Three Dimensional Modelling and Stress Analysis of a Powered Single Acting Disc Harrow Using FEA

The three-dimensional model of a powered single acting disc harrow was created in SolidWorks 2013 and then the stress analysis was carried out using Finite Element Analysis (FEA) well before development of the designed tillage machinery to obtain optimum dimensions of different parts and to analyze the maximum stress and deformation in each component of the system. Theoretical calculations were done for different components, and resulting values were used to apply force, moment and boundary constraints on designed 3D model. Designed central gearbox, side gear assembly, gang shaft, the shaft between U-joint and upper side gear and main frame were validated by doing static structural analysis in ANSYS R15.0 workbench software. The developed implement was rigorously field tested and operated successfully up to the depth of 14 cm and forward speed of 7 km h-1 in sandy clay loam soil at an average moisture content of 12±0.75% (db). The field capacity, field efficiency and fuel consumption were found to be 0.37 to 0.57 ha h-1, 71.23% to 81.35% and 4.95 to 6.42 l h-1, respectively during first pass when operated at forward speeds of 3.69 to 6.55 km h-1 and at an average operating depth of 12 cm. FEM enables to optimize and simulate the complex agricultural machinery and to investigate the stresses and deformations induced in the parts well before product development to avoid failure in the later phase of field evaluation. Article History Received: 3 August 2017 Accepted: 23 September 2017

softwares helps designers to invent, revise detailed drawings, simulate and optimize the parameters of designs according to the need.Failure situations in the field can be speculated and prevented by static simulations of the machine structure through appropriated machine design and selection of materials.Breakdown of any unit, system or equipment is an avoidable and costly occurrence and must be prevented or minimized.Analysis of such failures becomes a resourceful and affordable tool in addressing such unwanted occurrences 1 .
The use of numerical simulation can predict the behavior of the system under study in order to reduce risk in decision making, identifying problems before they occur, reducing costs in evaluating the technical and economic feasibility of a given project.In agricultural machinery industry, especially in small and middle scales, insufficient technical knowledge, usage of new technology and incautious design features can cause problems such as breakdowns, failures, etc., during the manufacturing or field operations.Failure of machinery devices is one of the biggest problems in engineering 2 .
There are mainly five major methods that had been used as approaches to solve problems in the area of soil-tool interaction and failure mechanism, namely empirical and semi-empirical, dimensional analysis, finite element method, discrete element method and artificial neural network 3 .The finite element method (FEM) is a very powerful method among various numerical methods, and is commonly used for analyzing soil related problems because FEM excels in the analysis of dynamic problems regarding material failure and large-scale deformation 4 .FE analysis is basically a computerized method to analyze complicated engineering problems and for predicting how a product reacts to real-world forces, vibration, heat and other physical effects.Results of FE analysis shows whether a product will break, wear out, or work the way it was designed.It is particularly useful for problems with geometric or material nonlinearities, as well as situations where underlying differential equations describing physical or biological phenomena are nonlinear.Since most soil-machine interaction problems involve both material and geometric nonlinearities, FEM has been widely used to analyze soil-machine interaction problems 4,5,6,7 .The FE model can also be employed for design and optimization of tillage tools 8,9,10 or for conducting stress and deformation analysis of any mechanical model before field investigations 11 .
Traditional passively driven disc harrows are being widely used for the preparation of seed bed considering its several advantages like the excellent ability to cut and incorporate the crop residues in the soil, effective inversion and pulverization of the soil sod with minimal compaction 12 .However, the draft required by the passively driven disc is generally very high and is transmitted through soil tool interface resulting in inefficient power transmission and poor penetration behavior 13 .These days' farmers are more inclined towards multi-powered tillage tools which have greater versatility in manipulating the soil with reduced draft requirements 14 .Many research findings indicates a significant reduction in draft requirement with improved soil tilth in terms of reduced soil cone index and better soil pulverization through powering of passively driven discs 15,16,17,18,19 .However, the complex design involved due to the use of rotary parts for supplying power to the gang shaft makes it necessary to design, optimize and simulate the model before any product development and field testing to avoid any failure complications in the later phase.
The objective of this study is to design and develop a powered single acting disc harrow with the help of computer-aided software's: SolidWorks 2013 and ANSYS R15.0 for three-dimensional solid modelling and FE analysis of the optimized model, respectively to avoid any failure situations during the product development and field testing phase.It also accelerated manufacturing process with reduced costs and timing.Rigorous field testing was done with the developed implement and its performance was evaluated.

