Volume 9, Issue 1, 2000

Interfacial Pathways in Wood

Caroline Baillie*, Delphine Tual and Jean Christophe Terraillon

Dept. Materials, Imperial College of Science, Technology and Medicine, Prince Consort Rd., London SW72BP

(Received 12/99; accepted 2/00)

*Author to whom correspondence should be addressed)

Abstract

Wood structure and properties have been established for many years. The interaction of structure with properties has also been studied, but rarely from a materials science perspective. This paper attempts to focus on a particular aspect of composite structure, that of the interface. In engineered fibre composites the interface is the most important feature as it is the medium by which the stress is transferred from the matrix to the fibres so that they may bear the load. Much research has been focused on solving the optimisation of the interfacial stress transfer, as it is always suggested that the interface needs to be weak for high toughness and strong for high strength of the composite. More recent studies have identified the fact that it may be more advantageous to create an interface, which is not destructive in its energy absorbing capacity. Another area of weakness at the interface is the resistance to water ingress in certain environmental conditions.

Biomimetics is an emerging approach to solving scientific issues by looking to nature to see what solutions are offered for the particular concerns of engineers and their products. In this case wood is the subject of study. It is assumed that wood has optimised its internal interfaces to cope with strength and toughness requirements as well as harsh environmental conditions. The internal interfaces thus need to be firstly examined and identified. This paper looks in a qualitative way at the three different interfacial crack paths which may be likened to those occurring in engineered composites: interfacial, interlaminar and intercellular (bundle/bundle interaction) and their proposed relation to energy absorption mechanisms, It also explores the influence of moisture on these fracture paths.