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Residual stresses in paperboard and the influence of drying conditions
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The drying sequence in the manufacturing process for paperboard involves evaporation of water, primarily from within the fibres. The vapour is then transported out of the web by pressure or concentration gradients. As the moisture transport from the paper web to the ambient is quicker than the moisture transport within the fibre network to the surfaces of the web, moisture gradients develop through the thickness of the web. This work concerns effects on the mechanics of paper drying from the variation in moisture through the relatively thin structures of paper and paperboard.

Distributions of inplane residual stresses through paper materials in the unloaded state after drying are believed to be caused by the varying moisture through the thickness during drying. The distributions in general exhibit compressive stress near the board surfaces and tensile stress in the interior of the board. This may be modified after drying and is also affected by structural variation in the material between different plies of multi-ply paperboards.

The stress development during drying is important because it influences the resulting material properties of the paper and because it can lead to curl, which is a quality problem. The residual stresses themselves are an error source in simulation or evaluation of the mechanical behaviour of paper.

In this work, residual stress distributions in paperboard were determined experimentally, to clarify the mechanisms of residual stress build-up. An experimental method for such tests was also developed. Based on the experimental findings, the mechanics of paper drying was modelled and the stress build-up simulated. Simulation offers a way of studying how the properties of paper develop during drying of wet paper webs.

Place, publisher, year, edition, pages
Stockholm: Hållfasthetslära , 2005. , 21 p.
Series
Trita-HFL. Report / Royal Institute of Technology, Solid mechanics, ISSN 1654-1472 ; 0393
Keyword [en]
paper, drying, mechanical properties, residual stress, curl
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-469OAI: oai:DiVA.org:kth-469DiVA: diva2:13448
Public defence
2005-11-18, F3, Lindstedtsvägen 26, 10:00
Opponent
Supervisors
Available from: 2005-11-02 Created: 2005-11-02 Last updated: 2013-01-14Bibliographically approved
List of papers
1. Experimental determination of residual stresses in paperboard
Open this publication in new window or tab >>Experimental determination of residual stresses in paperboard
2005 (English)In: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 45, no 6, 493-497 p.Article in journal (Refereed) Published
Abstract [en]

A method for the experimental determination of the through-thickness residual stress distribution in paper-board is presented.The successive removal of thin layers from strips of board through surface grinding changes the stress-state and the bending stiffness resulting in a changed curvature, which is measurable. From tests of strips in both in-plane directions, stress distributions can then be evaluated using the Treuting-Read method. Geometrically nonlinear effects at the large deformations taking place are avoided through a proper choice of strip dimensions. Typical results are presented and factors influencing the accuracy of the determination are thoroughly discussed.

Keyword
residual stress, paperboard, surface grinding, curl measurement, Treuting-Read method
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-8187 (URN)10.1007/BF02427902 (DOI)000233457600002 ()2-s2.0-28944433502 (Scopus ID)
Available from: 2005-11-02 Created: 2005-11-02 Last updated: 2011-08-31Bibliographically approved
2. The influence of drying restraints and beating degree on residual stress build-up in paperboard
Open this publication in new window or tab >>The influence of drying restraints and beating degree on residual stress build-up in paperboard
2004 (English)In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 30, no 11, 289-293 p.Article in journal (Refereed) Published
Abstract [en]

The through-thickness distribution of in-plane residual stress has been determined for laboratory-made paperboards, to study the causes of these stresses. The degree of restraint during drying is shown not to influence the residual stresses in a significant way. However, a higher level of beating of the pulp leads to higher residual stresses. The drying gradient through the sheet combined with the shrinkage of paper as moisture content decreases is suggested as the main reason for residual stress build-up. No effect an free shrinkage was seen when attempting to limit the drying gradients by decreasing the grammage.

Keyword
Curl, Drying, Mechanical Properties, Moisture Content, Paperboards, Stresses
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-8188 (URN)000227150000001 ()2-s2.0-14844340850 (Scopus ID)
Available from: 2005-11-02 Created: 2005-11-02 Last updated: 2011-09-15Bibliographically approved
3. The influence of drying conditions on residual stress build-up in paperboard
Open this publication in new window or tab >>The influence of drying conditions on residual stress build-up in paperboard
2004 (English)In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 30, no 11, 312-316 p.Article in journal (Refereed) Published
Abstract [en]

The through-thickness distributions of in-plane residual stress have been determined for some laboratory-made paperboards. The effects of drying variables such as temperature, moisture flow resistance at the surfaces and thickness of the boards on residual stresses were studied. The drying rate was shown to influence residual stresses only for relatively slow drying. Residual stresses correlate well with the moisture gradient during drying for various drying methods. Some effects of the drying conditions on paper tensile stiffness are discussed. One-sided heating for curl control is also discussed.

