| 1. |
- Borodulina, Svetlana, et al.
(författare)
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Constitutive modeling of a paper fiber in cyclic loading applications
- 2015
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Ingår i: Computational materials science. - : Elsevier BV. - 0927-0256 .- 1879-0801. ; 110, s. 227-240
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
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| 3. |
- Borodulina, Svetlana, et al.
(författare)
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Digital Analysis of Deformed Corrugated Boxes Using 3D Speckles
- 2010
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Konferensbidrag (refereegranskat)abstract
- During transportation from the manufacturer to the retailer packages are affected by vibrations, shocks, staticand dynamic loads, as well as by changes in temperature and humidity. In order to improve the quality of the packaging towithstand stresses during transportation it is important to know the parameters that characterize the deformation state inthe package. Corrugated boxes are affected by a phenomenon known as mechanosorptive creep, the basics of which arestill not well understood. That is why it is interesting to know how changes in moisture content affect corrugated boxesand how it is possible to prolong the lifetime of transportation packages. This paper presents an attempt to use the whitelight digital photography method for a three-dimensional analysis of the deformation states near collapse of a corrugatedbox during varying humidity, and attempts to obtain characteristic parameters that can be used to describe deformationstates close to collapse. A series of tests using an optical non-destructive testing method are reported and the results fordifferent test configurations are presented. Comparison is made between tests performed at different load levels andclimate conditions. The optical deformation measurement system used for analysis was ARAMIS® (GOM mbH,Braunschweig, Germany). Advantages and disadvantages of working with this system are also described and suggestionsfor future work are discussed.
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| 4. |
- Borodulina, Svetlana, et al.
(författare)
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Effect of fiber and bond strength variations on the tensile stiffness and strength of fiber networks
- 2016
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Rapport (refereegranskat)abstract
- 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.
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| 5. |
- Borodulina, Svetlana, et al.
(författare)
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Effect of fiber and bond strength variations on the tensile stiffness and strength of fiber networks
- 2018
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Ingår i: International Journal of Solids and Structures. - : Elsevier. - 0020-7683 .- 1879-2146. ; 154, s. 19-32
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Borodulina, Svetlana
(författare)
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Extracting fiber and network connectivity data using microtomography images of paper
- 2016
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Ingår i: Nordic Pulp & Paper Research Journal. - Stockholm : Arbor Publishing AB. - 0283-2631 .- 2000-0669. ; 31:3, s. 469-478
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Tidskriftsartikel (refereegranskat)abstract
- We apply image analysis methods based on micro-computed tomography (μCT) to extract the parameters that characterize the structure and bonding parameters in the fiber network of paper. The scaling and variational properties of μCT images are examined by analyzing paper structural properties of two 1 × 1 mm2 test pieces, which have been cut out from a low-grammage handsheet. We demonstrate the applicability of the methods for extracting the free fiber length, fiber cross-sectional data, the distances between the fibers, and the number of fiber-to-fiber bonds, which are the key properties required for the adequate representation of the network in numerical models. We compare the extracted connectivity data with the early reported analytical estimations and conclude that the number of contacts in three-dimensional networks is controlled by the fiber aspect ratio. In addition, we compare the cross-sectional data with those measured by the fiber morphology characterization tools and estimate the fiber shrinkage from completely wet to dry state to be nearly 20%.
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| 7. |
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| 8. |
- 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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| 9. |
- Borodulina, Svetlana
(författare)
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Micromechanics of Fiber Networks
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The current trends in papermaking involve, but are not limited to, maintaining the dry strength of paper material at a reduced cost. Since any small changes in the process affect several factors at once, it is difficult to relate the exact impact of these changes promptly. Hence, the detailed models of the network level of a dry sheet have to be studied extensively in order to attain the infinitesimal changes in the final product.In Paper A, we have investigated a relation between micromechanical processes and the stress–strain curve of a dry fiber network during tensile loading. The impact of “non-traditional” bonding parameters, such as compliance of bonding regions, work of separation and the actual number of effective bonds, is discussed. In Paper B, we studied the impact of the chemical composition of the fiber cell wall, as well as its geometrical properties, on the fiber mechanical properties using the three-dimensional model of a fiber with helical orientation of microfibrils at a range of different microfibril angles (MFA). In order to accurately characterize the fiber and bond properties inside the network, via statistical distributions, microtomography studies on the handsheets have been carried out. This work is divided into two parts: Paper C, which describes the methods of data acquisition and Paper D, where we discuss the extracted data. Here, all measurements were performed at a fiber level, providing data on the fiber width distribution, width-to-height ratio of isotropically oriented fibers and contact density. In the last paper, we utilize data thus obtained in conjunction with fiber morphology data from Papers C and D to update the network generation algorithm in order to produce more realistic fiber networks. We also successfully verified the models with the help of experimental results from dry sheets tested under uniaxial tensile tests. We carry out numerical simulations on these networks to ascertain the influence of fiber and bond parameters on the network strength properties.
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| 10. |
- Borodulina, Svetlana, et al.
(författare)
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Stress-strain curve of paper revisited
- 2012
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Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 27:2, s. 318-328
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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.
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