Modal Analysis, Fatigue Analysis and Optimization of Tractor Drop Arm Using FEM

Abstract

The Drop Arm is part of the steering component in a Tractor. It is connected to the sector shaft and moves in angular motion with the help of the sector shaft. This motion causes the wheels to move left or right, depending on which way the steering wheel is moved. It is important you have your drop arm in good working condition because poor steering can be hazardous to you and those around you. A performance study will be carried to perform Failure, Fatigue & Modal Analysis of pitman arm using Ansys. The structural optimization will be done on the drop arm by changing the structure of pitman arm by modifying the geometry where stress values are critical. The meshing and boundary conditions will be applied and analysis will be carried out using Ansys 16.0.

Introduction

I. INTRODUCTION

This The Drop arm is a steering component that is used in an automobile or Tractor. It is a linkage between sector shaft of the steering box and drag link. It transmits the angular motion to the linear motion that is required to steer the wheels in desired direction.

The arm is attached to the sector shaft and supports the drag link or centre link. It transmits the motion it receives from the steering box into the drag link, causing it to move Steering arm to turn the wheels in the appropriate direction. The track rod is attached between the opposite sides of the steering arms. A damaged or loose drop arm can cause inability to steer, wandering to the left or right while on the road, poor steering.

II. OBJECTIVES

1. To perform 3D Scanning of Drop Arm used in Tractor.
2. To perform Failure analysis of Drop Arm.
3. To analyse the fatigue life of the component.
4. To perform Modal analysis of the component.
5. Structural optimization for better design and increased efficiency.

III. METHODOLGY

1. Phase I- Literature Survey
2. Phase II- 3D Scanning & CAD Modelling
3. Phase III- Failure, Fatigue & Modal Analysis of Drop Arm
4. Phase IV- Optimization of Drop Arm
5. Phase V- Failure, Fatigue and Modal Analysis of Optimized Drop Arm
6. Phase VI- Validation and Report

IV. LITERATURE SURVEY

Pradeep B Patil et al. [1] Static and modal analysis results of existing pitman arm proved that the model is more stable and there is scope for optimization. The comparison, between modal analysis results of existing and optimized pitman arm has been performed and it is observed that the pitman arm is vibrationally stable.

Sijith PM et al. [2] Performance study is carried out followed by static structural analysis and optimization to minimize the weight of the pitman arm and thereby reducing the material cost. Optimized model is then verified by physical testing.

Vimal Rau Aparow et al. [3] has investigated 2 DOF mathematical models of Pitman arm steering system and derived using Newton’s law of motion and modelled in MATLAB/SIMULINK software. The performance of the electronically actuated Pitman arm steering system can be used to develop a firing-on-the-move actuator (FOMA) for an armoured vehicle.

Srilekha Aurulla, G. and Gopala Krishna [4] has presented the static and modal analysis of steering lever link of a tractor to check its deformation, maximum stress and natural frequencies by using three materials.

Aniket Kolekar et al. [5] has designed and fabricated the fixture which is used in the manufacturing of Pitman Arm of steering system. The fixture is designed by using software CATIAV5R21.The purpose of the fixture is to provide strength, holding, accuracy and interchangeability in the manufacturing of product. The main purpose of a fixture is to locate and, in the cases, hold a work piece during an operation.

Shatabdee Sonawane et al. [6] Static analysis results of existing pitman arm proved that the model is more stable and there was scope for optimization The Pitman arm is optimized. The weight of original model is 974 gm and that of the optimized model is 840 gm. Weight of the component is reduced successfully up to 14% after optimization. The study confirmed that optimized pitman arm is structurally stable with good fatigue life.

Pradeep B Patil et al. [7] Based on FEA it can be concluded that the optimized pitman arm has infinite life because it can withstand above 10,00,000 cycles. Weight reduction of 9.04 % is obtained without compromising the strength of pitman arm. Natural frequency of both conventional and optimized pitman arm is extracted.

