Tillage tool design by the finite element method:: Part 2.: Experimental validation of the finite element results with soil bin test

Laboratory soil bin tests of subsoiler cutting in a sandy loam soil were carried out in order to validate the results obtained from the finite element calculations reported in Part 1 of this study. Measured results of subsoiler draught force and soil failure dimension taken on the surface were presented for four combinations of the subsoiler shank rake angle and chisel angle. Soil bin tests also measured the variation of draught force with subsoiler displacement. It was observed that the angle of both the subsoiler parts affected the dimensions of the surface soil failure and the magnitude of subsoiler draught force. Finite element method predictions of the subsoiler draught force as well as the extent of surface soil failure agreed well with measurements made in the soil bin. The predicted draught force for all subsoiler types exceeded the measured ones. The overprediction error ranged from 11.76 to 20.04%. The finite element model provided a good approximation to the maximum upward soil movement for the experiments. Better finite element method predictions of the front soil failure was obtained for the two subsoiler designs with a small chisel angle of 15 degrees than for the designs with chisel angles of 23 and 31 degrees. Among the four investigated subsoiler types the best subsoiler design was devised, which required the lowest draught and developed good soil loosening qualities as estimated by soil volume change. This subsoiler had a shank of 75 degrees rake angle and an inclined chisel of 15 degrees angle. Keeping a good soil loosening performance was attributed to the smaller shank rake angle of 75 degrees, which indicated that the shank played an important role for the determination of the quality of soil loosening. (C) 1999 Silsoe Research Institute.