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Stiffness of aligned wood fiber composites: Effects of microstructure and phase properties
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
2008 (English)In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 42, no 22, 2377-2405 p.Article in journal (Refereed) Published
Abstract [en]

The effect of wood fiber anisotropy and their geometrical features on wood fiber composite stiffness is analyzed. An analytical model for an N-phase composite with orthotropic properties of constituents is developed and used. This model is a straightforward generalization of Hashin's concentric cylinder assembly model and Christensen's generalized self-consistent approach. It was found that most macro-properties are governed by only one property of the cell wall which is very important in attempts to back-calculate the fiber properties. The role of lumen (whether it filled by resin or not) has a very large effect on the composite shear properties. It is shown that several of the unknown anisotropic constants characterizing wood fiber are not affecting the stiffness significantly and rough assumptions regarding their value would suffice. The errors introduced by application of the Hashin's model and neglecting the orthotropic nature of the material behavior in cylindrical axes are evaluated. The effect of geometrical deviations from circular cross-section, representing, for example, collapsed fibers, is analyzed using the finite element method (FEM) and the observed trends are discussed.

Place, publisher, year, edition, pages
2008. Vol. 42, no 22, 2377-2405 p.
Keyword [en]
Anisotropic, Composite, Self-consistent, Transverse properties, Wood fiber
National Category
Mechanical Engineering Wood Science
URN: urn:nbn:se:kth:diva-6098DOI: 10.1177/0021998308095886ISI: 000259686200004OAI: diva2:10712
Uppdaterad från manuskript till artikel: 20100914 QC 20100914Available from: 2006-09-12 Created: 2006-09-12 Last updated: 2010-09-14Bibliographically approved
In thesis
1. Hygroelastic behaviour of wood-fibre based materials on the composite, fibre and ultrastructural level
Open this publication in new window or tab >>Hygroelastic behaviour of wood-fibre based materials on the composite, fibre and ultrastructural level
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Wood fibres can be used as reinforcement in plastics for load carrying purposes. Some advantages compared with conventional man-made fibres are that wood fibres come from a renewable resource, have high specific stiffness and strength, are generally less hazardous to health, biodegradable, and can be manufactured at low cost and high volumes. A clear disadvantage with cellulose-based materials for structural use is their dimensional instability in humid environments. The hygroelastic properties are of high importance in materials development of improved wood-fibre composites. This work deals with the stiffness and hygroexpansion of wood fibres for composite materials. The long-term aim is to design engineered wood fibre composites based on better basic knowledge of wood fibres.

Mechanistic models have been used to link the fibrous microstructure with macroscopic composite engineering properties. The properties have been characterized experimentally for various wood-fibre composites and their fibre-mat preforms, by means of curvature measurements at various levels of relative humidity, as well as tensile and compressive tests. From these test results and microstructural characterization, the longitudinal Young’s modulus and transverse coefficient of hygroexpansion of wood fibres were identified by inverse modelling. Some effects of various pulp processes and fibre modifications on the elastic properties of the fibre were observed, illustrating how the mixed experimental-modelling approaches can be used in more efficient materials screening and selection.

An improved micromechanical analysis for wood-fibre composites has been presented. The model is more appropriate to combine with laminate analogy, to link fibre properties on the microscale to the macroscopic composite properties and vice versa. It also offers the possibility to include the effects of ultrastructure since it can account for an arbitrary number of phases. An approach to model ultrastructure-fibre property relations has been demonstrated. It includes analytical modelling of multilayered cylindrical fibres as well as finite element modelling of fibres with irregular geometry characterized with microscopy. Both approaches are useful and could be combined with experiments to reveal insights that can pave way for a firmer link between the wood fibre ultrastructure and wood fibre properties.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. xiii, 31 p.
Trita-HFL. Report / Royal Institute of Technology, Solid mechanics, ISSN 1654-1472 ; 0414
wood fibres, ultrastructure, structure-property relations, microfibril angle, composites, characterization methods, hygroelastic properties, micromechanics, modelling, reinforcement potential
National Category
Engineering and Technology
urn:nbn:se:kth:diva-4098 (URN)
Public defence
2006-09-29, E2, Lindstedsvägen 3, Stockholm, 10:00

QC 20100914

Available from: 2006-09-12 Created: 2006-09-12 Last updated: 2013-01-14Bibliographically approved

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Neagu, Cristian R.Gamstedt, Kristofer E.
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