木材のレオロジーに関する研究 (第6報)

Abstract

It is well known that the mechanical properties of wood are very much affected by temperature and by relative humidity. In the light of the results previously considered of these effects, we expect that an investigation of the effects of moisture content and temperature on creep and stress relaxation of wood would be of interest. Of course, it is necessary first to establish the fundamental creep or relaxation behavior of wood under given conditions, and so we have investigated the static viscoelasticity of wood within low stress range in bending of Buna wood (Fagus crenata) beam. The results are as follows:Within the range of strain observed in this experiment, the stress-strain relation is linear and creep compliance, recovery compliance and relaxation modulus are independent of magnitude of loads. This facts suggests that wood behaves as a linear viscoelastic material.The scale factor of wet wood parallel to grain amounts to as much as four times of air dry wood. Such an influence of water sorption on creep behavior is discussed in connection with the variation in moisture effects on dynamic behavior of Buna wood and on stress relaxation of Hinoki wood treated by formaldehyde.The curves of D(t) or E(t) vs. logt of wood that are determind at different temperatures have been tried to be superposed by means of a horizontal translation along the logarithmic time axis and the result was found uncomplete. But when these curves are smoothed out and differentiated by logt, the shape of the curves obtained are analogous to the relaxation time spectra measured for long time scale. The temperature dependency of the shift factor is hereby discussed.