Effects of Biomimetic Surface Designs on Furrow Opener Performance

Journal of Bionic Engineering 6 (2009) 280–289

Effects of Biomimetic Surface Designs on Furrow Opener Performance Jin Tong1,2, Ballel. Z. Moayad3, Yun-hai Ma1,2, Ji-yu Sun1,2, Dong-hui Chen1,2, Hong-lei Jia1,2, Lu-quan Ren1,2 1. The Key Laboratory of Engineering Bionics (Ministry of Education, China), Jilin University, Changchun 130025, P. R. China 2. College of Biological and Agricultural Engineering, Jilin University, Changchun 130025, P. R. China 3. Department of Agricultural Engineering, University of Kordofan, Elobied, North Kordofan State, Sudan

Abstract The effects of biomimetic designs of tine furrow opener surface on equivalent pressure and pressure in the direction of motion on opener surface against soil were studied by finite element method (FEM) simulation and the effects of these designs on tool force and power requirements were examined experimentally. Geometrical structures of the cuticle surfaces of dung beetle (Copris ochus Motschulsky) were examined by stereoscopy. The structures of the cuticle surfaces and Ultra High Molecular Weight Polyethylene (UHMWPE) material were modeled on surface of tine furrow opener as biomimetic designs. Seven furrow openers were analyzed in ANSYS program (a FEM simulation software). The biomimetic furrow opener surfaces with UHMWPE structures were found to have lower equivalent pressure and pressure in the direction of motion as compared to the conventional surface and to the biomimetic surfaces with textured steel-35 structures. It was found that the tool force and power were increased with the cutting depth and operating speed and the biomimetic furrow opener with UHMWPE tubular section ridges showed the lowest resistance and power requirement against soil.. Keywords: furrow opener, UHMWPE, biomimetic surface design, tillage resistance, finite element analysis Copyright © 2009, Jilin University. Published by Elsevier Limited and Science Press. All rights reserved. doi: 10.1016/S1672-6529(08)60128-6

1 Introduction 1.1 Interfacial tribological phenomena of soil-tool Adhesion and friction are important tribological phenomena occurring during the operation of soil engaging tools against soil. The adhesion is the ability of two contacting bodies to withstand tensile force after being pressed together[1]. The friction is a phenomenon due to tangential forces transmitted across the mutual sliding contact interface under a normal force. Wismer and Luth[2] found that the horizontal component of tool force was dependent on soil unit weight, cutting depth, cutting width, acceleration due to gravity and tool rake angle. Mckyes[3] found that the soil cutting coefficient was governed by soil cohesion, soil adhesion, angle of internal friction of soil, angle of surface friction and angle of failure plane. These phenomena have severe impact on working quality, energy consumption and operating performance of soil engaging tools. Therefore, it is necessary to look for designing methods to minimize the impacts of the tribological factors on soil engaging tools of agricultural machines. Corresponding author: Jin Tong E-mail: [email protected]

1.2 Biomimetic methods for reducing tribological factors Improvement of shape and surface configuration design of soil engaging tools are two methods for reducing soil adhesion and interfacial friction. Biomimetic method is a technique of how to transfer biological solutions to engineering techniques and has been developed as the application of biological principles and methods to engineering. It was found that the cuticle surfaces of soil-burrowing animals have ability to reduce adhesion and friction against soil[4]. The principles of some soil-burrowing animals in low adhesion and low friction against soil comprise the effects of geometrically structured surfaces, body configurations and hydrophobic characteristics of their cuticle surfaces. The living surroundings of soil-burrowing animals, such as dung beetle, ground beetle and mole cricket are different from the living surroundings of animals on land or in water. Two adaptations to soil occurred in soil animals; the active adaptation and the passive adaptation. An interaction of soil animals with soil happens when they move in the soil. Soil engaging tools designed based on

