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  • 51. Thuvander, F.
    et al.
    Berglund, Lars A.
    In situ observations of fracture mechanisms for radial cracks in wood2000Inngår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 35, nr 24, s. 6277-6283Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents the findings of work carried out to describe the micromechanisms of radial crack growth in wood. TR and TL cracks are both radial cracks but TR grows radially and TL longitudinally. TR cracks are known to show higher fracture toughness than TL cracks. The TR fracture surfaces also indicate a more tortuous crack path. Since the reason for this is unclear, details of the TR crack growth mechanisms in green Pinus sylvestris L were studied. This was done by in-situ optical microscopy as the crack was cutting through alternating layers of soft earlywood and stiff latewood. At the scale of individual cells, the crack tip advanced by separating cell walls at the middle lamella in a splitting or peeling mode. At the scale of growth rings, stick-slip type of crack growth was observed and new crack planes were often formed. The stress distribution in a material with alternating stiff and soft layers is causing this. This stress distribution also contributes to the tendency for inclined cracks to deviate in the radial direction. For interpretation of fracture mechanisms, the importance of scale interaction and the combined influences of microstructure and stress state are emphasized.

  • 52. Thuvander, F.
    et al.
    Sjodahl, M.
    Berglund, Lars A.
    Measurements of crack tip strain field in wood at the scale of growth rings2000Inngår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 35, nr 24, s. 6267-6275Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The fracture mechanisms of wood have often been interpreted on the scale of cell walls. Although this scale is important, the scale of growth rings needs to be considered in the same context. In the present study, the crack tip strain field of radial TR cracks at the scale of growth rings is measured by electronic speckle photography. The methodology is discussed in detail as well as the data reduction scheme. The tip is in the earlywood layer and the crack plane of the TR crack is perpendicular to the stiffer latewood layer. Increasing opening mode load is applied in-situ as the crack is observed by reflected light optical microscopy. Strains are measured on direct images of the microstucture. In contrast to some other methodologies, this allows direct correlation between strain field and microstructure. In the softer earlywood, tangential strains extend considerable distances in the tangential direction. Due to the stiff latewood, the strain is heavily constrained in the radial direction. This nature of the local strain field has been largely neglected, despite its obuius significance to TR crack growth mechanisms.

  • 53.
    Trybula, Marcela E.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Polish Acad Sci, Inst Met & Mat Sci, PL-30059 Krakow, Poland..
    Szafranski, Przemyslaw W.
    Jagiellonian Univ, Coll Med, PL-30688 Krakow, Poland..
    Korzhavyi, Pavel A.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Structure and chemistry of liquid Al-Cu alloys: molecular dynamics study versus thermodynamics-based modelling2018Inngår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 53, nr 11, s. 8285-8301Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Classical molecular dynamics simulations, employing a modified embedded atom model (MEAM) parametrization recently developed by Trybula, have been performed and combined with thermodynamics-based modelling for weakly interacting compound-forming molten alloys, to investigate the structure and chemistry of liquid Al-Cu alloys over a broad Cu concentration range. The compound-forming model (CFM) based on experimental thermodynamic data revealed the importance of the Al2Cu "associate" in the determination of transport properties such as diffusion and viscosity as well as confirmation of the compound formation ability with regard to the available experimental data. Adequately to this fact, molecular dynamics simulation results showed strong evidence of deviation from regular metallic solution resulting from a preponderance of chemical short-range ordering, expressed by Warren-Cowley parameter and increasing abundance of icosahedral motifs with increasing Cu content. In addition, their strong impact on mass transport properties as well as the excess entropy has been detected which exhibits nonlinear compositional behaviour. Thus, we find that the Stokes-Einstein relation is unsuitable for atom transport properties determination at investigated Cu concentration range, while the Green-Kubo formalism can fully account for the experimentally observed physical phenomena. We obtain a compact and compatible view onto the structure and chemical behaviour, including atom kinetics and thermodynamics, of Al-Cu liquid alloys, which allowed us to find another hard-sphere-like metallic system in which transport properties and thermodynamics are strongly affected by packing effects. The hybrid approach presented herein gave a broader and deeper look into the liquid state of the Al-Cu alloys being missing in the literature.