Keyword
paperboards, stresses, drying, moisture content, curl, mechanical properties
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-8189 (URN)000227150000005 ()2-s2.0-14844355885 (Scopus ID)
Available from: 2005-11-02 Created: 2005-11-02 Last updated: 2011-09-15Bibliographically approved
4. Residual stresses in paperboard through the manufacturing process
Open this publication in new window or tab >>Residual stresses in paperboard through the manufacturing process
2005 (English)In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 31, no 4, 197-201 p.Article in journal (Refereed) Published
Abstract [en]

The residual stresses in a machine-made multi-ply board with chemical pulp in all plies were monitored as the board progressed after the initial drying through calendering, moisture treatments and coating. After drying, the stresses were compressive near the surfaces. In the coated board at the end of the machine, the stress state was reversed to a large extent with tensile stresses in the outermost layers. The various moisture applications on the board in the post-processing steps are regarded to have caused the change in the residual stress state. In another machine-made board, with mechanical pulp in the middle plies, the stresses after drying were limited to the surface plies made from chemical pulp, but were again compressive at the surfaces. This stress state was largely unaffected by post-processing. The possibility for stress reversal and the implications on in-plane and out-of-plane dimensional stability of the boards are discussed.

Keyword
multiply boards, stresses, tensile stress, chemical pulps, board machines
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-8190 (URN)000234572400007 ()2-s2.0-30844451592 (Scopus ID)
Available from: 2005-11-02 Created: 2005-11-02 Last updated: 2011-08-31Bibliographically approved
5. The influence of through-thickness variation on the mechanics of paper drying
Open this publication in new window or tab >>The influence of through-thickness variation on the mechanics of paper drying
2005 (English)In: ADVANCES IN PAPER SCIENCE AND TECHNOLOGY: TRANSACTIONS OF THE 13TH FUNDAMENTAL RESEARCH SYMPOSIUM, VOLS 1-3 / [ed] IAnson SJ, 2005, 213-240 p.Conference paper, Published paper (Refereed)
Abstract [en]

A material model for drying paper is presented. Moisture-dependent material parameters, hygroscopic shrinkage, the elastic and the time-dependent responses of the material to load, and the effect of unloading at a higher stiffness than the load was applied at are modelled. The model is used to determine the effects of a varying moisture ratio through the paper during drying on free shrinkage development and stiffness development at free drying. Simulation results for the stress development during drying and the state of residual stress immediately after drying are also presented. The model predicts a variation of in-plane elastic moduli through the paper, a prediction that is studied by experiments.

Keyword
RESIDUAL-STRESS BUILDUP
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-8191 (URN)000283529400009 ()978-0-9545272-3-5 (ISBN)
Conference
13th Fundamental Research Symposium on Advances in Paper Science and Technology, Univ Cambridge, Cambridge, ENGLAND, SEP, 2005
Note
QC 20110201Available from: 2005-11-02 Created: 2005-11-02 Last updated: 2011-02-01Bibliographically approved
6. Modeling the influence of drying conditions on the stress buildup during drying of paperboard
Open this publication in new window or tab >>Modeling the influence of drying conditions on the stress buildup during drying of paperboard
2006 (English)In: Journal of engineering materials and technology, ISSN 0094-4289, Vol. 128, no 4, 495-502 p.Article in journal (Refereed) Published
Abstract [en]

This paper concerns the drying process in the manufacturing of paperboard. Of particular interest are the effects of through-thickness property variation in paperboard during drying. In addition, resulting average properties from different drying histories are discussed. A mathematical model of the drying process is presented. It allows the moisture and temperature histories, the stress and strain histories, and the buildup of mechanical properties to be simulated. The temperature of the heating medium, the humidity and pressure of the ambient air, and either applied loads or prescribed strains are required input data. For symmetric convective drying, the ambient temperature, the humidity, and the thickness of the board were varied. For drying on a heated plate, the temperature of the plate and the thickness of the board were varied. Results regarding the moisture history, the stiffness development, and the buildup of residual stresses are presented and compared to literature experimental data. Also, sheets with a varying fiber base through the thickness, which affects both the moisture history and the influence of moisture on shrinkage, were studied. The model was shown to yield predictions qualitatively inline with empirical knowledge.

Keyword
Curl, Drying, Moisture gradient, Paperboard, Residual stress
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-8192 (URN)10.1115/1.2345440 (DOI)000241820400005 ()2-s2.0-33751434870 (Scopus ID)
Note
QC 20110831. Conference: Symposium on Time-Dependent Behaviors of Polymers and Polymer Matrix Composites. Orlando, FL.Available from: 2005-11-02 Created: 2005-11-02 Last updated: 2011-09-27Bibliographically approved

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