| 1. |
- Grolig, Jan Gustav, 1986
(author)
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Coated Ferritic Stainless Steels as Interconnects in Solid Oxide Fuel Cells - Material Development and Electrical Properties
- 2015
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Doctoral thesis (other academic/artistic)abstract
- Solid oxide fuel cells (SOFCs) are attracting increasing interest as devices with potentialuses in decentralized and clean electricity and heat production. Several challengeswith respect to materials have to be overcome to achieve efficiencies and life-spansthat are sufficient for long-term applications.An important element of an SOFC stack is the interconnect component, which connectstwo adjacent fuel cell elements. Interconnects, which are commonly composedof ferritic stainless steels, have to be corrosion-resistant, mechanically stable and costoptimized.This work aimed to investigate economic solutions for interconnect materials and tounderstand the underlying mechanisms of degradation and electrical conduction ofthese materials. Mainly two substrates, a commercially available steel (AISI 441) anda ferritic stainless steel that was optimized for an SOFC application (Sandvik SanergyHT) were combined with different barrier coatings and exposed to a cathode-sideatmosphere. A method was developed that allows for the electrical characterizationof promising material systems and model alloys, thereby facilitating a fundamentalunderstanding of the dominant electrical conduction processes linked to the oxidescales that grow on interconnects. The AISI 441 steel coated with reactive elementsand cobalt showed good corrosion and chromium evaporation profiles, while AISI 441coated with cerium and cobalt also had promising electrical properties. The SanergyHT steel was examined with coatings of copper and iron and copper and manganese,respectively. The corrosion and chromium evaporation profiles of Sanergy HT wereimproved by coating with copper and iron. The copper and iron-coated Sanergy HTshowed lower area specific resistance values than cobalt-coated Sanergy HT. Chromia,which is the main constituent of oxide scales, was synthesized using differentmethods. The electrical properties of chromia were found to be sensitive to not onlyimpurities, but also heat treatment. Finally the electrical properties of cobalt- andcobalt cerium-coated Sanergy HT steels were investigated. It was revealed that theaddition of cerium improved the conductivity of the interconnect by both slowingdown chromia growth and preventing the outward diffusion of iron into the spinel.
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| 2. |
- Jeong, Seung Hee, 1978-
(author)
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Soft Intelligence : Liquids Matter in Compliant Microsystems
- 2016
-
Doctoral thesis (other academic/artistic)abstract
- Soft matter, here, liquids and polymers, have adaptability to a surrounding geometry. They intrinsically have advantageous characteristics from a mechanical perspective, such as flowing and wetting on surrounding surfaces, giving compliant, conformal and deformable behavior. From the behavior of soft matter for heterogeneous surfaces, compliant structures can be engineered as embedded liquid microstructures or patterned liquid microsystems for emerging compliant microsystems.Recently, skin electronics and soft robotics have been initiated as potential applications that can provide soft interfaces and interactions for a human-machine interface. To meet the design parameters, developing soft material engineering aimed at tuning material properties and smart processing techniques proper to them are to be highly encouraged. As promising candidates, Ga-based liquid alloys and silicone-based elastomers have been widely applied to proof-of-concept compliant structures.In this thesis, the liquid alloy was employed as a soft and stretchable electrical and thermal conductor (resistor), interconnect and filler in an elastomer structure. Printing-based liquid alloy patterning techniques have been developed with a batch-type, parallel processing scheme. As a simple solution, tape transfer masking was combined with a liquid alloy spraying technique, which provides robust processability. Silicone elastomers could be tunable for multi-functional building blocks by liquid or liquid-like soft solid inclusions. The liquid alloy and a polymer additive were introduced to the silicone elastomer by a simple mixing process. Heterogeneous material microstructures in elastomer networks successfully changed mechanical, thermal and surface properties.To realize a compliant microsystem, these ideas have in practice been useful in designing and fabricating soft and stretchable systems. Many different designs of the microsystems have been fabricated with the developed techniques and materials, and successfully evaluated under dynamic conditions. The compliant microsystems work as basic components to build up a whole system with soft materials and a processing technology for our emerging society.
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| 3. |
- Mellin, Pelle, 1985-, et al.
