| 1. |
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| 2. |
- Fredriksson, Hans, 1974
(författare)
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Nanostructured carbon materials prepared by hole-mask colloidal lithography
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Research and development of nanofabrication methods can be motivated both formanufacturing of commercially available products like micro electronic componentsand for development of model systems for fundamental and applied science. Thefabrication process developed during this work, hole-mask colloidal lithography(HCL), is primarily oriented towards the latter two, specifically for research in thefields of catalysis, nanoparticle plasmons, and bio- and fundamental physics. Designof structured samples with precise control over size and shape of the nanostructuresare crucial components in all of these fields.The thesis describes the hole-mask colloidal lithography (HCL) technique, the generalprinciples of HCL and the technical and functional differences from standard colloidallithograpy (CL). The technique is illustrated with examples giving details on how tofabricate features with diameters from ~40 to 400 nm and with different shapes andmutual orientations. Some of the demonstrated geometries are discs, ellipses, cones,particle pairs and particles buried into a TiO2 surface.The nanostructuring of carbon materials using the HCL technique is described indetail. Nanostructured carbon surfaces are relevant as model systems to study theoptical properties of naturally occurring nanocarbon structures like aerosols andinterstellar dust. The applied fabrication process utilizes oxygen plasma to etch thepart of the carbon surfaces, not protected by the HCL mask. Analysis of the structuresize and shape resulting from the applied process parameters gives information aboutthe materials durability in reactive oxygen atmospheres, which is valuable forapplications where carbon materials are exposed to similar environments.The HCL technique is used to create etch-masks subsequently used to nanostructurecarbon surfaces via oxygen RIE. HOPG and GC surfaces are patterned in parallelusing identical fabrication processes. Careful characterization of the resulting size andshape of the carbon nanostructures, using SEM and AFM, revealed a significantdifference in response to oxygen plasma treatments for the two materials. On HOPGlateral etching under the etch mask is effectively suppressed thus resulting inpractically no undercut while GC is subject to severe etching under the masks. Theetch rate in the forward direction was found to be more than three times higher for GCthan HOPG (0.65 and 0.19 nm/s respectively). The HOPG nanostructuring processwas also followed with spectrophotometry, revealing decreased reflectance as a resultof the evolution of nanostructures. Part of the change in reflectance is due to thepresence of the etch mask, which consists of gold nanodiscs, but the major part isattributed to the carbon nanostructures.
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| 3. |
- Fredriksson, Hans, 1974, et al.
(författare)
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Resonant optical absorption in graphite nanostructures
- 2009
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Ingår i: Journal of Optics A: Pure and Applied Optics. - 1361-6617 .- 1464-4258. ; 11:11
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Tidskriftsartikel (refereegranskat)abstract
- A systematic investigation of the correlation between optical absorption and the size of graphitenanostructures is presented. Five different samples with structure diameters ranging from ∼160to 330 nm and heights from ∼60 to 190 nm were prepared. The disk-like nanostructures wereetched out of the basal plane surface of highly oriented pyrolytic graphite, using hole-maskcolloidal lithography and oxygen reactive ion etching. Optical absorption spectra forwavelengths between 200 and 2500 nm were then measured. Furthermore, electrodynamicscalculations were conducted to model the optical properties of graphite nanostructures ofsimilar sizes. Both the experimental and the theoretical work revealed resonant absorptioncorrelated to the nanostructure diameters and heights. These absorption peaks are red-shifted,from the visible for the smallest structures to near infrared for the largest. Simultaneously, theintensity of the absorption peaks increases for increasing structure heights, while increasingdiameters results in decreased absorption.
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| 4. |
- Komitov, Lachezar, 1944, et al.
(författare)
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Electrically commanded surfaces for nematic liquid crystal displays
- 2005
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 86
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Tidskriftsartikel (refereegranskat)abstract
- Electrically commanded surfaces (ECS) is a liquid crystal display concept whereby the switching of the alignment layer, which is driven by an electric field applied across the layer, is further transferred to the bulk liquid crystal material via elastic forces. This work presents the electro-optic response of a sandwich cell with alignment layer made of siloxane-based ferroelectric liquid crystal polymer, representing the ECS. The bulk liquid crystal material of choice was an in-house nematic mixture comprising fluorinated liquid crystalline compounds with negative dielectric anisotropy (Delta-epsilon < 0). We report a distinct linear electro-optic response, arising from the field-induced in-plane switching of the nematic which in turn is mediated by the ECS. © 2005 American Institute of Physics. [DOI: 10.1063/1.1849844]
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| 5. |
- Škarabot, Miha, et al.
(författare)
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Direct evidence of the molecular switching in electrically commanded surfaces for liquid crystal displays
- 2005
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Ingår i: Journal of Applied Physics. - 0021-8979 .- 1089-7550. ; 98
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Tidskriftsartikel (refereegranskat)abstract
- This work, performed by means of time-resolved high-resolution birefringence measurements, establishes the switching mechanism of electrically commanded surfaces _ECS_ for liquid-crystal displays. A distinct polar electro-optic response, due to the field-induced in-plane switching of the molecules of the 200-nm ferroelectric liquid crystalline polysiloxane alignment layer representing ECS, was detected in a cell filled with isotropic liquid _hexadecane_. The similarity between this response and the one reported recently in cells containing the same ECS but with a nematic liquid-crystal bulk with negative dielectric anisotropy (Delta-epsilon < 0) and field-free planar alignment provides direct and unambiguous proof that the switching in these cells is indeed mediated by the ECS. © 2005 American Institute of Physics. _DOI: 10.1063/1.2009071_
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| 6. |
- Ringsberg, Jonas, 1971, et al.
