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Stress Relaxation in Relation to the Non-equilibrium State in the Wood-water System
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The stress relaxation of Buna under constant deflection has been investigated in the conditions of both moisture transient and equilibrium states. The transient conditions are almost nearly equal to natural seasonings in the atmosphere (25℃ and 30℃, R.H.80).
The relaxations during drying from the waterlogged to the above air dry conditions were found to be increased enormously(Fig.3) at a course of drying. This conspicuous phenomenon of the relaxation seems to be followed with an extraordinary increase in residual deformation when deloaded. This was confirmed in Table 3 and its magnitude was as large as 90 per cent or more of the constant deformation given at first.
Over the range studied here, the rate of drying does not affect the course of relaxation but changes its time scale (Fig. 7). It was then concluded that the stress relaxation during drying went on in accordance with the progress of drying of wood. And the great increase in relaxation occured in the second decreasing rate of drying (Fig. 8). A further research for the plastic deformation due to the non-equilibrium state in moisture will be desired.
The Shimane Agricultural College