus on the fabrication of a single antenna array element based on gap waveguide technology. Depending on the complexity of each antenna layer’s design, three different micromachining techniques, SU8 fabrication, polydimethylsiloxane (PDMS) molding, and injection molding of the polymer (OSTEMER), together with gold (Au) coating, have been utilized to fabricate a single 140 GHz planar array antenna. The input reflection coefficient was measured to be below − 11 dB over a 14% bandwidth from 132 to 152 GHz, and the antenna gain was measured to be 31 dBi at 140 GHz, both of which are in good agreement with the simulations. © 2021, The Author(s).
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| 2. |
- Thalavai Pandian, Karthikeyan, 1985-
(författare)
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Microstructure and mechanical properties of Ti-6Al-4V manufactured by electron beam powder bed fusion
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ti-6Al-4V is an α+β titanium alloy that is widely used in aerospace engine applications due to its high specific strength. Typically, Ti-6Al-4V components are manufactured by conventional manufacturing processes such as castings or forgings. An alternative to conventional manufacturing processes is additive manufacturing (AM), which can be used to manufacture Ti-6Al-4V components, with increased geometrical complexity and potentially lower buy-to-fly ratio. AM material have been shown to have similar static mechanical properties as conventionally manufactured material, but the fatigue properties can be affected by the as-built surface quality and the defects in the AM material. Among several AM processes, the fatigue properties of electron beam powder bed fusion (PBF-EB) manufactured material have been primarily impacted by the as-built surface asperities. Therefore, for fatigue-critical applications, the as-built surfaces are typically removed by post-build treatment, making it challenging to manufacture net-shape geometries directly. Exploring ways to improve the surface quality of PBF-EB manufactured Ti-6Al-4V will reduce the post-finishing needs and increase sustainability. In the current thesis the effect of different contour settings on the as-built surface roughness and fatigue properties have been investigated.The results indicate that increasing the number of contours and melting the contours prior to the hatch positively affect the surface roughness. Among several roughness parameters, the parameter related to surface valley depths has a statistically significant influence on the fatigue life. Moreover, advanced characterization techniques such as x-ray computed tomography are needed to capture the hidden valleys open to the surface. Fatigue life prediction using these hidden valley depths resulted in life estimations comparable to experimental results.After eliminating the as-built surface asperities, defects in the bulk become critical for fatigue, typically addressed by post-build heat treatment such as hot isostatic pressing (HIP). HIP treatment of conventionally cast Ti-6Al-4V is typically performed at 920 ˚C, 100 MPa for 2 hours. This same HIP treatment has also viii been adapted for PBF-EB manufactured Ti-6Al-4V, which results in coarsening of α laths and reduction of yield strength compared to as-built material. Lowering the HIP treatment temperature to 800 ˚C and increasing the pressure to 200 MPa has recently been proven to close the porosity to a high degree while sustaining the as-built yield strength. However, the fatigue performance of the low-temperature HIP treatment needs to be evaluated which is performed in the current thesis. Even though the low-temperature HIP material had the lowest minimum life cycles to failure, the overall fatigue performance is comparable with that of the standard HIP material. Further, in aerospace engine applications, Ti-6Al-4V normally has a maximum operating temperature of 350 ˚C, therefore the elevated temperature tensile performance has also been investigated in this work. At 350 ˚C, the yield strength decreases to about 65% compared to the room temperature strength for all tested materials. An increase in ductility was observed at 150 ˚C compared to that at room temperature, but the ductility decreased between 150 – 350 ˚C because of the activation of different slip systems.
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| 3. |
- Balachandramurthi, Arun Ramanathan, 1989-, et al.