V. 3D SCANNING & CAD MODELLING

Finite element analysis is a computational technique that is used in engineering to obtain approximate solutions of boundary value problems.

The following are the steps for pre and post processing in FEM.

1. Define the geometry of the problem.
2. Discretise the model by meshing.
3. Define the element type(s) to be used.
4. Define the material properties of the elements.
5. Define the element connectivity.
6. Define the physical constraints (boundary conditions).
7. Define the loadings.
8. Solve the analytical problem.
9. Result evaluation.

TABLE I
Material properties of Alloy Steel

VI. FORCE CALCULATIONS

Total Mass of the vehicle,

M1=Curb weight + Driver weight + Tractor Implement Weight = 1713 + 80 + 1000 = 2793 kg      

This weight is divided into front axle weight and rear axle weight. 35% of the total weight is taken by front axle and 65% is by rare axle.

Therefore, Mass on the front axle, M2 = 977.55 kg

Mass on one of the front wheels, M = 488.775 kg

Width of tire, B = 132.08 mm

Centre of rotation (king pin) to wheel, E = 145 mm

Coefficient of friction, μ = 0.7

Distance from king pin centre to tie rod pin, L1 = 195 mm.

T=Torque required to rotate one wheel (torque at king pin),

T = M * g * µ * (B2/8) + E2                  T = 511296.4938 N

F = T/L1                                             F = 2622.0333 N

Since single steering arm will be handling two wheels so the force on steering arm will be doubled.

F = 5244.0666 N

A. Stress Calculation

σ = My/I

σ = Maximum bending stress

???? = Bending moment

???? = Vertical distance away from the neutral axis

???? = Moment of inertia

y = b/2                                                y = 17 mm.

I = (w * b3)/12                                  I = 63869 mm4.

M = F * L                                           M = 776121.8668 N-mm.

TABLE III
Vibration analysis (frequency calculation)

B. Fatigue Life Calculation

Sut = Ultimate tensile strength                        Sut = 450 Mpa = 45.887 kgf/mm2

Sa = Stress amplitude                                       Sa = 0.8Sut = 360 Mpa = 36.709 kgf/mm2

Se = Endurance                                                 Se = 0.5Sut = 225 Mpa = 22.943 kgf/mm2

b = (-1/3) * log [(0.8*Sut)/Se]                          b = -0.067989

c = log [(0.8*Sut )2/Se]                                      c = 1.768587

N = Number of life cycles before failure       N = 10(-c/b) * Sa(1/b) = 0.994846 × 106

The existing pitman arm will fail after 0.994846 × 106cycles. We say that component is having infinite life if it exceeds one lakh cycles.

VII. FINITE ELEMENT ANALYSIS OF DROP ARM

For analysis, one end of the pitman arm (larger side connected to sector shaft) is rigidly fixed and on another end, load is applied i.e., of 5244.0666 N.

1. Mesh Details: Nodes: 215655, Elements: 143218

2. Deformation Plot: Maximum Deformation is 0.63854 mm.

3. Stress Plot

Maximum Stress: 205.7 MPa

Minimum Stress: 0.0056274 MPa

Ultimate Strength: 450 MPa

Maximum Force component can withstand: 11472.026 N

As stress is well within the limit and deformation is less hence there is scope for optimization.

VIII. FATIGUE ANALYSIS OF DROP ARM

Minimum Damage: 1000, Maximum Damage: 43248

IX. MODAL ANALYSIS OF DROP ARM

Modal frequency results of 6 modes of drop arm calculated in Ansys 16.0 are as below.

TABLE IIIII
Modal Analysis of Drop Arm

X. OPTIMIZATION OF DROP ARM

A. Structural Optimization

The optimization of drop arm is done by modifying the geometry of drop arm where stress concentration is highest and lowest. Drop arm is optimized by modifying stress concentration areas and improving geometry for better stress distribution. Extra material is added on top side of drop arm to provide better stress distribution in z direction and extreme edges are smoothened.

A slot is also added in low stress areas to compensate for increased weight and netter stiffness in Y direction. The optimized geometry as below.

