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1.	Grolig, Jan Gustav, 1986 (författare) Coated Ferritic Stainless Steels as Interconnects in Solid Oxide Fuel Cells - Material Development and Electrical Properties 2015 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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.
2.	Jeong, Seung Hee, 1978- (författare) Soft Intelligence : Liquids Matter in Compliant Microsystems 2016 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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.
3.	Mellin, Pelle, 1985-, et al. (författare) Nano-sized by-products from metal 3D printing, composite manufacturing and fabric production 2016 Ingår i: Journal of Cleaner Production. - Sweden : Elsevier. - 0959-6526 .- 1879-1786. ; 139, s. 1224-1233 Tidskriftsartikel (refereegranskat)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.
4.	André, Benny (författare) Nanocomposites for Use in Sliding Electrical Contacts 2011 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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.
5.	Heshmati, Mohsen, 1987, et al. (författare) On the strength prediction of adhesively bonded FRP-steel joints using cohesive zone modelling 2018 Ingår i: Theoretical and applied fracture mechanics (Print). - : Elsevier BV. - 0167-8442 .- 1872-7638. ; 93, s. 64-78 Tidskriftsartikel (refereegranskat)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.
6.	Okda, Sherif, et al. (författare) Testing of the Aerodynamic Characteristics of an Inflatable Airfoil Section 2020 Ingår i: Journal of Aerospace Engineering. - 1943-5525 .- 0893-1321. ; 33:5 Tidskriftsartikel (refereegranskat)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.
7.	Hosseini, Seyedehsan, 1994, et al. (författare) Alkyl ketene dimer modification of thermomechanical pulp promotes processability with polypropylene 2024 Ingår i: Polymer Composites. - 1548-0569 .- 0272-8397. ; 45:1, s. 825-835 Tidskriftsartikel (refereegranskat)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.
8.	Marklund, Erik, et al. (författare) Stiffness of aligned wood fiber composites: Effects of microstructure and phase properties 2008 Ingår i: Journal of composite materials. - : SAGE Publications. - 0021-9983 .- 1530-793X. ; 42:22, s. 2377-2405 Tidskriftsartikel (refereegranskat)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.
9.	Hosseini, Seyedehsan, 1994 (författare) Additive-Driven Improvements in Interfacial Properties and Processing of TMP-Polymer Composites 2023 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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.
10.	Mahade, Satyapal, 1987-, et al. (författare) Incorporation of graphene nano platelets in suspension plasma sprayed alumina coatings for improved tribological properties 2021 Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 570 Tidskriftsartikel (refereegranskat)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.
11.	André, Benny, et al. (författare) Enhancing silver through embedding of fullerene like WS2 for sliding electrical contacts Annan publikation (övrigt vetenskapligt/konstnärligt)
12.	Mirkhalaf, S. Mohsen, 1982, et al. (författare) A finite element based orientation averaging method for predicting elastic properties of short fiber reinforced composites 2020 Ingår i: Composites Part B-Engineering. - : Elsevier BV. - 1359-8368. ; 202 Tidskriftsartikel (refereegranskat)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.
13.	Lindberg, Siv M, et al. (författare) A product semantic study of the influence of the sense of touch on the evaluation of wood-based materials 2013 Ingår i: Materials & design. - : Elsevier BV. - 0264-1275 .- 1873-4197 .- 0261-3069. ; 52, s. 300-307 Tidskriftsartikel (refereegranskat)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.
14.	Åkerfeldt, Maria, 1982, et al. (författare) 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 Ingår i: Fashion and Textiles. - : Springer Science and Business Media LLC. - 2198-0802. ; 1:1 Tidskriftsartikel (refereegranskat)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.
15.	Nyflött, Åsa, 1986- (författare) Structure-Performance Relations of Oxygen Barriers for Food Packaging 2017 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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.
16.	Forsgren, Lilian, 1990 (författare) Processing and properties of thermoplastic composites containing cellulose nanocrystals or wood-based cellulose fibres 2020 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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.
17.	Moldenhauer, Patrick, 1983, et al. (författare) Chemical-looping combustion with heavy liquid fuels in a 10 kW pilot plant 2017 Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820. ; 156, s. 124-137 Tidskriftsartikel (refereegranskat)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.
18.	Bjurhager, Ingela, et al. (författare) Towards improved understanding of PEG-impregnated waterlogged archaeological wood : A model study on recent oak 2010 Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 64:2, s. 243-250 Tidskriftsartikel (refereegranskat)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.
19.	Shaikh, Abdul Shaafi, 1989, et al. (författare) On the effect of building platform material on laser-powder bed fusion of a Ni-base superalloy HAYNES® 282® 2023 Ingår i: European Journal of Materials. - : Informa UK Limited. - 2688-9277. ; 3:1 Tidskriftsartikel (refereegranskat)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.
20.	Fu, Qilin, 1986- (författare) High dynamic stiffness nano-structured composites for vibration control : A Study of applications in joint interfaces and machining systems 2015 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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.
21.	Koptyug, Andrey, 1956-, et al. (författare) Electron Beam Melting: from Shape Freedom to Materials Properties Control at Macro- and Microscale 2021 Ingår i: Proceedings of the THERMEC 2020, Graz, Austria. - : Trans Tech Publications. ; , s. 755-759 Konferensbidrag (refereegranskat)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.
22.	Cantatore, Valentina, 1986, et al. (författare) Towards multifunctional coating in the boron-doped graphene/copper system 2017 Ingår i: Carbon. - : Elsevier BV. - 0008-6223. ; 115, s. 375-379 Tidskriftsartikel (refereegranskat)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.