(författare)
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Anisotropic fatigue properties of Alloy 718 manufactured by Electron Beam Powder Bed Fusion
- 2020
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Ingår i: International Journal of Fatigue. - : Elsevier. - 0142-1123 .- 1879-3452. ; 141
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Tidskriftsartikel (refereegranskat)abstract
- In this study, Alloy 718 specimens manufactured by Electron Beam Powder Bed Fusion process are subjected to two different post-treatments to have different microstructural features. Low cycle fatigue testing has been performed both parallel and transverse to the build direction. EB-PBF Alloy 718 exhibits anisotropic fatigue behaviour; the fatigue life is better along the parallel direction compared to the transverse direction. The anisotropy in fatigue life is related to the anisotropy in the Young’s modulus. The pseudo-elastic stress vs. fatigue life approach is presented as a potential solution to handle anisotropy in fatigue life assessment of additively manufactured engineering components. © 2020 The Authors
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| 4. |
- Falk, Thomas, 1964-
(författare)
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Safety Reviews of Technical System Modifications in the Nuclear Industry
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The function of safety reviews (here understood as expert judgements on proposals for design modifications and redesign of technical systems in commercial Nuclear Power Plants, supported by formalised safety review processes) plays a fundamental role for safety in nuclear installations. The primary aims of the presented case studies includes: critically examining and identifying the main areas for improvement of the existing technical safety review process as it is conducted at a Swedish nuclear power plant, developing a new process, and evaluating whether any improvements were accomplished. By using qualitative methods, observation/participation and interviews, data has been gathered on how the safety review process is perceived and conducted by experts involved in the safety review process, and ways to improve this process have been developed. This area is neglected in the larger safety literature. The novel approach here is to gather data directly from those involved in the safety review process, analysis of safety review reports as well as from inspection reports by the regulatory authority.The study presented in paper I shows that the partition between primary and independent review is positive, having supplementary roles with different focus and staff with different skills and perspectives making the reviews. The study identifies a number of areas for improvement, such as: - a tendency to put too much resource on minor assignments - a clearer prioritization would improve focus on the most critical projects - there is a need for improved guidance and direction for how to structure the work It is argued that future applications of safety review processes should focus more on communicating and clarifying the process and its adherent requirements, and improve the feedback system within the process. It is also recommended that the NPPs create introductory training for new reviewersThe study presented in paper II concluded that grading of the primary safety review reports facilitates improved experience feedback by providing easier access to good examples for reviewers. Improvements identified by implementing the revised process are primarily linked to the independent safety review function, including better planning and means for resource allocation as well as clearer and more unambiguous supporting instructions. Introduction of formalized independent review meetings provides increased exchange of knowledge and strengthened the independent safety review function in the organization.
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| 5. |
- Hansson, Thomas, 1964
(författare)
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Deformation and Fracture of Ceramics and Ceramic Composites
- 1993
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An understanding of the deformation and fracture behaviour of ceramic materials is of considerable importance in the development of ceramics as reliable structural materials. Of particular interest is how such behaviour is influenced by the microstructure, for example in multiphase materials such as composites. With this in mind a study was made of a variety of ceramics and ceramic composites at temperatures between 20 and 1500 °C. The fracture toughnesses of alumina and a variety of alumina based composites, containing SiC whiskers and particles of TiC, B4C and Ti(C,N), have been measured. Quantitative characterization of the crack profiles showed that crack deflection does not enhance toughening in these composites and the fracture toughness of the particulate composites was lower than that of alumina. The higher toughness of the SiC whisker composite was shown to be the result of a change in fracture mode from intergranular for unreinforced alumina to transgranular for the whisker composites. A variation in toughness with crack propagation direction was successfully predicted in terms of a crack deflection model in a composite with uniform whisker distribution. The fracture behaviour of the SiC whisker reinforced alumina was studied at temperatures up to 1400 °C in air and up to 1320 °C in vacuum. At temperatures below 1200 °C in air and 1100 °C in vacuum the material fractured in a linear elastic mode. Above these temperatures a rising R-curve and stable crack growth was observed and the fracture toughness rose substantially. The toughness enhancement was shown to be due mainly to such processes as crack deflection, crack branching, microcrack zone formation and crack tip blunting rather than any temperature-related increase in intrinsic fracture resistance of the material. In air, the fracture mechanisms were influenced by the formation of a glass phase. The fracture toughness of a hot pressed Si3N4 containing 10 vol.