(author)
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Nano-sized by-products from metal 3D printing, composite manufacturing and fabric production
- 2016
-
In: Journal of Cleaner Production. - Sweden : Elsevier. - 0959-6526 .- 1879-1786. ; 139, s. 1224-1233
-
Journal article (peer-reviewed)abstract
- Recently, the health and environmental perspective of nano-materials has gained attention. Most previous work focused on Engineered Nanoparticles (ENP). This paper examines some recently introduced production routes in terms of generated nano-sized by-products. A discussion on the hazards of emitting such particles and fibers is included. Fine by-products were found in recycled metal powder after 3D printing by Selective Laser Melting (SLM). The process somehow generated small round metal particles (~1e2 mm) that are possibly carcinogenic and respirable, but not small enough to enter by skin-absorption. With preventive measures like closed handling and masks, any health related effects can be prevented. The composite manufacturing in particular generated ceramic and carbonaceous particles that are very small and respirable but do not appear to be intrinsically toxic. The smallest features in agglomerates were about 30 nm. Small particles and fibers that were not attached in agglomerates were found in a wide range of sizes, from 1 μm and upwards. Preventive measures like closed handling and masks are strongly recommended. In contrast, the more traditional production route of fabric production is investigated. Here, brushing residue and recycled wool from fabric production contained few nano-sized by-products.
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| 4. |
- André, Benny
(author)
-
Nanocomposites for Use in Sliding Electrical Contacts
- 2011
-
Doctoral thesis (other academic/artistic)abstract
- In this thesis nanocomposite materials for use in high performance electrical contacts are tested. Self mating silver as coatings on cupper substrates are the most used material combination in power connectors today. In this work two new concepts were tested. The first one was to change one of the mating surfaces to a hard thin coating and keep the other surface made of silver. Tested coatings were nanocomposites with hard carbides in a matrix of amorphous carbon. TiC/a-C and Ti-Ni-C/a-C were tested both electrically and tribologically. The total amount of carbon and the amount of carbon matrix was important, both for the electrical and the tribological properties. The Ti-Ni-C coating also showed that substituting Ti in TiC with the weak carbide former Ni changed the stability of the carbides. The substitution resulted in more a-C matrix and less C in the carbides. Thin coatings of nc-TiC/a-C and Ti-Ni-C/a-C showed high potential as material candidates for use in electrical contacts. The other tested concept was to modify the used silver instead of replacing it. This was done by embedding nanoparticles of solid lubricant IF-WS2 in the silver. The results from reciprocating sliding displayed low friction and high wear resistance. The modified silver surfaces lasted for 8000 strokes with a friction of about 0.3 while at the same time allowing for a low contact resistance. The results for surfaces of pure silver coating displayed a friction of 0.8-1.2 and that the silver was worn through already after 300 strokes. A new method to investigate inherent hardness and residual stress of thin coatings, on complex geometries or in small areas, was also developed. An ion beam was used to create stress free coating as free standing micro pillars. Hardness measured on the pillars and on as-deposited coating were then used to calculate the residual stress in the coatings.
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| 5. |
- Heshmati, Mohsen, 1987, et al.
(author)
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On the strength prediction of adhesively bonded FRP-steel joints using cohesive zone modelling
- 2018
-
In: Theoretical and applied fracture mechanics (Print). - : Elsevier BV. - 0167-8442 .- 1872-7638. ; 93, s. 64-78
-
Journal article (peer-reviewed)abstract
- The variety of failure modes that are likely to occur in fibre-reinforced polymer (FRP)/steel joints used in the construction industry adds to the complexity associated with the design of these joints. This variation in possible failure modes is mainly attributed to the lack of a controlled application environment and to rather insufficient quality assurance protocols and procedures. The use of energy-based methods such as, cohesive zone modelling (CZM), can be a solution to circumvent such complexities. This paper investigates a number of issues related to CZM analyses of FRP/steel adhesive joints using various test configurations and a comprehensive numerical study. Parameters such as the effect of shape and type of cohesive law, crack path location, length of damage process zone, variations of adhesive and FRP properties, and different failure modes including cohesive, interfacial debonding and FRP failure on the strength of joints are investigated. The results show that the behaviour of the tested joints is accurately predicted provided that the variation of failure modes are taken into account. Moreover, it is shown that the damage process zone in adhesive layer is directly proportional to the shape of cohesive laws. This feature can be employed in the design phase to ensure sufficient overlap length and to account for important in-service parameters such as temperature and moisture.
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| 6. |
- Okda, Sherif, et al.
(author)
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Testing of the Aerodynamic Characteristics of an Inflatable Airfoil Section
- 2020
-
In: Journal of Aerospace Engineering. - 1943-5525 .- 0893-1321. ; 33:5
-
Journal article (peer-reviewed)abstract
- Inflatable structures are characterized by being light and easy to manufacture and deploy. Hence, they find many applications in aerospace and aeronautical engineering. In this paper, an inflatable segment with a The National Advisory Committee for Aeronautics (NACA) 0021 airfoil cross-section is designed, fabricated, and tested. The geometrical accuracy of the manufactured inflatable segment is measured using laser scanning. Measurements show that the average normalized error of the chord length and thickness are 2.97% and 0.554%, respectively. The aerodynamic behavior of the inflatable segment is then tested in a wind tunnel at different wind speeds and angles of attack. Lift forces are measured using a six-component balance, while the drag forces are calculated from the wake measurements. The lift and drag coefficients of the inflatable section are compared to those of a standard NACA 0021 airfoil. Finally, flow visualization is examined at different angles of attack using two methods: smoke and tufts. Both methods show that flow separation starts at 15° and full stall occurs at 25°. Results indicate that inflatables can find more applications in the design and construction of aerodynamic structures, such as wings.