23.	Svensson, Daniel (författare) Experimental methods to determine model parameters for failure modes of CFRP 2013 Licentiatavhandling (övrigt vetenskapligt/konstnärligt)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.
24.	Nikas, Dimitrios, 1984, et al. (författare) High temperature bi-axial low cycle fatigue behaviour of railway wheel steel 2019 Ingår i: ICMFF12 - 12TH INTERNATIONAL CONFERENCE ON MULTIAXIAL FATIGUE AND FRACTURE. - : EDP Sciences. - 2261-236X. ; 300 Konferensbidrag (refereegranskat)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.
25.	Liu, X., et al. (författare) Biomimetic Photonic Multiform Composite for High-Performance Radiative Cooling 2021 Ingår i: Advanced Optical Materials. - : Wiley. - 2162-7568 .- 2195-1071. ; 9:22 Tidskriftsartikel (refereegranskat)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.
26.	Lobov, Gleb, et al. (författare) Dynamic manipulation of optical anisotropy of suspended Poly-3-hexylthiophene nanofibers 2016 Ingår i: Advanced Optical Materials. - : Wiley. - 2162-7568 .- 2195-1071. ; 4:10, s. 1651-1656 Tidskriftsartikel (refereegranskat)abstract Poly-3-hexylthiophene (P3HT) nanofibers are 1D crystalline semiconducting nanostructures, which are known for their application in photovoltaics. Due to the internal arrangement, P3HT nanofibers possess optical anisotropy, which can be enhanced on a macroscale if nanofibers are aligned. Alternating electric field, applied to a solution with dispersed nanofibers, causes their alignment and serves as a method to produce solid layers with ordered nanofibers. The transmission ellipsometry measurements demonstrate the dichroic absorption and birefringence of ordered nanofibers in a wide spectral range of 400–1700 nm. Moreover, the length of nanofibers has a crucial impact on their degree of alignment. Using electric birefringence technique, it is shown that external electric field applied to the solution with P3HT nanofibers can cause direct birefringence modulation. Dynamic alignment of dispersed nanofibers changes the refractive index of the solution and, therefore, the polarization of transmitted light. A reversible reorientation of nanofibers is organized by using a quadrupole configuration of poling electrodes. With further development, the described method can be used in the area of active optical fiber components, lab-on-chip or sensors. It also reveals the potential of 1D conducting polymeric structures as objects whose highly anisotropic properties can be implemented in electro-optical applications..
27.	Al-Ramahi, Nawres, 1980-, et al. (författare) Investigation of end and edge effects on results of numerical simulation of single lap adhesive joint with non-linear materials 2018 Ingår i: International Journal of Adhesion and Adhesives. - : Elsevier BV. - 0143-7496 .- 1879-0127. ; 87, s. 191-204 Tidskriftsartikel (refereegranskat)abstract This paper presents systematic numerical study of stresses in the adhesive of a single-lap joint with the objective to improve understanding of the main material and geometrical parameters determining performance of adhesive joints. For this purpose a 3D model as well as 2D model, optimized with respect to the computational efficiency by use of novel displacement coupling conditions able to correctly represent monoclinic materials (off-axis layers of composite laminates), are employed. The model accounts for non-linearity of materials (adherend and adhesive) as well as geometrical non-linearity. The parameters of geometry of the joint are normalized with respect to the dimensions of adhesive (e.g. thickness) thus making analysis of results more general and applicable to wide range of different joints. Optimal geometry of the single-lap joint allowing to separate edge effect from end effects is selected based on results of the parametric analysis by using peel and shear stress distributions in the adhesive layer as a criterion. Three different types of single lap joint with similar and dissimilar (hybrid) materials are considered in this study: a) metal-metal; b) composite-composite; c) composite-metal. In case of composite laminates, four lay-ups are evaluated: uni-directional ([08]T and [908]T) and quasi-isotropic laminates ([0/45/90/-45]S and [90/45/0/-45]S). The influence of the abovementioned parameters on peel and shear stress distributions in the adhesive layer is examined carefully and mechanical parameters governing the stress concentrations in the joint have been identified, this dependence can be described by simple but accurate fitting function. The effect of the used material model (linear vs non-linear) on results is also demonstrated.
