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Interfibre Joint Strength under Mixed Modes of Loading
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). (BiMaC Innovation)
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The load carrying capacity of interbre joints are one of the key entities for build-up of strength inpaper materials. In order to gain insight in how to tailor the macroscopic properties of such materialsby chemical and/or mechanical treatments at a microscopic level, direct measurement of individualbre{bre crosses are typically performed. However, the state of loading in the interbre joint, intesting of individual bre{bre crosses, is in general very complex and an increased understandingfor how to evaluate the mechanical properties of interbre joints is desirable. In Paper A, amethod for manufacturing and measuring the strength of isolated interbre joints is presented. Themethod is applied to investigate the strength of bre{bre crosses at two dierent modes of loading.Also, an investigation on the manufacturing conditions is presented. The strength distribution ofindividually prepared bre{bre crosses is characterized and it was found that the median strengthin a peeling type of loading was about 20% compared to samples tested in the conventional shearingtype of loading. In Paper B, a procedure for evaluating interbre joint strength measurementsin terms of resultant forces and moments in the interbre joint region is presented. The methodis applied to investigate the state of loading in bre{bre crosses tested in peeling and shearing,respectively. It is shown that for a typical interbre joint strength test, the load components otherthan shear, cannot in general be neglected and is strongly dependent on the structural geometry ofthe bre{bre crosses. In Paper C, four distinctly dierent load cases; peeling, shearing, tearingand a biaxial type of loading was tested mechanically and evaluated numerically in order to gainmore information on how interbre joints behave in dierent modes of loading. In Paper D, thein uence of a chemical additive on the interbre joint strength is investigated on the microscopic(joint) scale and correlated to the eect previously observed on the macroscopic (sheet) scale. Xraymicrotomography and image analysis was used to understand structural changes in the brousnetwork in terms of the number of interbre joints as well as the average interbre joint contact area.The results showed that the median interbre joint strength increased by 18% upon adsorption, andthat the polyelectrolyte increased the number of contacts between the bres as well as an increasedarea of contact. In Paper E, the damage behaviour of individual interbre joints is analyzed. Froman extensive number of mechanical tests, the typical damage behaviour is identied and a failurecriterion is used to study the in uence of failure properties to give indications on how to tailor thematerial to optimize the joint strength.

Abstract [sv]

En av de viktigaste mekanismerna for den lastbarande formagan hos pappersmaterial ar brottegenskapernahos berfogarna. For att eektivt skraddarsy sadana materials egenskaper genom kemiskoch/eller mekanisk behandling samt for att forsta hur sadana modieringar paverkar egenskapernapa en mikroskopisk niva ar provning av individuella ber-ber-kors en allmant anvand metod. Belastningeni en berfog vid sadan provning ar dock generellt komplicerad och ytterligare kunskapom hur berfogars mekaniska egenskaper skall utvarderas ar onskvard. I Artikel A, presenterasen metod for tillverkning samt mekanisk provning av isolerade ber-kors vid tva olika typer avbelastning. Vidare undersoks hur torktrycket, torkmetoden samt graden av malning inverkar pafogstyrkan. Resultaten visar att brottlasten for en globalt akande belastning var omkring 20 % avbrottlasten for prov utforda med den konventionella skjuvande belastningen samt att styrkan hosindividuellt tillverkade berkors ar fordelade enligt en Weibull fordelning. I Artikel B, presenterasen numerisk metod for utvardering av fogstyrke-matningar med avseende pa kraft- och momentresultanternai gransytan mellan brerna. Metoden anvands for att studera belastningsmoden hosber-kors i tva principiellt olika lastfall. Resultaten visar att for ett typiskt berfogsprov, kan intelastkomponenterna, vid sidan av skjuvning, generellt forsummas da de ar starkt beroende avber-korsets geometri. I Artikel C, jamfors fogstyrkematningar under fyra principiellt olika lastfall; akande, skjuvande, rivande samt biaxiellt. De experimentella last-forskjutningskurvorna, samtde beraknade lastmoderna anvands for att undersoka vilket tillskott pa information de foreslagnalastfallen kan ge i hansyn till fogstyrkan hos massabrer. I Artikel D, undersoks en polymers (somabsorberats pa berytorna) inverkan pa saval berniva som pa natverksniva. Fiberfogstyrkan matsexperimentellt och eekten av den kemiska tillsatsen jamfors pa mikroskopisk niva (ber-kors) medtidigare uppmatt eekt pa makroskopisk niva (ark). Rontgentomogra och bildanalys anvands foratt undersoka de strukturella skillnaderna som uppstar i de brosa natverken vid absorption av enpolyamin och resultaten visar att antalet berfogar per berlangdenhet samt att medelkontaktareanokade. Resultaten visar ocksa att medianen av berfogsstyrkan okade med 18 %. Dessa eekter sammantagetar anledningen till varfor polyaminer, sasom PAH, ar sa eektiva for att oka torrstyrkanhos pappersmaterial. I Artikel E, karakteriseras skadebeteendet hos individuella berfogar franett omfattande antal matningar. Ett brottkriterium infors i den numeriska utvarderingsmetoden foratt studera skadebeteendet. Kanslighetsanalys och inverkan av brottparametrarna studeras ocksafor att ge indikationer pa hur egenskaperna kan skraddarsys for att optimera berfogstyrkan.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, School of Engineering Sciences , 2014. , viii, 22 p.
Series
TRITA HLF, ISSN 1104-6813 ; 0554
Keyword [en]
Interfibre joint strength, fibre-fibre cross, paper mechanics
National Category
Paper, Pulp and Fiber Technology
Research subject
Solid Mechanics
Identifiers
URN: urn:nbn:se:kth:diva-145669ISBN: 978-91-7595-107-2 (print)OAI: oai:DiVA.org:kth-145669DiVA: diva2:719507
Public defence
2014-06-12, H1, Teknikringen 33, KTH, Stockholm, 09:00 (English)
Opponent
Supervisors
Projects
BiMaC Innovation
Funder
Swedish Research Council, 2007-5380
Note

