  The hygro-mechanical behavior of a hierarchical cellular material, i.e.
growth rings of softwood is investigated using a two-scale micro-mechanics
model based on a computational homogenization technique. The lower scale
considers the individual wood cells of varying geometry and dimensions.
Honeycomb unit cells with periodic boundary conditions are utilized to
calculate the mechanical properties and swelling coefficients of wood cells.
Using the cellular scale results, the anisotropy in mechanical and swelling
behavior of a growth ring in transverse directions is investigated. Predicted
results are found to be comparable to experimental data. It is found that the
orthotropic swelling properties of the cell wall in thin-walled earlywood cells
produce anisotropic swelling behavior while, in thick latewood cells, this
anisotropy vanishes. The proposed approach provides the ability to consider the
complex microstructure when predicting the effective mechanical and swelling
properties of softwood.