Tong et al.: Effects of Biomimetic Surface Designs on Furrow Opener Performance

the cuticle features were found to have better properties of low adhesion and low friction against soil, and the biomimetic designs imitating the features of soil animals’ cuticle were found to have remarkable effects on improving implement performance[4]. The geometrically structured surfaces of soil animals associated with the natural activity of these animals. For examples, there exist varied geometrically textured structures on the clypeus, pronotum, elytra, abdomen and legs of all the lamellicornia beetles[5]. Tong et al.[4,6] and Cheng et al.[7] examined the geometrical surface morphologies of earthworm (Lumbricidae), centipede (Chilopoda), dung beetle (Copris ochus Motschulsky), ground beetle (Carabidae), ant (Formicidae), mole cricket (Gryllotalpidae) and others. The cuticle surfaces of many soil animals have a strong inherent hydrophobic nature, indicating that the attraction force between the cuticle surface and water molecules is very small, so, the cuticle surfaces of soil animals have ability to reduce adhesion and friction against soil[4,8]. The inherent hydrophobic ability of the cuticle surfaces of soil animals can be enhanced by their geometrically structured texture. The combination of geometrically structured surface and the hydrophobic nature enhanced the effects in preventing soil from sticking to the cuticle surfaces. Several biomimetic surfaces with low adhesion and low friction functions have been developed based on the characteristics of the cuticle surfaces of soil animals. Ren et al.[9] designed a bulldozing blade with biomimetic surfaces by simulating the structured surfaces with small convex domes on the clypeus and pronotum of dung beetle (Copris ochus Motschulsky). It was found that the biomimetic bulldozing blade has lower adhesion and lower friction as compared with the conventional blade. UHMWPE has extremely low moisture absorption and low coefficient of friction against soil, self lubricating property and high resistance to abrasive wear. Tong et al.[10] found that UHMWPE and polytetraflouropolyethylene (PTFE, teflon) possess lower adhesive force and friction force with soil because of their low surface energy and high hydrophobic property, suggesting that water and soil do not easily stick on it. Qaisrani et al.[11] showed that the forward resistance (measured by load) of biomimetic bulldozing blades with convex domes made from UHMWPE was reduced

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by 27.5 % to 34 % as compared with conventional bulldozing blade. Ren et al.[12] found that the biomimetic bulldozing blades with curved working surface imitating the curved surface configuration of the clypeus of the dung beetle can reduce sliding resistance by up to 32.9 %. Li et al.[13] found that the biomimetic bulldozing blade with convex dome structure surface reduced soil resistance by 18.1 % to 42.2 %. Soni and Salokhe[14] incorporated both shape and size of the convex domes of UHMWPE on the biomimetic surfaces and a dimensionless ratio of Height to Diameter (HDR) was introduced to characterize the effects of the figure of construction units. Experiments were conducted in Bangkok clay soil with dry (19.8 % d.b.), sticky (36.9 % d.b.) and flooded (60.1 % d.b.) conditions respectively. It was shown that protuberances with HDR ” 0.5 lowered sliding resistance by 10 % to 30 % and the normal adhesion was reduced by 10 % to 60 %. Soni and Salokhe[15] found that when UHMWPE protuberances were mounted on moldboard plough as embossed arrays and operated the plough on dry, sticky, wet, and flooded soils at 1 km·hí1, 3 km·hí1, and 5 km·hí1 speeds, the reduction in ploughing resistance for protuberances of HDR = 0.25 was 2 % to 7 % in dry soil, 18 % to 36 % in sticky soil, 17 % to 33 % in wet soil, and 15 % to 28 % in flooded soil, and the reduction in ploughing resistance for protuberances of HDR = 0.5 was 10 % to 16 % in sticky soil, 6 % to 17 % in wet soil, and 12 % to 26 % in flooded soil, while, the ploughing resistance was increased by 7 % to 29 % when HDR > 0.5. Soil tend to adhere on the smooth surface of conventional furrow opener, and this results in high stresses on the surface of opener, therefore, a increase force and power requirements for furrow opener. This study examines the geometrical structures with ridges on the cuticle surface of the dung beetle. The structured surfaces and UHMWPE as a typical hydrophobic material, are modeled on the surfaces of furrow openers. Conventional furrow opener, furrow opener surfaces with steel-35 and with UHMWPE biomimetic structures are simulated in a Finite Element Method (FEM) software. Soil bin tests were conducted for the opener with conventional surface and with biomimetic surface that showed the lowest pressure in the simulation in investigating the effects of biomimetic surface design on the tool force and power requirement to furrow openers.