B. Material Optimization

New Material selected for optimization of Drop arm is AISI 4304 - EN24T. Material properties of EN24T are as below-

TABLE IVV
Material properties of EN24T

C. Deformation Plot

Maximum Deformation is 0.62685 mm.

D. Stress Plot

Maximum Stress: 185.58 MPa

Minimum Stress: 0.0045697 MPa

Ultimate Strength: 862 MPa

Maximum Force component can withstand: 24357.64 N

XI. FATIGUE ANALYSIS OF OPTIMIZED DROP ARM

A. Results for Fatigue Analysis

Force Applied: 5244.0666 N

Minimum Fatigue Life (Cycles): 33730

Maximum Fatigue Life (Cycles): 1×106

Minimum Damage: 1000, Maximum Damage: 29647

XII. MODAL ANALYSIS OF OPTIMIZED DROP ARM

The Modal frequency results of 6 modes of Optimized drop arm calculated in Ansys 16.0 are as below.

TABLE V
Modal Analysis of Optimized Drop Arm

XIII. RESULTS AND DISCUSSIONS

A. Fatigue Analysis

TABLE VI
Comparison of Fatigue life

B. Structural Analysis

TABLE VII
Comparison of structural analysis results

C. Modal Analysis

TABLE VIII
Comparison of Modal Analysis Results

Conclusion

1) Static and modal analysis results of existing pitman arm proved that there is scope for optimization. 2) Von Mises stress in optimized drop arm is reduced by 9.78%, Maximum force drop arm can withstand is increased by 112% and deformation is reduced by 2% under same loading conditions. 3) The comparison, between fatigue life results of existing and optimized pitman arm has been performed and it is observed that the pitman arm is having infinite life. 4) The comparison, between modal analysis results of existing and optimized pitman arm has been performed and it is observed that the pitman arm is vibrationally stable. The above steady confirmed the optimized pitman arm is vibrationally and structurally stable with good fatigue life.

References

[1] Pradeep B Patil and P D Darade “Modal Analysis, Fatigue Analysis and Optimization of Pitman Arm Using FEM.” International Journal of Research and Scientific Innovation (IJRSI), Volume V, Issue IX, September 2018, ISSN 2321–2705. [2] Sijith PM, Prof. Shashank Gawade, Prof. S.S Kelkar “CAE Analysis and Structural Optimization of Pitman Arm” International Journal of Science, Engineering and Technology Research (IJSETR), Vol. 5, Issue 6, June2016, ISSN: 2278-7798, pp.1901-1903. [3] Vimal Rau Aparow, KhisbullahHudha, ZulkiffliAbdKadir, Megat Mohamad HamdanMegat Ahmad, and Shohaimi Abdullah “Modeling, Validation, and Control of ElectronicallyActuated Pitman Arm Steering for Armored Vehicle” International Journal of Vehicular Technology, Volume 2016, Article ID 2175204, pp. 1-12 [4] Srilekha Aurulla , G. Gopala Krishna “Modeling and Analysis of Steering Lever Link of a Tractor” IJIRSET Vol. 5, Issue 11, November 2016, pp. 19801-19808 [5] Aniket Kolekar, Mr. Shubham R. Gound, Mr. Mahesh S. Ban “Design of Fixture for Manufacturing of Pitman Arm” IRJET, Volume: 04, Issue: 05 May -2017, pp. 1714-1720 [6] Shatabdee Sonawane, Prof. P. M. Sonawane \"Structural Analysis and Optimization of Pitman ARM\", International Journal of Engineering Research & Technology (IJERT), ISSN: 2278-0181, Vol. 9 Issue 08, August-2020. [7] Pradeep B Patil and P D Darade “Vibrational Analysis, Life Prediction and Optimization of Pitman Arm Using FEM.” International Journal of Computational Engineering Research (IJCER), vol. 08, no. 05, 2018, pp. 18-23.

Copyright

Copyright © 2022 Raviraj Inamke, N. K. Nath, R. R. Arakerimath. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.