Change search
Refine search result
1 - 10 of 10
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Bahaloo, Hassan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Casselgren, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lycksam, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Mapping of density-dependent material properties of dry manufactured snow using μCT2024In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 130, article id 16Article in journal (Refereed)
    Abstract [en]

    Despite the significance of snow in various cryospheric, polar, and construction contexts, more comprehensive studies are required on its mechanical properties. In recent years, the utilization of μ CT has yielded valuable insights into snow analysis. Our objective is to establish a methodology for mapping density-dependent material properties for dry manufactured snow within the density range of 400–600 kg/m 3 utilizing μ CT imaging and step-wise, quasi-static, mechanical loading. We also aim to investigate the variations in the structural parameters of snow during loading. The three-dimensional (3D) structure of snow is captured using μ CT with 801 projections at the beginning of the experiments and at the end of each loading step. The sample is compressed at a temperature of − 18 o C using a constant rate of deformation (0.2 mm/min) in multiple steps. The relative density of the snow is determined at each load step using binary image segmentation. It varies from 0.44 in the beginning to nearly 0.65 at the end of the loading, which corresponds to a density range of 400–600 kg/m 3 . The estimated modulus and viscosity terms, obtained from the Burger’s model, show an increasing trend with density. The values of the Maxwell and Kelvin–Voigt moduli were found to range from 60 to 320 MPa and from 6 to 40 MPa, respectively. Meanwhile, the viscosity values for the Maxwell and Kelvin–Voigt models varied from 0.4 to 3.5 GPa-s, and 0.3–3.2 GPa-s, respectively, within the considered density range. In addition, Digital Volume Correlation (DVC) was used to calculate the full-field strain distribution in the specimen at each load step. The image analysis results show that, the particle size and specific surface area (SSA) do not change significantly within the studied range of loading and densities, while the sphericity of the particles is increased. The grain diameter ranges from approximately 100 μ m to nearly 400 μ m, with a mode of nearly 200 μ m. The methodology presented in this study opens up a path for an extensive statistical analysis of the material properties by experimenting more snow samples.

    Download full text (pdf)
    fulltext
  • 2.
    Bahaloohoreh, Hassan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lycksam, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Casselgren, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Material mapping strategy to identify the density-dependent properties of dry natural snow2024In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 130, no 2, article id 141Article in journal (Refereed)
    Abstract [en]

    The mechanical properties of natural snow play a crucial role in understanding glaciers, avalanches, polar regions, and snow-related constructions. Research has concentrated on how the mechanical properties of snow vary, primarily with its density; the integration of cutting-edge techniques like micro-tomography with traditional loading methods can enhance our comprehension of these properties in natural snow. This study employs CT imaging and uniaxial compression tests, along with the Digital Volume Correlation (DVC) to investigate the density-dependent material properties of natural snow. The data from two snow samples, one initially non-compressed (test 1) and the other initially compressed (test 2), were fed into Burger’s viscoelastic model to estimate the material properties. CT imaging with 801 projections captures the three-dimensional structure of the snow initially and after each loading step at -18C, using a constant deformation rate (0.2 mm/min). The relative density of the snow, ranging from 0.175 to 0.39 (equivalent to 160–360 kg/m), is determined at each load step through binary image segmentation. Modulus and viscosity terms, estimated from Burger’s model, exhibit a density-dependent increase. Maxwell and Kelvin–Voigt moduli range from 0.5 to 14 MPa and 0.1 to 0.8 MPa, respectively. Viscosity values for the Maxwell and Kelvin–Voigt models vary from 0.2 to 2.9 GPa-s and 0.2 to 2.3 GPa-s within the considered density range, showing an exponent between 3 and 4 when represented as power functions. Initial grain characteristics for tests 1 and 2, obtained through image segmentation, reveal an average Specific Surface Area (SSA) of around 55 1/mm and 40 1/mm, respectively. The full-field strain distribution in the specimen at each load step is calculated using the DVC, highlighting strong strain localization indicative of non-homogeneous behavior in natural snow. These findings not only contribute to our understanding of natural snow mechanics but also hold implications for applications in fields such as glacier dynamics and avalanche prediction.

