Research On Basic Theory Of Bionic Uprooted Mechanism Of Cassava Root Baesd On Clay

Researches on the design theory and methods of cassava harvester are not too much. The research on cassava root harvesting machinery in China is still in its infancy. Harvesting in the growth situation of cassava in China specifically in the clay by machine have not been reported in literatures. The mechanism of cassava root mechanical harvesting and the influencing factors of harvesting are complex. Therefore, with representative cassava variety and clay in China as the main research object, by the advanced research methods and techniques, the model of uprooting of cassava root and the control model of mechanical uprooted speed are established. The uprooted mechanism of cassava root and the laws and mechanism of cassava root loss are studied. The design principle and system parameters optimization method of cassava root harvester are discovered. The design theory of cassava root harvester is formed. It becomes a challenging and importance subject in the forefront. The authors are grateful for the financial supported by the National Natural Science Foundation of China "The basic theory and design method of cassava root harvesting machinery in hilly region"(Grant No.51065003). Aiming at the basic theory of bionic uprooted mechanism design of cassava root based on clay and calculation difficulty in the soil deformation and rupture phenomenon, the mechanism of soil shearing and uprooting of root are discovered,and that the mechanical and mathematical model of uprooted force on cassava root and the optimum model of uprooted speed are established. The design foundation is provided for bionic uprooted mechanism. The main conclusions are as follows:(1)Mechanical properties of cassava’s root and stem (South China205) are tested experimentally, such as axial tensile strength, axial and radial compression strength, axial and radial shear strength, axial and radial elastic modulus.(2)Based on the methods including Smoothed Particle Hydrodynamics(SPH)and FEM coupling algorithm, modified Mohr-Coulomb yield criterion, the coupling calculation model of uprooting of cassava root is established. The interaction mechanisms between uprooted cassava root and soil are discovered. The processes of soil shearing and the changing processes of root’s stress are analyzed. The studies show that:the effects of soil being extruded by the root expand gradually from inside to outside in the process of uprooting, and the uprooted force reaches the maximum value when the soil appears ring shear rupture; after the uprooted force reaches the maximum value, the root’s effective stress still increases gradually with the increasing of its bending deformation until the soil is separated, so the uprooted speed should be small after the soil appears the shear rupture surface, otherwise the root is very easy to be broken; when the maximum uprooted force on cassava root is analyzed, the interaction of a disc and its extension on the soil is regarded as the mechanical model of maximum uprooted force on cassava root.(3)Based on the methods including Smoothed Particle Hydrodynamics(SPH)and FEM, modified Mohr-Coulomb yield criterion, the numerical calculation model of direct shear test is established. The numerical simulation experiments of direct shear on four kinds of soil are carried out. The mathematic models of soil shear strength and shearing speed are established by regression analysis. The process of soil shear failure and the influence law and mechanism of shearing speed on shear strength are discovered. The studies show that:the main reason for soil fracture are that in the process of shearing, the extrusion deformation appears on the soil, and that the links among the soil particles are directly stretched fracture, and that extrusion and friction among the soil particles; with shearing speed increasing, the number of the soil particles which are stretched fracture in a moment increases so that shear strength increases; third-order relationship exits between shear strength and shearing speed with small shear modulus, and logarithm relationship exits between shear strength and shearing speed with large shear modulus; the effect of shear modulus on shear strength is large, and with large shear modulus, the soil is difficult to be deformed, because the links among the soil particles are directly stretched fracture and the number of the soil particles which is stretched fracture in a moment increases resulting in the large shear strength. (4)The mechanical model of uprooted force and mathematical model of multifactor coupling maximum uprooted force on cassava root are established by the soil dynamics theory and the friction theory of roots, and then the models are verified. The mathematical model of maximum uprooted force on cassava root has higher precision in uprooted force of cassava root, which distribution and growth both are like disc-shaped. The influence laws of factors on maximum uprooted force on cassava root are analyzed.(5)According to the principle of bionics, the acceleration curves of cassava root uprooted by the farmers with rich harvesting experience are tested. The changing laws of the curves are studied by statistical analysis and nonlinear fitting method. The optimized uprooted speed model manually is selected by the laws. The basis of the mechanical optimized uprooted speed model is established.