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

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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.