樹種が異なる針葉樹材の力学的性質への含水率の影響

気乾材と吸水材の圧縮に対する性質の比

抄録

Below the fibre saturation point, both Young's modulus and the compressive strength increase with decreasing moisture content. Consequently, most wood-handbooks show an approximate variation in mechanical properties with a change in moisture content below the fibre saturation point.
On the contrary, there are some growing apprehensions for the characteristic rate of mechanical changes associated with a 1% change in moisture content. Therefore, this study aimed to confirm the effect of moisture content on Young's modulus and the compressive strength. The nine softwood species and the eleven sugi-cultivars tested in the study are given in Tables I and IV.
Static compressive tests for small clear specimens gave Young's modulus E and the strength σ parallel to the grain. Both E_a/E_g and σ_a/σ_g were calculated to evaluate the effect of moisture content on the mechanical properties. E_a and E_g are Young's modulus in air-dry state and in water absorbed state. σ_a and σ_g are the strength in air-dry state and in water absorbed state.
The result from the experiments is summarized as follows:
(1) The E_a/E_g values for softwood species obtained in this experimental study are almost the same as shown in Table I, and the mean value calculated is 1.2.
(2) The σ_a/σ_g values for softwood species are given in Tables II and III, and the values for sugicultivars in Table IV. The tables show some difference in the σ_a/σ_g values, but the difference is smaller among cultivars than among softwood species.
(3) There is a tendency for nine softwood species that is apparently related to the cell wall percentage of latewood as shown in Fig. 5.