Splitting type wood cutting with wedge-shaped knife by stress field control.

本研究的目的是通过控制刀尖周围的应力场，研究在刀的运动方向与纤维角度不一致的情况下，用楔形刀进行劈裂式木材切割的可能性。与普通锯切相比，这种方法有许多改进，不会产生锯屑，几乎不会产生噪音。在实验中，我们使用云杉木材，尖角20度，厚度3 mm的楔形刀。为了对试件进行任意角度的横向加载，研制了液压式加载装置。我们的结论如下：1.当试件的整个侧面在足够的压力下被加压时，预期的切割类型是可能的。在控制切割试件的质量时，加载量比加载方向更重要。在用非线性有限元方法模拟应力场时，Tsai&Wu提出的指数能较好地解释实验结果。2.采用部分侧向加压的方法不能得到较好的结果，有限元分析证实了这一点。3.由于很难预测刀尖裂纹的扩展方向，我们不得不研究由各向异性塑性理论驱动的准则。在实际机器中，不需要改变与晶片角度同步的侧向力角度，但如果采用履带或其他设备的部分压缩系统，则需要足够大的压缩面积来减少裂纹。在该系统中，刀尖周围存在较大的塑性变形，因此使用超薄刀具是必不可少的。

The aim of this research is to investigate the possibility of a splitting type wood cutting with wedge-shaped knife, in the case where the direction of knife's movement dose not coincide with the fiber angle, by controlling the stress field around the knife tip. This method has many improvements, when compared with ordinary saw cutting, such that it will produce no sawdust and be almost noiseless. In the experiments, we used spruce wood, and wedge shaped knife with tip angle 20 degrees, thickness 3 mm. To charge lateral load on the specimens at any angles, hydraulic type loading equipment was made. The following are our conclusion:1. When the whole lateral surface of the specimen was pressed, with adequate pressure, expected type cutting was possible. The amount of the load was more important than the direction of the load on controlling the quality of the cut specimen. In the simulation of stress field by a non-linear finite element method, an index proposed by Tsai & Wu could explain rather good the experimental results. 2. By a partial lateral compression, we could not get good result and confirmed this fact by a finite element analysis. 3. As it was difficult to predict the direction of crack propagation at a knife tip, we were forced to investigate criteria driven from the anisotropic plastic theory.In practical machine, it would not be necessary to change the lateral force angle synchronized with the grain angle, but if it employs partial compression system using caterpillars or other equipments, sufficiently large compression area would be required to reduce the cracks. In this system, there exist rather large plastic deformation around the knife tip, and then it would be indispensable to use very thin knife.