Analysis of Wood-cutting Mechanism by Impact Fracture Theory

冲击断裂理论分析木材切削机理

• 批准号: 04454087
• 负责人: OHTA Masamitsu
• 金额: $ 4.67万
• 依托单位: The University of Tokyo
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (B)
• 财政年份: 1992
• 资助国家: 日本
• 起止时间: 1992 至 1993
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-04454087/
• 关键词: wood cutting; high-speed cutting; high-speed video camera; fracture type; apparent stiffness; impact fracture; crack; stress wave; 低速切削

The traditional static elastic-plastic theory seemed to be inadequate for the analysis of the cutting process of wood by the rotating knife like a circular saw. In this research, we aimed to clarify the difference of cutting mechanism of wood between in the slow- and high- speed cutting.For this purpose, testing machine was prepared which enables the cutting in the velocity range from 5 to 70 m/sec using a special made tip-saw. It was found by scanning microscope that the obtained cut surfaces were very rough, accompanied the deformation of the cell walls and the splits along the fiber in the slow-speed cutting, whereas those were rather smooth with less deformation of the cell walls in the high-speed cutting.The cutting process was investigated by high-speed video camera. For this purpose, cantilever shaped test specimens were employed. In high-speed cutting, the cantilever part of the test specimen was clearly cut, but in slow-speed cutting, the propagation of splits was observed. This cutting type difference was suspected to have concern with the change of the apparent stiffness of the test specimens. Therefor, cutting test of test specimens with different stiffness was done under a constant cutting speed. In this case, the result changed as follows with the increase of the specimens hight : escape of the specimen form the knife, then the break down at the support, and finally the amputation by the knife.Through the above mentioned experiments, we concluded that the difference of the cutting type under the various cutting speed depends on the apparent stiffness of the specimen, and numerically analyzed the cutting process by a simple spring-mass model. The result of the simulation affirmed our supposition qualitatively.

传统的静力弹塑性理论在分析圆锯片等旋转刀具对木材的切削过程时显得力不从心。为了弄清木材在低速和高速切削时切削机理的差异，研制了一台能在5 ~ 70 m/s速度范围内进行切削的试验机。通过扫描电镜观察发现，低速切割时，纤维表面粗糙，胞壁变形，沿纤维方向出现沿着的裂缝;高速切割时，纤维表面光滑，胞壁变形较小。为此，采用悬臂形状的试样。在高速切削中，试样的悬臂部分被清楚地切削，但在低速切削中，观察到裂纹的扩展。怀疑这种切割类型差异与试样表观刚度的变化有关。为此，在恒定的切削速度下，对不同刚度的试件进行了切削试验。在这种情况下，随着试样高度的增加，结果变化如下：通过上述实验，我们得出不同切割速度下切割类型的差异取决于试件的表观刚度，采用简单的弹簧-质量模型对切削过程进行了数值分析。仿真结果定性地证实了我们的假设。