This study investigates the effect of a wide range of moisture contents (0-177 %) on the Poisson's ratio of wood taken from Japanese cypress and magnolia by conducting longitudinal compression tests. Through analysis of variance and multiple comparisons, it was found that when the moisture content is below the respective fiber saturation point Poisson's ratio decreases with increasing moisture content. In contrast, at moisture contents above the fiber saturation point, the Poisson's ratio increases with moisture content. The same tendency was observed in both wood species, but the effect was more pronounced in magnolia than Japanese cypress.

No abstract

Microfibril angle (MFA) is a major structural variable that describes the fine structure of the cell wall in wood. In this study, the relationships between the MFA of the S2 layer and the Poisson’s ratios and Young’s moduli (modulus of elasticity, MOE) of five wood species (agathis, larch, Japanese cedar, Japanese cypress and ginkgo) were determined by analyzing both their normal and compression woods. It was found that both the longitudinal MOE (MOEL) and MOE of the cell-wall substance (MOEW) decreased with increasing MFA, while the peaks values of Poisson’s ratio (νLT) were obtained at MFAs of ≈25°. In particular, at MFAs lower than 25°, theνLTincreased with increasing MFA, and the opposite relationship was observed at MFA values exceeding 25°. This trend is in good agreement with the estimates obtained based on the theory of orthotropic elasticity with the underlying assumption that the orthotropic elasticity of materials is MFA-dependent. Hence, the MFA parameter incorporated into the orthotropic elasticity theory is useful for determination of the Poisson’s ratio.