(författare)
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Sheet metal fatigue near nuts welded to thin sheet structures
- 2008
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Ingår i: International Journal of Fatigue. - : Elsevier BV. - 0142-1123. ; 30:5, s. 877-887
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Tidskriftsartikel (refereegranskat)abstract
- One of the fatigue design processes of a car body is stress-based sheet metal fatigue near nuts welded to thin sheets (weld nuts). In this investigation, the influence from nut geometry and dimension, as well as sheet material and thickness on sheet metal fatigue life was studied by fatigue experiments and numerical analyses. The fatigue experiments were force-controlled and carried out on a weld nut specimen which, during the reversed loading that was applied, was designed to result in bending fatigue loading conditions of the sheet metal near the weld nut. The results from the experiments were Fa–N curves for various combinations of nut geometry and dimension, sheetmaterial and thickness. Numerical analyses of the experiments were carried out by linear elastic finite element (FE) analyses, in order to transform the Fa–N curves to Wöhler (sig_a–N) curves. A simplified FE model of the weld nut, which is suitable for structural analysis of car body structures, was used. The structural stresses calculated using the FE model showed good agreement with the structural stresses calculated using an analytical model that is based on plate theory. The conclusion was that the simplified representation of the weld nut, and the mesh density used in the FE model, was appropriate for computation of the stress response near a weld nut subjected to bending fatigue loading conditions. Finally, ra–N curves were computed for each weld nut configuration using its experimental data set. A sig_a–N curve fitted to all data sets resulted in the relation sig_a = 9888N^0.312. The sig_a–N curves for the 21 weld nut configurations tested were gathered within a factor of three in fatigue life from this curve.
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| 7. |
- Vuorinen, Esa, et al.
(författare)
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Laser surface hardening of steel with ausferritic structure
- 2008
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Ingår i: SMT22.
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Konferensbidrag (refereegranskat)abstract
- High strength steels can be produced by austempering of Si-containing steels. High toughness and good wear resistance are properties possible to achieve. Surface hardening of this group of steels can give an additional increase of the surface hardness and wear resistance. Laser surface hardening has been used in order to increase the surface hardness of the steel 55Si7. The effect of surface hardening on the ferritic-austenitic carbide- free microstructure created for this steel has been studied. Optical as well as scanning electron microscopy has been used in the characterization of the micro-structural changes.
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| 8. |
- Lyphout, Christophe, 1981-, et al.
(författare)
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Characterization of adhesion strenght of HVOF sprayed IN718 coatings
- 2009
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Ingår i: Proceedings of th 22nd Internationa Conference on Surface Modification technolgies - SMT22. Trollhättan, Sweden. - : VALAR Docs. - 9780981706511 ; , s. 11-18
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Konferensbidrag (refereegranskat)abstract
- The tensile adhesion strength of thermally sprayed coating is conventionally evaluated via the ASTM C633-69 standard. The maximum measurable adhesion is then limited by the adhesion strength of the polymer media. High velocity oxy-fuel (HVOF) spraying can exhibit very high bonding strength and thus it is essential to develop an alternative method to evaluate coating adhesion strength. In this work a Modified Tensile Adhesion Test (MTAT) is proposed replacing gluing with induction brazing. The method was evaluated for HVOF sprayed Inconel 718 coatings deposited on Inconel 718 substrates. The effect of induction brazing process and the characteristics of the braze-coating interface was given particular interest. The results indicate that the method is superior to the ASTM C633-69 for characterisation of adhesion of coatings with high bond strength.
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| 9. |
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| 10. |
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| 11. |
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| 12. |
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| 13. |
- Arsenault, B., et al.
(författare)
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Aluminum protective coatings - Fatigue and bond strength properties with respect to surface preparation techniques : Laser ablation, shot peening and grit blasting
- 2006
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Ingår i: Canadian metallurgical quarterly. - 0008-4433 .- 1879-1395. ; 45:1, s. 49-58
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Tidskriftsartikel (refereegranskat)abstract
- Aluminum coatings can provide galvanic cathodic protection for several metals and alloys. In order to be a suitable protective solution on structural components, the mechanical integrity must be preserved. In particular, the fatigue properties are a challenge for thermal spray protective coatings on mechanical structures. To address the issue of the fatigue integrity of 7075 aluminum alloy with an arc sprayed protective coating, different surface preparations prior to arc spraying were considered. In the present work, a feasibility study was performed using laser ablation as a surface preparation technique before or during arc spraying of coatings through collaboration between the LERMPS laboratory in France, the National Research Council of Canada and the Royal Military College of Canada. Both fatigue and adhesive properties of aluminum coatings were evaluated in relation to substrate surface preparation techniques including laser ablation (PROTAL® process), grit blasting and shot peening. Results indicate that a combination of key conditions including using nitrogen as the arc spray gas, shot peening and proper laser energy density for ablation provides high fatigue resistance of metallic coated 7075 alloy substrates. Specimens prepared under these conditions show a similar fatigue resistance to uncoated substrates. © Canadian Institute of Mining, Metallurgy and Petroleum.