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| 7. |
- Hosseini, Seyedehsan, 1994, et al.
(author)
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Alkyl ketene dimer modification of thermomechanical pulp promotes processability with polypropylene
- 2024
-
In: Polymer Composites. - 1548-0569 .- 0272-8397. ; 45:1, s. 825-835
-
Journal article (peer-reviewed)abstract
- Alkyl ketene dimers (AKDs) are known to efficiently react with cellulose with a dual polarity in their structure: a polar component and a nonpolar component. AKD of three different carbon chain lengths, 4, 10, and 16 carbons have been synthesized, and thermomechanical pulp (TMP) fibers were modified by them. The modification of TMP fibers with AKD resulted in an increased water contact angle, showing the presence of the AKDs on the TMP fibers and a new carbonyl peak in the IR spectra, suggesting modification of the TMP fibers with AKD groups. Calculating the Hansen solubility parameters of AKD and AKD conjugated to TMP in polypropylene (PP) indicates improved compatibility, especially of longer chain AKD and TMP AKD. The rheological studies of the composites showed that the AKD with the longest carbon chain decreases the melt viscosity of the PP-TMP-AKD composite, which combined with the shape and the color of the extruded composite filaments indicates improved flow properties and reduced stress build up during processing. The research findings demonstrate the ability of AKD to enhance the dispersibility and compatibility of natural fibers with PP.
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| 8. |
- Marklund, Erik, et al.
(author)
-
Stiffness of aligned wood fiber composites: Effects of microstructure and phase properties
- 2008
-
In: Journal of composite materials. - : SAGE Publications. - 0021-9983 .- 1530-793X. ; 42:22, s. 2377-2405
-
Journal article (peer-reviewed)abstract
- The effect of wood fiber anisotropy and their geometrical features on wood fiber composite stiffness is analyzed. An analytical model for an N-phase composite with orthotropic properties of constituents is developed and used. This model is a straightforward generalization of Hashin's concentric cylinder assembly model and Christensen's generalized self-consistent approach. It was found that most macro-properties are governed by only one property of the cell wall which is very important in attempts to back-calculate the fiber properties. The role of lumen (whether it filled by resin or not) has a very large effect on the composite shear properties. It is shown that several of the unknown anisotropic constants characterizing wood fiber are not affecting the stiffness significantly and rough assumptions regarding their value would suffice. The errors introduced by application of the Hashin's model and neglecting the orthotropic nature of the material behavior in cylindrical axes are evaluated. The effect of geometrical deviations from circular cross-section, representing, for example, collapsed fibers, is analyzed using the finite element method (FEM) and the observed trends are discussed.
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| 9. |
- Hosseini, Seyedehsan, 1994
(author)
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Additive-Driven Improvements in Interfacial Properties and Processing of TMP-Polymer Composites
- 2023
-
Doctoral thesis (other academic/artistic)abstract
- Efforts to address environmental concerns have resulted in new regulations designed to plan the reduction of plastic and synthetic polymer usage, necessitating the search for sustainable natural alternatives with comparable cost-effectiveness and mechanical performance. Thermomechanical pulp (TMP) fibres are one of the most affordable natural fibres that have no chemical refining in production, production have a high yield of 90-98% and TMP fibres have been demonstrated to improve the mechanical characteristics (strength, stiffness and toughness) of wood-polymer composites (WPCs) compared to the pure polymer. The integration of TMP fibres with non-polar synthetic polymers remains a challenge due to surface polarity differences. This PhD thesis aims to ease the processing of TMP fibre composites through the incorporation of additives. The hypothesis posits that incorporating magnesium stearate (MgSt), molybdenum disulfide (MoS2) and alkyl ketene dimer (AKD) as additives in TMP composites will enhance interfacial properties, resulting in improved processability and flow behaviour at high temperatures. MoS2 is known for its interaction with lignin, which exists in TMP and MgSt is recognised for its ability to improve flow in pharmaceutical processing when combined with cellulose, also a component of TMP. AKD modifies the hydrophilic properties of lignocellulosic surfaces. The experimental work explores the effect of these additives on the properties of TMP composites of ethylene acrylic acid copolymer (EAA) and polypropylene (PP) matrices. The dynamic mechanical analysis (DMA) and mechanical analysis results reveal that MoS2 exhibits superior interaction with TMP fibres, yielding enhanced interfacial properties compared to MgSt in between EAA and TMP fibres. Rheological studies elucidate the transition from a fluid-like state to a network-like structure upon the incorporation of TMP into the PP matrix. The incorporation of AKD with C18 reduces the viscosity of TMP-PP composites and PP itself, and, as determined through theoretical Hansen solubility parameter (HSP) calculations, increases compatibility between cellulose in TMP fibres and PP. The addition of AKD influences both the colour (lighter) and shape (smoother surface) of the extrudate filaments in the TMP-PP composites, indicative of improved processing. In addition, frictional analysis demonstrates the reduction of the coefficient of friction (COF) between metal and TMP fibre by MgSt and AKD treatments.
