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Constitutive modeling of a paper fiber in cyclic loading applications
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).ORCID iD: 0000-0003-3611-2250
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).ORCID iD: 0000-0002-7236-6365
2015 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 110, 227-240 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
2015. Vol. 110, 227-240 p.
Keyword [en]
Microfibril angle, Cell wall, Twist, Cyclic loading
National Category
Applied Mechanics
URN: urn:nbn:se:kth:diva-175896DOI: 10.1016/j.commatsci.2015.08.039ISI: 000362010800029ScopusID: 2-s2.0-84940925038OAI: diva2:870479

QC 20151113

Available from: 2015-11-13 Created: 2015-10-26 Last updated: 2016-06-13Bibliographically approved
In thesis
1. Micromechanics of Fiber Networks
Open this publication in new window or tab >>Micromechanics of Fiber Networks
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. 32 p.
TRITA-HFL. Report / Royal Institute of Technology, Solid Mechanics, ISSN 1654-1472 ; 97
Network simulation, Mechanical properties, Fibers, Fiber-to-fiber bonds, Free fiber length, Number of contacts, Contact density, Paper properties, X-ray microtomography
National Category
Paper, Pulp and Fiber Technology
Research subject
Solid Mechanics
urn:nbn:se:kth:diva-188481 (URN)978-91-7595-994-8 (ISBN)
Public defence
2016-09-02, Kollegiesalen, Brinellvägen 8, Stockholm, 10:00 (English)

QC 20160613

Available from: 2016-06-13 Created: 2016-06-10 Last updated: 2016-06-13Bibliographically approved

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Borodulina, SvetlanaKulachenko, ArtemTjahjanto, Denny
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