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| 14. |
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| 15. |
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| 16. |
- Ryttberg, Kristina, 1977, et al.
(författare)
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Electron microscopy of white-etching band generated by high-velocity parting-off of 100CrMn6 steel
- 2008
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Ingår i: Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing. - : Elsevier BV. - 0921-5093. ; 480:1-2, s. 489-495
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Tidskriftsartikel (refereegranskat)abstract
- High-velocity parting-off has been applied to 80 mm bars of pearlitic 100CrMn6, resulting in shear localisation and white-etching bands in a severely deformed region below the fracture surface. Electron microscopy showed that going from the bulk material towards the fracture surface the grains become elongated and refined. The region below the fracture surface can be divided into three subzones: 50–100 μm below the surface grains are elongated, cementite lamellae are distorted, break up and the lamellar spacing decreases.
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| 17. |
- Ryttberg, Kristina, 1977, et al.
(författare)
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High strain rate deformation induced by high-velocity forming of 100Cr6 steel
- 2008
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Ingår i: proceedings of The 9th International Conference on Technology of Plasticity (ICTP), Gyeongju, Korea, September 7-11, 2008. - 9788957081525 ; , s. On CD or www.ictp2008.org-
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Konferensbidrag (refereegranskat)abstract
- This paper concerns the development of the near-net-shape manufacturing technique of high-velocity forming. The microstructural response to the high strain-rate deformation was evaluated for 100Cr6 steel in two differently heat treated conditions: spheroidise annealed (hardness 250 HV) and quenched and tempered (330 HV). A high-velocity pressing machine was used to conduct the forming tests on cylindrical specimens. By applying different impact velocities on samples with varying sizes deformation mechanisms could be related to strain and strain rate. Extreme localization of deformation resulting in white etching bands was seen in quenched and tempered samples but not in spheroidise annealed samples. Furthermore, the strain and strain rates were shown to affect the tendency for extreme localization. No white etching bands were found in samples strained to less than 1. Appearance of white etching bands could be seen in the macroscopic shape of the samples where the more homogeneously deformed samples showed a typical barrel shape while the strongly localized samples were slightly more bell shaped. It can be concluded that for high-velocity forming to be applicable to 100Cr6 steel a careful choice of the combination strain/strain rate needs to be made.
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| 18. |
- Ryttberg, Kristina, 1977, et al.
(författare)
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Microstructural evolution during fracture induced by high strain rate deformation of 100Cr6 steel
- 2009
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Ingår i: Journal of Materials Processing Technology. - : Elsevier BV. - 0924-0136. ; 209:7, s. 3325-3334
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the influence on parting-off mechanisms of a significantly higher impact velocity compared to commercial methods. A specially developed method, allowing for parting-off velocities ranging from 38 to 285 m/s has been applied to 100Cr6 steel bars. Two different heat treatments; spheroidise annealing (SA) and quench and tempering (QT) were employed to produce two different microstructures of a hardness of 255 and 310HV, respectively. It appears that the failure mechanisms active in the current process are virtually identical to failure occurring during high-velocity parting-off using commercially available machines, which displays shear fracture and adiabatic shear banding. It was also concluded that the estimated energy consumed during parting-off is not dependent on microstructure. Prior to parting-off, impact results in shear localisation, which is somewhat increased with increased impact speed. Furthermore, shear strains at fracture also increaseswith impact speed, from a value of about 2.2 at the lowest impact velocity to almost 3.5 at an impact velocity of 285 m/s. The heavy deformation causes a grain refinement. Right below the fracture surface three subzones can be found in the microstructure; a white etching band (WEB) (only present on some locations), equiaxed grains and then elongated subgrains. The grain size within these zones varies between 50 and 150 nm. The findings of elongated subgrains of a mutual orientation, adjacent subgrains having {110} type of planes in parallel, support the theory of formation of white etching bands being a mechanically rate controlled process.
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| 19. |
- Ryttberg, Kristina, 1977, et al.
(författare)
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Microstructure and texture development during ring rolling of 100Cr6
- 2008
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Ingår i: Ceramic Transactions. - 1042-1122. - 9781574982961 ; 200, s. 301-309
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Konferensbidrag (refereegranskat)abstract
- Pre-turned 100Cr6 steel rings with spheroidised annealed microstructure have been cold ring rolled to two levels: expanding the outer diameter by 10 and 20%. The final microstructure was shown to be varying throughout the cross-section of the ring, where the largest deformation was found close to the surface of the inner diameter. This was reflected in the hardness profile showing the highest hardness values close to the inner surface. Scanning electron microscopy showed that the microstructure below the surface of the outer diameter consisted of a greatly refined ferrite. Close to the surface of the inner diameter the structure was even more refined. Electron back scatter diffraction together with X-ray diffractometry showed that cold ring rolling changed the existing texture of the ring blanks, where {110}-planes were parallel to the axial direction of the rings, towards {110}-planes becoming parallel to the rolling direction. This resulted in a weak {110}-texture. Close to the surface of the outer diameter the greatly refined ferrite had decomposed into a more random orientation distribution.
