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  • 1.
    A., Trubetskaya
    et al.
    National University of Ireland Galway.
    G. R., Surup
    University of Agder.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    T., Attard
    University of York.
    A., Hunt
    Khon Kaen University.
    V., Budarin
    University of York.
    V., Abdelsayed
    National Energy Technology Laboratory.
    D., Shekhawat
    National Energy Technology Laboratory.
    The Effect of Wood Composition and Supercritical CO2 Extraction on the Charcoal Production2019In: 2019 AIChE Annual Meeting proceedings, American Institute of Chemical Engineers, 2019, article id 552cConference paper (Other academic)
    Abstract [en]

    This work demonstrated that the coupling of supercritical carbon dioxide extraction with slow pyrolysis is effective to remove over half of extractives from low quality wood and to generate biochar from remaining solid wood fractions. The high yields of extractives from supercritical carbon dioxide extraction illustrates the potential utilizing of low quality wood as an alternative feedstock for the sustainable production of value-added chemicals. Results showed that supercritical carbon dioxide extraction has neither a strong impact on the physical properties of original wood nor on the yield of solid biochar. These results are promising as they show that the biochar obtained for this renewable feedstock could be used as an alternative to fossil-based coke in applications including ferroalloy industries. Moreover, the heat treatment temperature and supercritical carbon dioxide extraction had a significant impact on the tar yields, leading to the increase in naphthalene, polycyclic aromatic hydrocarbons, aromatic and phenolic fractions with the greater temperature. The differences in gasification reactivity and dielectric properties of solid biochars, composition and yields of liquid products of non-treated pinewood and extracted wood fraction emphasize the impact of supercritical carbon dioxide extraction on the pyrolysis process. 

  • 2.
    Bahaloo, Hassan
    et al.
    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.
    Forsberg, Fredrik
    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.
    Discrete element simulation of dry snow using the developed analytic bond model2021In: IOP Conference Series: Materials Science and Engineering, Institute of Physics (IOP), 2021, Vol. 1190, article id 012015Conference paper (Refereed)
    Abstract [en]

    Snow is a heterogenous, hot material which is constituted from ice particles. The bonding behavior of ice particles is an important parameter determining the macroscopic behavior of snow. Discrete Element Method (DEM) is usually used as a tool to model dry snow. The most important input data required into the DEM is bonding behavior of ice particles since ice particles can adhere to form bonds when they brought into contact. This study had two aims: first, an analytical formulation was derived to predict the bond diameter of ice-ice contacts as a function of time, compressive load, and strain rate. Using the previously published data for strain rate of ice, a solution method was developed. The results of bond diameter development with time were compared to experimental data and a good agreement was found. Second, a DEM for dry snow was developed and programmed in MATLAB and the developed bond model was employed in the simulation to study the deposition behavior of snow in a container under gravity acceleration. A specific beam element with implemented damage model was developed in implemented in the simulation using the bond data obtained from the analytical approach. The simulated parameters were macroscopic angle of repose, packing density, and surface conditions as a function of temperature and filling rate. The results showed that discrete element simulations were able to verify the existing published experimental data. Specifically, the simulation results showed that angle of repose of snow decreased rapidly with decreasing the temperature, the surface became very irregular due to the particles rotation and re-arrangement for lower falling speeds of particles, and density increased with depth of deposition. These findings were all matched with experimental observations.

  • 3.
    Bahaloo, Hassan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Eidevåg, Tobias
    Department of Chemistry and Chemical Engineering, Chalmers University of Technology, SE-41296 Gothenburg Sweden; Contamination and Core CFD, Volvo Car Corporation, SE-405 31 Gothenburg, Sweden.
    Gren, Per
    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.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Abrahamsson, Per
    Technical Analysis, Fluid Mechanics, AFRY, Gothenburg, Sweden 412 63.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ice Sintering: Dependence of Sintering Force on Temperature, Load, Duration, and Particle Size2022In: Svenska Mekanikdagar 2022 / [ed] Pär Jonsén; Lars-Göran Westerberg; Simon Larsson; Erik Olsson, Luleå tekniska universitet, 2022Conference paper (Refereed)
  • 4.
    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.

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  • 5.
    Bahaloo, Hassan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    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.
    Forsberg, Fredrik
    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.
    Capillary Bridge in Contact with Ice Particles Can Be Related to the Thin Liquid Film on Ice2024In: Journal of cold regions engineering, ISSN 0887-381X, E-ISSN 1943-5495, Vol. 38, no 1, article id 04023021Article in journal (Refereed)
    Abstract [en]

    We experimentally demonstrate the presence of a capillary bridge in the contact between an ice particle and a smooth aluminum surface at a relative humidity of approximately 50% and temperatures below the melting point. We conduct the experiments in a freezer with a controlled temperature and consider the mechanical instability of the bridge upon separation of the ice particle from the aluminum surface at a constant speed. We observe that a liquid bridge forms, and this formation becomes more pronounced as the temperature approaches the melting point. We also show that the separation distance is proportional to the cube root of the volume of the bridge. We hypothesize that the volume of the liquid bridge can be used to provide a rough estimate of the thickness of the liquid layer on the ice particle since in the absence of other driving mechanisms, some of the liquid on the surface must have been pulled to the bridge area. We show that the estimated value lies within the range previously reported in the literature. With these assumptions, the estimated thickness of the liquid layer decreases from nearly 56 nm at T = −1.7°C to 0.2 nm at T = −12.7°C. The dependence can be approximated with a power law, proportional to (TM − T)−β, where β < 2.6 and TM is the melting temperature. We further observe that for a rough surface, the capillary bridge formation in the considered experimental conditions vanishes.

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  • 6.
    Bahaloohoreh, Hassan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Eidevåg, Tobias
    Department of Chemistry and Chemical Engineering, Chalmers University of Technology, SE-41296 Gothenburg, Sweden; Contamination and Core CFD, Volvo Car Corporation, SE-405 31 Gothenburg, Sweden.
    Gren, Per
    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.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Abrahamsson, Per
    Technical Analysis, Fluid Mechanics, AFRY, Gothenburg 412 63, Sweden.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ice sintering: Dependence of sintering force on temperature, load, duration, and particle size2022In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 131, no 2, article id 025109Article in journal (Refereed)
    Abstract [en]

    We present experiments along with an approximate, semi-analytic, close-form solution to predict ice sintering force as a function of temperature, contact load, contact duration, and particle size during the primary stage of sintering. The ice sintering force increases nearly linear with increasing contact load but nonlinear with both contact duration and particle size in the form of a power law. The exponent of the power law for size dependence is around the value predicted by general sintering theory. The temperature dependence of the sintering force is also nonlinear and follows the Arrhenius equation. At temperatures closer to the melting point, a liquid bridge is observed upon the separation of the contacted ice particles. We also find that the ratio of ultimate tensile strength of ice to the axial stress concentration factor in tension is an important factor in determining the sintering force, and a value of nearly 1.1 MPa can best catch the sintering force of ice in different conditions. We find that the activation energy is around 41.4KJ/mol41.4KJ/mol, which is close to the previously reported data. Also, our results suggest that smaller particles are “stickier” than larger particles. Moreover, during the formation of the ice particles, cavitation and surface cracking is observed which can be one of the sources for the variations observed in the measured ice sintering force.

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  • 7.
    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.

