The large compressive deformation of wood in the transverse direction

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The stress strain diagrams of wood in compression in the transverse direction are known to be quite different from those in the longitudinal direction since in the transverse direction they depend on cell porous structure or cell arrangement. In the present report, we aimed at finding out universal expression for the stress strain diagrams of wood in the transverse direction. For this purpose, the compressive tests in the radial direction for seventeen kinds of hardwoods were conducted in three conditions, in the air-dried condition at 20ﾟC,in the wet condition at 20ﾟC and in the wet condition at 100ﾟC.Although the stress (sigma) -strain (epsilon) diagrams obtained were different in the different conditions, they could be expressed by the following expressions with two parameters of b and K.epsilon*epsilony sigma=Eepsilonepsilon>epsilony sigma/sigmay=1+b{epsilond/ [epsilond- (epsilon-sigmay/E) ] -1}epsilond=1-K (rho/rhos)where sigmay, epsilony, E,rho, and rhos refer to yield stress, yield strain, Young's modulus, specific gravity of wood, and specific gravity of the cell wall, respectively. The value epsilond is a measure of the strain at which all the pore space in wood is squeezed. The parameter b indicates the extent of the increase of stress with strain above the yield point. The parameter K is related to poisson's ratio in the large deformation. Although both parameters are little affected by the viscoelastic properties of the cell wall, they were shown to be affected by the water flow in wood during compression.