Speed ratio
The rotational direction of discs, operating depth and the speed ratio are the key factors which govern the design of powered disc harrow (PDH) 15,16 .Rotation of the discs in the direction of travel is called concurrent revolution and opposite to the direction of travel is called non-concurrent or reverse rotation.Forward rotation of the active tillage tools results  in the lowering the draft requirement compared to the reverse rotation as in the case of rotavator.Many studies 15,16 observed a major reduction in a draft requirement, specific draft requirement and sometimes penetration resistance also when discs rotate in the direction of travel.Peripheral speed of the disc blades (u) to the forward velocity of the travel (v) i.e. speed ratio (u/v) is an important factor which decides the soil pulverization at the price of fuel consumption.Higher speed ratio results in an undesied increase in the fuel consumption.Also, lesser speed ratio results in inadequate pulverization of the soil with unsteadiness in cutting resistance.Based on the above facts concurrent mode of rotation was chosen for tilling the soil.At 3.69, 4.67 and 6.55 km h -1 forward speed of tractor, speed ratios of 4.74, 3.75, 2.67 were achieved in the field at 80% throttle of tractor for 51 cm diameter disc blades.Field performance of the developed powered single acting disc harrow was evaluated at these three speed ratios.

Side Forces for lateral Stability
The transverse component of soil reactive force determines the lateral stability of the disc implement.The transverse soil reactive force i.e. side thrust on the forward-driven powered discs is generally very high due to positive cutting and throwing action of disc blades.It is, therefore, necessary to take into account the side thrust when designing the rear wheel of the powered disc.The side forces from the individual gangs in the single-acting disc harrow balances each other by throwing the soil in opposite directions which do not affect the lateral stability of the implement.Considering this fact in mind single acting disc harrow design was chosen without any rear thrust wheel, and power was supplied to both gang shafts by suitable side gear assemblies to balance out the side forces in the field.

Power Transmission System
Power was transmitted from the tractor PTO shaft to the central gearbox through suitable universal shaft and couplings.Gearbox was designed to transfer power to the both sides.A central shaft was used which runs from the center of crown gear to the universal joint on both sides.Two side gear assemblies were used each consisting of the side plate, dust cover, upper, middle and lower spur gear combination for transmitting PTO power to the gang shaft.The speed of PTO was initially reduced by central gear box in the ratio of 2:1 and then by side gear assemblies in the ratio of 4:3.

Three-Dimensional Modelling of PDH
The three-dimensional modeling of the implement was done in SolidWorks 2013.Schematic front, top,  PDH was used for tilling the soil and the attached leveller mounted behind the harrow leveled the ground for making the seedbed appropriate for sowing.Developed 3×3 single-acting PDH consisted of a central gear box along with telescopic shaft for connecting tractor PTO to the input shaft of gearbox, two universal joints to transmit power to both sides at gang angle of 20°, two gang shafts, four spool bearings and two side gear assemblies each consisting of one side plate, dust cover and three spur gears for rotating the shaft of disc gang with external power.

FE analysis of designed PDH
FEM is a common tool within various fields of engineering.It is used for advanced numerical calculations and is developed from the theories of continuum mechanics, which studies equilibrium, motion, and deformation of physical solids 20 .FEA uses a complex system of points called nodes which make a grid called a mesh.This mesh is programmed to contain the material and structural properties which define how the structure will react to certain loading conditions 21 .Three-dimensional model of the structure was created in SolidWorks 2013 and FEA was carried out by dividing it into a finite number of discrete sub-regions called elements, which was connected at discrete points called nodes.Then boundary conditions were applied such as fixed displacement and prescribed load to some nodes.Types and properties of elements and material properties were the other input parameters which were provided to the software.
Designed gang shaft, side gear assembly, central shaft, the shaft between U-joint and upper side gear, bevel gear shaft and main frame were validated by doing static structural analysis in ANSYS R15.0 workbench software.The equivalent stress and deformation obtained from FE analysis for each part were found to be less than the permissible stress and deformation of the material selected.The designed PDH was found suitable for carrying out the tillage operations under normal field conditions with a 50 hp tractor.

research Plan for Field Tests
The research plan for the field tests conducted is presented in Table 1.

instrumentation for Field Performance
All the field experiments for the developed PDH were conducted with a 46 hp Ford 3630, 2WD tractor.