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2 Materials and methods The surface of tine furrow opener of precision seeding machine was designed by imitating the geometrical structures of cuticle surface of the dung beetle Copris ochus Motschulsky. Then FEM simulation was run in ANSYS to determine the pressure for the tools with different surfaces, and the experimental tests were conducted to determine the force and power requirement of the opener with conventional surface and biomimetic surface. 2.1 Geometrical structured surfaces of dung beetle Dung beetle Copris ochus Motschulsky was collected in the suburb of Changchun city of Jilin Province, China. The specimen was cleaned and the outer ventral surface, longitudinal section of abdomen and clypeus were examined by stereoscopy. 2.2 FEM in soil-tool interaction In crop production there are many operations related to soil-machine interactions, especially tillage operations. Since soil is an extremely complex medium and the operations of agricultural machinery are usually dynamic processes, numerical methods can be applied for effective simulation[16,17]. Two groups of equations are basically required to formulate the virtual work equation: one represents compatibility of displacement and the other force equilibrium. The virtual work equation is given as[17]

³TG

i ui

A

dA  ³ U FiG ui dV V

³ V GH ij

ij

dV ,

K 0H , K1 ,

dH ij

dH ije  dH ijp ,

(3)

where, dH ij is the incremental total strain tensor, dH ije is the incremental elastic strain tensor, and dH ijp is the incremental plastic strain tensor. The yield function of the Drucker-Prager can be expressed by the following equation f ( I1 , J 2 ) D I1  J 2  k

0.

(4)

The steel-35 can be considered as elastic isotropic material, while UHMWPE as Mooney-Rivlin material. For the elastic isotropic, the total strain can be given as

H et

1

ª(H x  H y ) 2  (H y  H z ) 2  (H z  H x )2  2(1  Q ) ¬ 1 3 3 3 (H xy ) 2  (H yz ) 2  (H xz )2 º¼ 2 , 2 2 2

(5)

(1)

V

where, Ti is vector of surface force; įui is virtual displacement increments; A is area, m2; ȡ is soil bulk density; Fi is vector of body force; V is volume, m3; ıij is incremental stress, kPa; and įİij is virtual strain. In finite element analysis soil is considered as non-linear elastic-perfectly plastic material. Elasticperfectly plastic behavior under axial compression tests is shown in Fig. 1, which can be defined by two-stage of stress-strain relationship ­V ® ¯V

value at joint point, that is, the critical strain from the elastic deformation to the perfectly plastic deformation. Soil material can be considered as Drucker-Prager model, as shown in Fig. 2, since agricultural soils as bulk materials undergo plastic deformation after small displacement of tillage tools, the resulting total strain is composed of elastic and plastic strain as follows

0 d H d H0

H0 d H

,

Fig. 1 Elastic-perfectly plastic behavior of soil under uniaxial load. Stage-1 corresponds to elastic performance and stage-2 corresponds to the perfectly plastic deformation.

(2)

where, ı is stress, kPa; İ is compressive uniaxial strain in compression tests; Ko is constants, kPa; K1 is the stress in perfectly plastic deformation stage, kPa; İ0 is strain

Fig. 2 Tangential modulus at every load step. ı1 and ı3 are the major and minor principal stress in soil respectively, kPa, in compression test; İ is the compression tri-axial strain in compression test; Eti (i = 1, 2, 3) is tangential modulus with stress dependency.

