The large compressive deformation of wood in the transverse direction

Research Project

Project/Area Number	05660188
Research Category	Grant-in-Aid for General Scientific Research (C)
Allocation Type	Single-year Grants
Research Field	林産学
Research Institution	KYOTO UNIVERSITY
Principal Investigator	MOROOKA Toshiro Kyoto University, Wood Research Institute Assoc.Professor, 木質科学研究所, 助教授 (00192378)
Co-Investigator(Kenkyū-buntansha)	NORIMOTO Misato Kyoto University, Wood Research Institute Professor, 木質科学研究所, 教授 (20027163)
Project Period (FY)	1993 – 1994
Project Status	Completed (Fiscal Year 1994)
Budget Amount *help	¥1,900,000 (Direct Cost: ¥1,900,000) Fiscal Year 1994: ¥500,000 (Direct Cost: ¥500,000) Fiscal Year 1993: ¥1,400,000 (Direct Cost: ¥1,400,000)
Keywords	compressive test / large deformation / transverse direction / yield stress / wood / 圧変ひずみ / 降げ値 / 圧密歪
Research Abstract	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=Eepsilon epsilon>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.