SHRINKAGE AND ELASTICITY OF NORMAL AND COMPRESSION WOODS IN CONIFERS

The relationships of shrinkage to the specific gravity or to the Young 's modulus were investigated in normal and compression woods of sugi ( Cryptomeria japonica D.Don), hinoki (Chamaecyparis obtusa Endl.), and Sitka spruce (Picea sitchensis Carr.) as well as in agathis (Agathis b ornensis Warb.) and igem (Podocarpus imbricatus Bl.) which are tropica l conifers. The darkly colored portions of agathis wood, which are ran domly distributed all over the transverse surface of a stem, showed th e typical features of compression wood. Anisotropic shrinkage was obse rved in the transverse directions of agathis and igem woods, which hav e no distinct growth rings. In the longitudinal direction, there was n o definite correlation between the shrinkage and the specific gravity for normal wood, whereas the shrinkage for compression wood increased with increasing specific gravity. In the radial direction, the shrinka ge of normal wood generally increased with increasing specific gravity , whereas no clear correlation was observed for compression wood. In t he tangential direction, there was no correlation for either normal wo od or compression wood. In the radial and tangential directions, no cl ear correlation was observed between shrinkage and Young's modulus for either normal wood or compression wood except for normal wood in the radial direction. On the other hand, there was a high correlation betw een shrinkage and the specific Young's modulus in the longitudinal dir ection for both normal and compression woods. This relationship was ex pressed by a hyperbolic equation.