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| 20. |
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| 21. |
- Norman, Peter, et al.
(författare)
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A sophisticated platform for characterization, monitoring and control of machining
- 2006
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Ingår i: Measurement science and technology. - BRISTOL, ENGLAND : IOP Publishing. - 0957-0233 .- 1361-6501. ; 17:4, s. 847-854
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Tidskriftsartikel (refereegranskat)abstract
- The potential for improving the performance of machine tools is considerable. However, for this to be achieved without tool failure or product damage, the process must be sufficiently well understood to enable real-time monitoring and control to be applied. A unique sophisticated measurement platform has been developed and applied to two different machining centres, particularly for high-speed machining up to 24 000 rpm. Characterization and on-line monitoring of the dynamic behaviour of the machining processes has been carried out using both contact-based methods (accelerometer, force sensor) and non-contact methods (laser Doppler vibrometry and magnetic shaker) and numerical simulation (finite element based modal analysis). The platform was applied both pre-process and on-line for studying an aluminium testpiece based on a thin-walled aerospace component. Stability lobe diagrams for this specific machine/component combination were generated allowing selection of optimal process parameters giving stable cutting and metal removal rates some 8-10 times higher than those possible in unstable machining. Based on dynamic characterization and monitoring, a concept for an adaptive control with constraints based machine tool controller has been developed. The developed platform can be applied in manifold machining situations. It offers a reliable way of achieving significant process improvement
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| 22. |
- Alexe-Ionescu, Anca-Luiza, et al.
(författare)
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Anchoring of nematic liquid crystals on a thin polymeric film
- 2008
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Ingår i: PHYSICAL REVIEW E. - 1539-3755. ; 77
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Tidskriftsartikel (refereegranskat)abstract
- We analyze the influence of a thin polymer layer with lateral side groups on the anchoring of a nematic liquid crystal. We show that the effective anisotropic part of the anchoring energy depends on the coupling of the nematic with the polymer side groups, as well as on the coupling of the polymer side groups with the surface. The relaxation time for the nematic orientation induced by an external field is evaluated by considering the surface dissipation connected to the relative motion of the nematic director with respect to the polymer side groups.
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| 23. |
- Bengtsson, Magnus, 1973, et al.
(författare)
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Improving Yield and Shape in a Crushing Plant
- 2009
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Ingår i: Proceedings of 12th European Symposium on Comminution and Classification (ESCC2009).
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Konferensbidrag (refereegranskat)abstract
- There is increasing demand to optimise yield and increase capacity of crushing plants. Research in this area has resulted in the development of numerous optimisation tools, and resent research has shown that the quality aspects of production have great influence on the optimisation results. The quality and capacity of a product is influenced by several parameters, and in order to control all these parameters it is necessary to use some sort of optimisation software. In this paper, a novel approach to analyse parameters influence on product capacity and quality is presented. As an example a cone crusher and a vertical shaft impact crusher (VSI) is simulated in a tertiary stage. The simulation shows how capacity and product quality for a range of products will be affected when a parameter is changed. The paper also shows how wear will affect product capacity and quality.
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| 24. |
- Komitov, Lachezar, 1944, et al.
(författare)
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Controllable alignment of nematics by nanostructured polymeric layers
- 2009
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Ingår i: Liquid Crystals. - 1366-5855 .- 0267-8292. ; 36:6 & 7, s. 747-753
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Tidskriftsartikel (refereegranskat)abstract
- A method for a continuous control of the pretilt angle of the easy axis in the range 0-90° degrees and of the anchoring strength by using nanostructured polymers as alignment layers is described. The nanostructured polymers are blends of two different side-chain polymers each of them promoting planar and homeotropic alignment, respectively. A model to interpret the alignment of a nematic liquid crystal induced by such polymer layers is proposed. We show that in this case the anisotropic part of the surface tension can be approximated by a simple extension of the Rapini-Papoular expression. The predicted trend of the pretilt of the easy axis versus the concentration of the side-chain polymer promoting the planar alignment, for instance, is in good agreement with the experimental data. We also show that the effective anchoring strength of the system depends on the concentration of the side-chain polymer promoting planar alignment, and exhibits a minimum for a well-defined value of this quantity. The results obtained in this work seems to be of importance for liquid crystal displays technology since the control of the pretilt and the anchoring strength strongly affect the performance of liquid crystal displays.
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| 25. |
- Komitov, Lachezar, 1944, et al.
(författare)
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Nano-Structured Polymers for Alignment Layers in LCDs
- 2008
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Ingår i: SID Symposium Digest of Technical Papers. - : Wiley. - 0097-966X. ; 39:1, s. 598-599
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Tidskriftsartikel (refereegranskat)abstract
- By employing a nano-engineering approach, nano-structered polymers were designed, synthesised and used as materials for alignment layers in LCDs. Such materials make possible to control the molecular tilt angle in a broad range, from 0° to 90°, and they seems to enable the control of the anchoring strength as well.
