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An anisotropic fibre-network model for mechano-sorptive creep in paper
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).ORCID iD: 0000-0002-0307-8917
2008 (English)In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 45, no 22-23, 5765-5787 p.Article in journal (Refereed) Published
Abstract [en]

In this paper a simplified network model for mechano-sorptive creep is presented, which is a further development of an earlier paper [Strombro, J., Gudmundson, P., 2008. Mechanosorptive creep under compressive loading - a micromechanical model. International journal of Solids and Structures 45 (9), 2420-2450.]. It is assumed that the anisotropic hygro-expansion of the fibres leads to large stresses at the fibre bonds when the moisture content changes. The resulting stress state will accelerate creep if the fibre material obeys a constitutive law that is non-linear. Fibre kinks are included in order to capture experimental observations of larger mechano-sorptive effects in compression than in tension. Moisture dependent material parameters and anisotropy in the fibre distribution have been introduced. Theoretical predictions based on the model are compared to experimental results for an anisotropic paper both under tensile and compressive loading at varying moisture content and it is found that the important features in the experiments are captured by the model. Different kinds of drying conditions have also been examined.

Place, publisher, year, edition, pages
2008. Vol. 45, no 22-23, 5765-5787 p.
Keyword [en]
Mechano-sorptive creep, Accelerated creep, Paper, Modelling, Moisture changes, Humidity change, Sorption, Fibres, Creep, Network model, Fibre network, Mathematical model, Fibre bonding, Tension, Compression, Anisotropy
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-7946DOI: 10.1016/j.ijsolstr.2008.06.010ISI: 000260273300008Scopus ID: 2-s2.0-51649092462OAI: oai:DiVA.org:kth-7946DiVA: diva2:13132
Note
QC 20100910. Uppdaterad från submitted till published (20100910).Available from: 2008-01-31 Created: 2008-01-31 Last updated: 2010-09-10Bibliographically approved
In thesis
1. Micro-mechanical mechanisms for deformation in polymer-material structures
Open this publication in new window or tab >>Micro-mechanical mechanisms for deformation in polymer-material structures
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

In this thesis, the focus has been on micro-mechanical mechanisms in polymer-based materials and structures. The first part of the thesis treats length-scale effects on polymer materials. Experiments have showed that the smaller the specimen, the stronger is the material. The length-scale effect was examined experimentally in two different polymers materials, polystyrene and epoxy. First micro-indentations to various depths were made on polystyrene. The experiments showed that length-scale effects in inelastic deformations exist in polystyrene. It was also possible to show a connection between the experimental findings and the molecular length. The second experimental study was performed on glass-sphere filled epoxy, where the damage development for tensile loading was investigated. It could be showed that the debond stresses increased with decreasing sphere diameter. The debonding grew along the interface and eventually these cracks kinked out into the matrix. It was found that the length to diameter ratio of the matrix cracks increased with increasing diameter. The experimental findings may be explained by a length-scale effect in the yield process which depends on the strain gradients.

The second part of the thesis treats mechano-sorptive creep in paper, i.e. the acceleration of creep by moisture content changes. Paper can be seen as a polymer based composite that consists of a network of wood fibres, which in its turn are natural polymer composites. A simplified network model for mechano-sorptive creep has been developed. It is assumed that the anisotropic hygroexpansion of the fibres leads to large stresses at the fibre-fibre bonds when the moisture content changes. The resulting stress state will accelerate creep if the fibre material obeys a constitutive law that is non-linear in stress. Fibre kinks are included in order to capture experimental observations of larger mechano-sorptive creep effects in compression than in tension. Furthermore, moisture dependent material parameters and anisotropy are taken into account. Theoretical predictions based on the developed model are compared to experimental results for anisotropic paper both under tensile and compressive loading at varying moisture content. The important features in the experiments are captured by the model. Different kinds of drying conditions have also been examined.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. 40 p.
Series
Trita-HFL. Report / Royal Institute of Technology, Solid mechanics, ISSN 1654-1472 ; 0442
Keyword
Length-scale effects, Strain gradient, Moisture change, Humidity change, Network model, Fibre model, Mathematical model, Polymer, Micro-indentation, Particle composite, Interfacial debonding, Matrix cracking, Paper, Mechano-sorptive creep, Accelerated creep
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-4626 (URN)
Public defence
2008-02-22, F3, KTH, Lindstedtsvägen 26, Stockholm, 10:15
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Supervisors
Note

QC 20100910

Available from: 2008-01-31 Created: 2008-01-31 Last updated: 2013-01-14Bibliographically approved

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