Draft Measurement
Draft was measured in the field using three-point linkage dynamometer 22 and with dummy tractor method both to validate the results and are displayed in Fig. 2 and Fig. 3, respectively.Two tractors were used in dummy tractor method, John Deere 5055 E at the front and Ford 3630 at the rear.The front tractor was used to pull the rear tractor, which was always put in neutral.S-type load cell having 2-tonne capacity was attached between these two tractors through suitable chain linkage system as shown in Figs.tractor was used to pull the rear tractor.Readings of tensile force were recorded through a data logger system.The average of these forces gave the rolling resistance of rear tractor.Then in the same stripe of land implement was engaged and operated.This time PTO power was supplied to the implement and the rear tractor was put in neutral.Readings of tensile force were again recorded and an average of these gives the summation of rolling resistance and draft.Actual draft was calculated by subtracting rolling resistance from the summation of the draft and rolling resistance.Calibration of S-type load cell was carried out for tensile force by a mechanical floor crane.

Fuel Consumption Measurement System
Fuel consumption in the field was measured (Fig. 4) with the help of fuel flow meters (FFM) mounted on the fuel supply line and return line of Ford 3630 tractor respectively.A display board was connected to both FFMs to record and display the output.Power to the display board was provided from a 12 V DC battery.Display meter readings included total fuel consumption in the trip in units of l and l h -1 .The system was based on the principle of differential consumption.Contoil DFM-BC display meter deducts the readings of return line flow meter from the readings of supply line flow meter, to give the total fuel consumed during the operation.Also, time taken by the tractor during the operation was noted down using a stopwatch.Fuel consumption was calculated by dividing total fuel consumed during the operation with the time taken.For checking the accuracy of fuel flow meters, an auxiliary fuel tank was also placed in the supply line.Supply from the main fuel tank was cut during the tillage operation with the help of a three-way gate valve, and fuel is directed from the auxiliary fuel tank to the fuel injectors through fuel injection pump and supply line flow meter followed by secondary fuel filter.A connection was made for return line of fuel to the auxiliary tank.The auxiliary tank was filled to its neck before starting each trip.After completion of each trip amount of fuel required to fill the tank up to the neck level was measured with the help of measuring cylinder.Both measuring methods gave approximately same fuel consumption readings.

Cone index Measurement
Cone index values were measured with the aid of a hand operated instrumented cone penetrometer (Fig. 5).A hand operated cone penetrometer consisting of a 30° cone with a base area of 323 mm 2 and a 600 mm long circular shaft of 15.9 mm diameter was attached to a calibrated S-type load cell having 500 kg capacity and used to measure the average cone index value up to 120 mm depth of soil.The penetrometer was operated at the rate of 25-30 mm per second.Dial gauge of manually operated cone penetrometer was replaced by the load cell, and digital signals were procured through an 8-channel HBM Quantum-X DAQ system at 50 samples per second.Cone penetrometer was pushed into the soil up to 12 cm depth.Average force readings obtained in kg was converted into kg cm -2 by dividing it with the base area of cone penetrometer (3.23 cm 2 ).

Data Acquisition System
The outputs of all the load cells used were recorded through the HBM Quantum-X DAQ system (Fig. 6) at

Measurement of Speed of operation
The time taken by the tractor to travel 40 m distance was measured with a digital stopwatch, and the speed of operation was calculated using Eq. ( 1): where, v= speed of operation of tractor, km h -1 ; t = time, s

Measurement of Slip
The theoretical velocity and actual velocity were used to calculate slip using Eq. ( 2): where, s = slip, %; V t = theoretical velocity; V a = actual velocity

Field Capacity
Actual field capacity (A.F.C) is the total time required to carry out tillage operation including the time lost during the field operation for turning, idle travel, operator's skill etc. Field efficiency was calculated by dividing actual field capacity with theoretical field capacity.The yield strength of the material should be greater than the maximum equivalent stress induced (262.17N mm -2 ).Therefore, C-45 steel (yield strength = 430 N mm -2 ) was selected for gang shaft.The yield strength of the material should be greater than the maximum equivalent stress induced (79.06 N mm -2 ).Therefore, E250 steel (yield strength = 410 N mm -2 ) was selected the shaft between U-joint and upper side gear.2. From Table 2 it is evident that the stress induced were much less than the yield stress of the material selected.Hence, the design is safe, i.e. the developed PDH is suitable for carrying out the tillage operations under normal field conditions with a 50 hp tractor.

