| The research was in the following three main parts: Modelling using Finite Element Method (FEM), biomimetic design and indoor experiment.The application of three-dimensional FEM modeling using Ansys 10.0 software in the biomimetic design of a disc plough was carried out based on the body surface morphology of dung beetles (Dicranocara deschodt and Onthophagus gazelle). The main objective was to find out the effect of different biomimetic designs on reducing soil resistance. Therefore, horizontal force acting on the disc plough during soil deformation was measured. The biomimetic design was based on the cuticle surface of dung beetles which have some convex domes and concave hollows. The main challenge was to design a practical arrangement of the bionic units found on the dung beetle. The general factors considered in designing the arrangement of bionic units are distribution of normal stresses, soil motion tracks and choice of non smooth bionic units. Therefore, all the bionic units used in the plough discs were arranged in concentric circles.For the Finite Element Method (FEM), soil deformation is based on the Drucker - Prager elastic-perfectly plastic model and the model was applied only at the lowest speed. The material non-linearity of soil was dealt with using an incremental technique and inside each step, the Newton-Raphson iteration method was utilized. The model results were analysed and then summation of horizontal forces acting on the soil-disc interface was carried out.The experimental work on soil resistance force measurements was conducted in the indoor soil bin of the Key Laboratory of Terrain-Machine Bionics Engineering (Ministry of Education, China), Jilin University. Material used for modeling convex units was ultra high molecular weight polyethylene (UHMWPE). After designing the experiment, the equipment was fabricated at Changchun Chaoyan Experiment Equipment Company Limited (Changchun chaoyan shiyan yiqi youxian gongsi). The major challenge in the design was stabilizing the plough disc which was solved by using two plough discs acting in complementary directions, more like an offset disc harrow. 10 plough discs used in the experiment were bought from a company in Jiamusi called Jiamusi City Beixin Machinery Manufacturing Company Ltd. Indoor experiment was carried out over the following speeds: 1.2 km/h, 1.8 km/h, 2.2 km/h, 3.5 km/h and 4.1 km/h. The purpose of the experiment was to validate the FEM results and also observe the effects of different bionic designs at higher speeds which could not be incorporated in the Drucker - Prager elastic-perfectly plastic model.The samples were designed as follows: 2 plough discs were just left plain, 4 were drilled to form the concave hollows with depth of 1 mm and 3 mm each at bionic unit density of 10% and 30%, and the last 4 were fixed with concave domes made of UHMPE material with height of 1 mm and 3 mm each at bionic unit density of 10% and 30%. Therefore, the samples had the following parameters: Ordinary sample was just plain, Bionic sample 1 had concave dips of depth 1 mm, base diameter 20 mm and a density of 10 %, Bionic sample 2 had concave dips of depth 1 mm, base diameter 20 mm and a density of 30 %, Bionic sample 3 had concave dips of depth 3 mm, base diameter 20 mm and a density of 10 %, Bionic sample 4 had concave dips of depth 3 mm, base diameter 20 mm and a density of 30 %, Bionic sample 5 had convex domes of height 1 mm, base diameter 20 mm and a density of 10 %, Bionic sample 6 had convex domes of height 1 mm, base diameter 20 mm and a density of 30 %, Bionic sample 7 had convex domes of height 3 mm, base diameter 20 mm and a density of 10 %, Bionic sample 8 had convex domes of height 1 mm, base diameter 20 mm and a density of 30 %The FEM results are in agreement with the indoor experiment results with an acceptable error of less than or equal to 10 %, but there was tendency to underestimate the experimental results. In both cases, the FEM and the indoor experiment showed that Bionic sample 8 was the most effective in reducing soil resistance and the nature of bionic units (whether concave or convex) was also very critical in reducing the resistance. The convex units gave the highest resistance reduction.From the experiment results, bionic samples 1 to 8 showed a decreasing soil resistance in that respective order. Convex bionic units gave the highest resistance reduction reaching a maximum of 19% (from 1715.36 N to 1383.65N) reduction for bionic sample 8 at the highest speed of 4.1 km/h. In contrast, bionic sample 1 gave the least resistance reduction reaching 1591.62N compared to 1715.36 N for the plain disc (only 7.2% reduction). The higher resistance reduction for plough discs with convex domes could be explained by the hydrophobic nature of their UHMPE material. The material has low energy surface hence resulting in generally low adhesion hence low horizontal force was measured. The resistance reduction trend was conspicuous at higher speeds of 2.2 km/h, 3.5 km/h and 4.1 km/h. The effect of non smooth units was not very significant at the lowest speeds of 1.2 km/h and 1.8 km/h. The bionic disc plough had a higher resistance reduction as the forward speed of travel increases. Bionic sample 8 showed the biggest change of resistance reduction from 14% at lowest speed to 19% at the highest speed. Bionic samples with concave units of 1mm depth were most sensitive such that the soil resistance changed most significantly when the density was changed. This was shown in bionic samples 1 and 2 all of 1 mm depth where the soil resistances were 1578.26 N and 1507.02 N (5 % change) respectively. This is in contrast to bionic samples 3 and 4 all of depth 3mm which changed from 1487.00N to 1476.13N (only 1 % change). In addition, an increase in height or depth of the convex domes or concave hollows respectively resulted in reduced resistance. Bionic samples 1 and 3 showed the most significant change of 7% from 1592.62N to 1487.00N whilst bionic samples 5 and 7 showed the least significant change of 3% from 1465.55N to 1420.45 N. The 3 mm height or depth always gave the least soil resistance. Finally, the bionic unit density of 30 % which was highest also gave the highest resistance reduction compared to those with 0% and 10% density.In conclusion, the concept of bionic units can be applied to disc ploughs in order to reduce soil resistance. |
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