The large compressive deformation of wood in the transverse direction

木材在横向压缩时的应力应变图与纵向的有很大的不同，因为在横向上它们取决于孔洞结构或孔道排列。在本报告中，我们旨在找出木材横向应力应变图的普遍表达式。为此，对17种硬木进行了3种条件下的径向压缩试验，即20ﾟC风干条件、20ﾟC湿条件和100ﾟC湿条件。虽然在不同的条件下得到的应力-应变(Epsilon)图不同，但可以用b和k的两个参数来表示：Epsilony sigma/sigMay=1+b{epsilond/[epsilond-(epsilon-sigMay/E)]-1}epsilond=1-K(Rho/Rhos)，其中SigMay、epsilony、E、Rho和Rhos分别指屈服应力、屈服应变、杨氏模数、木材比重和细胞壁的比重。埃秒值是木材中所有孔隙空间被挤压的应变的量度。参数b表示在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。虽然这两个参数几乎不受细胞壁的粘弹性性质的影响，但它们被证明受到压缩过程中木材中的水流动的影响。

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.