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  • 8.
    Bahaloohoreh, Hassan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    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.
    Forsberg, Fredrik
    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.
    Capillary bridge in contact of ice particles reveals the thin liquid film on ice2023Manuscript (preprint) (Other academic)
  • 9.
    Berglund, Linn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Jonoobi, Mehdi
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Wood and Paper Science and Technology, Faculty of Natural Resources, University of Tehran, Karaj, Iran.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Fibre and Particle Engineering, University of Oulu, Oulu, Finland.
    Promoted hydrogel formation of lignin-containing arabinoxylan aerogel using cellulose nanofibers as a functional biomaterial2018In: RSC Advances, E-ISSN 2046-2069, Vol. 8, no 67, p. 38219-38228Article in journal (Refereed)
    Abstract [en]

    In this work, three-dimensional (3D) aerogels and hydrogels based on lignin-containing arabinoxylan (AX) and cellulose nanofibers (CNF) were prepared. The effects of the CNF and the crosslinking with citric acid (CA) of various contents (1, 3, 5 wt%) were evaluated. All the aerogels possessed highly porous (above 98%) and lightweight structures. The AX-CNF hydrogel with a CA content of 1 wt% revealed a favorable network structure with respect to the swelling ratio; nanofiber addition resulted in a five-fold increase in the degree of swelling (68 g of water per g). The compressive properties were improved when the higher CA content (5 wt%) was used; when combined with CNF, there was a seven-fold enhancement in the compressive strength. The AX-CNF hydrogels were prepared using a green and straightforward method that utilizes sustainable resources efficiently. Therefore, such natural hydrogels could find application potential, for example in the field of soft tissue engineering.

  • 10.
    Berglund, Linn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Direct preparation of alginate/cellulose nanofiber hybrid-ink from brown seaweed for 3D biomimetic hydrogelsManuscript (preprint) (Other academic)
  • 11.
    Berglund, Linn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Rakar, Jonathan
    The Center for Disaster Medicine and Traumatology, and Experimental Plastic Surgery, Department of Biomedical and Clinical Sciences, Linköping University, SE-581 83 Linköping, Sweden.
    Junker, Johan P. E.
    The Center for Disaster Medicine and Traumatology, and Experimental Plastic Surgery, Department of Biomedical and Clinical Sciences, Linköping University, SE-581 83 Linköping, Sweden.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Fibre and Particle Engineering, University of Oulu, FI-90014 Oulu, Finland. Mechanical & Industrial Engineering (MIE), University of Toronto, M5S 3G8 Toronto, Canada.
    Utilizing the Natural Composition of Brown Seaweed for the Preparation of Hybrid Ink for 3D Printing of Hydrogels2020In: ACS Applied Bio Materials, E-ISSN 2576-6422, Vol. 3, no 9, p. 6510-6520Article in journal (Refereed)
    Abstract [en]

    This study aims to utilize the natural composition of brown seaweed by deriving alginate and cellulose concurrently from the stipe (stem-like) and blade (leaf-like) structures of the seaweed; further, this is followed by fibrillation for the direct and resource-efficient preparation of alginate/cellulose nanofiber (CNF) hybrid inks for three-dimensional (3D) printing of hydrogels. The efficiency of the fibrillation process was evaluated, and the obtained gels were further studied with regard to their rheological behavior. As a proof of concept, the inks were 3D printed into discs, followed by cross-linking with CaCl2 to form biomimetic hydrogels. It was shown that the nanofibrillation process from both seaweed structures is very energy-efficient, with an energy demand lower than 1.5 kW h/kg, and with CNF dimensions below 15 nm. The inks displayed excellent shear-thinning behavior and cytocompatibility and were successfully printed into 3D discs that, after cross-linking, exhibited an interconnected network structure with favorable mechanical properties, and a cell viability of 71%. The designed 3D biomimetic hydrogels offers an environmentally benign, cost-efficient, and biocompatible material platform with a favorable structure for the development of biomedical devices, such as 3D bio printing of soft tissues.

  • 12.
    Bhuiyan, Iftekhar Uddin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Mouzon, Johanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Forsmo, S.P.E.
    LKAB, Research & Development, 983 81 Malmberget.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Consideration of X-ray microtomography to quantitatively determine the size distribution of bubble cavities in iron ore pellets2013In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 233, p. 312-318Article in journal (Refereed)
    Abstract [en]

    X-ray microtomography data of iron ore green pellets of approx. 12 mm in diameter were recorded using a commercial instrument. The reconstructed volume after thresholding represented a unique dataset consisting of a three-dimensional distribution of equiaxed objects corresponding to bubble cavities. This dataset was used to successfully validate a stereological method to determine the size distribution of spherical objects dispersed in a volume. This was achieved by investigating only a few cross-sectional images of this volume and measuring the profiles left by these objects in the cross-sectional images. Excellent agreement was observed between the size distribution of the bubble cavities obtained by directly classifying their size in the reconstructed volume and that estimated by applying the aforementioned stereological method to eight cross-sectional images of the reconstructed volume. Subsequently, we discuss the possibility of calibrating X-ray tomography data quantitatively using the size distribution of the bubble cavities as a figure of merit and the results obtained by applying the stereological method to SEM images as reference data. This was justified by considering the validity of the stereological method demonstrated by tomography, the accurate thresholding made possible by back-scattered electron imaging and the solid reproducibility of the results obtained by SEM. Using different threshold values for binarization of the X-ray microtomography data and comparing the results to those obtained by SEM, we found that X-ray microtomography can be used after proper calibration against SEM data to measure the total porosity of the bubble cavities but can only provide a rough estimate of the median diameter because of the limited resolution achieved in this study.

  • 13.
    Bhuiyan, Iftekhar Uddin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Mouzon, Johanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Forsmo, S.P.E.
    LKAB Research and Development.
    Forsberg, Fredrik
    Air bubbles in iron ore green pellets due to flotation reagent: characterization by scanning electron microscopy and X-ray microtomography2011Conference paper (Other academic)
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  • 14.
    Eppanapelli, Lavan Kumar
    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.
    3D analysis of deformation and porosity of dry natural snow during compaction2019In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, no 6, article id 850Article in journal (Refereed)
    Abstract [en]

    The present study focuses on three-dimensional (3D) microstructure analysis of dry natural snow during compaction. An X-ray computed microtomography (micro-CT) system was used to record a total of 1601 projections of a snow volume. Experiments were performed in-situ at four load states as 0 MPa, 0.3 MPa, 0.6 MPa and 0.8 MPa, to investigate the effect of compaction on structural features of snow grains. The micro-CT system produces high resolution images (4.3 μm voxel) in 6 hours of scanning time. The micro-CT images of the investigated snow volume illustrate that grain shapes are mostly dominated by needles, capped columns and dendrites. It was found that a significant number of grains appeared to have a deep hollow core irrespective of the grain shape. Digital volume correlation (DVC) was applied to investigate displacement and strain fields in the snow volume due to the compaction. Results from the DVC analysis show that grains close to the moving punch experience most of the displacement. The reconstructed snow volume is segmented into several cylinders via horizontal cross-sectioning, to evaluate the vertical heterogeneity of porosity distribution of the snow volume. It was observed that the porosity (for the whole volume) in principle decreases as the level of compaction increases. A distinct vertical heterogeneity is observed in porosity distribution in response to compaction. The observations from this initial study may be useful to understand the snow microstructure under applied stress.

