応力を受けている木材の収縮,膨潤(2) : 引張応力

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In this work, the effect of dead tensile stress on the shrinking and the swelling of wood was examined and the following results being obtained: the coefficient of shrinking (α) becomes smaller and the coefficient of swelling (β) becomes larger in proportion to the increase of stress. This means that wood became set in the stretched condition caused by the tensile stress.
Generally speaking, if wood is stretched below its proportional limit, it regains the original dimention when the load is removed. However, wood may act as a plastic material under prolonged strain, and as a result a permanent deformation may form, even though the load were never great enough to strain the wood beyond its proportional limit. And hence, we investigated that permanent deformation of wood in moisture-equilibrium state which is caused by the dead tensile stress. The value obtained was negligible even under maximum stress (15kg / <cm>^2) used in the firstly-mentioned examination.