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| 10. |
- Mahade, Satyapal, 1987-, et al.
(author)
-
Incorporation of graphene nano platelets in suspension plasma sprayed alumina coatings for improved tribological properties
- 2021
-
In: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 570
-
Journal article (peer-reviewed)abstract
- Graphene possesses high fracture toughness and excellent lubrication properties, which can be exploited to enhance tribological performance of coating systems utilized to combat wear. In this work, suspension plasma spray (SPS) process was employed to deposit a composite, graphene nano-platelets (GNP) incorporated alumina coating. For comparison, monolithic alumina was also deposited utilizing identical spray conditions. The as-deposited coatings were characterized in detail for their microstructure, porosity content, hardness, fracture toughness and phase composition. Raman analysis of the as-deposited composite coating confirmed retention of GNP. The composite coating also showed good microstructural integrity, comparable porosity, higher fracture toughness and similar alumina phase composition as the monolithic alumina coating. The as-deposited coatings were subjected to dry sliding wear tests. The GNP incorporated composite coating showed lower CoF and lower specific wear rate than the pure alumina coating. Additionally, the counter surface also showed a lower wear rate in case of the composite coating. Post-wear analysis performed by SEM/EDS showed differences in the coating wear track and in the ball wear track of monolithic and composite coatings. Furthermore, Raman analysis in the wear track of composite coating confirmed the presence of GNP. The micro-indentation and wear test results indicate that the presence of GNP in the composite coating aided in improving fracture toughness, lowering CoF and specific wear rate compared to the monolithic coating. Results from this work demonstrated retention of GNP in an SPS processed coating, which can be further exploited to design superior wear-resistant coatings.
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| 11. |
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| 12. |
- Mirkhalaf, S. Mohsen, 1982, et al.
(author)
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A finite element based orientation averaging method for predicting elastic properties of short fiber reinforced composites
- 2020
-
In: Composites Part B-Engineering. - : Elsevier BV. - 1359-8368. ; 202
-
Journal article (peer-reviewed)abstract
- Short fiber reinforced composites have a variety of micro-structural parameters that affect their macromechanical performance. A modeling methodology, capable of accommodating a broad range of these parameters, is desirable. This paper describes a micro-mechanical model which is developed using Finite Element Analysis and Orientation Averaging. The model is applicable to short fiber reinforced composites with a wide variety of micro-structural parameters such as arbitrary fiber volume fractions, fiber aspect ratios and fiber orientation distributions. In addition to the Voigt and Reuss assumptions, an interaction model is developed based on the self-consistent assumption. Comparisons with experimental results, and direct numerical simulations of Representative Volume Elements show the capability of the model for fair predictions.
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| 13. |
- Lindberg, Siv M, et al.
(author)
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A product semantic study of the influence of the sense of touch on the evaluation of wood-based materials
- 2013
-
In: Materials & design. - : Elsevier BV. - 0264-1275 .- 1873-4197 .- 0261-3069. ; 52, s. 300-307
-
Journal article (peer-reviewed)abstract
- Based on product semantics, this study investigated how the tactile attributes of wood and wood-based composites are perceived and interpreted semantically. The wood-based samples included ash, birch, elm, oak, pine, OSB (oriented strand board), two wood pulp-reinforced polylactide composites, Comp A and B and one wood-fiber reinforced polypropene composite, Comp C. The subjects rated the samples by the descriptive words natural, exclusive, eco-. friendly, rough, inexpensive, reliable, warm, modern, snug and solid. The most significant differences between the samples were found for roughness and for the descriptors, reliable, natural and solid. A principal component analysis yielded three attributes based on the tactile perceptions: reliable, old-. fashioned and smooth. The solid wood pieces were perceived as natural and oak was perceived as being exclusive. The composite materials presented a greater variation in terms of perceived attributes than the wood specimens.
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| 14. |
- Åkerfeldt, Maria, 1982, et al.