28.	Luo, Xin, 1983 (författare) Characterization of nano-scale materials for interconnect and thermal dissipation application in electronics packaging 2014 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract This thesis focuses on studies of nano-scale materials in electronic packaging applications with respect to following aspects: surface analysis of nano-scale oxide of lead-free solder particles, and thermal performance and mechanical property studies of nano-scale fiber and metal composite-based thermal interface materials. The composition and thickness of the solder oxide have a direct impact on the quality of interconnects and the reliability of a packaged system. The characterization of the nano-scale oxide of lead-free solder particles is investigated by transmission electron microscopy and scanning transmission electron microscopy. The solder powders are exposed to air at 150 oC for 0, 120 and 240 h. The oxide thickness is 6 nm and 50 nm measured by STEM for 0 h and 120 h samples, respectively. The increase in oxide thickness of solder particles is proportional to the rooting of the oxidation time. The intersection analysis method for analyzing Auger electron spectroscopy depth profiles is also presented which could be expand to analyze oxide of other alloy, i.e. Cu, Ag or stainless steel.In the next part of this thesis, a new composite design consisting of electrospun polyimide fiber networks and infiltrated metal matrix is presented. Three composites are fabricated including polyimide fiber-InSnBi, polyimide fiber-indium and polyimide fiber-SnAgCu composites. The microstructure of the composite is investigated by scanning electron microscopy, energy dispersive X-ray detector and X-ray diffraction, showing a good bonding between the fibers and the metal matrix. These composites demonstrate high thermal conductivity, low thermal contact resistance and reliable thermomechanical performance during thermal cycling. The polyimide fiber-indium composites are sandwiched between chips and heat spreaders with different packaged sizes to detect the junction temperature and junction-to-case thermal resistance. The shear strength of the polyimide fiber-indium composite between Sn surfaces can reach 4 MPa which is larger than that with Au and Cu surfaces. Both composites present good reliability during the humidity-heat aging tests. The polyimide fiber-indium composite’s ultimate tensile strength at 20 °C is five times higher than that of the pure indium, and the tensile strength of the composite exceeds the summation of those from its individual components. With the increase in temperature, the ultimate tensile strength declines but still precedes pure indium and the elongation at fracture increases. Contrary to most metallic materials, the ultimate tensile strength of the composite is inversely proportional to the logarithmic strain rate in a certain range. Finally, a new strengthening mechanism is presented based on mutually reinforcing structures formed by the indium and surrounding fibers, underlining the effect of compressing at the fiber-indium interfaces by dislocation pileups and slip pinning. The creep threshold of the composite corresponds to the fracture strength of the polyimide fiber, and the step-like sudden increases of the composite’s creep strain are due to the breakage of fibers. The fiber-indium interfaces are also beneficial to the composite’s creep resistance. In the final part of the thesis, two novel thermal interface materials are developed and characterized including boron nitride fiber-indium composite and carbon fiber-SnAgCu composite. Thermally conductive boron nitride fiber or carbon fiber is prepared via electrospinning and heat treatment. Afterward, the boron nitride/carbon fibers are sputtered with Ti/Au coatings and infiltrated with metal matrix. Good in-plane and through-plane thermal conductivity of the thermally conductive fiber-metal matrix composite are obtained using a laser flash apparatus.
29.	Almgren, Karin, et al. (författare) Role of fibre-fibre and fibre-matrix adhesion in stress transfer in composites made from resin-impregnated paper sheets. 2009 Ingår i: International Journal of Adhesion and Adhesives. - : Elsevier BV. - 0143-7496 .- 1879-0127. ; 29:5, s. 551-557 Tidskriftsartikel (refereegranskat)abstract Paper-reinforced plastics are gaining increased interest as packaging materials, where mechanical properties are of great importance. Strength and stress transfer in paper sheets are controlled by fibre-fibre bonds. In paper-reinforced plastics, where the sheet is impregnated with a polymer resin, other stress-transfer mechanisms may be more important. The influence of fibre-fibre bonds on the strength of paper-reinforced plastics was therefore investigated. Paper sheets with different degrees of fibre-fibre bonding were manufactured and used as reinforcement in a polymeric matrix. Image analysis tools were used to verify that the difference in the degree of fibre-fibre bonding had been preserved in the composite materials. Strength and stiffness of the composites were experimentally determined and showed no correlation to the degree of fibre-fibre bonding, in contrast to the behaviour of unimpregnated paper sheets. The degree of fibre-fibre bonding is therefore believed to have little importance in this type of material, where stress is mainly transferred through the fibre-matrix interface.
30.	He, Wenxiao, 1985 (författare) Biomimetic Formation of Calcium Phosphate Based Nanomaterials 2014 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract The intercellular material in bone is a nanocomposite of aligned “hard” inorganics—calcium phosphate (CaP) platelets embedded in the long-range ordered “soft” organic collagen matrix. This elaborate structural arrangement redeems the weaknesses of the individual components (being soft protein or brittle mineral) and gives bone its excellent mechanical properties for the protection and support of our bodies. The structural order and hierarchy in the soft matrix is organized via self-assembly of collagen molecules and is reinforced by intermolecular crosslinking. The subsequent growth of “hard” crystallites inside the “soft” matrix compartments, likely through the deposition of a transient amorphous calcium phosphate (ACP) phase, results in the interpenetrated composite structure.The aim of this thesis was to prepare synthetic mimetics of “hard” material (CaP) with well-defined nanostructures, soft organic matrices with long-range order and interpenetrated composites composing of the two. The work was inspired by the material deposition process in natural bone. Lyotropic liquid crystal (LC) phases self-assembled by block copolymers were used to mimic the structural order of the collagen matrix. Both the inorganic morphogenesis of CaP in LCs and the controlled crystallization of ACP were investigated. To explore ordered organic matrices, crosslinking of the LCs and the self-assembly of an amphiphilic peptide with designed sequence were performed. In addition, controlled mineralization within crosslinked LCs was examined for the formation of nanocomposites.ACP nanospheres, CaP nanowires and nanosheets were prepared from LCs via templated growth. The ACP nanospheres were capable of transforming into bone-like apatite by controlled aging in water and the prepared nanoparticles were shown to affect osteoblast gene expression. Dicalcium phosphate crystals (brushite and monetite) with structural hierarchy and distinct features were also grown in LCs through epitaxial overgrowth or a self-organization regime. Polymerized LCs were successfully prepared from a modified block copolymer (diacrylate derivative of Pluronic® F127), which served as a resilient matrix for the deposition of ACP nanospheres. A subsequent in situ crystallization of ACP into bone-like apatite resulted in mechanically stable composites retaining nanostructures that resembled that of natural bone. An amphiphilic peptide was designed using mainly natural amino acids and it was shown to self-assemble into distinct structures at different concentrations. Based upon the results presented in this thesis, nanomaterials with assorted structures can be further designed for bio-related applications.
