  The transverse hygro-expansion of the Norway spruce wood is studied on the
growth ring level using digital image correlation. This non-destructive
technique offers the possibility to contactless study deformation fields of
relatively large areas. The measured full-field strains are segmented into
individual growth rings. Whereas radial strains closely follow the density
progression with the maximum in the dense latewood, tangential and shear strain
remain constant except for positions around the edges of the sample. A simple
FE three phase growth ring model is in good agreement with the experimental
values. The selective activation of individual phases like earlywood,
transitionwood and latewood demonstrates that the radial hygro-expansion is
dominated by the earlywood deformation, whereas tangential deformation is a
complex interplay of expansion and compression that needs all tissues to fully
develop.