(author)
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Textile piezoelectric sensors – melt spun bi-component poly(vinylidene fluoride) fibres with conductive cores and poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) coating as the outer electrode
- 2014
-
In: Fashion and Textiles. - : Springer Science and Business Media LLC. - 2198-0802. ; 1:1
-
Journal article (peer-reviewed)abstract
- The work presented here addresses the outer electroding of a fully textile piezoelectric strain sensor, consisting of bi-component fibre yarns of β-crystalline poly(vinylidene fluoride) (PVDF) sheath and conductive high density polyethylene (HDPE)/carbon black (CB) core as insertions in a woven textile, with conductive poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS) coatings developed for textile applications. Two coatings, one with a polyurethane binder and one without, were compared for the application and evaluated as electrode material in piezoelectric testing, as well as tested for surface resistivity, tear strength, abrasion resistance and shear flexing. Both coatings served their function as the outer electrodes in the system and no difference in this regard was detected between them. Omission of the binder resulted in a surface resistivity one order of magnitude less, of 12.3 Ω/square, but the surface resistivity of these samples increased more upon abrasion than the samples coated with binder. The tear strength of the textile coated with binder decreased with one third compared to the uncoated substrate, whereas the tear strength of the coated textile without binder increased with the same amount. Surface resistivity measurements and scanning electron microscopy (SEM) images of the samples subjected to shear flexing showed that the coatings without the binder did not withstand this treatment, and that the samples with the binder managed this to a greater extent. In summary, both of the PEDOT:PSS coatings could be used as outer electrodes of the piezoelectric fibres, but inclusion of binder was found necessary for the durability of the coating.
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| 15. |
- Nyflött, Åsa, 1986-
(author)
-
Structure-Performance Relations of Oxygen Barriers for Food Packaging
- 2017
-
Doctoral thesis (other academic/artistic)abstract
- Food packaging should ensure the safety and quality of food, minimize spoilage and provide an easy way of storing and handling it. Barrier coatings are generally used to meet the demands placed on fibre-based food packages, as these have the ability to regulate the amount of gases that can enter them. Some gases are detrimental to food quality: oxygen, for example, initiates lipid oxidation in fatty foods. Using both experimental data and computer modelling, this thesis explains some aspects of how the structure of barrier coatings influences the mass transport of oxygen with the aim of obtaining essential knowledge that can be used to optimize the performance of barriers.Barrier coatings are produced from polyvinyl alcohol and kaolin blends that are coated onto a polymeric support. The chemical and physical structures of these barriers were characterized according to their influence on permeability in various climates. At a low concentration of kaolin, the crystallinity of polyvinyl alcohol decreased; in the thinner films, the kaolin particles were orientated in the basal plane of the barrier coating. The experimental results indicated a complex interplay between the polymer and the filler with respect to permeability.A computer model for permeability incorporating theories for the filled polymeric layer to include the polymer crystallinity, addition of filler, filler aspect ratio and surrounding moisture was developed. The model shows that mass transport was affected by the aspect ratio of the clay in combination with the clay concentration, as well as the polymer crystallinity. The combined model agreed with the experiments, showing that it is possible to combine different theories into one model that can be used to predict the mass transport.Four barrier coatings: polyethylene, ethylene vinyl alcohol + kaolin, latex + kaolin and starch were evaluated using the parameters of greenhouse gas emissions and product costs. After the production of the barrier material, the coating process and the end-of-life handling scenarios were analysed, it emerged that starch had the lowest environmental impact and latex + kaolin had the highest.
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| 16. |
- Forsgren, Lilian, 1990
(author)
-
Processing and properties of thermoplastic composites containing cellulose nanocrystals or wood-based cellulose fibres
- 2020
-
Doctoral thesis (other academic/artistic)abstract
- Cellulose nanocrystals (CNC) were surface modified with dialkylamines to increase the compatibility between the CNC and the polymeric matrix, and promising results were obtained, with a 300 % stiffness increase when the mixed dispersion was compression moulded on a laboratory scale. The manufacturing process was up-scaled using water-assisted mixing in a twin-screw extruder (TSE) followed by a second compounding step and injection moulding (IM). The composites were successfully produced using conventional melt-processing techniques but these did not show the same improvement in mechanical performance, probably due to the formation of CNC aggregates. There were indications of network formation when CNC was added, especially in the case of surface-modified CNC. Cellulose fibres and thermomechanical pulp were used as reinforcement in similar types of polymer matrices and the mixtures were similarly processed by TSE and IM. These materials were characterized with regard to appearance and durability. The discoloration of the composites due to excessive heat during processing did not significantly affect their mechanical properties, and the addition of the cellulose-based reinforcement to the polymer did not reduce its resistance to thermo-oxidative degradation compared to that of the pure matrix. In fact, the resistance to degradation was increased when lignin was present in the reinforcing element, showing a synergistic effect together with the added anti-oxidant. Superior properties were expected for the CNC composites compared to those of the larger cellulose fibre reinforcements, but in continuous production the stiffening effects were similar regardless of reinforcement type. These results confirm that the processing method and properties strongly affect the final properties of the composite.
