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Testing and Evaluation of Interfibre Joint Strength under Mixed-Mode Loading
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The failure properties of interfibre bonds are the key for the build-up of strength in fibrous materials such as paper and paperboard. In order to tailor the properties of such materials by chemical or mechanical treatments and to learn how such modifications influence the properties at a microscopic level, direct measurement of individual fibre--fibre crosses are typically performed. However, the state of loading in the interfibre joint, in testing of individual fibre--fibre crosses, is in general very complex and a greater understanding for how to evaluate the mechanical properties of interfibre joints is desirable.

In Paper A, a method for manufacturing multiple fibre--fibre cross specimens and a procedure for testing interfibre joints at different modes of loading is presented. The method is applied to investigate the strength of fibre-fibre crosses with different geometry and at two principally different modes of loading. Also, an investigation on the influence of drying pressure, the drying method as well as a comparison of pulp fibres from two different degrees of refining is presented. The force at rupture is scaled in terms of different geometric parameters; nominal overlap area, length and width of the joint region. It is shown that neither of the methods of scaling unambiguously reduced the coefficient of variation of the mean strength and that the force at rupture in a peeling type of loading was about 20% of the ones tested in the conventional shearing type of loading.

In Paper B, a procedure for evaluating interfibre joint strength measurements in terms of resultant forces and moments at rupture is presented. The method is applied to investigate the state of loading in fibre-fibre crosses tested in two principally different modes of loading. It is shown that for a typical interfibre joint test, the modes of loading other than pure shear, cannot in general be neglected and is strongly dependent on the structural geometry of the fibre-fibre crosses. Also, the stress state in the interface centroid was estimated in order to quantify how the mode of loading influence the amount of normal stresses that develop in relation to the amount of shear stresses in the interfibre joint.

Abstract [sv]

De brottmekaniska egenskaperna hos fiberfogar är nyckeln för uppbyggnaden av styrka hos fibrösa material såsom papper och kartong. För att effektivt skräddarsy sådana materials egenskaper genom kemisk eller mekanisk behandling och för att förstå hur sådana modifieringar påverkar egenskaperna på en mikroskopisk nivå är provning av individuella fiber-fiber-kors en allmänt använd metod. Belastningen i en fiberfog vid provning av individuella fiber-fiber kors är dock generellt mycket komplicerad och ytterligare kunskap om hur fiberfogars mekaniska egenskaper skall utvärderas är önskvärd.

I Artikel A, presenteras en metod för samtidig tillverkning av flera fiber-fiber kors samt en metod för mekanisk provning av dessa med olika typer av belastning. Metoden tillämpades för att studera styrkan av fiber-fiber-kors med olika geometri och vid två olika lastfall. En undersökning av hur torktrycket, torkmetoden samt graden av malning inverkar på fogstyrkan presenteras. De uppmätta brottlasterna skalades med olika karakteristiska längder för fogen; nominell överlapparea samt fogens längd och bredd. Resultaten visade att ingendera av normaliseringsmetoderna reducerade variationskoefficienten (av medelvärdet av styrkan) samt att brottlasten för en globalt fläkande belastning var omkring 20 % av brottlasten för prov utförda med den konventionella skjuvande belastningen.

I Artikel B, presenteras en metod för utvärdering av mätningar av styrkan hos fiberfogar med hänseende på kraft- och moment- resultanterna i gränsytan mellan fibrerna. Metoden används för att studera belastningsmoden hos fiber-fiber--kors provade i två principiellt olika lastfall. Resultaten visar att för ett typiskt fiberfogsprov av isolerade fiber-fiber-kors med långa fria fibersegment, så kan inte belastningsmoderna vid sidan av skjuvning försummas och att de är starkt beroende av fiber-fiber-korsets geometri. För att kunna jämföra fiberfogar av olika storlek och kvantifiera förhållandet mellan normal- och skjuvbelastningen i fogen skalades de resulterande krafterna och momenten med tvärsnittsstorheter baserade på en approximation av fogareans utformning.

Place, publisher, year, edition, pages
Sweden: KTH Royal Institute of Technology, 2013. , x, 13 p.
Series
Trita-HFL. Report / Royal Institute of Technology, Solid Mechanics, ISSN 1654-1472 ; 0532
Keyword [en]
interfibre joint, fibre-fibre bonding, paper strength
National Category
Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:kth:diva-116700ISBN: 978-91-7501-620-7 (print)OAI: oai:DiVA.org:kth-116700DiVA: diva2:600414
Presentation
2013-02-11, Seminarierummet, Teknikringen 8D, KTH, Stockholm, 14:15 (English)
Opponent
Supervisors
Projects
BiMaC Innovation
Funder
Swedish Research Council, 2007-5380
Note

QC 20130125

Available from: 2013-01-25 Created: 2013-01-24 Last updated: 2013-01-25Bibliographically approved
List of papers
1. Experimental evaluation of the interfibre joint strength ofpapermaking fibres in terms of manufacturing parameters and intwo different loading directions
Open this publication in new window or tab >>Experimental evaluation of the interfibre joint strength ofpapermaking fibres in terms of manufacturing parameters and intwo different loading directions
2012 (English)Report (Other academic)
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 suchmaterials by chemical or mechanical treatments of the fibre wall and fibre surfaces, improvedunderstanding 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 twoprincipally different modes of loading is presented.The method was applied to investigate the strength of Kraft pulp interfibre joints with differentgeometries and in two different modes of loading: the conventional shearing mode and also apeeling mode of loading. The method was also used to investigate the influence of dryingpressure, defined as the nominal pressure between two Teflon surfaces or between a rubbersurface and a Teflon one as well as a simple comparison of a pulp with two different degrees ofrefining.The results are presented in terms of rupture force and using different methods of normalizationsuch as nominal overlap area, length, and width of the joint region, measured using a microscope.It was shown in this study that neither of the methods of normalization unambiguously reducedthe large scatter of the strength measurements. The results of tests done with the peeling type ofloading were about 20 % of those done with the conventional shearing type of loading.

Publisher
31 p.
Series
Trita-HFL. Report / Royal Institute of Technology, Solid Mechanics, ISSN 1654-1472 ; 523
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-116694 (URN)
Funder
Swedish Research Council, 2007-5380
Note

QC 20130124

Available from: 2013-01-24 Created: 2013-01-24 Last updated: 2013-01-25Bibliographically 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
2012 (English)Report (Other academic)
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 to tailor the properties of such materials by chemical and/or mechanical treatments of the fibres, and to learn how such modifications influence the properties at the microscopic level, a greater understanding of how to evaluate the mechanical properties of interfibre joints is desirable. The methods reported in the literature for determining of the interfibre joint strength 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 method is applied to investigate the strength of Kraft pulp interfibre joints under two principally different modes of loading. The results show that for a typical interfibre joint test of an isolated fibre–fibre cross with long free fibre segments, 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.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2012. 37 p.
Series
Trita-HFL. Report / Royal Institute of Technology, Solid Mechanics, ISSN 1654-1472 ; 528
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-116696 (URN)
Funder
Swedish Research Council, 2007-5380
Available from: 2013-01-24 Created: 2013-01-24 Last updated: 2013-01-25Bibliographically approved

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