| Press roller, as a typical rolling soil-engaging component, was used to compactagricultural soil. Appropriate compaction of soil could decrease soil porosity, provide bettersoil-seed contact, strengthen the capillary action and increase crop yield. Conventional pressrollers were mainly made of stone, cast iron or low carbon steel. The surface of conventionalpress rollers was smooth with macroscopic scale. Soil has a tendency to adhere to the surfaceof conventional rollers during the process of tillage. Not only resulted in high energyconsumption and low work efficiency, but also consuming soil moisture and affecting thegermination. Besides, soil was pushed to the front of conventional press rollers in thecompaction process, hence an upheaval was formed, i.e., the hilling phenomenon. Not onlyresulted in uncompacted, but also consumed more energy, made the distance between seedsbecame non-uniform and, as a result, crop yield decreased.Reasonable compacting pressure was dependent upon soil moisture content. In thiswork, pressure-sinkage tests were carried out to get soil bulk density and sinkagecorresponding to different pressures for soil moisture content of20%d.b. and28%d.b.. Athree-parameter multiplicative model of soil compaction proposed by Bailey was used todescribe the relationship between stress and bulk density. Using Matlab nonlinear leastsquares method to fit experimental data, the equations of stress and bulk densitycorresponding to the two kinds of soil moisture content were obtained. The requiredoptimum bulk density for corn was introduced into the equation. The results showed that theappropriate pressure was25.25kg~88.48kg and13.95kg~70.26kg by conversion,corresponding with soil moisture content that were20%d.b. and28%d.b. respectively. Andthe sinkage could be used to validate the finite element simulation results.It was found that soil-burrowing animals, such as dung beetle and pangolin, could gothrough soil easily and had very little soil sticking to their bodies. The geometric structure ofthe cuticle surface of these soil-burrowing animals was one of the main reasons why theseanimals exhibited very low adhesion and friction against soil. Nine bionic press rollers with bionically ridged structures were designed learning from the geometric structure of theventral cuticle surface of dung beetle (Copris ochus Motschulsky). Bionically ridgedstructures made of ultra high molecular weight polyethylene (UHMWPE) were modeled byscrew on the substrate of press rollers, and the substrate was made of steel Q235. Orthogonaltests were performed in an indoor soil bin with soil moisture content of20%d.b. and28%d.b.respectively, and soil adhesion, tractive resistance, percent change of seed spacing and soilbulk density were taken as test indexes. The effects of the bottom width of bionically ridgedgeometrically structure, the ratio of section height to bottom width, loads and the area ratioof the projection of bionically ridged structures to the cylindrical roller surface on theoperating performance of bionically ridged geometrically structured press rollers weredetermined. According to the scale structure of the cuticle surface of pangolin (ManisPentadactyla), three bionically polyhedral geometrically structured press rollers weredesigned using steel Q235, which was the same with the conventional press roller. Theoperating performance of the conventional press roller and three bionically polyhedralgeometrically structured press rollers were compared under three kinds of normal loads andtwo kinds of soil moisture content. Bionically ridged geometrically structured press rollerand bionically polyhedral geometrically structured press roller with the best performancewere obtained by optimizing. Steel Q235, UHMWPE and enamel coating were applied to theoptimized bionically ridged geometrically structure and bionically polyhedral geometricallystructure. The effects of material on reducing adhesion and resistance for two kinds ofbionically geometrically structured press rollers were explored.The finite element software ABAQUS was used to model a three-dimensional soilcompaction process. The behavior of the soil-bionically ridged geometrically structuredpress roller and soil-bionically polyhedral geometrically structured press roller interfacewere investigated and compared with a conventional press roller. Simulation results showedthat the artificial strain energy was approximately0.1%of the internal energy, indicating thathourglassing had negligible influence on simulation results. For conventional press roller andtwo kinds of bionically geometrically structured press rollers, simulation results of resistanceand sinkage agreed well with the experimental results. It proved that the finite elementmodel was reliable. The Mises stress nephogram, contact area between soil and press rollerand displacement nephogram in X, Y and Z direction were adopted to compare the simulation results of the three press rollers. The mechanism of reducing adhesion and resistance forbionically geometrically structured press rollers was analyzed.Field tests were run under three kinds of weights and two kinds of velocities. Tractiveresistance, soil bulk density, the trend of bed soil moisture content, percent change of plantspacing and emergence rate were taken as test indexes, and the working quality of fieldoperations of the bionically ridged geometrically structured press roller and the bionicallypolyhedral geometrically structured press roller made of three kinds of materials wasexamined, and compared with the conventional press roller. Meanwhile, the effects ofmaterials of bionically geometrically structure, types of bionically geometrically structuredpress roller, velocities and loads on the operating performance of the bionicallygeometrically structured press rollers were examined. |
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