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| 26. |
- Fredriksson, Hans, 1974, et al.
(författare)
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Patterning of highly oriented pyrolytic graphite and glassy carbon surfaces by nanolithography and oxygen plasma etching
- 2009
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Ingår i: Carbon. - 0008-6223. ; 47:5, s. 1335-1342
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a process for the fabrication of nanostructures on two types of carbon surfaces; glassy carbon (GC) and the basal surface of highly oriented pyrolytic graphite (HOPG). Using hole-mask colloidal lithography, etch masks with three different feature diameters were prepared on each of the two surface types. Oxygen reactive ion etching of different durations was then used to transfer the mask pattern onto the surfaces, yielding nanopillars with diameters ranging from not, vert, similar40 to 470 nm and heights between not, vert, similar30 and 430 nm. The structures were characterized using atomic force microscopy, scanning electron microscopy and optical spectrophotometry. Identical preparation schemes applied to the two materials yield nanostructures with remarkably different geometrical properties. In general GC structures are higher and narrower than HOPG structures prepared at the same plasma conditions. From the nanostructure dimensions and the corresponding etch times we have estimated etch rates in the forward and lateral directions to 0.19 and 0.015 nm/s for HOPG and 0.65 and 0.15 nm/s for GC. The different rates are attributed to different (an)isotropic etching behavior of the two materials in oxygen plasma. In addition, optical characterization reveals interesting changes in the surface reflectance as a result of the nanostructuring.
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| 27. |
- Ericsson, Mikael, 1975-, et al.
(författare)
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Three dimensional simulation of robot path, heat transfer and residual stresses of a welded part with complex geometry
- 2005
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Ingår i: International jourrnal for the joining of materials. - 0905-6866. ; 17:2, s. 42-51
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Tidskriftsartikel (refereegranskat)abstract
- In this article a simulation system is presented that combines computer aided robotics software used to define the welding operation, with a finite element model that predicts temperature-time histories and residual stress distributions for welding applications. The objective is to develop a tool for engineering processes in which robot trajectories and welding process parameters can be optimized off-line on parts with complex geometries. The system was evaluated on a stainless steel gas turbine component. Temperature dependent properties and phase change were included in the analysis. The turbine component was welded using an in-house TIG welding cell. The assumptions and principles that underpin the modeling techniques are presented together with predicted temperature histories, residual stresses, and fixture forces. Predicted residual stresses were compared with neutron diffraction measurements.
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| 28. |
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| 29. |
- Nordström, Michael, et al.
(författare)
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An appearance-based measure of surface defects
- 2009
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Ingår i: International Journal of Material Forming. - : Springer Science and Business Media LLC. - 1960-6206 .- 1960-6214. ; 2:2, s. 83-91
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Tidskriftsartikel (refereegranskat)
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| 30. |
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| 31. |
- Sikström, Fredrik, 1971-, et al.
(författare)
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3D-Scanning for Weld Distortion Measuring
- 2006
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Ingår i: Instrumentation and Measurement Technology Conference, 2006. IMTC 2006. Proceedings of the IEEE. - : IEEE conference proceedings. - 0780393600 - 0780393597 ; , s. 2132-2137
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Konferensbidrag (refereegranskat)abstract
- Optical three dimensional scanning for weld distortion measurements have been performed for validation, inspection, general visualization and documentation of a robotized welding process. The planning, preparing and processing of the weld is done in a simulation-based concept where computer aided robotics software simulations are integrated with finite element analysis simulations with the objective to reduce global geometrical deformation during welding. The off-line programmed robot paths were used as an input for finite element calculations of temperature fields and distortion in the work piece. In order to validate the finite element model 3D-scannings have been performed before and after every single welding sequence. This paper describes a validation experiment with non-contact measurements of weld distortion and discusses limitations in optical 3D-scanning techniques used for this purpose
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| 32. |
- Frodelius, Jenny, et al.
(författare)
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Ti2AlC coatings deposited by High Velocity Oxy-Fuel spraying
- 2008
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 202:24, s. 5976-5981
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Tidskriftsartikel (refereegranskat)abstract
- High Velocity Oxy-Fuel has been utilized to spray coatings from Ti2AlC (MAXTHAL 211®) powders. X-ray diffraction showed that the coatings consist predominantly of Ti2AlC with inclusions of the phases Ti3AlC2, TiC, and Al–Ti alloys. The fraction of Ti2AlC in coatings sprayed with a powder size of 38 μm was found to increase with decreasing power of the spraying flame as controlled by the total gas flow of H2 and O2. A more coarse powder (56 μm) is less sensitive to the total gas flow and retains higher volume fraction of MAX-phase in the coatings, however, at the expense of increasing porosity. X-ray pole figure measurements showed a preferred crystal orientation in the coatings with the Ti2AlC (000l) planes aligned to the substrate surface. Bending tests show a good adhesion to stainless steel substrates and indentation yields a hardness of 3–5 GPa for the coatings sprayed with a powder size of 38 μm.
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| 33. |
- Gryczynski, I., et al.
