| A large amount of energy is consumed during tillage operations. The high draft on tillage tools also results in frictional and wear losses. Because of the high cost of energy and significant losses due to friction and wear, it is essential to develop tillage or soil cutting tools which require less energy and provide a satisfactory soil environment for seed emergence and crop growth.; Up to present time, almost all tillage tools were developed by experimental and trail and error methods. In recent years, a number of research projects have been carried out to find a theoretical means of developing an optimum design for tillage tools. Several analytical models were developed for predicting soil forces during tillage operations, based on Terzaghi's passive earth pressure theory. Since the geometry of three dimensional soil failure under a tillage tool is very complicated, these analytical models can not account for the effect of different shapes of a tillage blade.; In this research project, a non-linear 3-D finite element model was developed to simulate the soil failure process during tillage operations. The weighted residual method was applied to develop the finite element model. The Duncan-Chang hyperbolic stress-strain model of soil was used in the analysis. Triaxial tests were carried out to determine the parameters used for the hyperbolic stress-strain model. An interface element was developed to simulate the interaction between the soil and the tool surface. The parameters for the interface element were determined from shear tests.; A FORTRAN program was written to conduct the finite element analysis. The program consists of three main parts: (1) data generation, (2) analysis routine, and (3) post-processing routine. The analysis was conducted for two different blade shapes (flat and trianglular) under various rake angles. The reaction force, soil failure pattern, displacement field, and normal stress distribution were obtained from the finite element model. Laboratory tillage tests were carried out in a soil bin. The soil forces obtained from the finite element analysis were compared with results from the soil bin. The results show that the finite element analysis predicted a nearly correct draft force and reasonable vertical forces for the inclined blades. |