% SiC whiskers was studied at temperatures between 20 and 1400oC, and the crack propagation rates were measured for cyclic and static loading at 1300 and 1400 °C. A maximum in fracture toughness observed at 1300 °C is concluded to be due to crack shielding and crack morphology rather than a change in intrinsic toughness. Stable crack growth was shown to occur during the high temperature fracture toughness tests. The present material exhibited crack growth rates, da/dt, that increased with increasing frequency. This is explained by ligaments of the base material bridging the crack. The tensile creep behaviour of a sintered alumina was studied at temperatures between 1150 and 1350 °C and stresses between 4 and 67 MPa. The stress exponent was 1.3 and the activation energy for creep was 620 kJ/mol. Grain boundary sliding accompanied by diffusion creep (Nabarro-Herring) and cavitation are suggested as the dominating creep mechanisms under the present test conditions. Nucleation, growth and coalescence of cavities is suggested as the failure mechanism at lower loads while microcrack growth determines failure at higher loads. The knoop indentation hardness in SiC whisker reinforced alumina was shown to fall with increasing temperature up to 1365 °C, and SiC whiskers was shown to harden alumina at temperatures above 600 °C. In pin-on-plate sliding friction in vacuum, the coefficient of friction ( µ) decreases almost continuously with temperature. Stick-slip becomes significant above 900 °C and this is considered to reflect a tendency to increased adhesion. Formation of graphite, combined with very smooth wear track due to extensive plastic deformation of the surface, serves to keep µ low at temperatures above 900 °C. The tribological behaviour of the composite under these conditions was determined more by chemical effects than the micromechanical behaviour.
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| 6. |
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| 7. |
- Kjellsson, Henrik, et al.
(författare)
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High Temperature Fatigue Performance of Electron Beam Powder Bed Fusion Manufactured Alloy 718
- 2022
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer Nature. - 1073-5623 .- 1543-1940. ; 53, s. 2496-2514
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure and mechanical properties of additively manufactured (AM) parts have been shown to be different from that of cast and wrought counterparts. In this study, electron beam powder bed fusion (EB-PBF) fabricated Alloy 718 was exposed to three different heat treatment routes followed by strain-controlled fatigue testing at 550 degrees C. The fatigue tests were performed with specimens built with their center axis parallel and transverse relative to the build direction. The microstructure showed saturated precipitation of delta-Ni3Nb after repeated solution treatment at 954 degrees C. In contrast, no delta-Ni3Nb precipitates could be observed after a single-step solution treatment at 1025 degrees C. However, the disparity of secondary phases showed no noticeable influence on the fatigue life. A significant difference in fatigue behavior was noted between the parallel and transverse directions. The specimens loaded parallel to the elongated grains showed on average similar to 5x greater life in comparison to the perpendicularly loaded specimens. Compared to corresponding heat-treated material conditions tested at ambient temperature, the specimens showed lower life at high strain amplitude and superior life at low strain amplitude. Moreover, competitive internal and surface failure modes were observed at the lower strain amplitudes while for the higher strain ranges, surface failure modes dominated. (C) The Author(s) 2022
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| 8. |
- Linge, Anna, 1964-
(författare)
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Creative Musical Practice in an Educational Context
- 2015
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Ingår i: Contemporary approaches to activity theory. - Hershey : IGI Global. - 9781466666030 - 146666603X - 9781466666047 ; , s. 143-160
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- This chapter is based on the author's doctoral thesis. She provides an account of a project on creativity in music education, more specifically a musical classroom for developing creativity. The aim of the study is to find examples or mechanisms of creative pedagogy. This study complements the current tradition for studying methods in teaching and learning music. Creative, prescriptive, and communicative designs of teaching and learning interact during sessions of music making. The empirical findings enable a discussion of the conditions that define creative music making as art and/or play as a socio-cultural activity.
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| 9. |
- Mesch, Johanna, 1963-, et al.
