Laboratory studies of the effect of blade parameters and stem configuration on the dynamics of cutting grass

Abstract

Laboratory experiments were conducted to study the cutting of grass stems with single blades over a range of cutting speeds from 15 to 35 m/s. The blade rake angle was varied from 0 to 45°, using both sharp and blunt cutting edges, and blade thicknesses of 1 to 3 mm were used in a blunt condition. The effect of stem inclination away from the blade was studied over a range of 0 to 60° and the effect of cutting arrays of stems was examined. The blade force and energy during cutting were measured using a piezoelectric transducer. The stem deflection modes were recorded photographically by the use of a camera with an open shutter and the sequential firing of a series of flash guns using electronic control. Blade rake angle was found to have no significant effect on specific cutting force or energy when cutting above the critical speed. At lower speeds, however, increasing the blade angle resulted in an increasing number of uncut stems. The thickness of blunt blades had no significant effect on critical cutting speed or specific cutting force and energy. The bluntest blade (0–15 mm edge radius) required three times the specific cutting energy and twice the specific peak force as a sharp blade (0–325 mm edge radius). The principal effect of the angle of stem inclination was an increase in critical speed from 25 to 60 m/s, as the angle of inclination increased from 0 to 60°. When cutting groups of stems, the critical speed was not dependent on the configuration and number of stems in the group; the specific cutting energy was independent of the group configuration and equal to that when cutting single stems.