Variation of shear creep properties of wood within a stem: effects of macro- and microstructural variability

This study determined the structural factors affecting the shear creep characteristics of wood. The radial (R) distribution of shear creep characteristics within a stem of Japanese cedar was investigated under constant temperature and humidity conditions. The shear force was applied using an off-axis method. The investigated structural factors comprised the density of the wood and the width of the annual rings as macro-level factors and the microfibril angle (MFA) as a micro-level factor. The shear modulus [GTL(0)] was found to be widely distributed in the R direction within the stem. Furthermore, a multiple regression analysis revealed that GTL(0) was strongly influenced by a positive correlation with both the MFA and density. The wide distribution of GTL(0) within the stem was satisfactorily explained by the MFA-dependent theory of orthotropic elasticity. Furthermore, the shear creep compliance curve demonstrated a tendency to increase logarithmically, regardless of the location within the stem. The MFA also exhibited a significant effect on (positive correlation with) the rate at which the shear creep compliance increased, while the effect of density was found to be minimal, although it had a significant effect on the shear modulus GTL(0).