(författare)
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Swedish Sign Language resources from a user’s perspective
- 2024
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Ingår i: Proceedings of the LREC-COLING 2024 11th Workshop on the Representation and Processing of Sign Languages. - Paris : ELRA Language Resources Association (ELRA) and the International Committee on Computational Linguistics (ICCL). - 9782493814302 ; , s. 54-61
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Konferensbidrag (refereegranskat)abstract
- The Swedish Sign Language Dictionary [Svenskt teckenspråkslexikon] is one of the most visited websites at Stockholm University, with four million visits each year. The dictionary is an easy-to-use resource for the community, families, relatives, students, educators, researchers and other stakeholders that can be accessed through the website, app, and mobile platforms. STS-korpus is an online interface for the Swedish Sign Language Corpus that is linked to the STS Dictionary, enhancing its utility. Other applications, like TSP Quiz and the STS transcription tool, will also be evaluated. In January 2024, we conducted a survey to explore how users utilise Swedish sign language resources in their everyday lives, studies and work, regardless of hearing status and sign language skills. The purpose is to evaluate these resources from a user’s perspective, including aspects such as user-friendliness, relevance, comprehensibility and effectiveness in aiding language learning or communication.
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| 10. |
- Mesch, Johanna, 1963-, et al.
(författare)
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Teckenspråkslexikografi - utmaningar i en annan modalitet
- 2022
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Teckenspråkslexikon och -korpusar som flerspråkiga resurser har olika användningsområden, t.ex. andraspråksinlärning (Leeson et al., 2019) och framtida automatisk översättning (Kopf et al., 2021). Svenskt teckenspråkslexikon (Björkstrand, 2008), tillgängligt online sedan 2008, är välbesökt. Föregångarna var Teckenspråk (Österberg, 1916) och Svenskt Teckenspråkslexikon (1997), båda i bokform. I denna artikel presenterar vi följande: a) konstruktion av teckenspråkslexikon, där tekniska lösningar krävs för inspelningar, elicitering och insamling av tecken (Riemer Kankkonen et al., 2018), teckenbeskrivning för bl.a. handform och rörelseriktning, sökfunktioner, publicering i olika applikationer, samt samverkan mellan lexikon och korpus; och b) lexikografiska frågeställningar som lemma, fonologiska varianter, sammansättningar och munrörelser. Databasen för Svenskt teckenspråkslexikon består av över 23000 tecken varav 19700 är publicerade. Översättning av tecken till svenska tjänar som grund för s.k. teckenposter, vilket dock inte innebär att varje tecken har en motsvarighet i svenskan. De flesta teckenposter innehåller teckendemonstration, användningsexempel, fotoillustration och teckentranskription baserad på Bergman och Björkstrands (2015) transkriptionssymboler. Vidare har etymologisk beskrivning nyligen lagts till. I lexikonet har sökvägar skapats för att kunna söka på svenska ord, översättning, andra betydelser, alternativa tecken, handform, ämnesområde, m.m. Samverkan mellan lexikon och korpus har resulterat i web-applikationen STS-korpus (Öqvist et al., 2020) och ett nytt korpus- och forskningsbaserat lexikon, STS-signbank, som fortfarande är under konstruktion.Lexikografiska frågor är väsentliga i utvecklingsarbetet. Ett par exempel på dessa frågor är vilka tecken som är “tillåtna” i lexikonet, hur definiera vad som är ett lexikalt tecken, s.k. kärntecken, och vad som är lemma, d.v.s. grundformen av ett ord/uttryck. Val utifrån manuella komponenter möjliggör sökning baserad på teckenform, medan val av teckenbegrepp utifrån begreppsmässiga, semantiska grunder är inte kopplade till det manuella lemmat (Fenlon et al., 2015; McKee & Vale, 2017; Schermer, 2006). Ytterligare exempel på det utvecklingsarbete som nu pågår är införlivandet av sammansättningar, lexikaliserade avbildande tecken och bokstaveringar i lexikonets befintliga struktur.
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