31.	Nygren, Kristian (författare) Magnetron Sputtering of Nanocomposite Carbide Coatings for Electrical Contacts 2016 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract Today’s electronic society relies on the functionality of electrical contacts. To achieve good contact properties, surface coatings are normally applied. Such coatings should ideally fulfill a combination of different properties, like high electrical conductivity, high corrosion resistance, high wear resistance and low cost. A common coating strategy is to use noble metals since these do not form insulating surface oxides. However, such coatings are expensive, have poor wear resistance and they are often applied by electroplating, which poses environmental and human health hazards.In this thesis, nanocomposite carbide-based coatings were studied and the aim was to evaluate if they could exhibit properties that were suitable for electrical contacts. Coatings in the Cr-C, Cr-C-Ag and Nb-C systems were deposited by magnetron sputtering using research-based equipment as well as industrial-based equipment designed for high-volume production. To achieve the aim, the microstructure and composition of the coatings were characterized, whereas mechanical, tribological, electrical, electrochemical and optical properties were evaluated. A method to optically measure the amount of carbon was developed.In the Cr-C system, a variety of deposition conditions were explored and amorphous carbide/amorphous carbon (a-C) nanocomposite coatings could be obtained at substrate temperatures up to 500 °C. The amount of a-C was highly dependent on the total carbon content. By co-sputtering with Ag, coatings comprising an amorphous carbide/carbon matrix, with embedded Ag nanoclusters, were obtained. Large numbers of Ag nanoparticles were also found on the surfaces. In the Nb-C system, nanocrystalline carbide/a-C coatings could be deposited. It was found that the nanocomposite coatings formed very thin passive films, consisting of both oxide and a-C.The Cr-C coatings exhibited low hardness and low-friction properties. In electrochemical experiments, the Cr-C coatings exhibited high oxidation resistance. For the Cr-C-Ag coatings, the Ag nanoparticles oxidized at much lower potentials than bulk Ag. Overall, electrical contact resistances for optimized samples were close to noble metal references at low contact load. Thus, the studied coatings were found to have properties that make them suitable for electrical contact applications.
32.	Nilsson, Helena, et al. (författare) Compression molded wood pulp biocomposites : A study of hemicellulose influence on cellulose supramolecular structure and material properties 2012 Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 19:3, s. 751-760 Tidskriftsartikel (refereegranskat)abstract In this study, the importance of hemicellulose content and structure in chemical pulps on the property relationships in compression molded wood pulp biocomposites is examined. Three different softwood pulps are compared; an acid sulfite dissolving grade pulp with high cellulose purity, an acid sulfite paper grade pulp and a paper grade kraft pulp, the latter two both containing higher amounts of hemicelluloses. Biocomposites based the acid sulfite pulps exhibit twice as high Young's modulus as the composite based on paper grade kraft pulp, 11-12 and 6 GPa, respectively, and the explanation is most likely the difference in beating response of the pulps. Also the water retention value (WRV) is similarly low for the two molded sulfite pulps (0.5 g/g) as compared to the molded kraft pulp (0.9 g/g). The carbohydrate composition is determined by neutral sugar analysis and average molar masses by SEC. The cellulose supramolecular structure (cellulose fibril aggregation) is studied by solid state CP/MAS 13C-NMR and two forms of hemicellulose are assigned. During compression molding, cellulose fibril aggregation occurs to higher extent in the acid sulfite pulps as compared to the kraft pulp. In conclusion, the most important observation from this study is that the difference in hemicellulose content and structure seems to affect the aggregation behaviour and WRV of the investigated biocomposites.
33.	Harr Martinsen, Kristoffer, 1990 (författare) Preparation and characterization of graphene/metal composites 2021 Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract Since the isolation of graphene in 2004, much research has been conducted to understand this novel material and how its properties can be utilized in different applications. One type of venture involves graphene as a reinforcing filler in metal matrix composites (MMC) which is becoming increasingly prevalent in the automotive and aerospace industries. Such composites combine the machinability and processing flexibility of metals with the unique properties of graphene. In fact, copper-graphene composites have demonstrated ameliorated mechanical strength with thermal conductivities elevated beyond pristine copper. However, the challenges that remain to commercialize copper-graphene composites are numerous. The most challengeable one is that graphene must be uniformly dispersed in the matrix and adhere to copper through an industrially scalable and affordable process. Moreover, the volume fraction of graphene must be efficiently controlled, lest superfluous amounts lead to structural detriment. In this regard, the emphasis of this study was to investigate a scalable and simple method to obtain such MMC via powder metallurgy. Specifically, gas atomized copper powder was functionalized with 3-aminopropyl-triethoxysilane (APTES) in toluene (APTES-Cu), resulting in a positively charged surface; then aqueously dispersed and negatively charged graphene oxide (GO) could then be self-assembled on the surface APTES@Cu via electrostatic interaction (Cu@APTES-Cu). The thickness of GO layers and morphology on the powder was controlled by modulating APTES grafting duration and APTES concentration in toluene. Cu@APTES-Cu powders were thermally annealed before compaction and sintering in inert atmosphere. The results show that surface modification of metal powders serves as a scalable and versatile approach to coat graphene on metal particles for the preparation of graphene/metal composites. Surface modification of copper with 0.2 vol% APTES in toluene for 30 minutes was sufficient to obtain composite powders with incomplete GO coating, which nonetheless demonstrated improved hardness. However, cold working of sintered composites was essential to densify the porous structure created by reduced GO during sintering. On the other hand, sintered composite samples that exhibited higher thermal conductivity than copper was obtained with higher APTES and GO loading. After thermal annealing, these thicker GO coatings were found to improve thermal conductivity in sintered composites by acting as thermal bridges between individual composite particles. Despite incomplete sintering of these composites, a 20% increase in thermal conductivity was attainable. Finally, both polarization scans and etching measurements in concentrated HCl and ammonium persulfate (APS) indicate that the GO coating decomposes on the outer surface during sintering. However, the reduced GO coating can retard corrosion of the internal composite structure by diffusion inhibition.
