Endre søk
Begrens søket
12 1 - 50 of 58
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Treff pr side
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
Merk
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 1.
    Alimadadi, Majid
    et al.
    Mid Sweden Univ, Dept Nat Sci NAT, Sundsvall, Sweden..
    Lindström, Stefan B.
    Linköping Univ, Dept Management & Engn, Div Solid Mech, Linkoping, Sweden..
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Role of microstructures in the compression response of three-dimensional foam-formed wood fiber networks2018Inngår i: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 14, nr 44, s. 8945-8955Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High-porosity, three-dimensional wood fiber networks made by foam forming present experimentally accessible instances of hierarchically structured, athermal fiber networks. We investigate the large deformation compression behavior of these networks using fiber-resolved finite element analyses to elucidate the role of microstructures in the mechanical response to compression. Three-dimensional network structures are acquired using micro-computed tomography and subsequent skeletonization into a Euclidean graph representation. By using a fitting procedure to the geometrical graph data, we are able to identify nine independent statistical parameters needed for the regeneration of artificial networks with the observed statistics. The compression response of these artificially generated networks and the physical network is then investigated using implicit finite element analysis. A direct comparison of the simulation results from the reconstructed and artificial network reveals remarkable differences already in the elastic region. These can neither be fully explained by density scaling, the size effect nor the boundary conditions. The only factor which provides the consistent explanation of the observed difference is the density and fiber orientation nonuniformities; these contribute to strain-localization so that the network becomes more compliant than expected for statistically uniform microstructures. We also demonstrate that the experimentally manifested strain-stiffening of such networks is due to development of new inter-fiber contacts during compression.

  • 2.
    Borodulina, Svetlana
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Constitutive modelling of a paper fibre in cyclic loading applications2013Rapport (Annet vitenskapelig)
  • 3.
    Borodulina, Svetlana
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.). KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation.
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.). KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation.
    Galland, Sylvain
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Nygårds, Mikael
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.). KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation.
    Stress-strain curve of paper revisited2012Inngår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, nr 2, s. 318-328Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have investigated a relation between micromechanical processes and the stress-strain curve of a dry fiber network during tensile loading. By using a detailed particle-level simulation tool we investigate, among other things, the impact of "non-traditional" bonding parameters, such as compliance of bonding regions, work of separation and the actual number of effective bonds. This is probably the first three-dimensional model which is capable of simulating the fracture process of paper accounting for nonlinearities at the fiber level and bond failures. The failure behavior of the network considered in the study could be changed significantly by relatively small changes in bond strength, as compared to the scatter in bonding data found in the literature. We have identified that compliance of the bonding regions has a significant impact on network strength. By comparing networks with weak and strong bonds, we concluded that large local strains are the precursors of bond failures and not the other way around.

  • 4.
    Borodulina, Svetlana
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Tjahjanto, Denny
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Constitutive modeling of a paper fiber in cyclic loading applications2015Inngår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 110, s. 227-240Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The tensile response of dense fiber-based materials like paper or paperboard is mainly dependent of the properties of the fibers, which store most of the elastic energy. In this paper, we investigate the influence of geometrical and material parameters on the mechanical response of the pulp fibers used in paper manufacturing. We developed a three-dimensional finite element model of the fiber, which accounts for microfibril orientation of cellulose fibril, and the presence of lignin in the secondary cell wall. The results showed that the change in the microfibril orientation upon axial straining is mainly a geometrical effect, and is independent of the material properties of the fiber, as long as the deformations are elastic. Plastic strain accelerates the change in microfibril orientation and thus makes it material-dependent. The results also showed that the elastic modulus of the fiber has a non-linear dependency on microfibril angle, with elastic modulus being more sensitive to the change of microfibril angle around small initial values of microfibril angles. Based on numerical results acquired from a 3D fiber model supported by available experimental evidence, we propose an anisotropic-kinematic hardening plasticity model for a fiber within a beam framework. The proposed fiber model is capable of reproducing the main features of the cyclic tensile response of a pulp fiber, such as stiffening due to changing microfibril angle. The constitutive model of the fiber was implemented in a finite-element model of the fiber network. By using the fiber network model, we estimated the level of strain that fiber segments accumulate before the typical failure strain of the entire network is reached.

  • 5.
    Borodulina, Svetlana
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Motamedian, Hamid Reza
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Effect of fiber and bond strength variations on the tensile stiffness and strength of fiber networks2016Rapport (Fagfellevurdert)
    Abstract [en]

    As fiber and bond characterization tools become more sophisticated, the information from the fiber scale becomes richer. This information is used for benchmarking of different types of fibers by the paper and packaging industries. In this work, we have addressed a question about the effect of variability in the fiber and fiber bond properties on the average stiffness and strength of fiber networks. We used a fiber-scale numerical model and reconstruction algorithm to address this question. The approach was verified using the experimental sheets having fiber data acquired by a fiber morphology analyzer and corrected by microtomographic analysis of fibers in these sheets. We concluded, among other things, that it is sufficient to account for the average bond strength value with an acceptable number of samples to describe dry network strength, as long as the bond strength distribution remains symmetric. We also found that using the length-weighted average for fiber shape factor and fiber length data neglects the important contribution from the distribution in these properties on the mechanical properties of the sheets.

  • 6.
    Borodulina, Svetlana
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Motamedian, Hamid Reza
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Effect of fiber and bond strength variations on the tensile stiffness and strength of fiber networks2018Inngår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 154, s. 19-32Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    As fiber and bond characterization tools become more sophisticated, the information from the fiber scale becomes richer. This information is used for benchmarking of different types of fibers by the paper and packaging industries. In this work, we have addressed a question about the effect of variability in the fiber and fiber bond properties on the average stiffness and strength of fiber networks. We used a fiber scale numerical model and reconstruction algorithm to address this question. The approach was verified using the experimental sheets having fiber data acquired by a fiber morphology analyzer and corrected by microtomographic analysis of fibers in these sheets. We concluded, among other things, that it is sufficient to account for the average bond strength value with an acceptable number of samples to describe dry network strength, as long as the bond strength distribution remains symmetric. We also found that using the length-weighted average for fiber shape factor and fiber length data neglects the important contribution from the distribution in these properties on the mechanical properties of the sheets.