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  • 15.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    3D analys av deformationer i inhomogena material med röntgenbaserad mikrotomografi och digital volymkorrelation2009In: Svenska mekanikdagarna: Södertälje 2009, Stockholm: Svenska nationalkommittén för mekanik , 2009, p. 94-Conference paper (Other academic)
  • 16. Forsberg, Fredrik
    Measurements of deformations and flows inside optically nontransparent materials2005Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    When a material is mechanically loaded or experience environmental changes such as for example thermal or pressure variations it is affected, in some way, due to these new conditions. In order to measure engineering properties related to these structural changes, such as for example deformation and strain, we need to gain information about them that are precise and reliable. There exist many different methods for such measurements. However, most often these methods measure the pure surface response due to the deforming mechanism, since this is what can be observed directly by use of cameras and various sensors. We therefore know a lot about how the material surface behaves but not much about how the structure beneath the surface behaves. As long as the material structure is reasonably homogeneous this may be enough but as the complexity of the material structure increase it gets more important to obtain information from the inside of the material. In this thesis two techniques with the ability to measure internal deformations in optically non-transparent materials are presented. The fundamental principle of both the techniques is the same. The techniques utilize a correlation based routine to estimate deformations from two and three dimensional image data collected with x-ray-based methods. The first technique, called Digital Speckle Radiography (DSR), measures two-dimensional deformation fields, in a single plane within the examined material. The deformations are estimated by the use of image correlation applied to two-dimensional digital x-ray images. The second technique, called Tomographic 3D-DSP, measures the three-dimensional unrestricted deformation, in every point of the examined object. Here the correlation procedure is carried out on volumetric object data collected with computed tomography (CT). Three separate experiments have been carried out, to investigate the behaviour of the two techniques. In two of the experiments the two-dimensional technique is applied. In the first of these the flow profile of an alumina powder is measured as it flows through a silo configuration. In the second experiment the motion in a thin film of glue, sandwiched between two wooden plates, exposed to shear, is measured. Finally in the third experiment the three-dimensional technique is used to measure the deformations in bone tissue when being exposed to a mechanical load. In this case two measurements have been carried out, and compared. These differ through a small damage that has been introduced to the bone tissue in the second measurement.

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  • 17. Forsberg, Fredrik
    Mätning av 3-dimensionella deformationsfält2005In: Svenska Mekanikdagar 2005, Lund: Lund Institute of Technology , 2005Conference paper (Other academic)
  • 18. Forsberg, Fredrik
    Mätning av inre deformations- och hastighetsfält med digital speckleradiografi (DSR)2003In: SMD 03 : Svenska mekanikdagar : Göteborg 13-15 augusti 2003, Göteborg: Svenska nationalkommittén för mekanik , 2003Conference paper (Other academic)
  • 19.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Optimeringsstudie av datortomografisystem för användning inom 3D bildkorrelation2007In: Svenska Mekanikdagar 2007: Program och abstracts / [ed] Niklas Davidsson; Elianne Wassvik, Luleå: Luleå tekniska universitet, 2007, p. 65-Conference paper (Other academic)
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  • 20. Forsberg, Fredrik
    Tomografisk 3D-DSP: Mätningar av inre deformationer2004Conference paper (Other academic)
  • 21.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    X-ray microtomography and digital volume correlation for internal deformation and strain analysis2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A material that is exposed to mechanical load or experience a variation in its immediate environment (temperature, pressure, humidity etc.) will to some extent be affected by these new conditions, which is reflected through structural movements in the material. In order to measure engineering properties related to these structural changes, such as for example deformation and strain, we need to gain information about them that are precise and reliable. There exist many different methods for such measurements, which in most cases are based on the pure surface response due to the deforming mechanism. As long as the material structure is reasonably homogeneous the surface information may be enough but as the complexity of the material structure increase it gets more important to obtain information from the inside of the material. Here, a method for full 3D imaging and quantitative analysis of internal deformation and strain in inhomogeneous materials is presented. 3D structural information from the deforming material is obtained through use of x-ray microtomography. The deformation of the structure is analysed with a 3D pattern recognition technique called digital volume correlation, which is a 3D extension of digital image correlation. A thorough theoretical description of both image formation through x-ray microtomography as well as 2D and 3D structural deformation analysis is given. Complimentary, more practical aspects of the different x-ray imaging systems used in the research are described together with the different methods used for image quality assurance. Four different applications are presented. The first is an example of how rapid processes such as internal granular flow can be imaged and analysed with this kind of methods. The temporal resolution needed to resolve the process yields a sacrifice of spatial information and the analysis is carried out in 2D with digital image correlation. Secondly, the deformation and strain in 3D micro-scale wood structure exposed to three-point-bending is measured by use of synchrotron x-ray microtomography and digital volume correlation. Thirdly, the 3D structural swelling in wood microstructure due to water exposure is analysed using the same methods. Finally, the motion and induced strain in a granular material due to compaction is measured in 3D. The results show good agreement with corresponding 2D measurements, carried out for comparison. The experiments show that the method successfully can be used for analysis of various kinds of deformations and materials and that the results are trustworthy.

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  • 22.
    Forsberg, Fredrik
    et al.
    Luleå University of Technology.
    Grantham, Stephen G.
    University of Cambridge, UK.
    Internal deformation and velocity field measurements by use of digital speckle radiography2003In: Proceedings of SPIE: Optical Measurement Systems for Industrial Inspection III / [ed] Wolfgang Osten, Malgorzata Kujawinska, Katherine Creath, Bellingham, Wash.: SPIE - International Society for Optical Engineering, 2003, p. 545-555Conference paper (Refereed)
    Abstract [en]

    Using x-rays as information carriers it is possible to obtain data about motion inside an object that is opaque to visible light. An image correlation algorithm can be applied to a set of two X-ray images taken sequentially during a process, where the interior of the object is in motion. A displacement field describing the projected intermediate motion is thus obtained to sub-pixel accuracy. If this image set is expanded to contain several pictures separated in time, together describing the whole process, the images can be sequentially correlated to obtain a dynamic displacement field. In this paper, dynamical displacement field measurements have been carried out on two different objects, the first being a silo, where the motion of the flowing material in the centre plane is investigated. In the second case, the motion in a layer of glue between two wooden plates is examined during a process where a shearing force acts on the system. The plane in which the measurements are carried out is defined by the use of a contrast agent, usually a tungsten powder seeding. The obtained displacement field, together with the known intermediate time interval between exposures, gives the velocity field in the seeded plane. The results show good agreement with the expected motion in the respective processes, but also provide evidence of behaviour that would be undetectable using other existing techniques. A third experiment has also been carried out on a material requiring no contrast enhancing media. These measurements were performed on a chicken thigh being deformed by an external force. The results will be discussed in relation to their reliability and applicability. Further, the direction of future research will be indicated.

  • 23.
    Forsberg, Fredrik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hjortsberg, E.
    LKAB, Research & Development, 983 81 Malmberget.
    3D sequential imaging and analysis of iron ore pellets under reduction by X-ray microtomography2012In: 6th Int. Congress on the Science and Technology of Ironmaking 2012, ICSTI 2012: Including Proceedings from the 42nd Ironmaking and Raw Materials Seminar, and the 13th Brazilian Symp. on Iron Ore, 2012, Vol. 3, p. 1744-1753Conference paper (Refereed)
    Abstract [en]

    In this study, X-ray microtomography, combined with textural analysis, is used for 3D imaging of iron ore pellets and characterisation of interior cracks under a reduction process. The work is currently focused on the development of the methods and therefore the results mainly reflect the possibilities with the technique. Reduction experiments on a number of iron ore pellets were performed in 4 steps during the transformation from hematite to magnetite at 500°C. The pellet microstructure is imaged and visualized before reduction and after each subsequent reduction step using x-ray microtomography and the crack distribution characterized with image analysis. For the chosen pellet composition, networks of cracks are already visible in the unreduced state and show a successive growth during the first half of the reduction process. However, this growth stops during the second half of the process, and for the majority of the investigated samples a certain regression of the crack size is observed. Although further studies are needed, it can be concluded that the use of X-ray microtomography has the potential to become an important tool for material characterization in iron ore pellet research due to its ability to gather information from the bulk of the material at several different stages of a process.

