The large compressive deformation of wood in the transverse direction

木材在横向受压时的应力应变图与纵向受压时的应力应变图有很大的不同，这是因为木材在横向受压时的应力应变图取决于孔孔结构或孔孔排列。在本报告中，我们的目的是找出木材横向应力应变图的通用表达式。为此，对17种硬木进行了20ºC风干、20ºC湿化和100ºC湿化3种条件下的径向压缩试验。虽然在不同条件下得到的应力(sigma) -应变（epsilon）图不同，但可以用b和k两个参数表示为：epsilon*epsilony sigma=Eepsilonepsilon>epsilony sigma/sigmay=1+b{epsilond/ [epsilond- (epsilon-sigmay/E)] -1}epsilond=1- k （rho/rho）其中sigmay、epsilony、E、rho、rho分别表示屈服应力、屈服应变、杨氏模量、木材比、细胞壁比。值epsilond是木材中所有孔隙空间被挤压时的应变的度量。参数b表示屈服点以上应力随应变增加的程度。参数K与大变形时的泊松比有关。尽管这两个参数受细胞壁粘弹性特性的影响很小，但它们受到木材压缩过程中水流的影响。

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.