  • 7.
    Brandberg, August
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Compression failure in dense non-woven fiber networks2019Rapport (Annet vitenskapelig)
  • 8.
    Brandberg, August
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    The effect of geometry changes on the mechanical stiffness of fibre-fibre bonds2017Inngår i: Advances in Pulp and Paper Research, Manchester, 2017, s. 683-719Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this work, we discuss the effect of geometry on the compliance of the fibre bond regions against normal and tangent loads. Since the fibre bonds play a key role in defining the paper strength, the compliance of the bond regions can affect the amount of elastic energy stored in the bonds and thus change not only the strength but also the stiffness of paper products under certain conditions. Using finite element simulation tools, we overcome the major difficulty of performing controlled mechanical testing of the isolated bond region and reveal the key geometrical factors affecting the compliance of the bond region. Specifically, we show that the compliance of the fiber-fiber bond is strongly governed by its geometric configuration after pressing. Among the strongest factors is the collapse of the lumen and the crossing angle. Using the range of obtained stiffness values, we demonstrated the effect the bond stiffness has on the stiffness of the network using fiber-level simulation tools. We show how the dependence of tangent bond stiffness on fiber-to-fiber angle further softens the more compliance cross-machine direction.

  • 9.
    Brandberg, August
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Motamedian, Hamid Reza
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Hirn, Ulrich
    Technische Universität Graz.
    The Role of the Fiber and the Bond in the Hygroexpansion and Curl of Thin Freely Dried Paper Sheets2019Rapport (Annet vitenskapelig)
    Abstract [en]

    A computationally efficient method to study the in-plane and out-of-plane dimensional instability of thin paper sheets under the influence of moisture changes is presented. The method explicitly resolves the bonded and the free segments of fibers in the network, capturing the effect of anisotropic hygroexpansion at the fiber level. The method is verified against a volumetric model. The importance of longitudinal fiber hygroexpansion is demonstrated in spite of the absolute value of longitudinal hygroexpansion being an order of magnitude lower than the transverse hygroexpansion component. Finally, the method is used to demonstrate the formation of macroscopic sheet curl due to a moisture gradient in structurally uniform sheets in the absence of viscoelastic or plastic constitutive behavior and through-thickness residual stress profiles.

  • 10.
    Denoyelle, Thibaud
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.). KTH, Skolan för kemivetenskap (CHE), Centra, Centrum för Biofibermaterial, BiMaC.
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Galland, Sylvain
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Biokompositer.
    Lindström, Stefan B.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik. KTH, Skolan för kemivetenskap (CHE), Centra, Centrum för Biofibermaterial, BiMaC.
    Elastic properties of cellulose nanopaper versus conventional paper2011Inngår i: Progress in Paper Physics Seminar 2011 Conference Proceedings / [ed] U. Hirn, Graz, Austria: Verlag der Technischen Universität Graz , 2011, s. 131-133Konferansepaper (Fagfellevurdert)
  • 11.
    Fallqvist, Björn
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Kroon, Martin
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Cross-link debonding in actin networks: influence on mechanical properties2015Inngår i: International Journal of Experimental and Computational Biomechanics, ISSN 1755-8743, Vol. 3, nr 1, s. 16-26, artikkel-id b778558v5j17h4n8Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The actin cytoskeleton is essential for the continued function and survival of the cell. A peculiar mechanical characteristic of actin networks is their remodelling ability, providing them with a time-dependent response to mechanical forces. In cross-linked actin networks, this behaviour is typically tuned by the binding affinity of the cross-link. We propose that the debonding of a cross-link between filaments can be modelled using a stochastic approach, in which the activation energy for a bond is modified by a term to account for mechanical strain energy. By use of a finite element model, we perform numerical analyses in which we first compare the model behaviour to experimental results. The computed and experimental results are in good agreement for short time scales, but over longer time scales the stress is overestimated. However, it does provide a possible explanation for experimentally observed strain-rate dependence as well as strain-softening at longer time scales.

  • 12.
    Fallqvist, Björn
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Kroon, Martin
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Modelling of cross-linked actin networks - Influence of geometrical parameters and cross-link compliance2014Inngår i: Journal of Theoretical Biology, ISSN 0022-5193, E-ISSN 1095-8541, Vol. 350, s. 57-69Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A major structural component of the cell is the actin cytoskeleton, in which actin subunits are polymerised into actin filaments. These networks can be cross-linked by various types of ABPs (Actin Binding Proteins), such as Filamin A. In this paper, the passive response of cross-linked actin filament networks is evaluated, by use of a numerical and continuum network model. For the numerical model, the influence of filament length, statistical dispersion, cross-link compliance (including that representative of Filamin A) and boundary conditions on the mechanical response is evaluated and compared to experimental results. It is found that the introduction of statistical dispersion of filament lengths has a significant influence on the computed results, reducing the network stiffness by several orders of magnitude. Actin networks have previously been shown to have a characteristic transition from an initial bending-dominated to a stretching-dominated regime at larger strains, and the cross-link compliance is shown to shift this transition. The continuum network model, a modified eight-chain polymer model, is evaluated and shown to predict experimental results reasonably well, although a single set of parameters cannot be found to predict the characteristic dependence of filament length for different types of cross-links. Given the vast diversity of cross-linking proteins, the dependence of mechanical response on cross-link compliance signifies the importance of incorporating it properly in models to understand the roles of different types of actin networks and their respective tasks in the cell.

  • 13. HENTZE, Hans-Peter
    et al.
    SIEVÄNEN, Jenni
    KETTLE, John
    KULACHENKO, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    KORPELA, Antti
    KETOJA, Jukka
    HELLÉN, Erkki
    HJELT, Tuomo
    HILTUNEN, Jaakko
    TURUNEN, Eila
    SNECK, Asko
    METHOD OF MANUFACTURING PAPER AND PRODUCTS OBTAINED BY THE METHOD2010Patent (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    The invention relates to a method for manufacturing nanostructured paper or board and a novel paper or board. The method comprises providing a liquid suspension of nanocellulose-containing material, forming a web from the suspension, and drying the web in order to form paper or board. According to the invention the water content of the suspension from which the web is formed is 50 % or less by weight of liquids. By means of the invention, energy consumption of paper manufacturing can be significantly reduced.

