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- Bergström, Per
(author)
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Modelling Mechanics of Fibre Network using Discrete Element Method
- 2018
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Licentiate thesis (other academic/artistic)abstract
- Low-density fibre networks are a fundamental structural framework of everyday hygiene products, such as baby diapers, incontinence and feminine care products, bathroom tissue and kitchen towels. These networks are a random assembly of fibres, loosely bonded and oriented in the plane direction.Designing such a complex network structure for better performance, better use of materials and lower cost is a constant challenge for product designers, requiring in-depth knowledge and understanding of the structure and properties on the particle (fibre) level.This thesis concerns the development of a computational design platform that will generate low-density fibre networks and test their properties, seamlessly, with the aim to deepening the fundamental understanding of the micromechanics of this class of fibre networks.To achieve this goal, we have used a particle-based method, the Discrete Element Method (DEM), to model the fibres and fibre networks. A fibre is modelled as a series of linked beads, so that one can consider both its axial properties (stretching and bending) and transverse properties (shearing,twisting and transverse compression). For manufacturing simulations, we developed the models for depositing fibres to form a fibre network, consolidating the fibre network, compressing to make a 3D-structured network, and creating creping. For testing the end-use performance, we have developed two models and investigated the micromechanics of the fibre network in uniaxial compression in the thickness direction (ZD) and in uniaxial tension in the in-plane direction.In the ZD-uniaxial compression of entangled (unbonded) fibrenetworks, the compression stress exhibits a power-law relationship with density, with a threshold density. During compression, the fibre deformation mode changed from fibre bending to the transverse compression of fibre. Accordingly, the transverse properties of the fibreshad a large impact on the constitutive relation. By considering a realistic value for the transverse fibre property, we were able to predict the valuesof the exponent widely observed in the experimental literature. We havefound that the deviation of the experimental values from those predictions by the earlier theoretical studies is due to the neglect of the transverse fibre property.For tensile properties of bonded networks, we have investigated scaling of network strength with density and fibre–fibre bond strength. The network strength showed beautiful scaling behaviour with both density and bond strength, with exponents 1.88 and 1.08 respectively. The elastic modulus of the network, on the other hand, showed a changing exponent(from 2.16 to 1.69) with density in accordance with previous results in the literature. We have also reconfirmed that, with increasing density, the deformation mode changes from bending to stretching. The predicted results for both elastic modulus and strength agreed very well with experimental data of fibre networks of varying densities reported in the literature.We have developed a computational platform, based on DEM, for accurately modelling a fibre network from its manufacturing process to product properties. This is a tool that allows a versatile design of materials and products used for hygiene products, providing a promising venue for exploring the parameter space of new material and process design.
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| 2. |
- Bergström, Per, et al.
(author)
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Scaling Behaviour of Strength of 3D-, Semi-flexible-, Cross-linked Fibre Network
- 2019
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In: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683 .- 1879-2146. ; 166:July 2019, s. 68-74
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Journal article (peer-reviewed)abstract
- Anisotropic, semi-flexible, cross-linked, random fibre networks are ubiquitous both in nature and in a wide variety of industrial materials. Modelling mechanical properties of such networks have been done extensively in terms of criticality, mechanical stability, and scaling of network stiffnesses with structural parameters, such as density. However, strength of the network has received much less attention. In this work we have constructed 3D-planar fibre networks where fibres are, more or less, oriented in the in-plane direction, and we have investigated the scaling of network strength with density. Instead of modelling fibres as 1D element (e.g., a beam element with stretching, bending and/or shear stiffnesses), we have treated fibres as a 3D-entity by considering the features like twisting stiffness, transverse stiffness, and finite cross-link (or bond) strength in different deformation modes. We have reconfirmed the previous results of elastic modulus in the literature that, with increasing density, the network modulus indeed undergoes a transition from bending-dominated deformation to stretching-dominated with continuously varying scaling exponent. Network strength, on the other hand, scales with density with a constant exponent, i.e., showing no obvious transition phenomena. Using material parameters for wood fibres, we have found that the predicted results for stiffness and strength agree very well with experimental data of fibre networks of varying densities reported in the literature.
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| 3. |
- Dahlström, Christina, 1977-, et al.
(author)
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Microstructure Variations in Paper Coating : Direct Observations
- 2012
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In: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 51:24, s. 8246-8252
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Journal article (peer-reviewed)abstract
- Non-uniformities in the coating layer, such as porosity variations and binder distributions, are known to affect print uniformity and barrier properties. However, in the literature the results are rather scarce or sometimes conflicting.We acquired high quality images of coated paper cross sections using field emission scanning electron microscopy in combination with a new argon-ion-beam milling technique to directly observe and analyse the coating microstructures in relation to underlying base sheet structures.The results showed that coating porosity varied with mass density of the underlying base sheet for the relatively bulky clay/GCC coating, whereas for the more compact clay coating, the effect was small. Areas with more fibres in the base sheet were more compressed by calendering, resulting in a decreased coating porosity. A unique binder enriched layer of less than 500 nm thickness was found at the coating surface as well as at the coating/base sheet interface.
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| 6. |
- Holmvall, Martin, 1976-, et al.
(author)
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Transfer of a microfluid to a stochastic fibre network
- 2011
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In: Journal of Fluids and Structures. - : Elsevier BV. - 0889-9746 .- 1095-8622. ; 27:7, s. 937-946
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Journal article (peer-reviewed)abstract
- The transfer of a microscopic fluid droplet from a flat surface to a deformable stochastic fibre network is investigated. Fibre networks are generated with different levels of surface roughness, and a two-dimensional, two-phase fluid-structure model is used to simulate the fluid transfer. In simulations, the Navier-Stokes equations and the Cahn-Hilliard phase-field equations are coupled to explicitly include contact line dynamics and free surface dynamics. The compressing fibre network is modelled as moving immersed boundaries. The simulations show that the amount of transferred fluid is approximately proportional to the contact area between the fluid and the fibre network. However, areas where the fluid bridges and never actually makes contact with the substrate must be subtracted.
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| 9. |
- Hossain, Shakhawath, et al.
(author)
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Nonlinear Compression of Soft Fibre Network
- 2017
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In: Book Of Abstracts Deformation And Damage Mechanisms Of Woodfibre Network- Materials And Structures.
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Conference paper (peer-reviewed)
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| 10. |
- Hossain, Shakhawath, et al.
(author)
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Uniaxial Compression of Three-Dimensional Entangled Fibre Networks: Impacts of Contact Interactions
- 2019
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In: Modelling and Simulation in Materials Science and Engineering. - : IOP Publishing. - 0965-0393 .- 1361-651X. ; 27:1
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Journal article (peer-reviewed)abstract
- This paper concerns uniaxial compression of anisotropic fibre network, as typically seen in the end use of nonwoven and textile fibre assemblies. The constitutive relationship and deformation mechanism have been investigated by using a bead-model to represent the complex structures of the constituent fibres and the fibre networks. The compression stress shows a power-law dependency on the density with a threshold density for both experimental and numerical fibre networks. Unlike the widely studied tri-axial compression of the initially isotropic network, it was found that the contact interaction between the fibres, especially the fibre-fibre contact stiffness (or the transverse compression properties of fibres), has a large impact on all the constitutive parameters. In particular, the exponent values computed based on the softer contact stiffnesses agreed very well with the experimental values reported in the literature. The internal deformation mechanism was similar to the earlier studies that at low compression, the deformation is dominated by the low-energy-mode deformations (i.e. bending and shear), whereas at higher compression, the difference appears: the compression of fibre-fibre contacts, instead of the deformation in the fibre axial direction, takes over.
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