Design of PDH
The finalized dimensions adopted for the fabrication of 3x3 single acting PDH during design and finite element analysis of the implement in SolidWorks 2013 and ANSYS R15.0, respectively are presented in Table 3.The developed PDH is shown in Fig. 13.Central gearbox (300×270×290 mm) was used having bevel and crown gear assembly for transmitting power at 90°.The detailed specifications of bevel and crown gears used are provided in Table 4. Side gear assembly having a center to center distance between the upper and lower gear of 423.5 mm was used.The material selected for side spur gears was EN 8 carbon steel.The specifications of side gears are presented in Table 5.

Field Performance of the Developed implement width of operation
The width of cut of machine was measured by measuring the width of furrow with a measuring tape at an interval of about 3 m along the direction of travel.The average of five readings was taken to conditions.Within the test range of speed, depth, and cone index, the lowest and highest draft values were found to be 1.79 kN (at 9 cm depth, 3.69 km h-1 speed) and 2.80 kN (at 14 cm depth, 6.55 km h -1 speed) during first pass and 1.58 kN (at 9 cm depth, 3.69 km h -1 speed) and 2.64 kN (at 14 cm depth, 6.55 km h -1 speed) during second pass, respectively.When the forward speed was increased from 3.69 km h -1 to 6.55 km h -1 , the draft of the powered disc was increased by 43.57%, 31.84% and 36.58% at 9, 12 and 14 cm depth of operation, respectively.From Table 6, it is clear that that draft of powered disc was increased with increase in operating depth at all test conditions.When the depth of operation was increased from 9 to 14 cm, the draft of disc harrow was increased by 14.20%, 17.45% and 9.16% at 3.69, 4.67 and 6.55 km h -1 speed of operation, respectively during the first pass.Average slip of the developed implement was found to be 4.1% at an operating depth of 12 cm.

Actual Field Capacity
The data on the actual field capacity and field efficiency of the developed 3x3 single acting disc harrow are presented in Table 6.Actual field capacity increased with increase in forward speed of operation.Maximum field capacity of 0.60 ha h -1 was obtained at 6.55 km h -1 forward speed and 14 cm depth of operation during the first pass, while minimum field capacity of 0.35 ha h -1 was obtained at 3.69 km h -1 forward speed and 9 cm depth of operation during the second pass.

Fuel Consumption
The fuel consumption of 46 hp Ford 3630 tractor in l h-1 at all test conditions is presented in Table 6.Fuel consumption was found to be highest (6.83 l h -1 ) at 14 cm depth and 6.55 km h -1 speed of operation during the first pass and lowest (4.30 l h -1 ) at 9 cm depth and 3.69 km h -1 speed of operation during the second pass of tillage operation.Fuel consumption in l h -1 increased with increase in forward speed at all operating depths for first and second passes both.When the speed of operation was increased from 3.69 km h -1 to 6.55 km h -1 , the fuel consumption was increased by 39.90%, 29.70% and 31.09% during first pass and 27.90%, 24.55% and 21.79% during the second pass at 9, 12 and 14 cm depth of operation, respectively.

Fig. 3 :
Fig. 3: Draft measurement with dummy tractor method (b) Position of S-type load cell (a) implement, load cell and tractor positions

Fig. 4 :Fig. 5 :
Fig. 4: Fuel consumption measurement system and resulting values were used to apply force, moment and boundary constraints on the designed 3D model.The results of induced Von Mises stress and total deformation were analyzed, and necessary design changes were done accordingly in the 3D model to achieve optimum part dimensions for product development.Results of FE analysis are presented here in the form of coloured contours representing stress levels and deformation variation on the model.FE Analysis of Gang ShaftApplied forces and boundary conditions on gang shaft are shown in Fig.7(a).The results of finite element analysis are shown in Figs.7(b) and 7(c).

Fig. 8 :
Fig. 8: FEA results of the shaft between U-joint and upper side gear (c) total deformation

Fig. 9 :
Fig. 9: FEA results of the central crown gear shaft (c) total deformation

Fig. 10 :
Fig. 10: FEA results of bevel and crown gear (c) total deformation

Table 4 : Bevel and crown gear parameters. Parameters Bevel pinion Crown gear
Note: all dimensions are in mm.

: Data acquisition system sampling
frequency of 50 Hz.AC power supply to the data logger was provided by an inverter connected to the 12V DC battery source of the tractor.