  • 14. HENTZE, Hans-Peter
    et al.
    SIEVÄNEN, Jenni
    KETTLE, John
    KULACHENKO, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    KORPELA, Antti
    KETOJA, Jukka
    HELLÉN, Erkki
    HJELT, Tuomo
    HILTUNEN, Jaakko
    TURUNEN, Eila
    SNECK, Asko
    NOVEL PAPER AND METHOD OF MANUFACTURING THEREOF2009Patent (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    The invention relates to a method for manufacturing nanostructured paper or board and a novel paper or board. The method comprises providing a liquid suspension of nanocellulose-containing material, forming a web from the suspension and drying the web in order to form paper or board. According to the invention, the water content of the suspension at the time of beginning of the drying is 50 % or less by weight of liquids so as to form a paper or board having an average pore size between 200 and 400 nm. By means of the invention, very opaque paper, for example for printing applications, can be manufactured with low energy consumption.

  • 15.
    Huang, Fang
    et al.
    University of New Brunswick.
    Li, Kecheng
    University of New Brunswick.
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Measurement of interfiber friction force for pulp fibers by atomic force microscopy2009Inngår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 44, nr 14, s. 3770-3776Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Interfiber friction in paper exists in fiber suspensions, fiber flocs, and fiber networks. The interfiber friction force is, therefore, important both in papermaking and in the use of paper. The objective of this research is to develop a methodology using atomic force microscopy (AFM) for the direct measurement of the friction force between pulp fibers. Different factors such as AFM scanning velocity, contact area, and fiber surface roughness were investigated. The results show that AFM is an effective tool for measuring micro-scale interfiber friction forces. Both AFM scanning velocity and fiber surface roughness affect the measured results. The coefficient of friction increases, but the initial adhesion force decreases, with increasing fiber surface roughness.

  • 16.
    Isaksson, P.
    et al.
    Division of Solid Mechanics, Mid Sweden University, Sundsvall, Sweden.
    Gradin, P. A.
    Division of Solid Mechanics, Mid Sweden University, Sundsvall, Sweden.
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    The onset and progression of damage in isotropic paper sheets2006Inngår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 43, nr 3-4, s. 713-726Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An experimental investigation is performed and analyzed in order to examine the onset and evolution of damage processes in thin isotropic paper sheets made of mechanical pulp. A microscopy technique has been used to estimate the relative fraction of bond and fibre breaks. It has been found that the active damage mechanism is bond failure, hence supporting the assumption of an isotropic scalar valued damage variable. All experiments have been performed by simultaneous with the mechanical loading monitoring the acoustic emission activity. Three different experimental setups have been designed offering the possibility to analyze the influence of stress gradients, as well as different levels of the ratios between the in-plane normal stresses, on the onset of damage. It is concluded that stress gradients in the paper specimens have a large influence on the onset of damage. When stress gradients are present a non-local theory has to be used in the analysis. In this way compliance with an isotropic damage criterion is achieved. The characteristic length, determining the gradient sensitivity, has been found to be of the same order of magnitude as some average fibre length. To study the evolution of the damage processes, wide and short specimens have been loaded in tension resulting in stable damage processes. With the assumptions made regarding the mechanical behavior of the paper material after onset of damage, the damage and the cumulative number of acoustic events curve correlates very well. The experimentally obtained data is used to determine material parameters in a proposed damage evolution law. It is found that the assumed damage evolution law can, for isotropic paper materials with bond rupture as the prevalent failure mechanism, be further simplified as only one specific material dependent damage evolution parameter has to be determined in experiments.

  • 17. Kariniemi, M.
    et al.
    Parola, M.
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Sorvari, J.
    von Hertzen, L.
    Effect of Blanket Properties on Web Tension in Offset Printing2010Inngår i: Advances in Printing and Media Technology, Montreal, Canada, 2010Konferansepaper (Fagfellevurdert)
    Abstract [en]

    VTT and KCL together with several companies in the printing value chain have studied how to control web tension in different parts of a printing press. Extensive trials on printing presses, at pilot scale and at laboratory scale have yielded data for modeling work. Modeling was carried out with statistical methods and by finite element method (FEM). Results show the extent to which paper and printing blankets affect tension formation in a printing press. The main emphasis of this paper is on the effect different printing blanket types have on web tension.It was found that printing blankets have a clear effect on web tension. The degree of tension change is affected by the type of blanket, nip pressure, distances between the blankets, moisture, paper properties and the combination of blanket types in different printing units. Depending on their feeding properties and their effect on web tension, in general, the blankets can be distinguished as negative, neutral and positive. Also the blanket’s effect on web tension is influenced strongly by the type of adjacent blankets. The interactions of fountain solution, ink, nip, blanket and paper had also an effect on the tension formation. The paper experiences a very high rate of strain inside the printing nips, which can affect the paper’s response and therefore tension after the nips. Results suggest that tension cannot be solely predicted with the elastic paper properties measured by conventional methods.

  • 18.
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Mechanics of paper webs in printing press applications2006Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The mechanics of paper is a difficult subject because paper is a unique material. It is very thin, flexible at bending, unstable in compression and stiff at tension. Dealing with paper we have to account for orthotropy and heterogeneities created during the manufacturing process.

    This thesis addresses two topics in mechanics of paper webs in printing press applications. First is the dynamic behaviour of the travelling webs. Second is so-called “fluting” after heat-set web-fed offset printing.

    There are a number of challenges in simulating the dynamics of the paper web. It is necessary to include the influence of the paper web transport velocity. Due to initial sag or vibrations, gyroscopic forces affect the dynamics of the webs. Furthermore, the transport velocity reduces the stress stiffening of the web. A good theoretical model should account for large displacements and should be capable of simulating wrinkles, which is essentially a post-buckling phenomenon. Finally, the paper web is surrounded with air which reduces the natural frequencies substantially by “adding" mass to the paper. A non-linear finite element formulation has been developed in this study for simulation of travelling webs. The results of the studies shows that for the tension magnitudes used in the printing industry the critical web speed lies far above those used today. Speed limitations are rather caused by ink setting and tension control problems. If the web tension profile is skew, however, edge vibrations are inevitable even at small external excitations.

