| In order to solve the problem of the failure of soil-engaging components of the agricultural machinery,caused by the friction damage,and reduce forward resistance this thesis takes the sandfish(Scincus scincus)as the research object.The microstructure of the sandfish scales,surface topography and tribological behavior were analyzed.Reverse engineering reconstruction of the morphology of the sandfish head was conducted.The objectives of this research were: to understand the microstructure characteristics and tribological behavior of the scales of the sandfish,to reveal the wear resistance and friction reduction mechanism of epidermal scales,to provide theoretical and technical basis for design and manufacture of the bionic geometric surfaces,and to provide research basis for bionic wear-resistant and drag reduction materials for engineering applications.The specific research contents of this thesis are as follows:The micro-geometry of the scales of the sandfish was observed by transmission electron microscopy(TEM),scanning electron microscopy(SEM)and atomic force microscopy(AFM),and the size of the geometric structure was quantitatively analyzed.It was found that the scales were consisted by two parts,the epidermis layer and the dermis layer.The epidermis layer was consisted by four layers.From the inside to the outside,were the production layer,the living cell layer,the bio-flexible?-cuticle and the harder ?-cuticle respectively.The scales of the back epidermis were polygonal,bur the scales of the abdomen were hexagonal.The scales were arranged from the head to the tail in a like-tile form.Generally,the scales of the back epidermis was larger than the abdominal.The micro-stab of the scales of the back epidermis had fractal structure,but the micro-stab of the scales of the abdominal epidermis had no such structure.Compare the scales of the back to the abdominal epidermis,the ratio of the spacing was 0.11:1,of the center distance was 0.38:1,of the micro-thorn was 1.4:1,of the density of the micro-stab was 1.07:1,and the angle of the forward inclination was 14.9°.In order to obtain the geometrical characteristic curved surface.The point cloud data of the head was obtained by a three-dimensional scanner.Then the point cloud was extracted and processed by reverse engineering software-Geomagic Wrap and Imageware.And the two-dimensional point cloud curve was fitted to the polynomial equation in MATLAB software.Finally,the surface reconstruction was conducted by CATIA software.The results showed that the fitting curve of the head of the sandfish had high accuracy,which was suitable for the parameter setting of the surface reconstruction.This part of study could provide theoretical basis for the bionic drag reduction,soil-engaging components of the agricultural machinery.The wettability of the surface of the sandfish and its correlation with the friction characteristics were studied by the angle method with a contact angle measuring instrument.The results showed that the scale surface is hydrophilic.The contact angles of the back,abdomen and head scales were 77.58°,64.12°and 52.22°,respectively.The microstructure of the scale surface had certain correlation with the wettability,and the scales with micro-stab scale structure had higher hydrophilicity.Determined by AFM analysis software,the area ratios of the back,abdomen and head epidermis scales of the sandfish were 1.108,1.071 and 1.033.In the microscopic range,the contact angle of the scale surface increases with the density of the micro-stab scale structure,and increases with the height of the micro-thorn peak.The tribological performance of the sandfish scales was studied by reciprocating motion using a multi-function dial-type friction and wear tester.The results showed that the friction coefficients of the back and abdomen epidermis scales decreased with the increase of the friction load and friction frequency.The average friction coefficient of the back-epidermis scale was 0.2,and the average friction coefficient of the abdominal epidermis scale was 0.295.According to the microscopic geometry of the scales of the sandfish,four types of bionic geometric surface structure samples were designed,and a smooth surface structure sample was used as a control for experiment.Samples were prepared by 3D printing technology,and the friction and wear characteristics of each sample surfacewere tested by using a rotary friction and wear tester.The results show that the wear rate of the micro-stab structure which was designed according to the abdominal scale(sample No.1),the micro-stab structure which was designed according to the scale structure(sample No.2),the micro-stab scale which was designed according to the back scale structure and the smooth surface structure were 4.02%,0.84%,3.61%,0.27%,and 6.52%,respectively.Among the tested sample,the wear rate of the micro-stab scale structure was the lowest.It was proved that the micro-stab scale structure of the sandfish,could improve the wear-resisting characteristics of the surface of the sample.The wear rate of the sample No.2 was smaller than that of the sample No.1.It was proved that the wear resistance of the back-epidermis geometry of the sandfish is higher than that of the simulated abdominal epidermis geometry.Based on the analysis results of the rotating friction and wear test,three types of bionic geometric surfaces were prepared by the metal 3D printing technology,the surfaces of the scale,the micro-stab and the micro-stab scale were retrofitted to soil opener.Through indoor soil bin test,the forward resistance reduction characteristics of the bionic geometric surface were further verified and studied.The results showed that in bionic geometric surface openers,the traction resistance of the bionic micro-stab scale surface opener was 30.25 N;the traction resistance of the bionic micro-stab surface opener was 37.23 N;the highest traction resistance was from the bionic scale surface opener,and it was 44.32 N.When the forward speed was 0.4 m/s,the traction resistance is smaller than that of 0.2 m/s and 0.6 m/s.The drag reduction effect reached the maximum at this speed.The results obtained in this thesis indicates that the sandfish had wear-resisting and drag-resisting properties,and the micro-geometry of the sandfish scales played a key role.This conclusion can provide a theoretical basis for the design and manufacture of the bionic agricultural machinery to improve wear-resisting and drag-resisting properties. |
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