  • 24.
    Forsberg, Fredrik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hjortsberg, Erik
    LKAB.
    X-ray microtomography for sequential imaging and analysis of iron ore pellets under reduction2012In: Scanmet IV: 4th International Conference on Process Development in Iron and Steelmaking, Luleå: MEFOS , 2012, Vol. 2, p. 217-227Conference paper (Refereed)
    Abstract [en]

    This work has been a part of the development of a method where x-ray microtomography and image analysis are used to quantify the crack distribution and propagation in iron ore pellets during reduction.Reduction experiments on 7 pellets, were performed in 4 steps during the transformation from hematite to magnetite at 500 °C. The pellet microstructure is imaged and visualized at each step using x-ray microtomography and the crack distribution characterized with image analysis.For the chosen pellet composition, networks of cracks are already visible in the unreduced state and show a successive growth during the first 30 minutes of reduction. As the transformation to magnetite is complete, crack growth has stopped and in several cases a partial regression is observed.It can be concluded that the use of X-ray microtomography has the potential to become an important tool for material characterization in iron ore pellet research due to its ability to gather information from the bulk of the material at several different stages of a process.

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  • 25.
    Forsberg, Fredrik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Mooser, René
    Electronics/Metrology Laboratory, Swiss Federal Laboratories for Materials Testing and Research (Empa).
    Arnold, M.
    Wood Laboratory, Swiss Federal Laboratories for Materials Testing and Research (Empa).
    Hack, Erwin
    Electronics/Metrology Laboratory, Swiss Federal Laboratories for Materials Testing and Research (Empa).
    Wyss, Peter
    Electronics/Metrology Laboratory, Swiss Federal Laboratories for Materials Testing and Research (Empa).
    3D micro-scale deformations of wood in bending: synchrotron radiation μCT data analyzed with digital volume correlation2008In: Journal of Structural Biology, ISSN 1047-8477, E-ISSN 1095-8657, Vol. 164, no 3, p. 255-262Article in journal (Refereed)
    Abstract [en]

    A micro-scale three-point-bending experiment with a wood specimen was carried out and monitored by synchrotron radiation micro-computed tomography. The full three-dimensional wood structure of the 1.57 × 3.42 × 0.75 mm3 specimen was reconstructed at cellular level in different loading states. Furthermore, the full three-dimensional deformation field of the loaded wood specimen was determined by digital volume correlation, applied to the reconstructed data at successive loading states. Results from two selected regions within the wood specimen are presented as continuous displacement and strain fields in both 2D and 3D. The applied combination of synchrotron radiation micro-computed tomography and digital volume correlation for the deformation analysis of wood under bending stress is a novel application in wood material science. The method offers the potential for the simultaneous observation of structural changes and quantified deformations during in situ micro-mechanical experiments. Moreover, the high spatial resolution allows studying the influence of anatomical features on the fracture behaviour of wood. Possible applications of this method range from bio-mechanical observations in fresh plant tissue to fracture mechanics aspects in structural timber.

  • 26.
    Forsberg, Fredrik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Siviour, Clive R
    University of Oxford.
    3D deformation and strain analysis in compacted sugar using x-ray microtomography and digital volume correlation2009In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 20, no 9Article in journal (Refereed)
    Abstract [en]

    Understanding the displacement of granular beds under compaction is important for a range of industrial, geological and civil engineering applications. Such materials exhibit inhomogeneous internal displacements including strain localization, which mean that a method for the in situ evaluation of internal 3D displacement fields at high spatial resolutions would be a major development. This paper presents results from the compaction of a cylindrical bed of sugar, with diameter 7.0 mm and height 8.2 mm, using x-ray microtomography to evaluate the internal structure and digital volume correlation to calculate 3D displacement information from these data. In contrast to previous studies, which generally track a small number of marker particles, the research here uses the natural structure of the sugar to provide a random pattern for 3D image correlation, allowing full-field information to be captured. The results show good agreement when compared with a well-established 2D image correlation technique; moreover, they indicate structural features associated with deformation of granular materials that would not necessarily be observed in a 2D slice.

  • 27. Forsberg, Fredrik
    et al.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Calibrating the tomographic 3D-DSP system2006In: Photomechanics 2006: The International Conference 'Photomechanics 2006' was held from 10 to 12 July 2006 in Clermont-Ferrnad, France ... The resulting special issue contains 12 papers] / [ed] Michel Grédiac, Oxford: Blackwell Munksgaard, 2006Conference paper (Refereed)
  • 28. Forsberg, Fredrik
    et al.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Tomographic 3D-DSP: Measurement of internal deformations2004In: Proceedings of ICEM 12, 2004Conference paper (Refereed)
  • 29. Forsberg, Fredrik
    et al.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Mooser, René
    Electronics/Metrology Laboratory, Swiss Federal Laboratories for Materials Testing and Research (EMPA).
    Hack, Erwin
    Electronics/Metrology Laboratory, Swiss Federal Laboratories for Materials Testing and Research (EMPA).
    Wyss, Peter
    Electronics/Metrology Laboratory, Swiss Federal Laboratories for Materials Testing and Research (EMPA).
    Full three-dimensional strain measurements on wood exposed to three-point-bending: analysis by use of digital volume correlation applied to synchrotron radiation micro-computed tomography image data2010In: Strain, ISSN 0039-2103, E-ISSN 1475-1305, Vol. 46, no 1, p. 47-60Article in journal (Refereed)
    Abstract [en]

    A microscale three-point bend experiment on wood has been carried out. The full 3D strain field of the microscale wood structure has been determined by use of digital volume correlation, based on reconstructed 3D image data acquired with synchrotron radiation micro-computed tomography. The wood specimen, which measures 1.57 × 3.42 × 0.75 mm3, was scanned in different load states along the three-point bend load cycle, from unloaded state to failure. The correlation algorithm is based on a Chebyshev polynomial description of the displacements, which allows a continuous representation of the 3D deformation fields. The methodology of the correlation algorithm is described thoroughly and its performance is tested for a 3D structure that is exposed to a virtual pre-defined deformation. The performance is tested both for noise free volume data as well as for structures with additive noise content. The performance test shows that the correlation algorithm resolves the applied deformation satisfyingly well. In the real experiment, on wood microstructure, the displacement fields show a structural behaviour that is consistent with what is expected for a specimen exposed to three-point bend. However, there are also anomalous effects present in the displacement fields that can be coupled to characteristic features in the cellular structure of the wood. Furthermore, 3D strain calculations based on the obtained displacement data shows a concentration of tensile strain in the region where the specimen eventually collapses. The experimental results show that the use of X-ray-based tomography with high spatial resolution in combination with digital volume correlation can successfully be used to perform 3D strain measurements on wood, at the microscale

  • 30.
    Garskaite, Edita
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Stoll, Sarah L.
    Chemistry Department, Georgetown University, Washington, D.C. 20057, United States.
    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.
    Stankeviciute, Zivile
    Institute of Chemistry, Faculty of Chemistry and Geosciences, Vilnius University, Vilnius LT- 03225, Lithuania.
    Kareiva, Aivaras
    Institute of Chemistry, Faculty of Chemistry and Geosciences, Vilnius University, Vilnius LT-03225, Lithuania.
    Quintana, Alberto
    Physics Department, Georgetown University, Washington, D.C. 20057, United States.
    Jensen, Christopher J.
    Physics Department, Georgetown University, Washington, D.C. 20057, United States.
    Liu, Kai
    Physics Department, Georgetown University, Washington, D.C. 20057, United States.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    The Accessibility of the Cell Wall in Scots Pine (Pinus sylvestris L.) Sapwood to Colloidal Fe3O4 Nanoparticles2021In: ACS Omega, E-ISSN 2470-1343, Vol. 6, no 33, p. 21719-21729Article in journal (Refereed)
    Abstract [en]

    This work presents a rapid and facile way to access the cell wall of wood with magnetic nanoparticles (NPs), providing insights into a method of wood modification to prepare hybrid bio-based functional materials. Diffusion-driven infiltration into Scots pine (Pinus sylvestris L.) sapwood was achieved using colloidal Fe3O4 nanoparticles. Optical microscopy, scanning electron microscopy/energy-dispersive X-ray spectroscopy, transmission electron microscopy, and X-ray powder diffraction analyses were used to detect and assess the accessibility of the cell wall to Fe3O4. The structural changes, filling of tracheids (cell lumina), and NP infiltration depth were further evaluated by performing X-ray microcomputed tomography analysis. Fourier transform infrared spectroscopy was used to assess the chemical changes in Scots pine induced by the interaction of the wood with the solvent. The thermal stability of Fe3O4-modified wood was studied by thermogravimetric analysis. Successful infiltration of the Fe3O4 NPs was confirmed by measuring the magnetic properties of cross-sectioned layers of the modified wood. The results indicate the feasibility of creating multiple functionalities that may lead to many future applications, including structural nanomaterials with desirable thermal properties, magnetic devices, and sensors. 

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  • 31.
    Girlanda, Orlando
    et al.
    ABB Corporate Research, Västerås, Sweden.
    Sahlen, Fredrik
    ABB Corporate Research, Västerås, Sweden.
    Joffre, Thomas
    Ångströms Laboratory, Uppsala University, Uppsala, Sweden.
    Gamstedt, E. Kristofer
    Ångströms Laboratory, Uppsala University, Uppsala, Sweden.
    Schmidt, Lars E.
    ABB Figeholm, Figeholm, Sweden.
    Forsberg, Fredrik
    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.
    Analysis of the Micromechanical Deformation in Pressboard performed by X-ray Microtomography2015In: IEEE Electrical Insulation Conference (EIC): Seattle, Jun 07-10, 2015, Piscataway, NJ: IEEE Communications Society, 2015, p. 89-92Conference paper (Refereed)
    Abstract [en]

    A large number of electrical insulation components are produced in paper-based materials. Paper combines good insulating properties with the necessary mechanical and chemical stability. Paper consists of a system of fibers binding to each other creating a strong network. The presence of large open pores allows for impregnability of the material but also causes mechanical weakness in particular in the out-of-plane direction of the material. This aspect is important for pressboard components, where the resistance to compression stress is relevant for e.g. transformer windings. It is therefore relevant to understand the mechanisms that underlay the out-of-plane deformation of pressboard. In order to get a clear picture of the deformation patterns within the material, X-ray micro-computed tomography was used. Pressboard test pieces were subjected to in-situ out-of-plane compressive loading. 3D images of the sample could be captured before, during and after the loading sequence. Image analysis allowed for the definition of strain fields. The results revealed a strong correlation between the density variation within the sample and the strain calculated from the 3D images.

  • 32.
    Grantham, Stephen G.
    et al.
    Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge, UK.
    Forsberg, Fredrik
    Luleå University of Technology.
    Measurement of granular flow in a silo using digital speckle radiography2004In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 146, no 1-2, p. 56-65Article in journal (Refereed)
    Abstract [en]

    In this paper, the flow of a powder through a silo is investigated using Digital Speckle Radiography (DSR). This technique allows displacement measurements to be made on the sub-mm scale to an accuracy of 0.06 μm and a spatial resolution of 26 μm. The method performs an image cross-correlation on a random seeding of X-ray opaque material as it flows out of the silo with the powder. The flow is captured digitally using a continuous X-ray source and an image intensifier and Charge Coupled Device (CCD) camera to give real time measurements. The powder used is Al2O3 with an average particle size of 50 μm and the seeding material is tungsten powder, also with an average particle size of 50 μm. Clear flow behaviour is observed for two different sizes of outlet and the flow rate and strains occurring during the flow are also investigated.

  • 33.
    Hellström, J. Gunnar I.
    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.
    Lundström, T. Staffan
    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.
    Representative volume size when modelling flow through porous structures2014Conference paper (Refereed)
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  • 34.
    Hu, Xianfeng
    et al.
    Process Metallurgy Department, Swerea MEFOS AB, Sweden.
    Sundqvist-Öqvist, Lena
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering. Process Metallurgy Department, Swerea MEFOS AB, Sweden.
    Åström, Elin
    LKAB R&D.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. LKAB R&D.
    Checchia, Paolo
    INFN Sezione di Padova, Padova, Italy.
    Bonomi, Germano
    Universita degli Studi di Brescia, Brescia, Italy.
    Calliari, I.
    Universita degli Studi di Padova, Padua, Italy.
    Calvini, Piero
    Universita degli Studi di Genova, Genoa, Italy.
    Donzella, Antonietta
    Universita degli Studi di Brescia, Department of Mechanical and Industrial Engineering, Brescia, Italy.
    Faraci, Eros
    Centro Sviluppo Materiali S.p.A., Roma, Italy.
    Gonella, Franco
    Istituto Nazionale Di Fisica Nucleare, Frascati, Frascati, Italy.
    Klinger, Joel
    Istituto Nazionale Di Fisica Nucleare, Frascati, Frascati, Italy.
    Pagano, Davide
    Universita degli Studi di Brescia, Brescia, Italy.
    Rigoni, Andrea
    Consorzio Rfx, Padua, Italy.
    Zanuttigh, Pietro
    Universita degli Studi di Padova, Padua, Italy.
    Ronchese, Paolo
    Universita degli Studi di Padova, Padua, Italy.
    Urbani, Michele
    Universita degli Studi di Padova, Department of Physics and Astronomy, Padua, Italy.
    Vanini, Sara
    Universita degli Studi di Padova, Department of Physics and Astronomy, Padua, Italy.
    Zenoni, Aldo
    Universita degli Studi di Brescia, Department of Mechanical and Industrial Engineering, Brescia, Italy.
    Zumerle, Gianni
    Universita degli Studi di Padova, Department of Physics and Astronomy, Padua, Italy.
    Exploring the capability of muon scattering tomography for imaging the components in the blast furnace2018In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 58, no 1, p. 35-42Article in journal (Refereed)
    Abstract [en]

    Knowing the distribution of the materials in the blast furnace (BF) is believed to be of great interest for BF operation and process optimization. In this paper calibration samples (ferrous pellets and coke) and samples from LKAB’s experimental blast furnace (probe samples, excavation samples and core-drilling samples) were measured by the muon scattering tomography detector to explore the capability of using the muon scattering tomography to image the components in the blast furnace. The experimental results show that it is possible to use this technique to discriminate the ferrous pellets from the coke and it is also shown that the measured linear scattering densities (LSD) linearly correlate with the bulk densities of the measured materials. By applying the Stovall’s model a correlation among the LSD values, the bulk densities and the components of the materials in the probe samples and excavation samples was established. The theoretical analysis indicates that it is potential to use the present muon scattering tomography technique to image the components in various zones of the blast furnace.

  • 35.
    Huber, Johannes Albert Josef
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Local Stiffness of Softwood Based on Micro- and Macro-Scale Computed Tomography2023In: Proceedings ICM20: Experimental Mechanics in Engineering and Biomechanics: 20th International Conference on Experimental Mechanics / [ed] J.F. Silva Gomes, Institute of Science and Innovation in Mechanical and Industrial Engineering , 2023, p. 1001-1002, article id 20161Conference paper (Refereed)
    Abstract [en]

    Wood is a discontinuous cellular structure on a microscopic scale, but its mechanical behaviour resembles a continuum on a macroscopic scale. The structure of both domains can be studied by X-ray computed tomography (CT). A challenge for accurate CT-based models of wood is to set the values of the orthotropic stiffness tensor locally based on density. Micro-CT scans under in-situ loading may be used to estimate local stiffness in wood, based on strain fields derived from digital volume correlation. The goal of the present paper is to study how micro-CT scans of clearwood under in-situ loading can be used to predict stiffness locally as a function of the apparent macroscopic density, to improve the fidelity of FE models based on macro-CT scans.

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  • 36. Innings, Fredrik
    et al.
    Hultman, Erik
    Forsberg, Fredrik
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Understanding and analysis of wear in homogenizers for processing liquid food2011In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 271, no 9-10, p. 2588-2598Article in journal (Refereed)
    Abstract [en]

    The tribological research pertaining to homogenizers in processing liquid food has received much less attention compared to its potential in enhancing the efficiency and durability of the homogenization process equipment. Homogenization is a process used to disrupt fat globules in dairy products to reduce the formation of creamy layer (separation) and also to enhance the viscosity of certain products. This process takes place in a narrow gap in the homogenizer machine and this region is highly prone to wear. The occurrence of wear during processing not only impairs the homogenization effect but also leads to increased downtime of the machine. The aim of this work is to understand the occurrence of wear and wear mechanisms in the homogenization gap using both experimental and analytical approaches. Two experimental test rigs were used to study the differences in wear during operation, i.e. with and without particles. The trajectories of the particles have been simulated without the influence of cavitation using a CFD-code to investigate whether the particles are the cause of wear. The homogenizer gap has been simulated for a worn geometry to see how the occurrence of wear changes the particles trajectories. The results have shown that the presence of particles accelerates wear and most important parameters are the particle hardness and mass. When cavitation and particles are combined they create a synergistic effect on wear. This can be explained by the fact that cavitation can accelerate particles in random directions through the imploding action of cavities. A change in impact angle and increased velocity increases the amount of wear significantly. CFD-simulations and calculations show that the particles do not fully follow the streamlines and therefore create wear on the gap surfaces.

  • 37.
    Joffe, Roberts
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Swerea SICOMP.
    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.
    Sjögren, Anders
    Lund University.
    Characterization of defects in polymer composites used in medical devices by means of x-ray microtomography2017In: 3rd International Conference on Tomography of Materials and Structures (ICTMS2017), 2017Conference paper (Refereed)
    Abstract [en]

    This paper presents a study on micro-structural characterization of carbon fibre-reinforced plastics used inmedical devices. The focus of the investigation is on determination of void content in the materials, since voids act asdefects and will affect the service life of the composites/devices. The results show that x-ray microtomography is anaccurate and powerful technique to identify defects in composites, and it is of great value in quality control.

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  • 38.
    Joffre, Thomas
    et al.
    Department of Engineering Sciences, Uppsala University, Uppsala, Sweden.
    Girlanda, Orlando
    ABB Corporate Research, 721 78, Västerås, Sweden.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sahlen, Fredrik
    ABB Corporate Research, 721 78, Västerås, Sweden.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gamstedt, E. Kristofer
    Department of Engineering Sciences, Uppsala University, Uppsala, Sweden.
    A 3D in-situ investigation of the deformation in compressive loading in the thickness direction of cellulose fiber mats2015In: Cellulose, ISSN 0969-0239, E-ISSN 1572-882X, Vol. 22, no 5, p. 2993-3001Article in journal (Refereed)
    Abstract [en]

    Fiber mat materials based on cellulose natural fibers combines a useful set of properties, including renewability, stiffness, strength and dielectric insulation, etc. The dominant in-plane fiber orientation ensures the in-plane performance, at the expense of reduced out-of-plane behavior, which has not been studied as extensively as the in-plane behavior. Quantitative use of X-ray micro-computed tomography and strain analyses under in-situ loading open up possibilities to identify key mechanisms responsible for deformation. In the present investigation, focus is placed on the out-of-plane deformation under compressive loading of thick, high density paper, known as pressboard. The samples were compressed in the chamber of a microtomographic scanner. 3D images were captured before and after the loading the sample. From sequential 3D images, the strain field inside the material was calculated using digital volume correlation. Two different test pieces were tested, namely unpolished and surface polished ones. The first principal strain component of the strain tensor showed a significant correlation with the density variation in the material, in particular on the top and bottom surfaces of unpolished samples. The manufacturing-induced grooves generate inhomogeneities in the microstructure of the surface, thus creating high strain concentration zones which give a sensible contribution to the overall compliance of the unpolished material. More generally, the results reveal that, on the micrometer scale, high density fiber pressboard behaves as a porous material rather than a low density fiber network.

  • 39.
    Kuba, Matthias
    et al.
    BEST – Bioenergy and Sustainable Technologies GmbH, Inffeldgasse 21b, 8010, Graz, Austria. Institute of Chemical, Environmental and Bioscience Engineering, TU Wien, Getreidemarkt 9/166, 1060, Vienna, Austria.
    Fürsatz, Katharina
    BEST – Bioenergy and Sustainable Technologies GmbH, Inffeldgasse 21b, 8010, Graz, Austria.
    Janisch, Daniel
    Institute of Chemical, Environmental and Bioscience Engineering, TU Wien, Getreidemarkt 9/166, 1060, Vienna, Austria.
    Aziaba, Kouessan
    Institute of Chemical, Environmental and Bioscience Engineering, TU Wien, Getreidemarkt 9/166, 1060, Vienna, Austria.
    Chlebda, Damian
    Jagiellonian University, ul. Gronostajowa 2, 30-387, Kraków, Poland.
    Łojewska, Joanna
    Jagiellonian University, ul. Gronostajowa 2, 30-387, Kraków, Poland.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Umeki, Kentaro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hofbauer, Hermann
    Institute of Chemical, Environmental and Bioscience Engineering, TU Wien, Getreidemarkt 9/166, 1060, Vienna, Austria.
    Surface characterization of ash-layered olivine from fluidized bed biomass gasification2021In: Biomass Conversion and Biorefinery, ISSN 2190-6815, E-ISSN 2190-6823, Vol. 11, no 1, p. 29-38Article in journal (Refereed)
    Abstract [en]

    The present study aims to present a comprehensive characterization of the surface of ash-layered olivine bed particles from dual fluidized bed gasification. It is well known from operation experience at industrial gasification plants that the bed material is activated during operation concerning its positive influence on gasification reactions. This is due to the built up of ash layers on the bed material particles; however, the chemical mechanisms are not well understood yet. Olivine samples from long-term operation in an industrial-scale gasification plant were investigated in comparison to fresh unused olivine. Changes of the surface morphology due to Ca-enrichment showed a significant increase of their surface area. Furthermore, the Ca-enrichment on the ash layer surface was distinctively associated to CaO being present. The presence of CaO on the surface was proven by adsorption tests of carbon monoxide as model compound. The detailed characterization contributes to a deeper understanding of the surface properties of ash layers and forms the basis for further investigations into their influence on gasification reactions.

  • 40.
    Marattukalam, Jithin James
    et al.
    Department of Physics, Materials Physics, Uppsala University.
    Pacheco, Victor
    Department of Chemistry- Ångström Laboratory, Uppsala University.
    Karlsson, Dennis
    Department of Chemistry- Ångström Laboratory, Uppsala University.
    Riekehr, Lars
    Department of Chemistry- Ångström Laboratory, Uppsala University.
    Lindwall, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Jansson, Ulf
    Department of Chemistry- Ångström Laboratory, Uppsala University.
    Sahlberg, Martin
    Department of Chemistry- Ångström Laboratory, Uppsala University.
    Hjörvarsson, Björgvin
    Department of Physics, Materials Physics, Uppsala University.
    Development of process parameters for selective laser melting of a Zr-based bulk metallic glass2020In: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 33, article id 101124Article in journal (Refereed)
    Abstract [en]

    Parameters for selective laser melting of Zr59.3Cu28.8Al10.4Nb1.5 (trade name AMZ4), allowing crack-free bulk metallic glass with low porosity, have been developed. The phase formation was found to be strongly influenced by the heating power of the laser. X-ray amorphous samples were obtained with laser power at and below 75 W. The as-processed bulk metallic glass was found to devitrify by a two-stage crystallization process within which the presence of oxygen was concluded to play an essential role. At laser powers above 75 W, the observed crystallites were found to be a cubic phase (Cu2Zr4O). The hardness and Young’s modulus in the as-processed samples was found to increase marginally with increased fraction of the crystalline phase.

  • 41.
    Mellin, Pelle
    et al.
    Swerim AB, Kista, Sweden.
    Heino, Stefan
    Swerim AB, Kista, Sweden.
    Malmström, David
    Swerim AB, Kista, Sweden.
    Karlsson, Oskar
    Swerim AB, Kista, Sweden.
    Sefer, Birhan
    Swerim AB, Kista, Sweden.
    Shipley, James
    Quintus Technologies AB, Västerås, Sweden.
    Magnusson, Anders
    Quintus Technologies AB, Västerås, Sweden.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Forsgren, Björn
    Ringhals AB, Väröbacka, Sweden.
    Waernqvist, Per
    Ringhals AB, Väröbacka, Sweden.
    XCT-Tracking Pore Size Development, In PBF-LB Built 316L, During HIP And Subsequent Heat Treatments2023In: Euro Powder Metallurgy 2023 (Euro PM2023) Proceedings, European Powder Metallurgy Association (EPMA) , 2023Conference paper (Refereed)
  • 42.
    Mooser, René
    et al.
    Electronics/Metrology Laboratory, Swiss Federal Laboratories for Materials Testing and Research (EMPA).
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hack, Erwin
    Electronics/Metrology Laboratory, Swiss Federal Laboratories for Materials Testing and Research (EMPA).
    Székely, Gábor
    Computer Vision Laboratory, ETH Zurich.
    Sennhauser, Urs
    Electronics/Metrology Laboratory, Swiss Federal Laboratories for Materials Testing and Research (EMPA).
    Estimation of affine transformations directly from tomographic projections in two and three dimensions2013In: Machine Vision and Applications, ISSN 0932-8092, E-ISSN 1432-1769, Vol. 24, no 2, p. 419-434Article in journal (Refereed)
    Abstract [en]

    This paper presents a new approach to estimate two- and three-dimensional affine transformations from tomographic projections. Instead of estimating the deformation from the reconstructed data, we introduce a method which works directly in the projection domain, using parallel and fan beam projection geometries. We show that any affine deformation can be analytically compensated, and we develop an efficient multiscale estimation framework based on the normalized cross correlation. The accuracy of the approach is verified using simulated and experimental data, and we demonstrate that the new method needs less projection angles and has a much lower computational complexity as compared to approaches based on the standard reconstruction techniques.

  • 43.
    Neikter, Magnus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    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.
    Pederson, Robert
    University West, Div. Welding Material .
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Microstructure and Defects in Additive Manufactured Titanium: a Comparison Between Microtomography and Optical Microscopy2017Conference paper (Other academic)
    Abstract [en]

    The aim of this work has been to compare two different analysing methods;x-ray microtomography and light optical microscopy, when it comes to defects and microstructure of additively manufactured Ti-6Al-4V. The results showthat both techniqueshave theirpros and cons:microtomography is the preferred choicefor defect detectionby analysing the full 3D sample volume, while light optical microscopy is better for analysing finer details in 2D.

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  • 44.
    Neikter, Magnus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Pederson, Robert
    Department of Engineering Science, University West.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Åkerfeldt, Pia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Larsson, Simon
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Puyoo, Geraldine
    GKN-Aerospace Engine Systems.
    Defect characterization of electron beam melted Ti-6Al-4V and Alloy 718 with X-ray microtomography2018In: Aeronautics and Aerospace Open Access Journal, ISSN 2576-4500, Vol. 2, no 3, p. 139-145Article in journal (Refereed)
    Abstract [en]

    Electron beam melting (EBM) is emerging as a promising manufacturing process where metallic components are manufactured from three-dimensional (3D) computer aided design models by melting layers onto layers. There are several advantages with this manufacturing process such as near net shaping, reduced lead times and the possibility to decrease weight by topology optimization, aspects that are of interest for the aerospace industry. In this work two alloys, Ti-6Al-4V and Alloy 718, widely used within the aerospace industry were investigated with X-ray microtomography (XMT), to characterize defects such as lack of fusion (LOF) and inclusions. It was furthermore possible to view the macrostructure with XMT, which was compared to macrostructure images obtained by light optical microscopy (LOM). XMT proved to be a useful tool for defect characterization and both LOF and un-melted powder could be found in the two investigated samples. In the EBM built Ti-6Al-4V sample high density inclusions, believed to be composed of tungsten, were found. One of the high-density inclusions was found to be hollow, which indicate that the inclusion stems from the powder manufacturing process and not related with the EBM process. By performing defect analyses with the XMT software it was also possible to quantify the amount of LOF and un-melted powder in vol%. From the XMT-data meshes were produced so that finite element method (FEM) simulations could be performed. From these FEM simulations the significant impact of defects on the material properties was evident, as the defects led to high stress concentrations. It could moreover, with FEM, be shown that the as-built surface roughness of EBM material is of importance as high surface roughness led to increased stress concentrations.

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  • 45.
    Olsson, Erik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Forsberg, Fredrik
    Three-dimensional selective imaging of sound sources2009In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 48, no 3Article in journal (Refereed)
    Abstract [en]

    A technique for 3-D selective imaging of sound sources is described analytically and demonstrated experimentally. One-dimensional recordings of the acoustic field is measured using laser vibrometry. By applying digital holographic and tomographic algorithms to the acquired 1-D data, the full 3-D complex amplitude is reconstructed. The use of multiple frequencies in the spectral content of the acoustic field gives a number of advantages: higher spatial resolution, less noise in the reconstructed image, less sensitivity to noise in the measurements, and the possibility to perform selective imaging. Theory for all three steps-the measurement of sound using light, numerical propagation of waves, and finally the tomographic reconstruction in the process are given. In the experiment, the positions of three ultrasound sources are accurately determined and two different types of transducers are distinguished from each other. This multiwavelength technique could show to be a useful addition to optoacoustic imaging.

  • 46.
    Pérez-Ràfols, Francesc
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, Gunnar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    A Stochastic Two-Scale Model for Rarefied Gas Flow in Highly Heterogeneous Porous Media2020In: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 135, no 1, p. 219-242Article in journal (Refereed)
    Abstract [en]

    This paper presents the development of a model enabling the analysis of rarefied gas flow through highly heterogeneous porous media. To capture the characteristics associated with the global- and the local-scale topology of the permeable phase in a typical porous medium, the heterogeneous multi-scale method, which is a flexible framework for constructing two-scale models, was employed. The rapid spatial variations associated with the local-scale topology are accounted for stochastically, by treating the permeability of different local-scale domains as a random variable. The results obtained with the present model show that an increase in the spatial variability in the heterogeneous topology of the porous medium significantly reduces the relevance of rarefaction effects. This clearly shows the necessity of considering a realistic description of the pore topology and questions the applicability of the results obtained for topologies exhibiting regular pore patterns. Although the present model is developed to study low Knudsen number flows, i.e. the slip-flow regime, the same development procedure could be readily adapted for other regimes as well.

  • 47.
    Rajput, Moeen S
    et al.
    KTH Royal Institute of Technology, Stockholm.
    Burman, Magnus
    KTH Royal Institute of Technology, Stockholm.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hallström, Stefan
    KTH Royal Institute of Technology, Stockholm.
    Experimental and numerical study of the response to various impact energy levels for composite sandwich plates with different face thicknesses2019In: Journal of Sandwich Structures and Materials, ISSN 1099-6362, E-ISSN 1530-7972, Vol. 21, no 5, p. 1654-1682Article in journal (Refereed)
    Abstract [en]

    Composite sandwich structures find wide application in the aerospace sector thanks to their lightweight characteristics. However, composite structures are highly susceptible to low-velocity impact damage and therefore thorough characterization of the impact response and damage process for the used material configurations is necessary. The present study investigates the effect of face-sheet thickness on the impact response and damage mechanisms, experimentally and numerically. A uni-directional, non-crimp fabric is used as reinforcement in the face-sheets, and a closed cell Rohacell 200 Hero polymer foam is used as core material. Low-velocity impact tests are performed in a novel instrumented drop-weight rig that is able to capture the true impact response. A range of impact energies are initially utilized in order to identify when low level damage (LLD), barely visible impact damage (BVID) and visible impact damage (VID) occur. A thorough fractography investigation is performed to characterize the impact damage using both destructive and non-destructive testing. The damage from the impacts in terms of dent depth, peak contact force, deflection and absorbed energy is measured. The results show bilinear responses in dent depth vs. impact energy and absorbed energy vs. impact energy. It is found than the BVID energy works well as an indication for the onset of excessive damage. Fractography reveals that there is a failure mode shift between the LLD and the VID energy levels, and that delaminations predominantly grow along the fiber direction and rotate in a spiral pattern through the thickness, following the laminate ply orientations. Finally, a progressive damage finite element model is developed to simulate both the impact response and the delamination extent, incorporating both intra-laminar and inter-laminar damage modes. The simulation shows good agreement with the experiments.

  • 48.
    Rodiouchkina, Maria
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Berglund, Kim
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Rodushkin, Ilia
    ALS Laboratory Group, ALS Scandinavia AB, SE-977 75 Luleå, Sweden.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Influence of Counter Surface Roughness and Lay on the Tribological Behaviour of Self-Lubricating Bearing Materials in Dry Sliding Conditions at High Contact Pressures2022In: Lubricants, E-ISSN 2075-4442, Vol. 10, no 8, article id 167Article in journal (Refereed)
    Abstract [en]

    In Kaplan turbines, the most critical components are the self-lubricating polymer composite bearings used to control the guide vanes and the turbine blades. Reducing the sliding wear and friction of these bearings can benefit both the economy and the environment, including longer useful life, lower operational costs, and higher efficiency. In this study, the influence of stainless-steel counter surface roughness and lay on the tribological behaviour of three bearing materials used in hydropower applications were investigated using a linear reciprocating flat-on-flat configuration under high contact pressure and low sliding speed. The surface roughness was measured using white light interferometry. SEM and EDS analysis were used to investigate the worn surfaces. Results from this study show that overly smooth surfaces result in higher friction and wear of the counter surface, while rougher surfaces have a negative effect on the wear of the polymers. Highest surface coverage using protective transfer layers is found on the steel surfaces with the perpendicular lay and is accompanied with a lower coefficient of friction compared to the parallel lay. The dominant wear mechanism of the bearing materials changes from delamination wear to abrasive wear between the lowest and the intermediate roughness for steel surfaces with the parallel lay. It can be concluded that counter surface topography has a significant influence on the tribological behaviour of these bearing materials and that the effect differs between the self-lubricating polymer composites.

  • 49.
    Rodiouchkina, Maria
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Berglund, Kim
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Mouzon, Johanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Shah, Faiz Ullah
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Rodushkin, Ilia
    ALS Laboratory Group, ALS Scandinavia AB.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Material Characterization and Influence of Sliding Speed and Pressure on Friction and Wear Behavior of Self-Lubricating Bearing Materials for Hydropower Applications2018In: Lubricants, ISSN 2075-4442, Vol. 6, no 2, article id 39Article in journal (Refereed)
    Abstract [en]

    Nowadays, hydropower plants are forced to have more frequent power control and the self-lubricated bearings used in the applications are one of the most critical components affected by the continuously changing operating conditions. In this study, microstructure and composition of two commercially available bearing materials (Orkot TXM Marine and Thordon ThorPlas) used in hydropower turbines were studied. In addition, the influence of sliding speed and applied pressure on the friction and wear behavior of the materials was investigated systematically for dry sliding conditions. The bearing materials were characterized using X-ray microtomography, Nuclear Magnetic Resonance (NMR) spectroscopy and Inductively Coupled Plasma–Sector Field Mass Spectrometry (ICP-SFMS) techniques. Friction and wear tests were carried out with a polymer pin sliding against a stainless steel (SS2333) plate with a linear reciprocating motion. Test conditions were: room temperature, 9–28 MPa pressure and 10–40 mm/s sliding speed ranges. Surface analysis of the polymer pins and the wear tracks were performed by optical profilometry, Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) techniques. Test results show that, for both materials, the coefficient of friction (COF) is decreasing at higher pressures. Surface analysis reveals higher concentrations of solid lubricants in the transfer layers formed at higher pressures, explaining the decrease in COF. Furthermore, the specific wear rate coefficients are increasing at higher sliding speeds, especially at lower pressures. Results of this study demonstrate that, under dry sliding conditions, changes in sliding speed and pressure have a significant influence on the tribological behavior of these bearing materials.

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  • 50.
    Sandell, Viktor
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hansson, Thomas
    GKN Aerospace Sweden AB, 461 38 Trollhättan, Sweden.
    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.
    Åkerfeldt, Pia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    X-ray Micro Tomography Study of Internal Defects of Electron Beam Melted Ti6Al4V and Their Effect on Fatigue Behavior2020In: / [ed] P. Villechaise, B. Appolaire, P. Castany, M. Dehmas, C. Delaunay, J. Delfosse, A. Denquin, E. Gautier, L. Germain, N. Gey, T. Gloriant, J.-Y. Hascoët, S. Hémery, Y. Millet, D. Monceau, F. Pettinari-Sturmel, M. Piellard, F. Prima and B. Viguier, EDP Sciences, 2020, article id 03029Conference paper (Refereed)
    Abstract [en]

    In this work, the fatigue behaviour of Ti6Al4V manufactured using electron beam melting, its dependency on porosity, distance from the base plate and build layer height were investigated. XCT scans of the fatigue sample gauge lengths were correlated to SEM investigations of the fracture surfaces. A comparison between the top and bottom halves of the builds in terms of defect population and fatigue behaviour was also made. Larger pores were detected in samples with a larger build layer height and lower position in the build chamber. Results also indicate that part geometry and pore location, specifically closeness to the surface, are important factors regarding the initiation location of fatigue fractures at 1 % strain. Furthermore, a fatigue critical lack of fusion defect was undetectable in the XCT scan.

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