    Fluting is a permanent wavy distortion of the paper web after heat-set web offset printing. It is often seen in high quality printing products, especially in areas covered with ink. It is generally accepted that tension and heat are required to create fluting. However, there have been certain disputes as to the mechanism of fluting formation, retention and key factors affecting this phenomenon. Most of the existing studies related to fluting are based on linear buckling theories. A finite element model, capable of simulating a post-buckling behaviour has been developed and experimentally verified. Studies show that none of the existing theories can consistently explain fluting. A new basic mechanism of fluting formation has been proposed and numerically demonstrated. Fluting was explained as a post-buckling phenomenon due to small scale moisture variations developing during through-air drying. It was concluded that air permeability variation is the key factor affecting fluting tendency. Fluting is retained due to inelastic deformations promoted by high drying temperatures.

  • 19.
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Moisture-induced deformations2011Inngår i: Mechanics of Paper Products / [ed] Niskanen, Kaarlo, De Gruyter , 2011Kapittel i bok, del av antologi (Fagfellevurdert)
  • 20.
    Kulachenko, Artem
    KTH, Tidigare Institutioner, Hållfasthetslära.
    Printing press paper web mechanics2004Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 21.
    Kulachenko, Artem
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Denoyelle, Thibaud
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Galland, Sylvain
    KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Lindström, Stefan B.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi. Linköping University, Sweden.
    Elastic properties of cellulose nanopaper2012Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 19, nr 3, s. 793-807Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nanopaper is a transparent film made of network-forming nanocellulose fibers. These fibers are several micrometers long with a diameter of 4-50 nm. The reported elastic modulus of nanopaper often falls short of even conservative theoretical predictions based on the modulus of crystalline cellulose, although such predictions usually perform well for other fiber composite materials. We investigate this inconsistency and suggest explanations by identifying the critical factors affecting the stiffness of nanopaper. A similar inconsistency is found when predicting the stiffness of conventional paper, and it is usually explained by the effects introduced during drying. We found that the effect of the drying cannot solely explain the relatively low elastic modulus of nanopaper. Among the factors that showed the most influence are the presence of non-crystalline regions along the length of the nanofibers, initial strains and the three-dimensional structure of individual bonds.

  • 22.
    Kulachenko, Artem
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Gradin, Per
    Koivurova, Hannu
    Modelling the dynamical behaviour of a paper web. Part I2007Inngår i: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 85, nr 3-4, s. 131-147Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new shell element has been proposed for geometrically non-linear, finite element analyses of axially moving paper web. Web instability problems of paper travelling in a printing system, such as wrinkling and fluttering, pose special challenges in the numerical analyses. For examples, theme are finite bending stiffness (as opposed to membrane), orthotropy, and non-uniform distributions of mechanical and hygro-properties (in different length scales). The new formulation has accounted for paper transport velocity and paper bending stiffness based on a mixed -1-agrangian-Eulerian description of the motion. A natural coordinate system has been employed in the analytical and finite element formulations. Benchmarking with different finite elements in various tests showed that the proposed element is indeed more stable and reliable for the chosen application than existing elements. The usability of the shell element has been successfully demonstrated by two example p:,-oblems: wrinkling of stretched isotropic and orthotropic membranes, and the vibration of a web showing a speedtensioning effect above a critical web transport velocity.

  • 23.
    Kulachenko, Artem
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Gradin, Per
    Kolvurova, Hannu
    Modelling the dynamical behaviour of a paper web. Part II2007Inngår i: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 85, nr 3-4, s. 148-157Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, a finite element procedure is used to study the dynamic behaviour of a paper web in a free span between two rollers, including effects of transport velocity and surrounding air. The paper web is modelled as a three-dimensional orthotropic structure. The influence of air is accounted for by utilizing fluid-solid interaction analyses based on acoustic theory. The contribution of transport velocity is included through gyroscopic matrices and forces. The structural response on harmonic excitations has been studied using linear and non-linear models. Results show that air significantly reduces eigenfrequencies of the web. So called "edge-flutter" is nothing but the result of skew tension profile. Excessive web vibration can be eliminated by adjusting the web tension.

  • 24.
    Kulachenko, Artem
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Gradin, Per
    Uesaka, Tetsu
    Basic Mechanisms of Fluting2006Inngår i: Annual Meeting of the Pulp and Paper Technical Association of Canada (PAPTAC), 2006, s. A161-A173Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Out-of-plane deformations of paper, such as fluting, significantly deteriorate the quality of a printed product. There are several explanations of fluting presented in the literature but there is no unanimously accepted theory regarding fluting formation consistent with all field observations. The present paper reviews the existing theories and proposes a mechanism that might give an answer to most of the questions regarding the fluting. The fluting formation has been considered as a post-buckling phenomenon which is analysed with the help of the finite element method. Fluting retention has been modelled by introducing an ink layer over the paper surface with ink stiffness estimated from experimental results. The impact of fast drying on fluting has been assessed numerically and experimentally. The result of the study suggests that fluting occurs due to small-scale strain variations, which in turn are caused by the moisture variations created during fast convection drying. The result also showed that ink stiffening alone cannot explain the fluting amplitudes observed in practice, suggesting the presence of other mechanisms of fluting retention.

  • 25.
    Kulachenko, Artem
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Gradin, Per
    Uesaka, Tetsu
    Basic mechanisms of fluting formation and retention in paper2007Inngår i: Mechanics of materials (Print), ISSN 0167-6636, E-ISSN 1872-7743, Vol. 39, nr 7, s. 643-663Artikkel i tidsskrift (Fagfellevurdert)
  • 26.
    Kulachenko, Artem
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Gradin, Per
    Uesaka, Tetsu
    Tension Wrinkling and Fluting in Heatset Web Offset Printing process. Post buckling analyses2005Inngår i: ADVANCES IN PAPER SCIENCE AND TECHNOLOGY: TRANSACTIONS OF THE 13TH FUNDAMENTAL RESEARCH SYMPOSIUM, VOLS 1-3 / [ed] IAnson, SJ, The Pulp and Paper Fundamental Research Society , 2005, s. 1075-1099Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Geometrically non-linear, large scale post-buckling analyses were carried out to investigate the influence of different parameters on residual waviness (fluting) after printing in a heat set web offset printing press. Mixed implicit-explicit finite element techniques were used in the analyses. The numerical procedure was verified by experimentally acquired data. Results show that when the paper web is perfectly flat before printing, fluting patterns after drying and moisture recovery generally have higher wavelength than those typically observed in fluted samples. Initial cockles of imprinted sheets were found to have impacts on the fluting patterns and amplitudes. Among the factors investigated, ink thickness and hygroexpansivity had significant influences on fluting: increasing these factors increased fluting amplitudes.

