Finite element analysis of subsoiler cutting in non-homogeneous sandy loam soil

Abstract A verified finite element model will be a cheap and useful tool in the development procedure of subsoilers and other soil loosening devices, and can be used to investigate and analyse the performance of resulting prototypes. This study was undertaken to emphasis that the finite element method (FEM) is a proper technique to model soil cutting processes in non-homogeneous soils. This method was used to investigate and analyse soil loosening processes. The effect of geometry on subsoiler performance was investigated by the FEM and compared to results of soil bin tests for four subsoiler geometry types; S1 – vertical shank with 31° angle inclined chisel, S2 – vertical shank with 23° angle inclined chisel, S3 – vertical shank with 15° angle inclined chisel and S4 – 75° rake angle shank with 15° angle inclined chisel. The research was done at the Department of Agricultural and Environmental Engineering, PANNON Agricultural University from 1995 to 1997. A three-dimensional FEM model was developed for cutting of non-homogeneous sandy loam soil by a subsoiler having a chisel and shank with different angles and effective cutting widths. The numerical analysis was performed with COSMOS/M 1.71 FEM software (Structural Research and Analysis Corporation, CA). The soil material was considered as elastic-perfectly plastic, and the Drucker–Prager elastic-perfectly plastic material model was adopted with the flow rule of associated plasticity. Soil-tool interaction was simulated adopting Coulomb's law of friction. Total draught force calculated from the FEM model for different subsoiler geometrical types ranged from 12.43 to 15.32 kN. For the S2 subsoiler, that had a vertical shank and an inclined chisel of 23° angle, the chisel and shank contributed to the total draught force by nearly 60 and 40%, respectively. The FEM model consistently over-predicted the measured subsoiler draught force at all chisel angles. The over-prediction of draught estimation ranged from 11 to 16.8% for a non-homogeneous model and from 15 to 18.4% for a homogeneous one. The smallest draught force, measured (11.20 kN) and predicted (12.43 kN), was recorded for the S4 subsoiler having a shank of 75° rake angle and a chisel of 15° angle. The minor principal stress field showed positions of soil tensile failure situated beneath the chisel as well as within the upper soil layers. Zones under distortion (shear failure) were generated directly in front of the shank and along the whole cutting edge of the chisel extending along a hard pan layer. The S4 subsoiler would consume the least amount of energy and perform proper soil loosening. The FEM proved a good tool for modelling of non-homogeneous soils and development and analysis of subsoiler performance and soil loosening processes.