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| 17. |
- Moldenhauer, Patrick, 1983, et al.
(author)
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Chemical-looping combustion with heavy liquid fuels in a 10 kW pilot plant
- 2017
-
In: Fuel Processing Technology. - : Elsevier BV. - 0378-3820. ; 156, s. 124-137
-
Journal article (peer-reviewed)abstract
- In this study, chemical-looping combustion was performed with highly viscous vacuum residue. A fuel reactor with a fuel-injection system for liquid fuels was designed and built for a chemical-looping reactor with the nominal fuel input of 10 kWth. The gas velocities in the riser section and at the gas-distribution nozzles of this unit are comparable to those of industrial circulating fluidized-bed boilers. Reference experiments were performed with an ilmenite oxygen carrier and two different fuel blends that contained 40 wt.% and respectively 80 wt.% of vacuum residue in fuel oil 1. Fuel conversion was in line with that of experiments from an earlier campaign, where fuel oil 1 was used as fuel. The fuel contained a significant fraction of sulfur, but no SO2 was detected in the flue gas of the air reactor. More experiments were performed using an oxygen carrier based on calcium manganite. The oxygen carrier was exposed to fluidization at hot conditions (more than 600°C) for about 95 h, out of which fuel was injected during a total of 9.6 h. Undiluted vacuum residue, fuel oil 1 as well as different blends of these two were used as fuel. Furthermore, the parameters fuel flow, fuel-reactor temperature and air flow in the air reactor were varied to observe trends in fuel conversion. The experiments were carried out with a fuel flow corresponding to 4.0-6.2 kWth and an oxygen carrier-to-fuel ratio of about 1300-2000 kg/MWth (fuel-reactor bed mass per thermal fuel-power). With undiluted vacuum residue as fuel and a fuel-reactor temperature of 1000°C, up to 93% of all carbon leaving the fuel reactor was in the form of CO2. Carbon leakage from fuel reactor to air reactor was usually below 1% for all fuel types tested, but no SO2 was detected in the off-gas from the air reactor. The reactivity of the calcium manganite-based material decreased over the course of the experiments, which is likely due to sulfur poisoning. No defluidization or agglomeration problems were experienced over the course of the experimental campaign.
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| 18. |
- Bjurhager, Ingela, et al.
(author)
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Towards improved understanding of PEG-impregnated waterlogged archaeological wood : A model study on recent oak
- 2010
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In: Holzforschung. - 0018-3830 .- 1437-434X. ; 64:2, s. 243-250
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Journal article (peer-reviewed)abstract
- To prevent deformation and cracking of waterlogged archaeological wood, polyethylene glycol (PEG) as a bulk impregnation agent is commonly applied. PEG maintains the wood in a swollen state during drying. However, swelling of wood can reduce its mechanical properties. In this study, the cellular structure of oak and cell wall swelling was characterized by scanning electron microscopy (SEM) of transverse cross-sections, and the microfibril angle of oak fibers was determined by wide angle X-ray scattering (WAXS). Samples of recent European oak (Quercus robur L) impregnated with PEG (molecular weight of 600) were tested in axial tension and radial compression. Mechanical tests showed that axial tensile modulus and strength were only slightly affected by PEG, whereas radial compressive modulus and yield strength were reduced by up to 50%. This behavior can be explained by the microstructure and deformation mechanisms of the material. Microfibril angles in tensile test samples were close to zero. This implies tensile loading of cellulose microfibrils within the fiber cell walls without almost any shear in the adjacent amorphous matrix. These results are important because they can help separate the impact of PEG on mechanical properties from that of chemical degradation in archaeological artifacts, which display only small to moderate biological degradation.
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| 19. |
- Shaikh, Abdul Shaafi, 1989, et al.