  • 54. Vahtikari, Katja
    et al.
    Rautkari, Lauri
    Noponen, Tuula
    Lillqvist (nee Laine), Kristiina
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Byggnadsmaterial.
    Hughes, Mark
    The influence of extractives on the sorption characteristics of Scots pine (Pinus sylvestris L.)2017Inngår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 52, nr 18, s. 10840-10852Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The sorption behaviour of extracted and un-extracted Scots pine (Pinus sylvestris L.) heartwood was analysed using dynamic vapour sorption apparatus. In addition to the sorption isotherm and hysteresis, the moisture increments and decrements were determined as well as the rate of sorption. Parallel exponential kinetics model was used for further analysis. The effect of cyclic humidity loading on the sorption characteristics was studied by exposing samples to ten repeated sorption cycles and by determining the amount of accessible hydroxyl (OH) groups before and after the cyclic humidity loading. Removal of extractives led to an increase in EMC both in adsorption and in desorption. Hysteresis decreased due to the removal of extractives. Cyclic humidity loading reduced the sorptive capacity of wood material for both extracted and un-extracted wood, but was more pronounced in un-extracted wood. However, despite the decrease in the sorptive capacity, the amount of accessible OH groups increased after ten repeated dry-humid cycles.

  • 55. Woldegiorgis, A.
    et al.
    Jansson, K.
    Roeraade, Johan
    KTH, Skolan för kemivetenskap (CHE), Kemi, Analytisk kemi.
    Fabrication of silica nano wires on the internal perimeter of narrow bore fused silicia tubing by non-isothermal etching2005Inngår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 40, nr 3, s. 583-589Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An method for fabrication of long silica nano wires is presented. The nano structured material is an integral part of the inner surface of narrow bore fused silica capillary tubing. The wire preparation method is based on a hydrothermal action and decomposition of 2-chloro-1,1,2-trifluoroethyl methyl ether at elevated temperature. In our previous work, reproducible nano wire outgrowth could only be accomplished in capillaries with an inner diameter less than 10 mum [1], and the centre of the capillary lumen remained free of wires. In the present article we report on nano wire outgrowth in capillaries with larger inner diameters. These wires are entangled via carbon nucleating particles and stretch across the entire lumen of the capillary. The long nano wire outgrowth was induced by a time dependent, non isothermal etching of the capillaries. Suggested mechanisms for the growth process are discussed.

  • 56.
    Wretfors, Christer
    et al.
    SLU, Alnarp.
    Cho, Sung-Woo
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Kuktaite, R.
    SLU, Alnarp.
    Hedenqvist, Mikael S.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Marttila, S
    SLU, Alnarp.
    Nimmermark, S
    SLU, Alnarp.
    Johansson, Eva
    SLU, Alnarp.
    Effects of fiber blending and diamines on wheat gluten materials reinforced with hemp fiber2010Inngår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 45, nr 15, s. 4196-4205Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Wheat gluten (WG) is a promising base material for production of "green" plastics, although reinforcement is needed in more demanding applications. Hemp fiber is a promising reinforcement source but difficulties exist in obtaining desired properties with a WG-based matrix. This study aimed at improving fiber dispersion and fiber-matrix interactions using a high speed blender and a diamine as a cross-linker. Samples were manufactured using compression molding, two types of blenders and addition of diamine. Mechanical properties were assessed with tensile testing. Tensile-fractured surfaces were examined with scanning electron microscopy (SEM). Protein polymerization and fiber-protein matrix interactions were examined using high performance liquid chromatography (HPLC) and confocal laser scanning microscopy (CLSM). The results showed that a higher-speed grinding yielded a more even distribution of fibers and a more polymerized protein structure compared to a lower-speed grinding. However, these improvements did not result in increased strength, stiffness, and extensibility for the higher-speed grinding. The strength was increased when the grinding was combined with addition of a diamine (Jeffamine(R) EDR-176). HPLC, SEM, and CLSM, indicated that diamine added samples showed a more "plastic" appearance together with a stiffer and stronger structure with less cracking compared to samples without diamine. The use of the diamine also led to an increased polymerization of the proteins, although no effect on the fiber-protein matrix interactions was observed using microscopical techniques. Thus, for future successful use of hemp fibers to reinforce gluten materials, an appropriate method to increase the fiber-protein matrix interaction is needed.

  • 57.
    Xuan, Changji
    et al.
    Uddeholms AB, Uvedsvagen 15, SE-68385 Hagfors, Sweden.
    Mu, Wangzhong
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Composition evolution and coalescence behavior of titanium oxide particles in Iron-Nickel binary alloy melt2019Inngår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 54, nr 11, s. 8684-8695Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Particle coalescence refers to the dispersed particles in a suspension sticking to each other through the random collisions. This phenomenon is of vital importance for the process control and mechanical property of the metallic materials, such as Iron-Nickel binary alloy. The present work performed a fundamental study of the composition evolution and coalescence behavior of the Ti-oxide particles in the liquid Iron-Nickel binary alloy. The effect of the titanium addition amount on the composition of the inclusion particles is investigated through the Ti deoxidation experiments. The particle features are characterized by using a potentiostatic electrolytic extraction method. It shows that when the amount of the Ti addition arrives at a certain degree, the state of the oxide particles changes from the liquid to the solid. Meanwhile, the formation of the cluster can occur. The coalescence efficiency and attraction forces of the particles are calculated theoretically. It is found that the coalescence degree of the solid TiOx (x=1.5-1.67) particle is close to that of the Al2O3 particle. The initial sintering behavior of the particles after coalescence-collision is analyzed by measuring the sintered neck radius. The apparent self-diffusion of the TiOx (x=1.5-1.67) particle is approximately 1.7 times larger than that of the Al2O3 particle.