(författare)
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Directional two-photon induced surface plasmon-coupled emission
- 2005
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090. ; 491:1-2, s. 173-176
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Tidskriftsartikel (refereegranskat)abstract
- We measured a directional surface plasmon-coupled emission (SPCE) induced by a two-photon absorption. A 60 nm thick layer of poly(vinyl alcohol) film doped with rhodamine 123 was deposited on a silvered (50 nm Ag) glass slide, which was attached to a hemicylindrical glass prism. The 820 nm excitation from a femtosecond Ti:Sapphire laser was used either in reverse Kretschmann or Kretschmann configuration. The angular distribution of two-photon induced SPCE does not depend on the used configuration. The two-photon induced SPCE can be applied to improve immunoassays and deoxyribonucleic acid detection. © 2005 Elsevier B.V. All rights reserved.
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| 34. |
- Josefson, Lennart, 1954, et al.
(författare)
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Assessment of uncertainties in life prediction of fatigue crack initiation in rails – influence of residual stresses from manufacturing
- 2007
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Ingår i: Proceedings of The 8th International Conference on Multiaxial Fatigue & Fracture (ICMF&M8). ; , s. 1-8
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Konferensbidrag (refereegranskat)abstract
- The risk for initiation of fatigue cracks in the web in the weld zone of a rail is studied. The interaction between the welding residual stress field and the stress field caused by service loads is simulated in a nonlinear finite element (FE) analysis where the welding residual stress distribution (shape) and magnitude, the service load magnitude, and the material parameters used in the fatigue life estimation are varied. The initiation of fatigue cracks is assessed using the shear-stress-based multiaxial fatigue criterion proposed by Dang Van. In addition, the accuracy in the fatigue life assessment is evaluated by statistical uncertainty analysis where the variances according to the Gauss approximation formula are studied. It is seen that the welding residual stress enhances the risk for fatigue crack initiation in the rail web, and that the uncertainty in load level dominates the uncertainty in the fatigue assessment.
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| 35. |
- Svoboda, Ales, et al.
(författare)
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Integrated approach for prediction of stability limits for machining with large volumes of material removal
- 2008
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Ingår i: International Journal of Production Research. - : Informa UK Limited. - 0020-7543 .- 1366-588X. ; 46:12, s. 3207-3222
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Tidskriftsartikel (refereegranskat)abstract
- High-speed machining of thin-walled structures is widely used in the aeronautical industry. Higher spindle speed and machining feed rate, combined with a greater depth of cut, increases the removal rate and with it, productivity. The combination of higher spindle speed and depth of cut makes instabilities (chatter) a far more significant concern. Chatter causes reduced surface quality and accelerated tool wear. Since chatter is so prevalent, traditional cutting parameters and processes are frequently rendered ineffective and inaccurate. For the machine tool to reach its full utility, the chatter vibrations must be identified and avoided. In order to avoid chatter and implement optimum cutting parameters, the machine tool including all components and the work piece must be dynamically mapped to identify vibration characteristics. The aim of the presented work is to develop a model for the prediction of stability limits as a function of process parameters. The model consists of experimentally measured vibration properties of the spindle-tool, and finite element calculations of the work piece in (three) different stages of the process. Commercial software packages used for integration into the model prove to accomplish demands for functionality and performance. A reference geometry that is typical for an aircraft detail is used for evaluation of the prediction methodology. In order to validate the model, the stability limits predicted by the use of numerical simulation are compared with the results based on the experimental work.
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| 36. |
- Fredriksson, Hans, 1974
(författare)
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Nanostructures of Graphite and Amorphous Carbon - Fabrication and Properties
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nanoscience is a well-established research area, which concerns properties and fabrication of objects with typical dimensions on the 1-100 nanometer length scale. A central issue has been the development of techniques for fabrication and characterization of nanometer sized objects, which have contributed considerably to progress in both practical applications and fundamental research. Still, a standing challenge in nanofabrication is to further decrease the size limit and increase the precision in structure fabrication, with a simultaneous increase in reliability and cost-efficiency. Other goals are to facilitate fabrication of nanostructures in a variety of materials, with different geometries and spatial distributions. Examples of practical applications of nanofabrication are, electronic devices, nanoparticle reinforced composite materials, materials for extraction and storage of energy, sensors and biomedical applications. In this thesis, the development and application of a nanofabrication technique termed hole-mask colloidal lithography (HCL) is described. The technique is based on self-assembly of nanospheres in combination with spin coating and thin film evaporation to produce supported nanostructured masks for etch and/or deposition processes. HCL relies on a parallel process and uses relatively simple laboratory equipment. Therefore it is fast and cost-effective and can be used to structure large surface areas in a reasonable time. Furthermore, HCL is suited for fabrication of nanostructures with a variety of different shapes, with well-defined sizes and in a large variety of different materials. Demonstrated examples include discs, ellipses, bi-metallic particle pairs, cones and inverted ring structures in Au, Ag, Cr. Specifically, the use of HCL to fabricate nanostructures in three different carbon materials, highly oriented pyrolytic graphite (HOPG), glassy carbon (GC) and amorphous carbon, is described. Such nanostructured materials are relevant both in technical applications and in model studies of e.g. soot particles. The manufactured nanostrucutres have been characterized with respect to their geometrical, mechanical, and optical properties, using microscopy and spectroscopy techniques, and their reactivity towards oxidation has been explored. From studies of such samples, it is concluded that the etch rate in oxygen plasma is different for HOPG and GC, which influences the resulting size and shape of the nanostructures after the applied oxidation treatment. It is also shown that the atomic arrangement of the HOPG nanostructures is similar to that of the bulk material. Investigations of the optical properties reveal resonant absorption and scattering of light for nanostructures in all three materials, i.e. peak position, amplitude and width of the measured optical spectra are shown to correlate with the nanostructure sizes. This correlation is used to optically monitor oxidation, and the resulting decrease in volume, of carbon nanostructures under high temperature oxidation conditions and is proposed as a general sensing method to study oxidation/combustion of soot and other carbon nanostructures.
