Study On Tillage Mechanics Of Typical Soil And Subsoiling Performance In Chongqing

Chongqing is located in the eastern part of Sichuan Basin,its terrain mainly being hilly and mountainous,and mini-tillers are often used in the region.Long-term shallow plowing caused problems of plow pan thickening and soil hardening,which seriously affects crop root development,soil water storage and moisture conservation capacity,and limits the development of agricultural production level.As one of the four technologies of agricultural conservation tillage,subsoiling technology can break the hard plow pan,and improve soil perviousness and efficiency of water use,and thereby it can improve crop growth environment and yield.The subsoiler is the key part to achieve subsoiling.The energy consumption of a subsoiler in the field mainly comes from the work by the subsoiler to overcome the soil resistance.The structure size of the subsoiler has an important effect on the tillage resistance of the subsoiling.Reasonable structural parameters can effectively reduce tillage resistance and energy consumption,decrease the wear of the subsoiler in the course of tillage,and increase its service life.Therefore,in order to improve the performance of drag reduction and wear resistance of a subsoiler,and achieve a better effect of tillage,it is necessary to study the movement process and tillage resistance of a subsoiler.In this paper,a new kind of bionic drag reducing subsoiler was used as the research object,based on the study of soil properties in Chongqing,numerical simulation analysis of the process of subsoiler tillage was conducted by Smoothed Particle Hydrodynamics(SPH).The key structural parameters of subsoiler were optimized by virtual orthogonal experiment,so as to design a subsoiler,with high effective drag reduction,suitable for subsoiling in Chongqing.The study can provide the theoretical basis for the subsequent design and research of the subsoiler.The main contents and conclusions of the study are as follows:(1)Three typical soils in Chongqing were sampled by orthogonal experiment.The relationship between parameters of density,moisture content,shear strength index and factors of soil types,sampling points,sampling depth were studied.Error analysis and verification were conducted as well.The results show that the basic physical and mechanical properties of topsoil are mainly dependent on soil types,and soil sampling points and sampling depth has less impact on these parameters.The parameters of soil can also be obtained by mathematical methods of several groups of parallel test results.(2)The 3D solid modeling of the subsoiler was constructed by using 3D modeling software Creo 3.0.Based on the SPH method,the LS-DYNA module in ANSYS was used to simulate the soil cutting dynamics of a subsoiler.Comparison of results from simulation with existing experimental results was done,with the relative error 3.3%,which proves that the prediction of tillage resistance by soil cutting dynamic simulation is feasible.(3)The soil properties of purple soil in Chongqing were used as the material parameters of SPH particle model to simulate the soil cutting dynamics of a subsoiler.The results show that the tillage resistance curve of a subsoiler is largely the same as previous study,which shows that the simulation results are correct,and then the correctness of parameters measured of the soil is verified.Thus the parameters of the measured soil can be used to simulate the soil cutting dynamics of a subsoiler.(4)Using virtual orthogonal experiment method,depth ratio(L/D),angle of cutting edge and penetration angle(?)were selected as control factors.By means of soil cutting dynamics simulation of a subsoiler,tillage resistance as the evaluation index,the influence of the factors on the tillage resistance of a subsoiler was analyzed.The results show that the significance order of the control factors is A>B>C.Then the optimal structure combination of factor levels is A1 B1 C3: depth ratio 0.7,angle of cutting edge 55°,and penetration angle 27°,and in such case the subsoiler can obtain the minimum tillage resistance.(5)The soil cutting dynamic simulation under the same conditions was carried out for the original and optimized subsoilers,and the changes of the tillage resistance were compared.By adopting Workbench module in ANSYS,the finite element static analysis was carried out for the optimized subsoiler,and the deformation,stress and elastic strain of the subsoiler under static condition were obtained.The results showed that the tillage resistance of the optimized subsoiler decreased 25.7%.Then,the effect of optimization is obvious.The maximum equivalent stress under the static conditions of optimized subsoiler is 161.11 MPa,much less than the allowable stress of the material 1041 MPa,which means that the optimized subsoiler can meet the requirements of strength and stiffness in the tillage process.