QC 20140527

Available from: 2014-05-27 Created: 2014-05-26 Last updated: 2014-05-27Bibliographically approved
List of papers
1. Experimental Evaluation of the Interfibre Joint Strength of Papermaking Fibres in Terms of Manufacturing Parameters and in Two Different Loading Directions
Open this publication in new window or tab >>Experimental Evaluation of the Interfibre Joint Strength of Papermaking Fibres in Terms of Manufacturing Parameters and in Two Different Loading Directions
2013 (English)In: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 53, no 9, 1621-1634 p.Article in journal (Refereed) Published
Abstract [en]

The strength properties of interfibre bonds play a vital role in the response of fibrous materials, such as paper and paperboard, under mechanical loading. To help tailor the properties of such materials by chemical or mechanical treatments of the fibre wall and fibre surfaces, improved understanding of the microscopic damage and failure mechanisms of interfibre joints is desirable. In this paper, a method for manufacturing and testing of interfibre joint specimens in two principally different modes of loading is presented. The method was applied to investigate the strength of Kraft pulp interfibre joints with different geometries and in two different modes of loading: the conventional shearing mode and also a peeling mode of loading. The method was also used to investigate the influence of drying pressure, defined as the nominal pressure between two Teflon surfaces or between a rubber surface and a Teflon one as well as a simple comparison of a pulp with two different degrees of refining. The results are presented in terms of rupture force and using different methods of normalization such as nominal overlap area, length, and width of the joint region, measured using a microscope. It was shown in this study that normalising the force at rupture by either geometric parameter reduced the scatter of the strength measurements slightly, but, neither were unambiguously more successful than the other. The results of tests done with the peeling type of loading were about 20 % of those done with the conventional shearing type of loading.

Keyword
Interfibre joint strength, Interfibre bond, Fibre-fibre joint, Fibre-fibre cross, Paper strength, Paper mechanics
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-134559 (URN)10.1007/s11340-013-9757-y (DOI)000326045800011 ()2-s2.0-84886237059 (Scopus ID)
Funder
Swedish Research Council, 2007-5380
Note

QC 20131125

Available from: 2013-11-25 Created: 2013-11-25 Last updated: 2017-12-06Bibliographically approved
2. Numerical evaluation of interfibre joint strength measurements in terms of three-dimensional resultant forces and moments
Open this publication in new window or tab >>Numerical evaluation of interfibre joint strength measurements in terms of three-dimensional resultant forces and moments
2013 (English)In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 20, no 4, 1691-1710 p.Article in journal (Refereed) Published
Abstract [en]

