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- Borodulina, Svetlana
(författare)
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Micromechanical Behavior of Fiber Networks
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Paper is used in a wide range of applications, each of which has specific requirements on mechanical and surface properties. The role of paper strength on paper performance is still not well understood. This work addresses the mechanical properties of paper by utilizing fiber network simulation and consists of two parts.In the first part, we use a three-dimensional model of a network of fibers to describe the fracture process of paper accounting for nonlinearities at the fiber level (material model and geometry) and bond failures. A stress-strain curve of paper in tensile loading is described with the help of the network of dry fibers; the parameters that dominate the shape of this curve are discussed. The evolution of network damage is simulated, the results of which are compared with digital speckle photography experiments on laboratory sheets. It is concluded that the original strain inhomogeneities due to the structure are transferred to the local bond failure dynamics. The effects of different conventional and unconventional bond parameters are analyzed. It has been shown that the number of bonds in paper is important and that the changes in bond strength influence paper mechanical properties significantly.In the second part, we proposed a constitutive model for a fiber suitable for cyclic loading applications. We based the development of the available literature data and on the detailed finite-element model of pulp fibers. The model provided insights into the effects of various parameters on the mechanical response of the pulp fibers. The study showed that the change in the microfibril orientation upon axial straining is mainly a geometrical effect and is independent of material properties of the fiber as long as the deformations are elastic. Plastic strains accelerate the change in microfibril orientation. The results also showed that the elastic modulus of the fiber has a non-linear dependency on a microfibril angle,with elastic modulus being more sensitive to the change of microfibril angle around small initial values of microfibril angles. These effects were incorporated into a non-linear isotropic hardening plasticity model for beams and tested in a fiber network in cycling loading application model, using the model we estimated the level of strains that fiber segments accumulate at the failure point in a fiber network.The main goal of this work is to create a tool that would act as a bridge between microscopic characterization of fiber and fiber bonds and the mechanical properties that are important in the papermaking industry. The results of this work provide a fundamental insight on mechanics of paper constituents in tensile as well as cyclic loading. This would eventually lead to a rational choice of raw materials in paper manufacturing and thus utilizing the environment in a balanced way.
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| 4. |
- Heyden, Susanne
(författare)
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A Network Model Applied to Cellulose Fibre Materials
- 1996
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A network mechanics model for analysis of materials made of dry-shaped cellulose fibres is proposed. In terms of the model, the network is composed of fibres of arbitrary distribution in length, curvature, cross-section. stiffness and strength. The fibres are arranged in a random structure according to an arbitrary orientation distribution. Where fibres meet there may be fibre-to-fibre interaction, modelled by a linear or non-linear spring coupling representing stick-slip performance. The connection is of arbitrary distribution in stiffness and strength.The network geometry is periodic, any cell under observation being regarded as one of many identical cells that make up a global structure. A set of cyclic boundary and loading conditions facilities obtaining relevant results even in the case of small network cells.A two-dimensional implementation of the model was carried out, and several examples of simulation results are provided. The results concern geometrical properties of the network, and the effects on network stiffness and fracture behavior due to variations of sample size, boundary conditions and the various micro-level parameters mentioned above.
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| 6. |
- Heyden, Susanne
(författare)
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How to Derive an Analytical Network Mechanics Theory
- 1998
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report was originally written as a part of the course material in the FPIRC course Paper Mechanics given at STFI/KTH. The aim of the report is to explain the ideas behind analytical network theories based on the homogeneous strain assumption in a simple way. One example, corresponding to the Cox model, [2], is also worked out in detail in the report.
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| 9. |
- Heyden, Susanne, et al.
(författare)
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Modelling of Hygroexpansion of Paper
- 2002
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Ingår i: ; , s. 76-80
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Konferensbidrag (refereegranskat)abstract
- The effect of fibre hygroexpansion on sheet hygroexpansion has been studied by means of two different methods; computer simulation and analytical modelling. The influence of network density, fibre orientation distribution, fibre geometry and stiffness properties was examined.
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