  • 58.
    Yar, Mazher Ahmed
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Funktionella material, FNM.
    Wahlberg, Sverker
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Funktionella material, FNM.
    Abuelnaga, Mohammad Omar
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Funktionella material, FNM.
    Johnsson, Mats
    Muhammed, Mamoun
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Funktionella material, FNM.
    Processing and sintering of yttrium-doped tungsten oxide nanopowders to tungsten-based composites2014Inngår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 49, nr 16, s. 5703-5713Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Innovative chemical methods are capable of fabricating nanoscale tungsten oxide compounds doped with various rare-earth elements with high purity and homogeneity, which can be processed under hydrogen into nanostructured oxide-dispersed tungsten composite powders having several potential applications. However, hydrogen reduction of doped tungsten oxide compounds is rather complex, affecting the morphology and composition of the final powder. In this study, we have investigated the reduction of tungstic acid in the presence of Y and we provide the experimental evidence that Y2O3 can be separated from Y-doped tungstic acid via hydrogen reduction to produce Y2O3-W powders. The processed powders were further consolidated by spark plasma sintering at different temperatures and holding times at 75 MPa pressure and characterized. The optimized SPS conditions suggest sintering at 1400 A degrees C for 3 min holding time to achieve higher density composites with an optimum finer grain size (3 A mu m) and a hardness value up to 420 H (V). Major grain growth takes place at temperatures above 1300 A degrees C during sintering. From the density values obtained, it is recommend to apply higher pressure before 900 A degrees C to obtain maximum density. Oxides inclusions present in the matrix were identified as Y2O3 center dot 3WO(3) and Y2O3 center dot WO3 during high resolution microscopic investigations.

  • 59. Zhang, Rui
    et al.
    Mao, Huahai
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Halli, Petteri
    Taskinen, Pekka
    Experimental phase stability investigation of compounds and thermodynamic assessment of the BaO–SiO2 binary system2016Inngår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 51, nr 10, s. 4984-4995Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Phase equilibria were experimentally investigated at 1173 and 1523 K at the BaO-rich region in the BaO–SiO2 system. The phase assemblages were characterized by X-ray diffraction and scanning electron microscopy with energy dispersive X-ray analysis. Substitutional solution model and associate model were employed to describe the liquid phase. Two sets of self-consistent thermodynamic parameters were derived based on the obtained experimental results and literature data. Phase diagrams and thermodynamic properties were calculated using the thermodynamic parameters acquired. All the calculated results were compared with the experimental data in the present work and literature. Some new experimental studies of the melting behavior of the phase Ba3SiO5 and liquidus at the SiO2-rich corner are recommended to get a better fit for this system.

  • 60.
    Zhou, Jing
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Odqvist, Joakim
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Ruban, Andrei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Thuvander, M.
    Xiong, W.
    Ågren, John
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Olson, G. B.
    Hedström, Peter
    Effect of solution treatment on spinodal decomposition during aging of an Fe-46.5 at.% Cr alloy2017Inngår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 52, nr 1, s. 326-335Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Spinodal decomposition is a key phase transition in advanced materials and a significant effort is paid to the quantitative modeling of the phenomenon. The initial materials condition is often assumed to be random during modeling, but this may be an oversimplification. In this work, the effect of solution treatment above the miscibility gap, on spinodal decomposition during subsequent aging, has been investigated for an Fe-46.5 at.% Cr alloy. By atom probe tomography (APT), it is found that different extents of quenched-in Cr clustering exist after solution treatments at different temperatures. The clustering is pronounced at 800 °C but decreases significantly with increasing temperature to 900 °C. Thermodynamic Monte Carlo simulations show that there is a difference in atomic short range order between the different solution treatment temperatures. By APT, it is, furthermore, found that the kinetics of spinodal decomposition at 500 °C, i.e., within the miscibility gap, is enhanced in the initial alloy condition, where Cr was less randomly distributed. These observations are supported by kinetic Monte Carlo simulations, predicting a similar but less pronounced qualitative effect on spinodal decomposition kinetics. Other possible reasons for the enhanced kinetics could be related to clustering of interstitial elements and/or sigma phase, but neither was found in the experiments. Nonetheless, the observations in this work suggest that it is necessary to implement a modeling strategy, where the initial structure is properly accounted for when simulating spinodal decomposition.