(author)
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On the effect of building platform material on laser-powder bed fusion of a Ni-base superalloy HAYNES® 282®
- 2023
-
In: European Journal of Materials. - : Informa UK Limited. - 2688-9277. ; 3:1
-
Journal article (peer-reviewed)abstract
- Additive manufacturing (AM) by laser powder bed fusion (LPBF) involves melting of layers of powder onto a substrate, called a building platform. Due to cost or convenience considerations, building platform materials rarely match the LPBF material, especially for high temperature materials. To ensure tolerances in component geometries, AM components are often stress-relieved/heat-treated while still attached to the building platform. It is therefore important to understand the effect of dissimilar building platform materials on the properties of the built-up material. These effects may be particularly important for high performance materials such as Ni-base superalloys used for critical applications in the aerospace and energy industries. To investigate this effect, samples of a Ni-base superalloy HAYNES® 282® were built onto a carbon steel building platform in several configurations. The samples were removed from the building platform after heat treatment and subjected to detailed composition analysis and microstructural characterization to investigate the effect of the building platform material on the properties of the additively manufactured part. Room temperature and high temperature tensile testing were used to characterize the material. Results showed no risk of large-scale chemical composition change, or mechanical property degradation of built-up material from on-platform heat treatment.
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| 20. |
- Fu, Qilin, 1986-
(author)
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High dynamic stiffness nano-structured composites for vibration control : A Study of applications in joint interfaces and machining systems
- 2015
-
Doctoral thesis (other academic/artistic)abstract
- Vibration control requires high dynamic stiffness in mechanical structures for a reliable performance under extreme conditions. Dynamic stiffness composes the parameters of stiffness (K) and damping (η) that are usually in a trade-off relationship. This thesis study aims to break the trade-off relationship.After identifying the underlying mechanism of damping in composite materials and joint interfaces, this thesis studies the deposition technique and physical characteristics of nano-structured HDS (high dynamic stiffness) composite thick-layer coatings. The HDS composite were created by enlarging the internal grain boundary surface area through reduced grain size in nano scale (≤ 40 nm). The deposition process utilizes a PECVD (Plasma Enhanced Chemical Vapour Deposition) method combined with the HiPIMS (High Power Impulse Magnetron Sputtering) technology. The HDS composite exhibited significantly higher surface hardness and higher elastic modulus compared to Poly(methyl methacrylate) (PMMA), yet similar damping property. The HDS composites successfully realized vibration control of cutting tools while applied in their clamping interfaces.Compression preload at essential joint interfaces was found to play a major role in stability of cutting processes and a method was provided for characterizing joint interface properties directly on assembled structures. The detailed analysis of a build-up structure showed that the vibrational mode energy is shifted by varying the joint interface’s compression preload. In a build-up structure, the location shift of vibration mode’s strain energy affects the dynamic responses together with the stiffness and damping properties of joint interfaces.The thesis demonstrates that it is possible to achieve high stiffness and high damping simultaneously in materials and structures. Analysis of the vibrational strain energy distribution was found essential for the success of vibration control.
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| 21. |
- Koptyug, Andrey, 1956-, et al.
(author)
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Electron Beam Melting: from Shape Freedom to Materials Properties Control at Macro- and Microscale
- 2021
-
In: Proceedings of the THERMEC 2020, Graz, Austria. - : Trans Tech Publications. ; , s. 755-759
-
Conference paper (peer-reviewed)abstract
- Electron beam melting (EBM) is one of the constantly developing powder bed fusion (PBF) additive manufacturing technologies (AM) offering advanced control over the manufacturing process. Freedom of component shapes is one of the AM competitive advantages already used at industrial and semi- industrial scale. Development of the additive manufacturing today is targeting both widening of the available materials classes, and introducing new enabling modalities. Present research is related to the new possibilities in tailoring different material properties within additively manufactured components effectively adding “fourth dimension to the 3D-printing”. Specific examples are given in relation to the electron beam melting, but majority of the conclusions are valid for the laser-based PBF techniques as well. Through manipulating beam energy deposition it is possible to tailor quite different material properties selectively within each manufactured component, including effective material density as well as thermal, mechanical, electrical and acoustic properties. It is also possible to acquire by choice both metal-metal composite and completely alloyed material, when blends of precursor powder are used together with the beam energy manipulation.
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| 22. |
- Cantatore, Valentina, 1986, et al.
(author)
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Towards multifunctional coating in the boron-doped graphene/copper system
- 2017
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In: Carbon. - : Elsevier BV. - 0008-6223. ; 115, s. 375-379
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Journal article (peer-reviewed)abstract
- A route to achieve multi-functional graphene coating is explored. Chemical bonding between copper substrate and coating results if the graphene is a priori boron doped. After pair-wise binding of boron sites to the Cu(111) surface, co-existence of pseudo-gap property in the graphene subsystem and a metallic density of states in the Cu subsystem at the common Fermi energy emerges. Apparently a paradox is that the two subsystems preserve and even recover their individual integrities upon formation of surface chemical bonds. Sensor capabilities are inferred. Employing pyridine as test molecule, conditioned ability of a nucleophile to offer competitive dative bonding, with the sub-strate, for boron sites is demonstrated. It is shown to occur for the case of half coverage and for adsorption to boron atoms originally bound to the on-top site on Cu(111). The ability of complementary boron sites to compensate for loss of binding between on-top site and boron, resulting from said bonding to the incoming nucleophile, is emphasized. Multifunctional substrate-coating system for catalysis as well as enhanced sensitization is inferred.