The interfibre joint is one of the key elements in creating the strength of self-binding fibrous materials such as paper and board. In order evaluate the strength properties of interfibre joints using direct measurements, a greater understanding on how the mode of loading influences the results is desirable. The methods reported in the literature do not in general distinguish between the contributions of normal and shear stresses in the bonded region. This paper presents a numerical analysis procedure, based on the finite element method, for evaluating interfibre joint strength measurements in terms of the normal, shear, and moment loading components during testing. The target is to estimate the resultant forces and moments, that acts in the interfibre joint region at rupture, of Kraft pulp interfibre joints tested under two principally different modes of loading. The results show that for a typical interfibre joint test, modes of loading other than pure shear cannot, in general, be neglected, and are strongly dependent on the structural geometry of the fibre-fibre crosses. In addition, the resultant forces and moments were scaled in terms of the interface area and the twisting and bending resistance of the interface approximated as an ellipse to account for differences in interface area between the measurements. These scaled resultants were used to quantify how the mode of loading influences the relation between the amount of normal stress and the amount of shear stress that develop in the interfibre joint.

Keyword
Fibre-fibre cross, Fibre-fibre joint, Finite rotations, Interfibre joint strength, Mode of loading, Paper mechanics, Paper strength
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-132214 (URN)10.1007/s10570-013-9939-x (DOI)000322673000014 ()2-s2.0-84881024839 (Scopus ID)
Funder
Swedish Research Council, 2007-5380
Note

QC 20131028

Available from: 2013-10-28 Created: 2013-10-24 Last updated: 2017-12-06Bibliographically approved
3. Interfibre joint strength under peeling, shearing and tearing types of loading
Open this publication in new window or tab >>Interfibre joint strength under peeling, shearing and tearing types of loading
2013 (English)In: Advances in Pulp and Paper Research, Cambridge 2013: Transactions of the 15th Fundamental ResearchSymposium / [ed] S.J. I'Anson, 2013, 103-124 p.Conference paper, Published paper (Refereed)
Abstract [en]

The mechanical properties of interfibre joints are essential for the load carrying capacity of fibre network materials such as paper and board. Mechanical measurements of fibre–fibre crosses can been used to characterize the strength of these interfibre joints in order to obtain knowledge on how these hierarchical network materials behave at the micrometer scale. The general method for these interfibre joint strength experiments has been to pull one of the fibres of a fibre–fibre cross and attribute the force at rupture to the shear strength of the interfibre joint. However, without taking the geometry of the fibres and the resulting mixed mode of loading at the interfibre joints into account, limited information on the strength properties can be obtained using this technique. In this study, isolated fibre–fibre crosses have been tested mechanically using four distinctly different load cases; peeling, shearing, tearing and a biaxial type of loading, in order to gain more information on how interfibre joints behave in different modes of loading. The centerline geometry of the fibres, microfibril angles, initial twists as well as the wall thickness of each individual test piece was used to model each experiment using the finite element method, and from the simulation results, the local state of loading in the interfibre joints at failure was obtained for each specific experiment. The force–displacement curve for the experiments as well as the estimated local state of loading was also used to compare the different load cases and to evaluate the information that can be obtained on the strength properties of interfibre joints using these load cases.

National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-136444 (URN)978-0-9926163-0-4 (ISBN)
Conference
15th Fundamental Research Symposium Held in Cambridge: September 8-13, 2013
Note

QC 20140317

Available from: 2013-12-05 Created: 2013-12-05 Last updated: 2014-05-27Bibliographically approved
4. New insights intothemechanisms behind the strengthening of ligno-cellulosic fibrous networks with polyamines
Open this publication in new window or tab >>New insights intothemechanisms behind the strengthening of ligno-cellulosic fibrous networks with polyamines
Show others...
(English)Manuscript (preprint) (Other academic)
Identifiers
urn:nbn:se:kth:diva-145688 (URN)
Note

QS 2014

Available from: 2014-05-26 Created: 2014-05-26 Last updated: 2014-05-27Bibliographically approved
5. Failure behaviour of interfibre joints using cohesive zone modelling and how totailor their properties for strength
Open this publication in new window or tab >>Failure behaviour of interfibre joints using cohesive zone modelling and how totailor their properties for strength
(English)Manuscript (preprint) (Other academic)
Identifiers
urn:nbn:se:kth:diva-145687 (URN)
Note

QS 2014

Available from: 2014-05-26 Created: 2014-05-26 Last updated: 2014-05-27Bibliographically approved

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