34.	Noè, C., et al. (författare) Frontal-Photopolymerization of Fully Biobased Epoxy Composites 2022 Ingår i: Macromolecular materials and engineering. - : Wiley. - 1438-7492 .- 1439-2054. ; 307:6, s. 2100864- Tidskriftsartikel (refereegranskat)abstract The radical-induced cationic frontal photopolymerization (RICFP) of fully biobased epoxy composites is successfully demonstrated. This curing strategy considerably reduces the curing time and improves the efficiency of the composite fabrication. Two different natural fiber fabrics made of cellulose and flax fibers are embedded in two epoxy matrices, one derived from vanillin (diglycidylether of vanillyl alcohol-DGEVA) and the other from petroleum (3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate-CE). After RICFP the composites are characterized by means of dynamic mechanical thermal analysis and tensile tests. The mechanical properties improved with increasing fiber content, confirming a strong adhesion between the matrix and the reinforcing fiber fabrics, which is further evidenced by scanning electron microscopy analyses of the fracture surfaces. Furthermore, these fully bio-based composites possess comparable or even higher mechanical strength compared with the corresponding epoxy composites fabricated with conventional CE resin. A promising facile route to high-performing natural fiber-biobased epoxy resin composites is presented.
35.	Sanchez Heres, Luis Felipe, 1984, et al. (författare) Optimization of composite maritime structures - effects of uncertainties on design criteria limits 2011 Ingår i: Advances in Marine Structures - Proceedings of the 3rd International Conference on Marine Structures (MARSTRUCT 2011). - 9780415677714 ; , s. 707-714, s. 707-714 Konferensbidrag (refereegranskat)abstract Composite materials have been used successfully in vessels since the 1960s. Changes during the last decade in international regulations, fuel prices and environmental concerns have dramatically increased the interest of the marine industry in lightweight composite materials. There are many questions regarding the material’s properties and behaviour that still remain, leading, in some instances to too robustly designed crafts. There-fore, the new generation of composite vessels requires a finer tuning of safety and weight, which can be achieved by analyzing thoroughly the behaviour of the material and the effects of uncertainties and approxi-mations found in the design process. This paper presents the study of two design methodologies with different degrees of complexity, through deterministic and probabilistic analyses, in order to determine their benefits, drawbacks and challenges.
36.	Kuzmenko, Volodymyr, 1987, et al. (författare) FREESTANDING CARBON NANOFIBERS/GRAPHENE COMPOSITE ELECTRODES FOR SUPERCAPACITORS 2016 Ingår i: The World Conference on Carbon - Carbon 2016, July 10-15, State College, PA, USA. Konferensbidrag (refereegranskat)
37.	Williams Portal, Natalie, et al. (författare) Evaluation of pull-out behaviour in textile reinforced concrete 2014 Ingår i: Proceedings of the 10th fib International PhD Symposium in Civil Engineering. - : Universite Laval. - 9782980676215 - 9782980676222 ; , s. 97-102 Konferensbidrag (refereegranskat)abstract Concrete reinforced with conventional steel is one of the most commonly used building materials, yet it has historically shown disadvantages in terms of durability and vulnerability to corrosion attack. Various remedial methods have been applied to overcome the shortcomings of this building material, such as increasing the concrete cover, which, however, leads to an increased self-weight of the structure. Over the past decade, Textile Reinforced Concrete (TRC), encompassing a combination of finegrained concrete and non-corrosive multi-axial textile fabrics, has emerged as a promising novel altemative offering corrosion resistance, as well as thinner and light-weight structures such as foot bridges and façade elements. Although TRC has been extensively researched, the formalization of experimental methods and design standards is still in progress. The aim of this paper is to quantify and model the bond behaviour of TRC basalt fibre meshes. The bond between the textile fibre mesh and fine-grained concrete matrix is a critical element influencing the overall performance of this composite material. The yam structure is rather complex including a multitude of outer and inner filaments; thus inevitably, the constituents of one yam are unevenly bonded to the concrete matrix. As such, experiments help quantify complex material behaviour which can be further used to develop and calibrate analytical and non-linear finite-element models. The bond behaviour of TRC was characterized through means of direct pull-out tests with un-symmetrical embedment lengths such that the test specimens were notched at a prescribed breaking point. The test specimens consisted of one-layer of reinforcement mesh, centrally cast, made of basalt fibres. The applied force and average deformation of the test specimen were measured. The evaluation of varying embedment lengths was explored in order to quantify pull-out and textile rupture failure modes. The experimental results were thereafter evaluated using an analytical 1 D bond model. Pull-out and rupture failure were observed in the experimental pull-out results. A local bond stress-slip curve was calibrated for the basalt specimens based on the experimental results. Finally, it was observed that the simulation results from the 1 D bond model had a reasonable correlation with the experimental results in spite ofthe complex bond behaviour of TRC.
