Shrinkage, wood anisotropic

Boyd (39) has reviewed the published data and theories of anisotropic transverse shrinkage. He has concluded, in agreement with Bosshard s (40) contention, that the dominant factor is the greater degree of lignification in the radial walls. This characteristic reduces sorption of water (Figure 11). Boyd also attributes a significant effect to the preponderance of radially flattened thick-walled cells in the latewood of some woods, particularly conifers. 

This arises simply because of the anisotropic shrinkage of wood (Figure 8.14). Spiral grain, cross-grain and reaction wood contribute, and warping is especially likely in corewood. Drying under heavy restraint (1000 kg m"" ) mitigates the problem. 

Barber NF and Meylan BA (1964) The anisotropic shrinkage of wood. Holrforschung, 18 5) 146-56... 

FIGURE 12.5 Schematic indication of the deformations of the sections, cansed by the anisotropic shrinkage of wood dnring drying, due to the deformations in the tangential direction being greater than in the radial direction. 

---