  • 27.
    Kulachenko, Artem
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Gradin, Per
    Westerlind, Bo
    Analysis of paper web tension profiles2005Inngår i: Journal of Graphic Technology, ISSN 1544-9599, E-ISSN 1544-9602, Vol. 2, s. 72-81Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The tension profiles of paper webs are very important for determining the runnability in printing presses. Uneven tension profiles, with lower web tension toward the edges, develop in the paper machine due to many factors such as moisture content, residual strains related to drying and draw conditions, fibre orientation etc. This study presents some simple relations regarding the initial strain distribution, but also a method for adjusting the tension profile by choosing an appropriate moisture distribution. The method is verified on web tension and moisture measurements in a pressroom.

  • 28.
    Kulachenko, Artem
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Lindström, Stefan
    Linköping university.
    Uesaka, Tetsu
    Mid Sweden University.
    Strength of wet fiber networks - Strength scaling2009Inngår i: Papermaking Research Symposium, Kuopio, Finland, 2009Konferansepaper (Fagfellevurdert)
  • 29.
    Kulachenko, Artem
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Uesaka, T.
    Mid Sweden University.
    Simulation of Wet Fiber Network Deformation2010Inngår i: Progress in Paper Physics, Montreal, Canada, 2010Konferansepaper (Fagfellevurdert)
  • 30.
    Kulachenko, Artem
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Uesaka, T.
    The Effect of Fibre Orientation Streaks on Out-of-plane Instabilities in Paper2007Inngår i: Proceedings of 61st Appita Annual Conference and Exhibition, Gold Coast, Australia: Appita Inc , 2007Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Variations in in-plane fibre orientations have been discussed as a possible reason for out-of-plane distortions in paper, such as cockling and fluting. Irregularities in fibre orientations can potentially result in local strain variations during tensioning or moisture change, and thus can cause local buckling in paper. In this work, the impacts of the fibre orientation on out-of-plane instabilities in paper were systematically examined with the help of non-linear finite element analyses. In the simulation local variations in fibre orientation were introduced artificially as streaks in the machine direction (MD). Such streaks can appear in a real paper due to cross flows of jet originated from headbox, for example. The results of this work suggest that the fibre orientation streaks surprisingly have a limited effect on out-of-plane instabilities in paper, as compared with the local moisture variations that the authors investigated previously.

  • 31.
    Kulachenko, Artem
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Uesaka, Tetsu
    Mid Sweden University.
    Direct simulations of fiber network deformation and failure2012Inngår i: Mechanics of materials (Print), ISSN 0167-6636, E-ISSN 1872-7743, Vol. 51, s. 1-14Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A finite element model for 3D random fiber networks was constructed to simulate deformation and failure behavior of networks with dynamic bonding/debonding properties. Such fiber networks are ubiquitous among many living systems, soft matters, bio-materials, and engineering materials (papers and non-woven). A key feature of this new network model is the fiber–fiber interaction model that is based on AFM measurements from our earlier study. A series of simulations have been performed to investigate strain localization behavior, strength statistics, in particular, the variations of strength, strain-to-failure and elastic modulus, and their size dependence. Other variables investigated are fiber geometries. The result showed that, in spite of its disordered structure, strength and elastic modulus of a fiber network varied very little statistically, as long as the average number of fibers in the simulated specimen and the degree of fiber orientation are kept constant. However, strain-to-failure showed very significant statistical variations, and thus more sensitivity to the disordered structures.

  • 32.
    Kulachenko, Artem
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Uesaka, Tetsu
    Lindström, Stefan
    Reinventing mechanics of fibre network2008Inngår i: Progress in Paper Physics Seminar, Espoo, Finland: HUT , 2008, s. 185-193Konferansepaper (Fagfellevurdert)
  • 33.
    Lagerblad, Ulrika
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Wentzel, Henrik
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Kulachenko, Artem
    A fixed-lag smoother for solving input force and support motion identification problems in structural dynamics2016Manuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    In this work, the problem of joint input and state estimation based on measured response in a dynamic system is addressed.A fixed-lag smoother for support motion or input force estimation in linear structural dynamics is proposed. The unknown inputs are estimated in conjunction with the states in an augmented state description of the system. A fixed-lag smoother maximizes the use of information available in the measurements by allowing a small time lag in the estimation, leading to a recursive non-causal filter. This type of filter has not previously been implemented in the field of structural dynamics. The filter is capable of handling any combination of measured displacement, velocity and acceleration; furthermore are both measurement noise and model errors accounted for and simulated as stochastic processes. In this study, estimations are based on sparse noisy measurements of system displacement and model errors are simulated through the use of deliberately incorrect model descriptions. The proposed algorithm is verified by numerical simulations and the qualities of the estimations are compared to those of the augmented Kalman filter.It is shown that with this filter, significant improvements of the input estimations are achieved, especially of inputs located far away from measurement sensors. The improvement consists of noise reduction, phase correction and by a more accurate division of the individual contribution of multiple inputs.

