Analysis of Wood-cutting Mechanism by Impact Fracture Theory

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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.