Tong et al.: Effects of Biomimetic Surface Designs on Furrow Opener Performance

where, H et is the total strain; H x is the strain in x direction; H y is the strain in y direction; H z is the strain in z direction; H xy , H yz , H xz are the strains in xy, yz and xz planes respectively. While, in the Mooney-Rivlin model the strain energy potential can be expressed as W





C10 ( I1  3)  C01 ( I 2  3) 

1 ( J  1)3 , d

(6)

where, W is the strain energy potential, C10 and C01 are material constants characterizing the deviatoric deformation of the material, I1 is the first deviatoric strain invariant, I 2 is the second deviatoric strain invariant, d is the material incompressibility parameter, J is the determinant coefficient related to the elastic deformation gradient. 2.3 Finite element formulation The simplified incremental form of the equation for the basic FEM is expressed as[18,19] [ K ]{dU } {dR} ,

(7)

where, [K] is total stiffness matrix; ^dU ` [dU1 ,dU 2 , ......., dU n ]T is a vector of the total displacement increments; {dR} [dR1 , dR2 ,......., dRn ]T is the vector of the total load increments; and T indicated the vector transpose. The incremental strain {dİ} for the element can evaluated from the kinematic conditions and it can be expressed at element level as follow {dİ} = [B]{dU} ,

(9)

The stress increment {dı} can be obtained by using the elastic-plastic material matrix [Dep]. {dı} = [Dep]{dİ} ,

measured as listed in Table 1. Soil texture was determined using the mechanical test apparatus, soil moisture content was measured on dry base, and tri-axial test apparatus was used to determine soil cohesion and internal angle of friction, soil adhesion forces with steel-35 and with UHMWPE were measured using soil adhesion measurement apparatus, as shown in Fig. 3. Table 1 Mechanical parameters in simulation and tests Parameters

Values

Clay Silt

62 % wt 20 % wt

Sand

18 % wt

Soil cohesion

10 kPa

Soil-steel adhesion

1.47 kPa

Soil-UHMWPE adhesion

0.32 kPa

Soil modulus of elasticity

6750 kPa

Moisture content of soil

12.25 % d.b.

Bulk density of soil

1650 kg·mí3

Soil-steel friction angles

23Û

Soil-UHMWPE friction angles

17Û

Soil internal angle of friction

34Û

Poisson’s ratio

0.35

Coefficient of soil-steel friction

0.42

Coefficient of soil-UHMWP friction

0.31

(8)

where, [B] = [L][N] is the transformation matrix, [L] is the differential operator matrix, and [N] is the element shape function matrix. At the structure level the vector of the total displacement increments can be expressed as follow {dU} = [K]í1{dR} .

283

(10)

2.4 Soil properties and furrow opener surface designs for finite element analysis Soil tests were carried out to determine soil parameters required as inputs for simulation in ANSYS 7.1 (ANSYS, Inc., USA). Soil samples were taken from soil bin of scales 40 m × 2.8 m × 1.8 m, and their physical properties were

Fig. 3 Soil adhesion measurement apparatus.

Geometrically structured surfaces imitating the geometrical structures on the cuticle surfaces of dung beetle were modeled on the surface of a tine furrow opener with inter space of 30 mm. The prototype of the furrow opener for simulation has two triangular surfaces, which were made by Gongzhuling Agricultural Machine Ltd, China, as shown in Fig. 4. Surface designs of the furrow opener model were analyzed in ANSYS. The analysis included equivalent pressure (Von Mises stress which is the value of pressure in a single uniaxial state, equals to yield strength), and force in X (vertical), Y (lateral), and Z (horizontal, direction of motion). Comparisons between different designs were run with respect to equivalent pressure and pressure in X, Y, and Z directions.

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Furrow opener shank 120Û

mm 120

200

Right surface of furrow opener

mm

150 mm Left surface of furrow opener

Fig. 4 Schematic diagram of a furrow opener used for simulations and tests.

2.5 Soil material model for mesh generation Solid with 8 nodes, 185 element type and DruckerPrager material model with inputs in Table 1 were used for soil meshing. 2.6 Steel-35 and UHMWPE material model for mesh generation Solid with 10 nodes, 45 element type and elastic isotropic material model were used for conventional steel-35 surface and biomimetic geometrically structured steel-35 surfaces. Mooney-Rivlin 3D, 8 node, 86 element type, non-linear elastic, hyper-elastic, MooneyRivlin material model were used for the biomimetic geometrically structured UHMWPE surfaces.