38.	Jacobsson, Jonny, et al. (författare) Weldability of superalloys alloy 718 and ATI® 718Plus™ : A study performed by Varestraint testing 2017 Ingår i: Materialprüfung (München). - : Walter de Gruyter GmbH. - 0025-5300 .- 2195-8572. ; 59:9, s. 769-773 Tidskriftsartikel (refereegranskat)abstract In this study, the old and well-known alloy 718 is compared with the newly developed ATI® 718Plus™ from the weldability point of view. This is done in order to gain new information that have not been documented and established yet among the high-temperature materials with high strength, oxidation resistance, thermal stability and sufficient weldability, yet. ATI® 718Plus™ shows a lower sensitivity to hot cracking than alloy 718 with approximately 10 mm total crack length (TCL) difference in Varestraint testing. In the solution-annealed condition at 982°C for 4.5 h followed by air cooling, the crack sensitivity is decreased as compared to the mill-annealed condition. Along the crack path and also ahead of the crack tip, γ-Laves eutectic is present in both alloys. The microhardness measurements showed similar hardness level of 250 HV in the weld metal of both alloys and even in the parent material of alloy 718. ATI® 718Plus™ parent metal had hardness of 380 HV and a small increase of less than 50 HV was observed for both studied alloys in the heat affected zone (HAZ). For the same grain size of ATI® 718Plus™ (8.3 μm) and alloy 718 (15.6 μm), the susceptibility to liquation cracking may increase with increasing grain size. With a small grain size, there is a possibility to accommodate more trace elements (B, S, P) due to the larger grain boundary area. The impurity elements were found in relatively small precipitates, typically borides (0.2 μm), phosphides (0.1 to 0.5 μm) and carbo-sulphides. The solidification sequence of alloy 718 and ATI® 718Plus™ is relatively similar, where the liquid starts to solidify as γ-phase followed by γ/MC reaction at about 1260 °C and then final γ/Laves eutectic reaction at around 1150 °C. Detailed knowledge about weldability of alloy 718 and ATI® 718Plus™ can be used for material selection.
39.	Jafari, R., et al. (författare) KCl-induced corrosion behavior of HVAF-sprayed Ni-based coatings in ambient air 2017 Konferensbidrag (övrigt vetenskapligt/konstnärligt)
40.	Jafari, Reza, et al. (författare) KCl-Induced High Temperature Corrosion Behavior of HVAF-Sprayed Ni-Based Coatings in Ambient Air 2018 Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 27:3, s. 500-511 Tidskriftsartikel (refereegranskat)abstract KCl-induced high temperature corrosion behavior of four HVAF-sprayed Ni-based coatings (Ni21Cr, Ni5Al, Ni21Cr7Al1Y, and Ni21Cr9Mo) under KCl deposit has been investigated in ambient air at 600°C up to 168h. The coatings were deposited onto 16Mo3 steel - a widely used boiler tube material.Uncoated substrate, 304L and Sanicro25 were used as reference materials in the test environment.SEM/EDS and XRD techniques were utilized to characterize the as-sprayed and exposed samples.The results showed that the small addition of KCl significantly accelerated degradation to the coatings. All coatings provided better corrosion resistance compared to the reference materials. The alumina-forming Ni5Al coating under KCl deposit was capable of forming a more protective oxide scale compared to the chromia-forming coatings as penetration of Cl through diffusion paths was hindered. Both active corrosion and chromate formation mechanisms were found to be responsible for Page 1 of 23ASM the corrosion damages. The corrosion resistance of the coatings based on the microstructure analysis and kinetics had the following ranking (from the best to worst): Ni5Al >Ni21Cr> Ni21Cr7Al1Y>Ni21Cr9Mo.
41.	Kuzminova, Yulia O., et al. (författare) Structural and mechanical properties of the additive manufactured CrFeCoNi(Al,Ti) high-entropy alloys produced using powder blends 2023 Ingår i: Materialia. - : Elsevier. - 2589-1529. ; 32 Tidskriftsartikel (refereegranskat)abstract High-entropy Alloys (HEAs) are considered prospective materials demonstrating the new approach of alloy design creating new compositions for harsh conditions. However, searching for alloy chemical composition providing the best material properties is a costly process. Additive manufacturing (AM) can be an effective technique for adjusting the alloy composition by using several initial materials. The powder bed fusion (PBF) AM process allows the printing of solid parts using powder blends. In the present study, the CrFeCoNi(Al,Ti) HEAs were printed by the PBF technique using the blends of three powders. The structural and phase investigations revealed the chemical inhomogeneity in the materials that led to the new phase formations affecting the mechanical characteristics. The high-temperature annealing at 1200 °C can be considered a post-treatment process for the printed alloys as a homogenization process while the annealing at a lower temperature of 800 °C initiates the decomposition of the initially formed f.c.c. phase.