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| 37. |
- Dimkovski, Zlate, 1974-, et al.
(författare)
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Towards 3D Characterisation of Cylinder Liner Surfaces
- 2008
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Ingår i: Proceedings / XII. International Colloquium on Surfaces January 28th and 29th, 2008, Chemnitz, Germany = XII. Internationales Oberflächenkolloquium. - Aachen : Shaker Verlag. - 9783832269128 ; , s. 15-24
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Konferensbidrag (refereegranskat)abstract
- Cylinder liner surface has a direct impact on the oil consumption and frictional losses in the internal combustion engines which are in common interest to be as lower as possible. Thus, the optimisation of the liner surface, its function and manufacture is often on the agenda of the automotive industry. Since the liner surface finish is a subject of improving, there is a need of improving and facilitating of its 3D characterisation preliminary when the parameter control limits are unknown, as well as later when it is experimentally verified and the limits are better determined. For that purpose a method for quality control in 3D of cylinder liners is proposed here. A tool was developed and implemented for rating of cylinder liner surfaces, computing of 3D groove parameters (groove width, height and distance between grooves) and determination of a needed number of measurements.
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| 38. |
- Desmaris, Vincent, 1977
(författare)
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Processing, Characterization and Modeling of AlGaN/GaN HEMTs
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- III-Nitrides electronic properties make them currently the materials of choice for high-power high-frequency applications. Their wide bandgaps, high breakdown fields, the high electron peak and saturation velocities combined with the large conduction band offset and the high electron mobility observed in AlGaN/GaN heterostructures enable excellent microwave power performance of AlGaN/GaN high electron mobility transistors (HEMTs). These devices have demonstrated a tenfold increase in output power densities at microwave frequencies compared to standard III-V technologies, opening great perspective for high power microwave electronics. III-Nitride technology has just emerged in the last decade; it is yet neither mature nor completely understood.This thesis deals with the fabrication, characterization, modeling of the RF performance of AlGaN/GaN HEMTs. The physical and electrical properties of the III-Nitrides are described before the operation of these transistors is reviewed. Advanced processing issues are discussed, before presenting the results achieved on this type of transistors. RF modeling of Schottky diodes and transistors are also presented prior to the demonstration of the enhancing performance of circuit demonstrators using such device.A complete fabrication process for the realization of such transistors has been developed and is described in details. The development of a simple and effective method for obtaining very low ohmic contacts (0.23 Ωmm), its characterization and understanding are major achievement. Further development of the in-house process enabled the fabrication of high power transistors HEMTs without field-plate demonstrating a continuous wave output power density of 5 W/mm and 9.7 W/mm at 3 GHz on sapphire and SiC respectivelyA new method for the characterization of microwave Schottky diodes was developed as well as a non linear large signal model for AlGaN/GaN HEMTs. Demonstrating the possibilities of AlGaN/GaN HEMTs for high linearity mixers, the worlds first resistive mixer based on AlGaN/GaN transistors was fabricated using in-house components, exhibiting a minimum conversion loss of 7.3 dB, an IIP3 of 36 dBm for a LO power of 30 dBm.
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| 39. |
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| 40. |
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| 41. |
- Christiansson, Anna-Karin, 1947-, et al.
(författare)
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Automation of a robotised metal deposition system using laser melting of wire
- 2008
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Ingår i: 18th International Conference on<em> </em>Flexible Automation and Intelligent Manufacturing (FAIM 2008). - 9789163327575 ; , s. 122-129
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents a system for full automation of free-form-fabrication of fully dense metal structures using robotized laser melting of wire. The structure is built of beads of melted wire laid side by side and layer upon layer governed by synchronized robot motion. By full automation is here meant that the process starts with a product specification of a component, and ends in a geometrically validated dense metal component fulfilling industrial material requirements. Due to the complexity of this flexible manufacturing system, a number of different disciplines are involved. This paper discusses mainly the system design, which includes how off-line programming is used for automatic generation of code and how feedback control is used for on-line adjustment of parameters based on desired building properties. To meet industrial needs, the project is carried out in a close cooperation between research and development activities in academy and industry.
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| 42. |
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| 43. |
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| 44. |
- Heralic, Almir, 1981-, et al.