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| 23. |
- Svensson, Daniel
(author)
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Experimental methods to determine model parameters for failure modes of CFRP
- 2013
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Licentiate thesis (other academic/artistic)abstract
- The focus of this thesis is to develop methods to predict the damage response of Carbon Fibre Reinforced Polymers (CFRP). In the pursuit of reducing the manufacturing cost and weight of CFRP components, it is crucial to enable modelling of the non-linear response associated with various failure modes. Two failure modes are considered in this thesis: fibre compressive failure and interlaminar delamination. Multidirectional laminated composites are commonly used when a low weight is desired due to their high specific strength and stiffness. In a carbon/epoxy composite, almost exclusively the fibres carry the load. However, along the fibre direction, the compressive strength is considerably lower than the tensile strength. With the same reasoning, the transverse strength is considerably lower than the in-plane strength. This makes delamination and fibre compressive failure two of the major concerns in structural design. Moreover, the presence of delaminations severely reduces the compressive strength of a laminate. This can cause catastrophic failure of the structure. In Paper A, we suggest a test method for determining fracture properties associated with fibre compressive failure. A modified compact compression specimen is designed for this purpose and compressive failure takes place in a region consisting exclusively of fibres oriented parallel to the loading direction. The evaluation method is based on a generalized J-integral and full field measurements of the strain field on the surface of the specimen. Thus, the method is not restricted to small damage zones. Paper B focuses on measuring cohesive laws for delamination in pure mode loading. The cohesive laws in mode I and mode II are measured with the DCB- and ENF-specimen, respectively. With a method based on the J-integral, the energy release rate associated with the crack tip separation is measured directly. From this, the cohesive laws are derived. It is concluded that the nonlinear response at the crack tip is crucial in the evaluation of the mode II fracture energy.
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| 24. |
- Nikas, Dimitrios, 1984, et al.
(author)
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High temperature bi-axial low cycle fatigue behaviour of railway wheel steel
- 2019
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In: ICMFF12 - 12TH INTERNATIONAL CONFERENCE ON MULTIAXIAL FATIGUE AND FRACTURE. - : EDP Sciences. - 2261-236X. ; 300
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Conference paper (peer-reviewed)abstract
- One of the most important aspects in railway operation is the interaction between rail and wheel. Railway wheels are commonly made from medium carbon steels (similar to 0.55 wt.% C), heat treated to a near pearlitic microstructure with some 5-10% pro-eutectoid ferrite. During the operation of freight trains, where block brakes are used, high thermal loads are evolved because of recurring braking and occasional slippage. Thus the combination of mechanical and thermal loads leads to changes in the mechanical properties of the material. The focus of the current investigation is to evaluate the mechanical behaviour of wheel material (UIC ER7T) subjected to non-proportional biaxial fatigue loading, as this simulates the actual working conditions in a better way than uniaxial loading. Axial-torsional low cycle fatigue tests were performed at room temperature and elevated temperatures using thin walled specimens to study the cyclic stress-strain properties of this material. The results showed large influence of temperature on the ratcheting behaviour of the material. Biaxial non-proportional loading gave much higher strain hardening as compared to uniaxial loading. Hardening due to dynamic strain ageing can be seen in the biaxial tests at temperatures around 300 degrees C.
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| 25. |
- Liu, X., et al.
(author)
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Biomimetic Photonic Multiform Composite for High-Performance Radiative Cooling
- 2021
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In: Advanced Optical Materials. - : Wiley. - 2162-7568 .- 2195-1071. ; 9:22
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Journal article (peer-reviewed)abstract
- Nanostructures on bodies of biological inhabitants in severe environments can exhibit excellent thermoregulation, which provide inspirations for artificial radiative cooling materials. However, achieving both large-scale manufacturing and flexible form-compatibility to various applications needs remains as a formidable challenge. Here a biomimetic strategy is adopted to design a thermal photonic composite inspired by the previously unexplored golden cicada's evolutionarily optimized thermoregulatory ability. A microimprint combined with phase separation method is developed for fabricating a biomimetic photonic material made of porous polymer–ceramic composite profiled in microhumps. The composite demonstrates high solar reflectance (97.6%) and infrared emissivity (95.5%) in atmospheric window, which results in a cooling power of 78 W m−2 and a maximum subambient temperature drop of 6.6 °C at noon. Moreover, the technique facilitates multiform manufacturing of the composites beyond films, as demonstrated by additive printing into general 3D structures. This work offers biomimetic approach for developing high-performance thermal regulation materials and devices.
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