Scale effect in the anisotropic deformation change of tracheid cells during water adsorption

The dependence of the deformation change on the location and number of cells during water adsorption was examined by microscopy combined with a charged-coupled device camera and image analysis based on the digital image correlation method. The deformation change ratio (DCR) vs. moisture content (MC) in the radial direction approached linearity with MC with increasing in number of cells between measurement points in earlywood, whereas its relation in latewood was various such as swelling, swelling after shrinking, or remaining constant with MC. The number of cells between observation points clearly affected the DCR vs. MC, i.e., its relationship had the so-called scale effect that a certain physical property appears clearly with increasing scale. The mechanism of the scale effect differed in the radial and tangential directions.