(författare)
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Automation of Robotized Laser Metal-Wire Deposition
- 2007
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Ingår i: Proceedings of the ninth IASTED International Conference on Control and Applications. - : ACTA Press. - 9780889866652 ; , s. ID 658-075-
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Konferensbidrag (refereegranskat)
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| 45. |
- Iannuzzi, Giovanna, 1977
(författare)
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On the Characterization and Generation of Flow Marks on Polymeric Surfaces
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Polymer-based materials are widely used in the automotive industry for producing vehicle parts, for instance car bumpers, dash boards etc. A common manufacturing process for such components is injection moulding. Injection-moulded thermoplastics can however exhibit a number of surface defects such as flow marks (or tiger stripes), weld lines, air traps and sink marks. All these imperfections lower the perceived quality of the final products.The attention is here focused on the surface defect commonly denoted “flow marks” or “tiger stripes”. Tiger stripes are alternating glossy and dull bands on the polymer surface. They are approximately perpendicular to the flow directions and often opposite in phase. In other words, if one side of the moulded part shows a dull area, the corresponding region on the opposite side will be glossy. The reasons for the appearance of these stripes are not entirely clear; however a slip-stick phenomenon and/or an unstable flow front during the mould filling are two main hypotheses which might account for their formation. Materials typically used for injection moulding of car components are often based on elastomer-modified polypropylene (PP) containing talc as a filler. The PP-grades in this work here contained between 10 and 15 wt% talc and a very low amount of elastomeric particles.By means of stereographic scanning electron microscopy, it was observed that the surface of the dull bands was rougher than that of the glossy bands. Furthermore, the surface regions of the dull bands contained less filler particles than the corresponding regions of the glossy bands. In order to further understand the relation between the surface topography and the gloss of textured polymeric surfaces, the same SEM technique, combined with a filtering procedure, was used to characterize the surface structure of a number of injection-moulded specimens. The results indicated that small differences in gloss in the low gloss region could be associated with small-scale variations in the surface topography.It is to be expected that the rheological properties of the polymer melts can influence the generation of the flow marks. Hence, the flow properties, mainly in shear, of three different grades of elastomer-modified PP containing mineral fillers were correlated with their propensity for defect generation. It was noted that a higher melt elasticity, as reflected in the pressure losses during flow through a capillary, the degree of die swell and to some extent the dynamic-mechanical behaviour, led to less severe flow marks or retarded the formation of such defects. Elongational draw-down experiments also indicated a more stable behaviour in the case of the melt exhibiting the highest elasticity.
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| 46. |
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| 47. |
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| 48. |
- Ståhlberg, Daniel, et al.
(författare)
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Mechanical response of thermoset polymers under high compressive loads, 1
- 2005
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Ingår i: Macromolecular materials and engineering. - : Wiley. - 1438-7492 .- 1439-2054. ; 290, s. 1063-1072
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Tidskriftsartikel (refereegranskat)abstract
- The present Study describes the mechanical response of thermoset polymers under high compressive loads. A well-defined free radically cured vinyl ester resin has been used and studied in six different geometries in order to determine the dependence of apparent mechanical properties on the particular size and shape of a sample. The mechanical response in compression has also been compared to the response in tensile tests. Variation of the film thickness, boundary conditions and loading conditions reveal that there is a significant effect on the mechanical performance (apparent properties) of the polymer. When the thickness-to-width ratio of the sample is reduced in a compression test, the friction between the sample and the compression plates proves to be I of great importance. The yield stress increases dramatically when the thickness of the sample is reduced, whereas it decreases when the friction between sample and the compression plate is reduced. The creep decreases when the thickness of the material is reduced and it decreases even more due to reaction of the material surrounding the compressed part of I! the sample. The described test conditions and observed I phenomena will be subject to simulation in Part 2 of this study.
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| 49. |
- Bahbou, M. Fouzi, 1973-, et al.
(författare)
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On-Line measurement of plasma-sprayed ni-particles during impact on a ti-surface : influence of surface oxidation
- 2007
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Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 16:6, s. 506-511
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this study was to analyze the impact of plasma-sprayed Ni5%Al particles on polished and grit-blasted Ti6Al4V samples under oxidized and nonoxidized conditions. For this purpose, measurements of thermal radiation and velocity of individual plasma-sprayed particles were carried out. From the thermal radiation at impact, splat diameter during flattening and temperature evolution during cooling were evaluated. Characteristic parameters related to the quality of contact between the splat and the substrate were retrieved. The flattening speed was introduced to characterize wetting, while the cooling rate was used to characterize solidification. The idea was to get a signature of particle impact for a given surface roughness and oxidation state by identifying parameters which strongly affect the splat behavior. Sieved Ni5%Al powder in a narrow range (+65 −75 μm) was sprayed on four sets of titanium alloy surfaces, consisting of polished and grit-blasted samples, one set had a nonoxidized surface and the other one was oxidized in an oven at 600 °C for two hours. Resulting splats after impact were characterized by scanning electron microscopy, the splats on oxidized surface showed pores in their core and detached fingers at the periphery. The cooling rate and flattening degree significantly increased on the oxidized smooth surface compared to the nonoxidized one. This trend was not found in grit-blasted surfaces, which implies that impact phenomena are different on grit-blasted surfaces than on smooth surfaces thus further work is needed.
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| 50. |
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