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Fracture processes in wood chipping
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics. (FSCN – Fibre Science and Communication Network)
2008 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In both the chemical and mechanical pulping process, the logs are cut into wood chips by a disc chipper before fibre separation. To make the wood chipping process more efficient, one have to investigate in detail the coupling between theprocess parameters and the quality of the chips. The objective of this thesis is to obtain an understanding of the fundamental mechanisms behind the creation of wood chips. Both experimental and analytical/numerical approaches have been taken inthis work. The experimental investigations were performed with an in‐house developed equipment and a digital speckle photography equipment. The results from the experimental investigation showed that the friction between the log and chipping tool is probably one crucal factor for the chip formation. Further more it was found that the indentation process is approximately self‐similar, and that the stress field over the entire crack‐plane is critical for chip creation. The developed analytical model predicts the normal and shear strain distribution. The analytical distributions are in reasonable agreement with the corresponding distributions obtained from a finite element analysis.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University , 2008. , 27 p.
Series
Mid Sweden University licentiate thesis, ISSN 1652-8948 ; 32
Keyword [en]
Wood chipping, chip formation, digital speckle photography, friction, fracture processes, analytical model
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:miun:diva-7827ISBN: 978-91-86073-02-2 (print)OAI: oai:DiVA.org:miun-7827DiVA: diva2:132439
Presentation
(English)
Supervisors
Available from: 2009-05-20 Created: 2008-12-18 Last updated: 2009-06-08Bibliographically approved
List of papers
1. A Method for Experimental Investigation of the Wood Chipping Process
Open this publication in new window or tab >>A Method for Experimental Investigation of the Wood Chipping Process
2008 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 23, no 3, 339-342 p.Article in journal (Refereed) Published
Abstract [en]

SUMMARY: To be able to formulate criteria’s for determining the onset of the creation of a wood chip; it is desirable to be able to study the deformation fields in a vicinity of the edge of the chipping tool. To that end, an experimental setup has been developed in which the chipping can be performed under very well defined conditions. In this setup it is possible to control the rate of indentation of the chipping tool and also to measure the force on the tool. The setup admits also that the angle of the wood specimen with respect to the cutting plane can be varied in both a horizontal and a vertical plane. To determine the deformations, a Digital Speckle Photography (DSP) equipment is used, which together with image processing software makes it possible to determine the strain field on the surface of the wood specimen. One observation that can be made in these studies is that prior to the creation of a chip, there is a localization of strains in a thin region starting from the edge of the tool and directed parallel to the grain. Another observation made during the experimental work is that there exist different types of fracture processes, each giving different chip thicknesses.

Keyword
Fracture Processes
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:miun:diva-6847 (URN)10.3183/NPPRJ-2008-23-03-p339-342 (DOI)000260397100013 ()2-s2.0-53849111967 (Scopus ID)6046 (Local ID)6046 (Archive number)6046 (OAI)
Projects
Flisningsprocessen
Available from: 2008-11-30 Created: 2008-11-02 Last updated: 2010-08-16Bibliographically approved
2. An Analytical and Numerical Study of some aspects of the Wood Chipping Process
Open this publication in new window or tab >>An Analytical and Numerical Study of some aspects of the Wood Chipping Process
2009 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 24, no 2, 225-230 p.Article in journal (Refereed) Published
Abstract [en]

SUMMARY: In order to model the wood chipping process, the primary process parameters have been identified and their first order interaction studied. The model is analytical and incorporates, in particular, the influence of sliding friction between the wood chipping tool and the log. To estimate the accuracy of the analytical model, a Finite Element (FE) analysis of the problem considered was also performed. The analytical model and the FE analysis are both restricted to small deformations and linear elastic orthotropic material behaviour. The most severe limitation with both the analytical and the FE model is the assumption of linearly elastic material. On the other hand, it is felt that existing models of anisotropic plasticity in metals are lacking too much of physical relevance, if applied to wood. The analytical model predicts the normal and shear strain distribution in the crack-plane prior to crack initiation. The analytical distributions are in reasonable agreement with the corresponding distribution of the FE analysis. Based on experimental findings, it is suggested that the stress field over the entire crack-plane, in conjunction with the stress field close to the tip of the chipping tool, are critical for chip creation, rather than just the latter.

Keyword
Wood chipping; Chip formation; Analytical model; Friction
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:miun:diva-7127 (URN)10.3183/NPPRJ-2009-24-02-p225-230 (DOI)000268735100015 ()2-s2.0-68049117085 (Scopus ID)
Projects
Flisningsprocessen
Available from: 2008-12-10 Created: 2008-11-21 Last updated: 2016-09-26Bibliographically approved

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Citation style
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