42.	Fu, Qilin, 1986-, et al. (författare) High dynamic stiffness mechanical structures with nanostructured composite coatings deposited by high power impulse magnetron sputtering 2016 Ingår i: Carbon. - : Elsevier. - 0008-6223 .- 1873-3891. ; 98, s. 24-33 Tidskriftsartikel (refereegranskat)abstract Nanostructured Cu:CuCNx composite coatings with high static and dynamic stiffness were synthesized by means of plasma-enhanced chemical vapor deposition (PECVD) combined with high power impulse magnetron sputtering (HiPIMS). Scanning electron microscope (SEM) images and energy-dispersive X-ray spectroscopy (EDS) mapping from cross-sectioned samples reveals a multi-layered nanostructure enriched in Cu, C, N, and O in different ratios. Mechanical properties of the coatings were investigated by Vickers micro-indention and model tests. It was observed that copper inclusions as well as copper interlayers in the CNx matrix can increase mechanical damping by up to 160%. Mechanical properties such as hardness, elastic modulus and loss factor were significantly improved by increasing the discharge power of the sputtering process. Moreover the coatings loss modulus was evaluated on the basis of indentation creep measurements under room temperature. The coating with optimum properties exhibited loss modulus of 2.6 GPa. The composite with the highest damping loss modulus were applied on the clamping region of a milling machining tool to verify their effect in suppressing regenerative tool chatter. The high dynamic stiffness coatings were found to effectively improve the critical stability limit of a milling tool by at least 300%, suggesting a significant increase of the dynamic stiffness.
43.	Atashipour, Seyed Rasoul, et al. (författare) On the Shear Buckling of Clamped Narrow Rectangular Orthotropic Plates 2015 Ingår i: Mathematical problems in engineering (Print). - : Hindawi Limited. - 1024-123X .- 1563-5147. ; 2015 Tidskriftsartikel (refereegranskat)abstract This paper deals with stability analysis of clamped rectangular orthotropic thin plates subjected to uniformly distributed shear load around the edges. Due to the nature of this problem, it is impossible to present mathematically exact analytical solution for the governing differential equations. Consequently, all existing studies in the literature have been performed by means of different numerical approaches. Here, a closed-form approach is presented for simple and fast prediction of the critical buckling load of clamped narrow rectangular orthotropic thin plates. Next, a practical modification factor is proposed to extend the validity of the obtained results for a wide range of plate aspect ratios. To demonstrate the efficiency and reliability of the proposed closed-form formulas, an accurate computational code is developed based on the classical plate theory (CPT) by means of differential quadrature method (DQM) for comparison purposes. Moreover, several finite element (FE) simulations are performed via ANSYS software. It is shown that simplicity, high accuracy, and rapid prediction of the critical load for different values of the plate aspect ratio and for a wide range of effective geometric and mechanical parameters are the main advantages of the proposed closed-form formulas over other existing studies in the literature for the same problem.
44.	Xu, Johanna, 1989, et al. (författare) A multicell structural battery composite laminate 2022 Ingår i: EcoMat. - : Wiley. - 2567-3173. ; In Press Tidskriftsartikel (refereegranskat)abstract Multifunctional materials facilitate lightweight and slender structural solutions for numerous applications. In transportation, construction materials that can act as a battery, and store electrical energy, will contribute to realization of highly energy efficient vehicles and aircraft. Herein, a multicell structural battery composite laminate, with three state-of-the-art structural battery composite cells connected in series is demonstrated. The experimental results show that the capacity of the structural battery composite cells is only moderately affected by tensile loading up to 0.36% strain. The multicell structural battery laminate is made embedding the three connected structural battery composite cells between carbon fiber/glass fiber composite face sheets. Electrochemical performance of the multicell structural battery is demonstrated experimentally. High charge transfer resistance for the pack as well as the individual cells is reported. Mechanical performance of the structural battery laminate is estimated by classical laminate theory. Computed engineering in-plane moduli for the multicell structural battery laminate are on par with conventional glass fiber composite multiaxial laminates.
45.	Duan, Shanghong, 1992, et al. (författare) Determination of transverse and shear moduli of single carbon fibres 2020 Ingår i: Carbon. - : Elsevier BV. - 0008-6223 .- 1873-3891. ; 158C, s. 772-782 Tidskriftsartikel (refereegranskat)abstract Carbon fibres are extensively used for their high specific mechanical properties. Exploiting their high axial stiffness and strength, they are employed to reinforce polymer matrix materials in advanced composites. However, carbon fibres are not isotropic. Data of the elastic properties in the other directions of the fibres are still largely unknown. Furthermore, standardised methods to characterise these properties are lacking. In the present work, we propose a methodology to determine the transverse and shear moduli of single carbon fibres. An experimental procedure is developed to fabricate high-quality, flat fibre cross-sections in both longitudinal and transverse directions using Focused Ion Beam, which gives full control of the specimen geometry. Indentation modulus on those surfaces are obtained using both Atomic Force Microscopy (AFM) and nanoindentation tests. Hysteresis was found to occur in the nanoindentation tests. The hysteresis response was due to nano-buckling and reversible shear deformation of the carbon crystals. For this reason, indentation tests using AFM is recommended. From the AFM indentation tests the transverse and shear moduli of three different carbon fibres (IMS65, T800 and M60J) are successfully determined.
46.	Johansen, Marcus, 1994, et al. (författare) Mapping nitrogen heteroatoms in carbon fibres using atom probe tomography and photoelectron spectroscopy 2021 Ingår i: Carbon. - : Elsevier BV. - 0008-6223. ; 179, s. 20-27 Tidskriftsartikel (refereegranskat)abstract Carbon fibres show great potential as multifunctional negative electrode for novel structural battery composites – a rechargeable electrochemical cell with structural function. The electrochemical performance of carbon materials can be enhanced with nitrogen heteroatoms, which conveniently are inherent in polyacrylonitrile (PAN)-based carbon fibres. However, it is not fully understood how the electrochemical performance is governed by microstructure and composition of the carbon fibres, particularly the distribution and chemical states of nitrogen heteroatoms. Here we reveal the atom-by-atom three-dimensional spatial distribution and the chemical states of nitrogen in three PAN-carbon fibre types (M60J, T800 and IMS65), using atom probe tomography (APT) and synchrotron hard X-ray photoelectron spectroscopy (HAXPES), and correlate the results to electrochemical performance. The findings pave the way for future tailoring of carbon fibre microstructure for multifunctional applications.
