Mechanics of soil-blade interaction
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The main objective of this research work is to develop a simulation procedure for modeling the soil-tool interaction for a blade of arbitrary shape. The primary motivation for this study is developing agricultural robots with limited power and pulling force to help farmers in crop production. In this thesis, a finite element (FE) investigation of soil-blade interaction is presented. The soil is considered as an elastic-plastic material with the non-associated Drucker-Prager constitutive law. A separation procedure to model the cutting of soil and a method of calculating the forces acting on the blade are proposed and discussed in detail. The procedure uses a separation criterion that becomes active at consecutive nodes on the predefined separation surfaces. In order to mimic soil-blade sliding and soil-soil cutting phenomena contact elements with different properties are applied. To verify correctness of the FE model developed and the procedures used, the FE results are first compared with analytical results available for straight rectangular blades from classical soil mechanics theories; and then the FE results are compared with the experimental ones. Also the effects of blade width, depth and rake angle on blade’s draft force were studied by simulating soil-blade interaction with different blade’s dimensions. After the analytical and experimental validation of the results for straight rectangular blade, the rectangular curved shape blade was modeled in order to investigate the effects of changing the blade’s radius of curvature on the blade’s draft force. The soil interaction with straight triangular blade in different rake angles was simulated next. Since the analytical solutions are limited to rectangular blades, calculated draft forces for triangular blade were verified only experimentally. The triangular and rectangular blades with the same width and depth of interaction were also investigated. The results showed that triangular blade draft force is around half of the amount of force acting on the rectangular blade with the same rake angle. Also the effect of triangular blade’s sharpness and changing the blade’s radius of curvature on draft force was discussed. By changing the blade’s sharpness, the draft forces of triangular blade were calculated in two conditions of constant blade’s width and constant blade’s contact length. The approach presented in this thesis can be used to investigate the soil-tool interactions for real and more complex blade geometries and soil conditions, and ultimately for improving design of blades to be used in tillage operations.
DegreeDoctor of Philosophy (Ph.D.)
SupervisorFotouhi, Reza; Szyszkowski, Walerian
CommitteeSzpunar, Jerzy A.; Johnston, James; Boulfiza, Mohamed
Copyright DateAugust 2014
finite element analysis, soil-blade contact modeling, blade force