Nonlinear mechanical behaviour and analysis of wood and fibre materials

The mechanical behaviour of wood was studied from a micro up to a macro level. Wood is a cellular material possessing a high degree of anisotropy. Like other cellular solids, it often exhibits a highly nonlinear stress-strain behaviour. In the present study the mechanical properties of the cellular structure of wood are characterized and modelled. the irregular cell shape, the anisotropic layered structure of the cell walls and the periodic variations in density being taken into account. The continuum properties were derived by use of a homogenization procedure and the finite element method. Stiffness and shrinkage properties determined by this procedure are presented and are compared with measured data. The constitutive properties thus determined at various structural levels can be used in numerical simulations of the behaviour of wood in different industrially related areas. One such area is that of the refining process in mechanical pulp manufacture. Simulations of the deformation and fracturing of wood specimens loaded under conditions similar to those found in the refining process are presented. The numerical and experimental results obtained are compared. (C) 1999 Elsevier Science Ltd. All rights reserved.