| 1. |
|
|
| 2. |
|
|
| 3. |
- Borodulina, Svetlana
(författare)
-
Micromechanical Behavior of Fiber Networks
- 2013
-
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.
|
|
| 4. |
- Borodulina, Svetlana, et al.
(författare)
-
Stress-strain curve of paper revisited
- 2012
-
Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 27:2, s. 318-328
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 5. |
|
|
| 6. |
- Fallqvist, Björn, et al.
(författare)
-
Modelling of cross-linked actin networks - Influence of geometrical parameters and cross-link compliance
- 2014
-
Ingår i: Journal of Theoretical Biology. - : Elsevier BV. - 0022-5193 .- 1095-8541. ; 350, s. 57-69
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 7. |
- HENTZE, Hans-Peter, et al.
(författare)
-
METHOD OF MANUFACTURING PAPER AND PRODUCTS OBTAINED BY THE METHOD
- 2010
-
Patent (populärvet., debatt m.m.)abstract
- 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.
|
|
| 8. |
- Kariniemi, M., et al.
(författare)
-
Effect of Blanket Properties on Web Tension in Offset Printing
- 2010
-
Ingår i: Advances in Printing and Media Technology. - Montreal, Canada.
-
Konferensbidrag (refereegranskat)abstract
- 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.
|
|
| 9. |
- Kulachenko, Artem, 1978-, et al.
(författare)
-
Direct simulations of fiber network deformation and failure
- 2012
-
Ingår i: Mechanics of materials. - : Elsevier BV. - 0167-6636 .- 1872-7743. ; 51, s. 1-14
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 10. |
- Kulachenko, Artem, 1978-, et al.
(författare)
-
Elastic properties of cellulose nanopaper
- 2012
-
Ingår i: Cellulose. - : Springer. - 0969-0239 .- 1572-882X. ; 19:3, s. 793-807
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