2.8 Material and geometrical non-linearity solution The reaction between the tools and soil is non-linear process. The contact unit was established. The ANSYS software is programmed for predicting the contact and separation between the tool and soil automatically. The analysis was conducted by adopting the surface-surface contacting (Target 170 for opener, and Contact 174 for soil). The solution criterion was selected as large static displacement. Calculation control and result processing were accomplished within Postprocessor 1. Equivalent pressure and pressure in X, Y, and Z directions were concerned. 2.9 Soil bin tests The biomimetic furrow opener with the lowest pressure against soil determined in ANSYS simulation and the conventional furrow opener were tested in soil bin. The experiments to measure tool force was conducted in the indoor soil bin by using an electric carriage moving on rail tracks on both sides of soil bin as a source of power (Fig. 6). Soil was loosened using rotary tines. Scraper blade and roller were used for soil leveling and compaction, respectively. A force sensor was set up between the furrow opener shank and the front bar of the carriage, as shown in Fig. 7.

2.7 Boundary conditions Soil model was constrained at 5 faces while the upper face left unconstrained. Nodes displacements UXi = 0, UYi = 0 and UZi = 20 in X, Y, and Z directions, respectively.

­UX i 0 ° ®UYi 0 °UZ 20 mm ¯ i

(11)

FEM and boundary conditions for soil and opener model were shown in Fig. 5. Fig. 6 Electric carriage used for soil resistance tests in operation.

Fig. 5 Finite element mesh and boundary conditions.

Fig. 7 Furrow opener and force sensor. Left is the conventional furrow opener. Right is biomimetic furrow opener.

Tong et al.: Effects of Biomimetic Surface Designs on Furrow Opener Performance

The sensor was connected to a instrumentation system, as sketched in Fig. 8. Each opener was operated at depths of 100 mm and 135 mm and at speeds of 0.28 m·sí1 and 0.92 m·sí1 respectively. Each experiment was repeated three times and the average value of the three runs was taken as the resultant one. The regression equation of conversion between the load force and the sensor voltage output was as follows R = 2.066V í 0.0032,

(a)

285

(b)

(12)

where, R was load (tool force), kN; and V was sensor voltage output, in volt. Power requirement per meter of soil bin working length (30 m) was calculated as follow RuS (13) / 30 , C where, P is the power requirement; kW·mí1; S is the speed, m·sí1; C is the conversion factor.

(c)

(d)

P

Fig. 9 Geometrical structured surface of dung beetle Copris ochus Motschulsky. (a) Stereoscopy photograph of the clypeus[8]; (b) SEM photograph of the cuticle surface of the clypeus showing the details of convex domes[8]; (c) Stereoscopy photograph of the ridges on longitudinal section of the ventral surface; (d) Stereoscopy photograph of the ridges on the ventral surface. 2

Fig. 8 Schematic diagram of the instrumentation system.

3 Results and discussion (a) Dimensions of convex domes 2

20

20, 35, 50, 65 (b) Dimensions of cylindrical ridges

20

The geometrically structured surfaces of the dung beetle are shown in Fig. 9. It can be found that the surfaces have convex domes, cylindrical section ridges and tubular section ridges. In the simulation, the geometrical structures on the cuticle surfaces were modeled on the surface of a tine furrow opener. The dimensions of convex domes, cylindrical section ridges and tubular section ridges were designed as shown in Fig. 10, and the dimensions of these structures were referred to the results of Ref. [11]. The conventional smooth furrow opener and biomimetic designs of furrow opener surface are shown in Fig. 11. Results of simulation for conventional furrow opener and biomimetic furrow opener were listed in Table 2. The soil bin test results of the tool force and power requirement for conventional and UHMWPE tubular section ridge surface furrow opener were shown in Table 3.

(c) Dimensions of tubular ridges

Fig. 10 Dimensions of geometrical structures used for biomimetic furrow opener (mm).

