Nonlinear mechanical behaviour and analysis of wood and fibre materials

The mechanical behaviour of wood was studied from a micro up to a macro lev el. Wood is a cellular material possessing a high degree of anisotropy. Lik e 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 varia tions in density being taken into account. The continuum properties were de rived by use of a homogenization procedure and the finite element method. S tiffness and shrinkage properties determined by this procedure are presente d and are compared with measured data. The constitutive properties thus det ermined at various structural levels can be used in numerical simulations o f the behaviour of wood in different industrially related areas. One such a rea is that of the refining process in mechanical pulp manufacture. Simulat ions of the deformation and fracturing of wood specimens loaded under condi tions similar to those found in the refining process are presented. The num erical and experimental results obtained are compared. (C) 1999 Elsevier Sc ience Ltd. All rights reserved.