  • 61. Zhu, Feng
    et al.
    Li, Cuiping
    Ha, Minh Ngoc
    Liu, Zhifu
    Guo, Qiangsheng
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Shanghai Inst Technology, China.
    Molten-salt synthesis of Cu-SrTiO3/TiO2 nanotube heterostructures for photocatalytic water splitting2016Inngår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 51, nr 9, s. 4639-4649Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A series of Cu-loaded SrTiO3/TiO2 nanotube heterostructures were synthesized by a facile molten salts method and an impregnation-calcination method. Through adjusting the molar ratio of Sr/Ti, the photocatalytic performance of the samples changed regularly. When Sr/Ti = 0.2, the catalyst showed the highest performance in water splitting and the H-2 generation amount was 0.597 mmol under UV irradiation for 8 h. The enhanced performance of Cu-loaded SrTiO3/TiO2 nanotubes could be attributed to the heterostructures, the small crystallite size, and the reduced band gap inside them.

  • 62.
    Zhu, Jiqing
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Balieu, Romain
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Lu, Xiaohu
    Nynas AB.
    Kringos, Niki
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Numerical investigation on phase separation in polymer modified bitumen: Effect of thermal condition2017Inngår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 52, nr 11, s. 6525-6541Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    With the aim to understand the effect of thermal condition on phase separation in polymer-modified bitumen (PMB), this paper numerically investigates four PMB binders under five thermal conditions between 140 and 180 °C. Based on a phase-field model previously developed by the authors for PMB phase separation, the updated model presented in this paper uses temperature-dependent parameters in order to approach the concerned temperature range, including mobility coefficients, interaction and dilution parameters. The model is implemented in a finite element software package and calibrated with the experimental observations of the four PMBs. The experimental results are well reproduced by the model, and it is thus believed that the calibrated parameters can represent the four PMBs. The simulation results indicate that the model proposed in this paper is capable of capturing the stability differences among the four PMBs and their distinct microstructures at different temperatures. Due to the transition of some PMBs from the thermodynamically stable state at 180 °C to the unstable state at 140 °C, a homogenization process may occur during the cooling applied numerically. After the transition, the PMBs start to separate into two phases and gradually form the binary structures controlled by the temperature. It is indicated that the cooling rate slightly affects the final pattern of the PMB binary microstructure, although the process can be more complicated in reality due to the potential dynamic reasons.

  • 63. Čermák, Petr
    et al.
    Vahtikari, Katja
    Rautkari, Lauri
    Laine, Kristiina
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Byggnadsmaterial.
    Horáček, Petr
    Baar, Jan
    The effect of wetting cycles on moisture behaviour of thermally modified Scots pine (Pinus sylvestris L.) wood2016Inngår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 51, nr 3, s. 1504-1511Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The moisture behaviour of thermally modified Scots pine (Pinus sylvestris L.) exposed to cyclic conditions was analysed. Specimens of dimensions 15 × 15 × 5 mm3 were thermally modified at 180 °C (TM1) and 220 °C (TM2) using atmospheric pressure and superheated steam. Radial, tangential, volumetric swelling and anti-swelling efficiency (ASE) were calculated during six consecutive drying–soaking cycles. Afterwards, additional specimens were exposed to ten relative humidity cycles (0 and 95 %) at temperature 25 and 40 °C in order to analyse its influence on sorption behaviour. Application of thermal modification led to significant reduction of swelling from original 18.4–13.3 % for TM1 and to 10.5 % for TM2. However, after exposure to six consecutive soaking–drying cycles, the swelling of control specimens slightly decreased, whereas the swelling of thermally modified specimens increased. Due to the increased swelling after repeated cycles, the original ASE (28.6 and 42.7 %) decreased to 22.5 % for TM1 and to 36.88 % for TM2. The presence of leachable compounds and release of internal stresses are mainly attributed to that phenomenon. The EMC of the reference specimens decreases over the repeated humidity cycles for approximately 1 %–units. Same trend was found for the mild thermal modification TM1, but decreasing only in the range of 0.5 %–units. However, the EMC of the TM2 specimens during humidity cycles behaved differently. The results provide a better insight into details of thermal modification of wood and its behaviour under cyclic conditions.

12 51 - 63 of 63
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