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The cellular level mode I fracture behaviour of spruce and birch in the RT crack propagation system

  • Pekka Tukiainen EMAIL logo and Mark Hughes
From the journal Holzforschung

Abstract

The effect of the microscopic structure and the moisture content (MC) of wood on its fracture behaviour has been investigated. Green and air-dried spruce (Picea abies [L.] Karst.) and birch (Betula pendula Roth.) wood were subjected to pure mode I loading in the radial- tangential (RT) crack propagation system. Tests were carried out in situ in an environmental scanning electron microscope to observe crack propagation at the cellular level. Crack-tip displacement fields were computed by digital image correlation, and crack propagation was observed from the images captured during testing. Both the MC and the microscopic structure were found to affect the fracture process. In the air-dried birch and spruce, only microcracking caused large displacements ahead of the crack-tip. In spruce, the microcracking zone was larger than in birch. In green birch and spruce, microcracking was less evident than in the air-dried specimens, and in some cases, there were notable deformations in a few cells ahead of the crack-tip before crack extension. Microcracking is considered to be the main toughening mechanism in spruce and birch in the RT crack propagation system.


Corresponding author: Pekka Tukiainen, Department of Forest Products Technology, School of Chemical Technology, Aalto University, P.O. Box 16400, FI-00076 Aalto, Finland, e-mail:

Acknowledgments

This work formed part of “E-Wood”, a project supported by the Multidisciplinary Institute of Digitalisation and Energy (MIDE, http://mide.aalto.fi). The work was also supported by the Academy of Finland (Decision number 1127759). The ESEM tests were carried out at the Max Planck Institute of Colloids and Interfaces, Department of Biomaterials. The authors would like to thank Dr. Ingo Burgert, Dr. Michaela Eder, and Ms. Susann Weichold for their kind co-operation. P. Tukiainen’s short-term scientific mission to the Max Planck Institute was funded under the auspices of COST Action E35.

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Received: 2014-10-9
Accepted: 2015-3-3
Published Online: 2015-4-14
Published in Print: 2016-2-1

©2016 by De Gruyter

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