47.	Johansen, Marcus, 1994 (författare) Microstructure of Carbon Fibres for Multifunctional Composites: 3D Distribution and Configuration of Atoms 2021 Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract Lightweight energy storage is a must for increased driving range of electric vehicles. “Mass-less” energy storage can be achieved by directly storing energy in structural components. In such multifunctional devices called structural composite batteries, carbon fibres carry mechanical load and simultaneously act as negative battery electrode by hosting lithium ions in its microstructure. Little is known of how the microstructure of carbon fibres is optimised for multifunctionality, and deeper understanding of the configuration and the distribution of atoms in carbon fibres is needed. Here synchrotron hard X-ray photoelectron spectroscopy and atom probe tomography are used to reveal the chemical states and three-dimensional distribution of atoms in commercial carbon fibres. This thesis presents the first ever guide for how to perform atom probe tomography on carbon fibres, and the first ever three-dimensional atomic reconstruction of a carbon fibre. The results show that the chemical states and distribution of nitrogen heteroatoms in carbon fibres affect the electrochemical performance of the fibres. Carbon fibres performed electrochemically better with higher amount of nitrogen with pyridinic and pyrrolic configurations. Additionally, the nitrogen concentration varies throughout the carbon fibre, which may suggest that the electrochemical properties also vary throughout the carbon fibre. The knowledge provided by this thesis can lead to future carbon fibre designs with enhanced electrochemical performance for multifunctional applications.
48.	Amiandamhen, Stephen, 1983-, et al. (författare) Recycling sawmilling wood chips, biomass combustion residues, and tyre fibres into cement-bonded composites : Properties of composites and life cycle analysis 2021 Ingår i: Construction and Building Materials. - : Elsevier Ltd. - 0950-0618 .- 1879-0526. ; 297 Tidskriftsartikel (refereegranskat)abstract This study investigated the properties and sustainability of cement-bonded composites containing industrial residues such as wood chips, tyre fibres and biomass combustion residues, i.e. bottom ash (BA) and fly ash (FA). The effect of cement-to-raw material (wood/tyre fibre) ratio (C/RM) and the aggregate content (BA and FA) on thermal and mechanical properties of the composites were investigated. Scanning electron microscopy (SEM) and life cycle analysis (LCA) were also conducted. The results revealed that as the aggregate content increased in wood composites, the mechanical properties also increased. The mean thermal conductivity and volumetric heat capacity of tyre composite samples were 0.37 W/mK and 1.2 MJ/m3K respectively, while the respective values for wood composite samples were 0.29 W/mK and 0.81 MJ/m3K. SEM analysis showed adequate bonding between wood/tyre fibres and cement matrix. LCA revealed that the materials share of the total primary energy use was about 60% for all analysed composites. © 2021 The Author(s)
49.	Pejryd, Lars, 1955-, et al. (författare) Computed Tomography as a Tool for Examining Surface Integrity in Drilled Holes in CFRP Composites 2014 Ingår i: Procedia CIRP. - : Elsevier BV. - 2212-8271 .- 2212-8271. ; 13, s. 43-48 Tidskriftsartikel (refereegranskat)abstract In light weight structures the joining of composite materials and of composites to metals are key technologies. A manufacturing method associated with joining is the drilling of holes. The hole creation in CRFP through drilling is associated with several defects related to the process, both on the entry and exit sides of the hole and also with dimensional and surface roughness issues of the hole wall. The detection of damage due to the process is not trivial. Especially interesting is non-destructive methods. In this work X-ray computed tomography is used to determine defects due to drilling of holes in a CFRP composite using twist drills with different geometrical features at different drilling parameters. The results can be used to establish relationship between different geometrical features of drills in combination with cutting parameters and resulting surface integrity of holes. © 2014 The Authors. Published by Elsevier B.V.
50.	Gaska, Karolina, 1986, et al. (författare) Gas Barrier, Thermal, Mechanical and Rheological Properties of Highly Aligned Graphene-LDPE Nanocomposites 2017 Ingår i: Polymers. - : MDPI AG. - 2073-4360. ; 9:7, s. 294- Tidskriftsartikel (refereegranskat)abstract This contribution reports on properties of low-density polyethylene-based composites filled with different amounts of graphene nanoplatelets. The studied samples were prepared in the form of films by means of the precoating technique and single screw melt-extrusion, which yields a highly ordered arrangement of graphene flakes and results in a strong anisotropy of composites morphology. The performed tests of gas permeability reveal a drastic decrease of this property with increasing filler content. A clear correlation is found between permeability and free volume fraction in the material, the latter evaluated by means of positron annihilation spectroscopy. A strong anisotropy of the thermal conductivity is also achieved and the thermal conductivity along the extrusion direction for samples filled with 7.5 wt % of GnP (graphene nanoplatelets) reached 2.2 W/m·K. At the same time, when measured through a plane, a slight decrease of thermal conductivity is found. The use of GnP filler leads also to improvements of mechanical properties. The increase of Young’s modulus and tensile strength are reached as the composites become more brittle.

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