    Download full text (pdf)
    fulltext
  • 3.
    Comini, E.
    et al.
    INFM-CNR Sensor Lab.
    Bianchi, S.
    INFM-CNR Sensor Lab.
    Faglia, G.
    INFM-CNR Sensor Lab.
    Ferroni, M.
    INFM-CNR Sensor Lab.
    Vomiero, Alberto
    INFM-CNR Sensor Lab.
    Sberveglieri, G.
    INFM-CNR Sensor Lab.
    Functional nanowires of tin oxide2007In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 89, no 1, p. 73-76Article in journal (Refereed)
    Abstract [en]

    Quasi-one-dimensional nanostructures of tin oxide were produced in controlled conditions through condensation from the vapor phase. The preparation was assisted by noble metal catalysts and uniform single-crystalline nanowires were produced. The nucleation of nanowires was achieved at 470 °C, owing to the vapor-liquid-solid growth mechanism activated by the catalytic Pt clusters. The peculiar microstructural properties of these semiconducting metal oxide nanostructures will be summarized. The high aspect ratio and the high degree of crystallinity achieved for the nanowires foresee their functional exploitation. © 2007 Springer-Verlag.

  • 4.
    Da Silva, Adrien
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Volpp, Joerg
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander F.H
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Acceleration of metal drops in a laser beam2021In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 127, no 1, article id 4Article in journal (Refereed)
    Abstract [en]

    Different processes require the detachment of metal drops from a solid material using a laser beam as the heat source, for instance laser drop generation or cyclam. These techniques imply that the drops enter the laser beam, which might affect their trajectory. Also, many laser processes such as laser welding or additive manufacturing generate spatters that can be accelerated by the laser beam during flight and create defects on the material. This fundamental study aims at investigating the effects of a continuous power laser beam on the acceleration of intentionally detached drops and unintentionally detached spatters. Two materials were studied: 316L steel and AlSi5 aluminium alloy. High-speed imaging was used to measure the position of the drops and calculate their acceleration to compare it to theoretical models. Accelerations up to 11.2 g could be measured. The contributions of the vapor pressure, the recoil pressure, and the radiation pressure were investigated. The recoil pressure was found to be the main driving effect but other phenomena counteract this acceleration and reduce it by an order of magnitude of one to two. In addition, two different vaporization regimes were observed, resulting respectively in a vapor plume and in a vapor halo around the drop.

    Download full text (pdf)
    fulltext
  • 5.
    Kvien, Ingvild
    et al.
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Orientation of cellulose nanowhiskers in polyvinyl alcohol2007In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 87, no 4, p. 641-643Article in journal (Refereed)
    Abstract [en]

    The goal of this study was to align cellulose nanowhiskers in a polymer using a strong magnetic field and thereby obtain a unidirectional reinforced nanocomposite. Cellulose whiskers (2 wt.%) were incorporated in a polyvinyl alcohol matrix using solution casting with water as the solvent. The suspension was cast and the water was evaporated while a homogeneous magnetic field of 7 T was applied. Different microscopy investigations of prepared nanocomposites indicated that the cellulose whiskers were oriented perpendicular to the direction of the magnetic field. Dynamic mechanical thermal analysis further strengthened the idea of alignment because the results showed that the dynamic modulus of the nanocomposite was around 2 GPa higher at room temperature in the aligned direction compared to the transverse direction.

  • 6.
    Mannelquist, Anders
    et al.
    Luleå University of Technology.
    Almqvist, Nils
    Luleå University of Technology.
    Fredriksson, Sverker
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Influence of tip geometry on fractal analysis of atomic force microscopy images1998In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 66, no Supplement 1, p. S 891-S 895Article in journal (Refereed)
    Abstract [en]

    Fractal analysis of data from atomic force microscopy (AFM) is often necessary for studying surfaces with scale-invariant roughness. However, the fractal parameters are influenced by the finite-sized tip geometry of the AFM stylus. We make an extended study of such little-known effects. The so-called successive random algorithm is used to generate by computer ideal fractal surfaces with known fractal dimensions and varying height magnitudes. Tip-distorted AFM images are simulated from the ideal surfaces for the case of a strictly geometrical interaction between surface and tip. The AFM-induced error, taken as the difference in estimated parameters between ideal and distorted images, is shown to be largest for small scan sizes and high fractal dimensions. The dependence on AFM tip radius and surface height magnitude is analyzed by the structure function, variance and a Fourier method. The latter is shown to be unreliable for analyzing AFM images. We exemplify how the results can be applied to AFM images of real surfaces.