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X

(a) Conventional smooth surface

(b) Biomimetic surface with convex domes

(c) Biomimetic surface with cylindrical section ridges

(d) Biomimetically structured surface with tubular section ridges

Fig. 11 Biomimetic designs of furrow opener surface. Table 2 Finite element analysis results of stress for conventional furrow opener and opener surface with biomimetic structures Surfaces Conventional surface 35#-Steel domes

Stress in three directions (1×108 Pa)

Von Mises stress 1×108 Pa

X-direction

Y-direction

Z-direction

1.360 1.200

0.263 0.303

0.468 0.687

0.380 0.478

35#Steel cylindrical section ridges

1.180

0.216

0.361

0.274

35#Steel tubular section ridges

1.170

0.258

0.428

0.234

UHMWPE domes

1.160

0.311

0.199

0.203

UHMWPE cylindrical section ridges

0.976

0.630

0.286

0.181

UHMWPE tubular section ridges

0.968

0.220

0.415

0.166

Table 3 Test results of the forward resistance and power consumption for conventional and UHMWPE tubular section ridge surface furrow opener. Opener surface design Conventional design Biomimetiec design

100 mm working depth Speed 0.28 m·sí1 Speed 0.92 m·sí1

135 mm working depth Speed 0.28 m·sí1 Speed 0.92 m·sí1

R (kN)

P (kW·mí1)

R (kN)

P (kW·mí1)

R (kN)

P (kW·mí1)

R (kN)

P (kW·mí1)

0.72r0.03 0.62r0.02

0.20 0.16

1.11r0.01 0.80r0.04

1.00 0.72

0.93r0.01 0.76r0.03

0.25 0.21

1.50r0.02 0.95r0.04

1.35 0.85

R denotes the resistance and each value of resistance is its mean value plus the standard error; P denotes the average of power requirement for the operating for unit length

3.1 Effects of geometrical structures on pressure Simulation results show that the furrow openers with steel-35 domes, steel-35 cylindrical section ridges and steel-35 tubular section ridges reduce the equivalent

pressure by 11.8 %, 13.2 % and 14.0 % respectively, as compared with conventional furrow opener. In a similar way, the opener surfaces with UHMWPE domes, UHMWPE cylindrical section ridges and UHMWPE

Tong et al.: Effects of Biomimetic Surface Designs on Furrow Opener Performance

tubular section ridges reduce the equivalent pressure by 14.7 %, 28.2 % and 28.8 % respectively. Comparing the opener surfaces with steel-35 biomimetic structures, the opener with convex domes recorded the highest equivalent pressure, while the opener with tubular section ridges recorded the lowest equivalent pressure. In case of the biomimetic structures which were made of UHMWPE, the highest equivalent pressure was recorded by the opener with UHMWPE domes, while the lowest equivalent pressure was recorded by the opener with tubular section ridges. The biomimetic surfaces with UHMWPE biomimetic structures showed the lower equivalent pressure than that with steel-35 structures. The biomimetic opener with UHMWPE tubular section ridges recorded the least equivalent pressure as compared to the others. The results shown that the biomimetic furrow opener with steel-35 cylindrical section ridges and with steel-35 tubular section ridges reduced pressure in the direction of motion (Z direction) by 28.0 % and 38.4 % as compared with conventional furrow opener. The biomimetic furrow openers with UHMWPE domes, UHMWPE cylindrical section ridges and UHMWPE tubular section ridges showed 46.6 %, 52.4 % and 56.3 % reduction in pressure in the direction of motion respectively as compared with conventional opener. To the biomimetic surfaces with steel-35 structures, the opener with domes recorded the highest stress in the motion direction, while the opener with tubular section ridges recorded the lowest pressure. To the UHMWPE structures, the highest pressure in the direction of motion was recorded by the furrow opener with domes, while the lowest pressure was recorded by the opener with tubular section ridges. The biomimetic surfaces with UHMWPE structures showed the lower pressure in motion direction than the surfaces with steel-35 structures. It was demonstrated that the biomimetic opener with UHMWPE tubular section ridges recorded the least pressure in motion direction as compared to the others. UHMWPE material has low surface energy and strong hydrophobic property[10]. There will be no affinity for water film to be created at the soil-material interface, thus soil adhesion on UHMWPE was reduced, and the pressure in the direction of motion was decreased. It was found that the negative air pressure existing within the closed structural units plays an important role in soil adhesion[20]. The reason of the reduction of soil

