As the primary factor of the shrinkage during drying, it has been considered the internal stresses and the difference of the structure. The former is the time-changes of the stresses due to the moisture gradients which occurs the strain, and it gives the change of the basic shrinkage of wood itself. On the other hand, the latter is influenced to the structure of cell-wall or its arrangement and amounts of any tissues, for instance, medullary ray tissue or wood parenchyma cell.
Now, when the wood is dried, the water is evaporated from the surface of a board. Consequently, it raises the difference of the shrinkage between the surface and the inside of a board, therefore, it raises the tensile stresses on the surface of a board and compressive stresses into a board.
Thus, the wood during drying always are given the stresses internally and outernally. It is seemed that drying wooa suffer the thermochemical change of the wood structure components, and the elastic change of the quality of the materials are partly nonhomogenity and irregularity, the dimension of the board chenges phenominally.
This report was discussed how to show some behavior of the shrinkage due to the temperatures under the tensile loads, on the assumption that is the surface of a board through the initial stage of drying. The experimental apparatus is shown in Fig 1, and the experimental results are shown in Fig. 2-7.
Experimental results are summarized as follows ;
1. As regards the effects of the temperature for the shrinkage under the constant load, the time of the start of shrinkage become early increasing the temperature.
2. The relation between the maximum shrinkage and the temperature under each constant tensile load are hardly dependence on the temperature.