Mechanical Properties of Fibre-Reinforced Materials: the Wood-Water System

The mechanical properties of wood are investigated from a "quasi-elastic point of view that makes allowance for variation in moisture content. The theoretical work is divided into three parts. The first part shows that wood may be regarded as a fibre-reinforced composite material and then builds up models of wood structure in terms of an assemblage of basic fibre-composite elements. The second part derives the constitutive relations for a fibre-reinforced composite consisting of, an inert fibrous phase embedded in a water reactive matrix; and the third part is concerned with the properties of the matrix of wood substance. The theoretical work is then tested against mechanical data from a set of specimens for which individual models have been devised. From this work, functions describing the behaviour of the matrix with moisture contest are obtained and the structural modelling procedures and the constitutive relation are shown to be not inconsistent with the observations. It was found that in addition to the mean cellulose microfibril angle, the matrix sorption properties are of great importance in correctly predicting Longitudinal shrinkage behaviour.