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adhesion on furrow opener surfaces with biomimetic structure is that the contacting area of soil-opener interface was decreased and vent openings on interface connecting it to surrounding environment reduced the opportunity of the negative air pressure formation. Accordingly the equivalent pressure and pressure in direction of motion on the soil-opener interfaces were decreased. Biomimetic structures on opener surfaces may reduce the contact area of soil-tool interfaces, hence, resulting in lower soil adhesion, and consequently, lower pressure. 3.2 Effects of geometrical structures on force and power for furrow opener At 100 mm depth and 0.28 m·sí1 speed, the biomimetic furrow opener with UHMWPE tubular section ridges showed 14 % and 20 % reduction in force and power respectively as compared with the conventional furrow opener, while at 0.92 m·sí1 speed, the biomimetic furrow opener with UHMWPE tubular section ridges showed 28 % reduction in force and power (Table 3). At 135 mm depth and 0.28 m·sí1 speed, the biomimetic furrow opener with UHMWPE tubular section ridges showed 18.3 % and 16 % reduction in force and power respectively, while at 0.92 m·sí1 speed, the biomimetic opener with UHMWPE tubular section ridges showed 36.7 % and 37 % reduction in force and power respectively (Table 3). The reduction in force and power showed by the biomimetic opener with UHMWPE tubular section ridges was due to lower pressure on this design as compared to conventional one. These results were found to be coincide with Qaisrani et al. [11]. and Li, et al.[13] findings in the varying trend in general. It can be deduced that the force of each opener increases with the speed within the test range from 0.28 m·sí1 to 0.92 m·sí1. The increase in speed might result in more rapid acceleration of soil mass which can increase the normal load on the soil-tool surface due to the frictional force and kinetic energy transmitted to the soil. It was also shown that the force increases with the working depth, which tends to increase the soil compaction and soil bulk density. Consequently, the soil shear strength, the soil cohesion, and the soil penetration resistance will increase. To over-consolidated soils, the force and power may even increase with depth. The main reason is probably that with the increase in work-

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ing depth, the created furrow will be deeper and thus more soil will be displaced, lead to the increase in the force. Therefore, the force for each furrow opener increases with the depth from 100 mm to 135 mm. Since power is dependent upon the force and speed of the tool, thus power requirement for each furrow opener will increase with the depth and speed. It can be deduced that the reduction of pressure, tool force and power requirement indicate the reduction of soil adhesion and friction resulted by biomimetic structures on the furrow opener surface.

4 Conclusions Geometrical structures (domes, cylindrical section ridges and tubular section ridges) on cuticle surface of dung beetle Copris ochus Motschulsky were imitated and modeled on furrow opener surface. UHMWPE as hydrophobic material was used to cover the surfaces of the furrow opener during the FEM simulation and soil bin test. ANSYS software was used to do the simulation and estimation of equivalent pressure and pressure in directions X, Y, Z for different biomimetic surface designs of furrow opener. The experimental results showed that furrow opener with biomimetic UHMWPE tubular section ridges recorded the lowest pressure. Experimental values of the tool force and the power for furrow opener with UHMWPE tubular section ridges were lower than those for conventional furrow opener at all combinations of depths and speeds. The tool force and the power increase with the working depth and operation speed.

Acknowledgement This project was supported by the National Natural Science Foundation of China (Grant no. 50675087 and Grant no. 50635030), the National Hi-tech Project (863 Project) (Grant no. SQ2008AA04ZX1478650), the Key Project of Science and Technology Research of Ministry of Education of China (Grant no. 106061), the National Key Technologies R&D Program (Grant no. 2006BAD11A08), the National Science Fund for Distinguished Young Scholars of China (Grant no. 50025516), and the “985 Project” of Jilin University.

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