  • 34.
    Lagerblad, Ulrika
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Wentzel, Henrik
    Scania, SE-151 87 Södertälje, Sweden.
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Dynamic response identification based on state estimation and operational modal analysis2019Inngår i: Mechanical systems and signal processing, ISSN 0888-3270, E-ISSN 1096-1216, Vol. 129, s. 37-53Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents and experimentally validates an augmented Kalman filter extended with a fixed-lag smoother for solving joint state and input estimation problems. Sparse acceleration measurements from a truck side skirt excited by road-induced vibrations from a vibration test track are analysed. The system model is obtained experimentally from an operational modal analysis, reducing modelling errors and avoiding the need for a finite element model and it serves itself as a numerical model. The motion of the truck component is estimated and the results are compared to those of a joint input-state estimation filtering algorithm, in addition to the actual measured motion. Both algorithms are tuned according to a novel process based on minimal a priori information concerning the system states and inputs. The focus of this work is to assess the robustness, performance, and tuning of the algorithms. Two sensor configurations are studied: one where the number of response measurement sensors is high compared to the number of estimated motions and participating modes, and another where the number of response measurements is reduced. Both algorithms perform very well within the first configuration. With a reduced number of response measurements, the fixed-lag smoother is superior to the joint input-state filter in capturing the individual motion of each position on the side skirt.

  • 35.
    Lagerblad, Ulrika
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Wentzel, Henrik
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Kulachenko, Artem
    Dynamic response identification based on state estimation and operational modal analysis applied to a truck side skirt2016Manuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    This work presents an experimental verification of a fixed-lag smoother for solving joint state and input estimation problems.Sparse acceleration measurements from a truck side skirt excited by road induced vibrations from the Scania vibration test track are analysed. The system model is obtained experimentally from an operational modal analysis, reducing the modelling errors and avoiding the need of a numerical model. The work is focused on estimating the motion of the side skirt in positions where no measurements are available. The estimated motions are compared to those of a joint input-state estimation algorithm and to the actual measured motion. Two sensor configurations are studied: one where the number of measurement sensors is high compared to the number of estimated motions and participating modes, and another where the number of sensors are reduced. With the first configuration, both algorithms perform very well. With the reduced numbers of sensors, the fixed-lag smoother excels the joint input-state estimator in capturing the individual motion of each position on the side skirt.

  • 36.
    Lagerblad, Ulrika
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Wentzel, Henrik
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Fatigue damage prediction based on strain field estimates using a smoothed Kalman filter and sparse measurements2018Inngår i: Proceedings of ISMA 2018 - International Conference on Noise and Vibration Engineering and USD 2018 - International Conference on Uncertainty in Structural Dynamics, KU Leuven - Departement Werktuigkunde , 2018, s. 2805-2817Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this work, we address the problem of fatigue damage prediction in a truck component excited by road induced vibrations. The damage is computed from strains estimated from sparse measurements of the dynamic response. Two different fixed-lag smoothing algorithm are employed, an augmented Kalman filter extended with a fixed-lag smoother and a smoothed joint input-state estimation algorithm. The system is described with a finite element model, and due to the complexity of reproducing the system by the model, the resulting representation may contain a number of discrepancies. Nevertheless, both smoothing algorithms succeed in capturing the dynamic behaviour of the component, although the estimated strains are affected more by the large model error than the estimated acceleration are. Furthermore, it is shown that the proposed methodology of strain estimation and fatigue damage calculations correlate well with the observed failure of a component when tested in a full-scale fatigue test of a truck chassis- International Conference on Uncertainty in Structural Dynamics.

  • 37. Lindström, Stefan B.
    et al.
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Jawerth, Louise M.
    Vader, David A.
    Finite-strain, finite-size mechanics of rigidly cross-linked biopolymer networks2013Inngår i: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 9, nr 30, s. 7302-7313Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The network geometries of rigidly cross-linked fibrin and collagen type I networks are imaged using confocal microscopy and characterized statistically. This statistical representation allows for the regeneration of large, three-dimensional biopolymer networks using an inverse method. Finite element analyses with beam networks are then used to investigate the large deformation, nonlinear elastic response of these artificial networks in isotropic stretching and simple shear. For simple shear, we investigate the differential bulk modulus, which displays three regimes: a linear elastic regime dominated by filament bending, a regime of strain-stiffening associated with a transition from filament bending to stretching, and a regime of weaker strain-stiffening at large deformations, governed by filament stretching convolved with the geometrical nonlinearity of the simple shear strain tensor. The differential bulk modulus exhibits a corresponding strain-stiffening, but reaches a distinct plateau at about 5% strain under isotropic stretch conditions. The small-strain moduli, the bulk modulus in particular, show a significant size-dependence up to a network size of about 100 mesh sizes. The large-strain differential shear modulus and bulk modulus show very little size-dependence.

  • 38.
    Lindström, Stefan B.
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Vader, David A.
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Weitz, David A.
    Biopolymer network geometries: Characterization, regeneration, and elastic properties2010Inngår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 82, nr 5, s. 051905-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study the geometry of biopolymer networks and effects of the geometry on bulk mechanical properties. It is shown numerically that the physical network geometry can be quantified statistically and regenerated from its statistical description, so that the regenerated network exhibits the same network mechanics as the physical network in the elastic regime. A collagen-I biopolymer network is used for validation. The method enables parametric studies of the network geometry, whose parameters are often difficult to vary independently in experiments.

  • 39.
    Lindström, Stefan
    et al.
    Linköping University, Sweden.
    Karabulut, Erdem
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Sehaqui, Houssine
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Wågberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Mechanosorptive creep in nanocellulose materials2012Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 19, nr 3, s. 809-819Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The creep behavior of nanocellulose films and aerogels are studied in a dynamic moisture environment, which is crucial to their performance in packaging applications. For these materials, the creep rate under cyclic humidity conditions exceeds any constant humidity creep rate within the cycling range, a phenomenon known as mechanosorptive creep. By varying the sample thickness and relative humidity ramp rate, it is shown that mechanosorptive creep is not significantly affected by the through-thickness moisture gradient. It is also shown that cellulose nanofibril aerogels with high porosity display the same accelerated creep as films. Microstructures larger than the fibril diameter thus appear to be of secondary importance to mechanosorptive creep in nanocellulose materials, suggesting that the governing mechanism is found between molecular scales and the length-scales of the fibril diameter.