  • 7.
    Mannelqvist, Anders
    et al.
    Luleå University of Technology.
    Groth, Margareta Ring
    Luleå University of Technology.
    Comparison of fractal analyses methods and fractal dimension for pre-treated stainless steel surfaces and the correlation to adhesive joint strength2001In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 73, no 3, p. 347-355Article in journal (Refereed)
    Abstract [en]

    The fractal dimensions of six differently mechanically pre-treated stainless steel samples were investigated using five fractal algorithms. The surfaces were analyzed using a profiler, atomic force microscopy (AFM), scanning electron microscopy (SEM) and light microscopy (LM), and thereafter adhesively bonded and tested in single-overlap joints to test their tensile strength. All samples showed different fractal behavior, depending on the microscopic methods and fractal algorithms. However, the overall relation between fractal dimension and tensile strength is qualitatively the same, except for the SEM images. This verifies that tensile strength is correlated to fractal dimension, although only within the length-scale of the profiler and the light microscope (,0.5-100 7m). The AFM method was excluded in this comparison, since the limitation in the z-direction for the AFM scanner made it difficult to scan the rougher parts of the blasted samples. The magnitude of the surfaces is a parameter not often considered in fractal analysis. It is shown that the magnitude, for the Fourier method, is correlated to the arithmetic average difference, Ra, but only weakly to the fractal dimension. Hence, traditional parameters, such as Ra, tell us very little about the spatial distribution of the elevation data.

  • 8. Soldatov, Alexander
    et al.
    Andersson, O.
    Thermal conductivity of pressure polymerized C601997In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 64, no 3, p. 227-229Article in journal (Refereed)
    Abstract [en]

    We have studied the kinetics of C60 polymerization in the temperature interval \rangeunit{450}{500}{K} at pressures below \valunit{1}{GPa} by measurements of the time dependence of the thermal conductivity. It has been found at \valunit{450}{K} that the polymerization process at \valunit{0.8}{GPa} is slower than the reverse transformation from "polymeric" to "monomeric" phase at \valunit{0.08}{GPa}. The thermal conductivity \lambda of polymerized C60 was measured in the temperature range \rangeunit{100}{430}{K} and found to increase with increasing temperature, which reflects strong phonon scattering. Both the presence of non-bonded C60 molecules and a high degree of structural disorder in the crystalline lattice of the polymeric phase might be responsible for the behaviour of \lambda(T). The results for \lambda(T) are qualitatively similar to those reported previously for C60 polymerized at higher p, T but an order of magnitude smaller.

  • 9.
    Volpp, Jörg
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Impact of fume particles in the keyhole vapour2019In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 125, no 1, article id 70Article in journal (Refereed)
    Abstract [en]

    During laser material processing, the energy of the laser beam needs to be efficiently and constantly transported to theprocessing zone to guarantee constant processing. However, spatters or ejected particles from the keyhole can absorb andscatter the laser energy leading to inhomogeneous heat input and can initiate defect occurrence like pore formation. Theimpact of ejected particles from the keyhole on the energy transport of the laser beam is not completely understood sincethey are difficult to observe due to the small size and high speeds of the ejections. In this work, the particle characteristicswere derived from a simulation of the keyhole wall movement. The behavior of the calculated particles in a side shielding gasjet was calculated to derive the height, at which the particles leave the laser beam and are not interrupting the laser energytransfer to the processing zone. Low impulse values of the particles were calculated e.g., at defocusing positions slightlyunderneath the material surface, where also highest melt pool sizes were found. These observations indicate that the fumeparticles can be one reason to limit the energy delivery. An efficiency increase can be achieved by adjusting the keyholeparameters to a more stable keyhole.

    Download full text (pdf)
    fulltext
  • 10. Winter, J.
    et al.
    Burger, B.
    Hulman, M.
    Kuzmany, H.
    Soldatov, Alexander
    Experimental access to doped fullerene polymers1997In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 64, no 3, p. 257-262Article in journal (Refereed)
    Abstract [en]

    We present Raman measurements performed to study the experimental access to doped fullerene polymers. The polymeric orthorhombic AC60 compound could be obtained by slow cooling the high temperature fcc phase and by quenching with subsequent annealing. The various phases after quenching and during annealing were studied in detail. No evidence for a direct doping of undoped C60 to the polymeric AC60 phase was found. Due to the local character of the doping process the formation of A3C60 clusters is observed. The same results were obtained from doping experiments performed with undoped polymeric structures like phototransformed and pressure polymerized C60.

1 - 10 of 10
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf