Impact cutting behaviour of forage crops I. Mathematical models and laboratory tests

Abstract Theoretical and experimental investigations of the impact cutting process were conducted under conditions chosen to simulate rotary mowing in the field. Laboratory tests revealed that energy consumption in cutting groups of grass and oat straw stems decreased by approximately 25% as blade velocity increased from 20 to 60 m/s. The extent of the decrease was less than that predicted by theory probably due to stem acceleration and blade-stem friction during and after cutting. These factors were also responsible for greatly increasing the impact cutting energy as compared to the static shear energy which in all cases accounted for less than 5% of total energy consumption. The minimum cutting velocity for both grass and oat straw was approximately 20 m/s which confirmed theoretical predictions arising from models of the forage stem as a beam or as a particle. The minimum cutting velocity was independent of blade type whereas slight reductions in energy consumption were observed when the blade knife angle was reduced from 90° to 45° and when the blade bevel was increased from 45° to 60°. A comparison of impact with quasi-static and counter edge (cutting against a fixed blade) data suggested that future studies should express cutting energies on a per unit dry cross-sectional area basis so that the influence of internal pore space, moisture content and stem diameter may be diminished.