  • 40.
    Lindström, Stefan
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation.
    Karabulut, Erdem
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi.
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Wågberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi.
    Discriminating between different mechanosorptive creep hypotheses2011Inngår i: Progress in Paper Physics Seminar 2011: Conference Proceedings / [ed] U. Hirn, Graz: Verlag der Technischen Universität Graz , 2011, s. 121-126Konferansepaper (Fagfellevurdert)
  • 41.
    Lindström, Stefan
    et al.
    Linköping university.
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Uesaka, Tetsu
    Mid Sweden University.
    New insights in paper forming from particle-level process simulations2009Inngår i: Papermaking Research Symposium 2009, Kuopio, Finland: University of Kuopio , 2009, s. 38-Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    By virtue of the recent developments in simulation techniques for fibre suspensions flows, it is now possible to directly simulate forming of the paper sheet at a particle level under realistic flow conditions. This opens up a window of opportunity to better understand the microscale development of the paper structure, and to attribute particular features of the structure to different drainage elements.The simulations are based on a particle-level fibre suspension model, in which fibres are represented by chains of cylindrical fibre segments. The fibre model includes curled shapes and the torsion and bending of the fibres. It also captures the two-way interactions between the fibres and the fluid phase. The fluid motion is integrated from the Navier--Stokes equations.To illustrate the usage of the simulation tool, a sample parametric study of the effects of different fibre furnishes on the paper structure and wet strength is presented. Such an investigation could almost as easily have been performed with experiments. Simulations, however, have some advantages: First, the cost is almost nothing as compared to pilot trials. Secondly, the parameters of the simulations can be controlled one at a time, whereas in pilot trials, changing one process parameter will affect the others. Thirdly, every detail of the evolving paper structure is accessible at every instant in the simulations. That is, the forming process needs no longer be considered a "black box". Simulations also have some drawbacks. For instance, it is not possible to include the smallest particles, due to their vast number, while maintaining sufficiently large flow geometry. Therefore, simulations must target paper grades of low fines contents.In this communication, the pros and cons of particle-level simulations are discussed, and put into the context of previous forming and dewatering models in the literature. The development of the paper microstructure predicted in the simulations shows that thickening is the dominant forming mechanism, while filtration only occurs in the most dilute end of the typical range of consistencies used in the industry. This predicted behaviour is compared with the conventional view of dewatering, which holds filtration as the dominant forming mechanism.

  • 42.
    Mansour, Rami
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Chen, W.
    Olsson, Mårten
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Stochastic constitutive model of isotropic thin fiber networks based on stochastic volume elements2019Inngår i: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, nr 3, artikkel-id 538Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Thin fiber networks are widely represented in nature and can be found in man-made materials such as paper and packaging. The strength of such materials is an intricate subject due to inherited randomness and size-dependencies. Direct fiber-level numerical simulations can provide insights into the role of the constitutive components of such networks, their morphology, and arrangements on the strength of the products made of them. However, direct mechanical simulation of randomly generated large and thin fiber networks is characterized by overwhelming computational costs. Herein, a stochastic constitutive model for predicting the random mechanical response of isotropic thin fiber networks of arbitrary size is presented. The model is based on stochastic volume elements (SVEs) with SVE size-specific deterministic and stochastic constitutive law parameters. The randomness in the network is described by the spatial fields of the uniaxial strain and strength to failure, formulated using multivariate kernel functions and approximate univariate probability density functions. The proposed stochastic continuum approach shows good agreement when compared to direct numerical simulation with respect to mechanical response. Furthermore, strain localization patterns matched the one observed in direct simulations, which suggests an accurate prediction of the failure location. This work demonstrates that the proposed stochastic constitutive model can be used to predict the response of random isotropic fiber networks of arbitrary size.

  • 43.
    Motamedian, Hamid Reza
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.). Graz Univ Technol, CD Lab Fiber Swelling & Paper Performance, Inffeldgasse 23, A-8010 Graz, Austria.
    Halilovic, Armin
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.). Graz Univ Technol, CD Lab Fiber Swelling & Paper Performance, Inffeldgasse 23, A-8010 Graz, Austria.
    Mechanisms of strength and stiffness improvement of paper after PFI refining with a focus on the effect of fines2019Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 26, nr 6, s. 4099-4124Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Refining (i.e., mechanical beating of pulp) is a common procedure that is used in paper-making to improve the mechanical properties of the final product. The improvements caused by refining are mainly attributed to increased density and to a better bonding between fibers. In this work, we study how various mechanisms that can be triggered by refining affect the tensile behavior of the sheets. Consequently, we use direct numerical simulations of fiber networks. We relate our finding to the experimental measurements that we conducted on handsheets. We have found that fibrillar fines with size distributions below the resolution of modern state-of-the art pulp characterization tools have a substantial contribution to the increased strength and stiffness of the sheets.

  • 44.
    Motamedian, Hamid Reza
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    A Robust Algorithm for Normal and Tangential Beam-to-Beam Contact2016Rapport (Fagfellevurdert)
    Abstract [en]

    In this paper, we present a robust formulation for 3D beam-to-beam contact based on a penalty method. Although restricted to penalty methods, the present formulation is very stable in non-linear problems solved in implicit time integration. Apart from its simplicity in implementation, we demonstrate that compared to the previously presented methods, it requires fewer iterations in problems involving large deformations. In addition, the present formulation allows a larger range of values for the penalty stiffness without compromising the convergence rate, which often favors the accuracy of the solution. Finally, the present method allows the use of arbitrary shape functions for the beam elements, which was difficult in the previous formulations due to the immensely increased complexity of the implementation upon an increased order of the elements. In addition, we propose a robust method to handle frictional sliding contact with the present formulation.

  • 45.
    Motamedian, Hamid Reza
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    In-plane Rotational Contact of Beams in 3D Space2016Rapport (Fagfellevurdert)
    Abstract [en]

    In this paper, we develop two alternative formulations for the in-plane rotational contact of beams with large deformations in 3D space. Such a formulation is useful for modeling bonded/welded connections between beams. The first formulation is derived by linearizing the variation of the strain energy and by assuming linear shape functions for the beam elements. This formulation can be used with both the Lagrange multiplier and the penalty stiffness method. The second formulation assumes that the contact normal is independent of the nodal displacements at each iteration, and is updated between iterations. This assumption yields simpler equations and requires no specific assumption regarding the shape functions for the underlying beam elements. However, it is limited to the penalty method. We demonstrate the performance of the presented formulations in solving problems using implicit time integration. We also present a case showing the implications of ignoring the in-plane rotational contact.

