Finite element modelling of mechanical properties of geometrically characterized wood fibres

Geometrical data of Norway spruce fibres has been obtained using microscopy and three-dimensional reconstruction. The geometry is imported into the comercial finite element software Abaqus, and one shell model and one solid model are created. Elastic properties of the different cell wall layers are calculated with a micromechanical model and implemented into the numerical model. A parametric study has been made on a typical latewood fibre segment with the lenght of 260 micrometers where the micro fibri angle (MFA) has been varied. The numerical model representing the fibre geometry has been compared with an analytical model under tensile load with two different boundary conditions. The result from this comparison is that the analytical model overestimates the axial stiffness by about 12 % in a MFA range of 0-30 degrees in a case where rotation is restrained. In the other extreme case, when the fibre is free to rotate due to the twist-extension coupling, there is a deviation by about 4 %, except for the MFA interval 0-10 degrees where it is higher