  • 46.
    Motamedian, Hamid Reza
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Rotational Constraint between Beams in 3-D Space2018Inngår i: Mechanical Sciences, ISSN 2191-9151, E-ISSN 2191-916X, Vol. 9, nr 2, s. 373-387Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we develop two alternative formulations for the rotational constraint between the tangents to connected beams with large deformations in 3-D space. Such a formulation is useful for modeling bonded/welded connections between beams. The first formulation is derived by consistently linearizing the variation of the strain energy and by assuming linear shape functions for the beam elements. This formulation can be used with both the Lagrange multiplier and the penalty stiffness method. The second non-consistent formulation assumes that the contact normal is independent of the nodal displacements at each iteration, and is updated consistently between iterations. In other words, we ignore the contribution due to the change of the contact normal in the linearization of the contact gap function. This assumption yields simpler equations and requires no specific assumption regarding the shape functions for the underlying beam elements. However, it is limited to the penalty method. We demonstrate the performance of the presented formulations in solving problems using implicit time integration. We also present a case showing the implications of ignoring this rotational constraint in modeling a network of beams.

  • 47.
    Motamedian, Hamid Reza
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Simulating the hygroexpansion of paper using a 3D beam network model and concurrent multiscale approach2019Inngår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 161, s. 23-41Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A number of problems associated with dimensional stability of paper products have to do with hygroexpansion in response to changes in humidity or moisture content. The main underlying mechanism of hygroexpansion in paper is the effect of the change of fiber cross-sections transferred through fiber bonds. In fact, the transverse expansion of fibers can be an order of magnitude greater than the longitudinal expansion. Addressing such problems using modeling on the microscale is associated with large computational costs since both the bonds and the fibers need to be resolved. We present a method for modeling the hygro or thermal expansion of interconnected fiber networks modeled with beam elements and connected through beam-to-beam contact. Being a line structure, beams can only support point wise contact, which poses a challenge for modeling the force transfer induced by the deformation of the cross-sections at the contact point. The idea of implementing the stress transfer is to use a concurrent multiscale approach in which the bond level is resolved in detail using the configuration of the fibers and the computed strains are passed over to the beam elements. We verify and prove the applicability of this approach by comparing it with continuum models. We demonstrate the advantage of using this approach in terms of its tremendous saving in time. The use of beam models for modeling the hygro- or thermal expansion of fiber networks enables considering relevant sizes in the problems involving dimensional stability, in particular those associated with embedded inhomogeneities. We will show the applicability of the model by providing insights into published experimental observations on the hygroexpansion properties of paper products. Finally, we will demonstrate that the use of a 2D model to simulate the inter-fiber bonds in a network, not only leads to underestimation of out-of-plane deformations, but also to overestimation of the contribution of the transverse deformation of fibers to the in-plane dimensional change of the network.

  • 48. Sorvari, J.
    et al.
    Parola, M.
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Leppänen, T.
    Effect of some printing nip variables on web tension2016Inngår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 31, nr 3, s. 491-498Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Good runnability of paper web is an important factor for improving performance of printing process. Printing nips cause web tension variations which are known to affect web runnability. However, rather little is known about the exact effect of the nips on web tension. In this work, two dimensional finite element simulations are used to study the effect of some printing nip variables on web tension. In addition, the simulations results are compared with press trial results. The results show that nip blanket type and indentation depth has great impact on web tension. Particularly, mixing of different blanket types in adjacent printing units can cause severe variations to web tension. It is concluded that to attain good runnability the feeding characteristics of the printing blankets as well as the press settings should be known.

  • 49.
    Srinivasa, Prashanth
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    A three-dimensional numerical model for large strain compression of nanofibrillar cellulose foams2018Inngår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 33, nr 2, s. 256-270Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate the suitability of three-dimensional Voronoi structures in representing a large strain macroscopic compressive response of nanofibrillar cellulose foams and understanding the connection between the features of the response and details of the microstructure. We utilise Lloyd's algorithm to generate centroidal tessellations to relax the Voronoi structures and have reduced polydispersity. We begin by validating these structures against simulations of structures recreated from microtomography scans. We show that by controlling the cell face curvature, it is possible to match the compressive response for a 96.02% porous structure. For the structures of higher porosity (98.41%), the compressive response can only be matched up to strain levels of 0.4 with the densification stresses being overestimated. We then ascertain the representative volume element (RVE) size based on the measures of relative elastic modulus and relative yield strength. The effects of cell face curvature and partially closed cells on the elastic modulus and plateau stress is then estimated. Finally, the large strain response is compared against the two-dimensional Voronoi model and available experimental data for NFC foams. The results show that compared to the two-dimensional model, the three-dimensional analysis provides a stiffer response at a given porosity due to earlier self-contact.

  • 50.
    Srinivasa, Prashanth
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Analysis of the compressive response of Nano Fibrillar Cellulose foams2015Inngår i: Mechanics of materials (Print), ISSN 0167-6636, E-ISSN 1872-7743, Vol. 80, nr Part A, s. 13-26Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nano Fibrillar Cellulose (NFC) is fast emerging as a biomaterial with promising applications, one of which is cellular foam. The inner structure of the foam can take various shapes and hierarchical micro-structures depending on the manufacturing parameters. The compressive response of foams developed from these materials is currently a primary criterion for the material development. In this work, we focus on the connection between the non-linear part of the response and the inner structure of the material. We study the effect of internal contact and its contribution to gradual stiffening in the energy absorbing region and accelerated stiffening in the densification region of the large strain compressive response. We use the finite element method in this study and discuss the applicability and efficiency of different modelling techniques by considering well defined geometries and available experimental data. The relative contribution of internal contact is singled out and mapped onto the overall compressive response of the material. The effect of initial non-straightness of the cell walls is studied through superposing differing percentages of the buckling modes on the initial geometry. The initial non-straightness is seen to have a significant effect for only strains up to 1%. The secant modulus measured at slightly higher strains of 4%, demonstrates lesser effect from the non-straightness of cell walls. The simulations capture the compressive response well into the densification regime and there is an order of magnitude agreement in between simulations and experiments. We observed that internal contact is crucial for capturing the trend of compressive response.

12 1 - 50 of 58
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf