Performance Evaluation and Optimization of Tie rod in Suspension System of Car for a Buckling study using Theoretical and Experimental approach

Performance Evaluation and Optimization of Tie Rod in Suspension

System of Car for a Buckling Study using Theoretical and Experimental

Approach

Ganesh B. Baraskar

1

_{Dr. V. S. Joshi}

2

_{M. P. Nagarkar}

3

1

_{P.G. Scholar}

2

_{Associate Professor}

3

_HOD

1,2,3

_{Department of Mechanical Engineering}

1,2

_{JNEC, Aurangabad}

3

_{SCSMCOE, Ahmednagar}

Abstract— A tie rod is a slender structural rod that is used as a tie and capable of carrying tensile and compressive loads. As the ratio of its length to the radius of gyration of its cross section is normally quite large, it would likely buckle under the action of compressive forces. When it becomes worn out, steering will producing clunking noise and also the vehicle will typically be pulling or (dragging) to either side (left or right) it will cause the accident which is not safe for passenger life in the car. Thus the aim of the project is to analyze tie rod for active to improve the mass and buckling load of tie rod. This paper is aimed to assess buckling strength and compare buckling performance of Tie rod for different dimensions. Theoretically calculate the critical buckling load of Tie rod for taking different diameter of it and keeping the same material and length. Experimentally test the same Tie rod on UTM machine. Based on the experimental test results, theoretical calculation results the critical buckling load for different dimensions of tie rod were compared and it validated by checking its performance on quarter car test rig for suspension system of car.

Key words:Tie Rod, Critical Buckling Load, UTM, Quarter Car Test Rig

I. INTRODUCTION

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For the past century a great deal of research has been invested to help predict the critical buckling loads of cylindrical columns. Research (both theory and experimental) has indicated that geometrical imperfections and modified boundary conditions greatly impact the critical buckling load magnitudes and scatter of cylindrical columns.

Fig. 1: Tie Rod

A tie rod contains such geometrical imperfections and modified boundary conditions from a perfect cylindrical shell, since a tie rod typically consists of two outer rod ends threaded into a cylindrical rod body, with varying end conditions. It is very important to accurately predict the buckling loads of structural tie rods, especially ones that are compression critical in automobile industries and aerospace applications. There are several applications where a tie rod is utilized to help secure and support equipment on an

automobile and aircraft, such as on the fuselage of an airplane. These are purely structural members, so a robust knowledge of the design loads is required to ensure the part will satisfy its function on the automobile. In certain cases, these tie rods need to be designed to buckle at a specific load to avoid puncturing or damaging nearby components. Based on the design criteria of minimizing compression margin safety coupled with the degree of difficulty to predict buckling behavior, accurately calculating the critical buckling load is of high importance. This report is that gives a designer a systematic approach to accurately predict the buckling load of a structural tie rod. The goal of the report is to establish an acceptable method of predicting the buckling load of a structural tie rod due to axial compression.

II. PARAMETERS AFFECTING THE CRITICAL BUCKLING LOAD OF A STRUCTURE

We know that, critical buckling load is given by

𝑃𝑐𝑟 =

𝜋2𝐸𝐼

4𝐿2………..equation (1) Here,

π is constant, E, I and L are variables which can control the

critical load value.

In order to get the higher Pcr value  ‘E’ and ‘I’ must be higher  ‘L’ should lower

 ‘L/D’ ratio shall be minimum

Now, I = πD 4

64 ………..equation (1) So the value D value affects in quadratic.

Hence for design against the buckling loads, one should select the material having maximum E value, keeping length as minimum as possible, select maximum outer diameter in order to maximize the inertia value and lower the L/D ratio.

In case of tie rod we have carried out many such combinations / iterations that will give the maximum value of critical load with lowest invest of mass (optimized solution).

A. Buckling Performance:

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Fig. 2: Graph 1.Critical buckling load (Pcr) Vs Diameter (D) Above is the graph of critical buckling load against diameter. We have checked the critical buckling load against various diameters. The diameter starts from 16 to 22. As the inertia depends on the diameter. From equation of inertia, it can be seen that I value is cubically affected by diameter. This is the reason why there is sharp rise in critical buckling value. So conclusion is to keep the outer diameter of structure as maximum as possible. From the above two discussions, we concluded that the value of inertia and diameter should be maximum. This is one parameter that can be set in order to decide the optimum value for diameter and or inertia of structure. The parameter is ratio of I/A.

B.

Critical Buckling Load Evaluation Theoretical Calculations for Critical Buckling Load

1) Linear buckling of Euler column

For clamped-free boundary conditions the critical load is:

𝑃𝑐𝑟 =

𝜋2𝐸𝐼

4𝐿2 ………..equation (1) Here, for Existing Tie rod

D= 16 mm, d= 10.5 mm, E= 210000 N/mm2, I= 2598.32 mm4, L=320mm Pcr=13275.0 N

In order to optimized the diameter of tie rod while keeping the length and material should be same. So critical buckling load for different diameter of tie rod is shown in table below.

Description D (mm)

d (mm)

M (kg)

Pcr (N)

Existing 16 10.5 0.290 13275

Tie rod.1 16.5 13.5 0.179 10173

Tie rod.2 17 14 0.184 11196

Tie rod.3 17.5 14.5 0.190 12308

Tie rod.4 18 15 0.196 13149

Tie rod.5 18.5 15.5 0.202 14748

Tie rod.6 19 16 0.208 16080

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Tie rod.7 19.5 16.5 0.215 17493 Table 1: Theoretical Result of Critical buckling Load for tie

rods using different diameter

From above table critical buckling load for the different diameter of tie rod calculate in which tie rod having diameter D= 18.5 mm, d= 16.5 mm is optimized diameter for tie rod. Because if we compare the mass of this tie rods with existing tie rod percentage difference of mass saving of optimized tie rod is 30.2% which is more than

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III. BUCKLING TEST: TEST CONDUCTED ON UTM MACHINE

Fig. 2: Buckling test set up of Tie Rod on UTM machine Above figure 2 Shows the test set up of UTM. The tie rod is screwed on one end of UTM and kept free at the other end. Load is applied from the top end of UTM vertically in Z-direction in pure axial Z-direction. Initial load applied is 10N and it is gradually increasing at 10N/s. The load is applied gradually to avoid any slippage of the rod during testing.

Sr. No. Load (N)

Displacement (mm)

1 15 0.001

2 3000 0.54

3 6000 0.92

4 9000 1.31

5 12000 1.65

6 15000 2.05

7 21000 2.75

8 24000 3.45

9 26560 4.45

10 24000 5.40

11 21000 6.15

12 18000 7.05

13 15000 7.75

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14 14600 8.05

Table 2: UTM Test Result of Load and Displacement of existing tie rod

Fig. 3: Graph 2: Load (X) Vs Displacement (Y) results on UTM for existing tie rod.

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to 21 KN. After 21 KN to 26 KN the lateral buckling is significant; which is sign of plasticity in the tie rod.

Sr. No. Load (N)

Displacement (mm)

1 15 0.001

2 3000 0.05

3 6000 0.06

4 12000 0.08

5 16000 0.10

6 20000 0.10

7 24000 0.18

8 28000 0.40

9 32000 1.20

10 35880 2.45

11 32000 3.60

12 28000 4.90

13 24000 5.80

14 20000 7.20

Table 3: UTM Test Result of Load and Displacement of optimized tie rod

Fig. 4: Graph3: Load (X) Vs Displacement (Y) results on UTM for optimized tie rod.

From the test in case of proposed tie rod is observed that, up to 24kN load there is very small compressive axial straining of rod occurs and lateral straining is almost negligible. After 28kN load lateral buckling is occurs significantly; which is increasing to 21kN. After 21kN to 32kN the lateral buckling is significant; which is sign of plasticity in the tie rod. From comparing the results of proposed design with existing design; it can be noted that load Carrying capacity of proposed design is much higher that existing design. This is especially higher in the elastic region. The elastic strain region for existing design is much higher than the proposed design. This is advantageous as occurrence of plasticity is considered as a failure for ductile material.

Description Existing Tie Rod

Optimized Tie Rod Critical Buckling

Load (N) 26560.0 35880.0

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Table 4: Critical Buckling Load Results on UTM From the UTM load test result and test graphs we can see that the maximum load carrying capacity of existing design tie rod is 26KN and proposed design tie rod is 35KN After reaching this point there is drop in load. The point is called as “instability” where there is loss of stiffness of structure.

Fig 3 : Post Buckling shape of Existing and Optimized Tie rod

Above figure shows the post buckling image of both existing and proposed design of tie rod. It is to be noted that for pure buckling test the tie rod is cut at the neck after the ball joint. As ball joint cannot be kept while performing the test; as the rod may get slips while axial loading. The location of maximum displacement is at the center of rod.

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IV. EXPERIMENTATION SETUP AND RESULTS

Fig 4 : Quarter Car Test Rig

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Fig 5 : Existing Tie Rod Test set up onQuarter Car Test Rig

Fig 6 : Optimized Tie Rod Test set up onQuarter Car Test Rig

As shown in the above, we can see the two pictures of test ring. The left side picture is a front view of test rig. Here the pneumatic excitation is given to the test rig from the bottom side. We can keep the mass at the top of suspension. For measurement of acceleration an accelerometer is kept at the top of test rig. Excitation is given by the use of timer to set the frequency of excitation. According to reading getting from the accelerometer we can generate graph to check response of tie rod for given excitation which can give the feel of ride on uneven road surface. Hence from the accelerometer result we generate the graph for existing and proposed design tie rod test rig

Fig. 7: Graph 4: Time (X) Vs Acceleration in Z-direction (Y) For Existing Tie rod

Fig. 8: Graph 5: Time (X) Vs Acceleration in Z-direction (Y) For Optimized Tie rod

Figure above shows the graph of acceleration excitation Vs time. From the graphs it is observed that, the response of proposed design is in line with the existing design. The output acceleration excitations are within the limit of 0.6 to 1.2 in both proposals. This signifies that, the implementation of proposed design does not affect the overall performance of suspension system. Hence the proposed design can be successfully implemented in the vehicle.

V. CONCLUSION

Theoretical calculated critical buckling load of proposed design Tie rod is 14748 N which is more than the critical buckling load of Existing Tie rod is 13275 N. Experimental result of compressive test perform on UTM in which critical buckling load of proposed tie rod is 35880N which is 35% more than critical buckling load of existing tie rod 26560N.By checking the performance of this both tie rod on quarter car test rig. Results getting from accelerometer by generating the graphs of acceleration excitation Vs time it is observed that, the response of proposed design is in line with the existing design. This signifies that, optimized design of tie rod is better economic design it take 35% more buckling load and also weight reduction of 14% achieved hence the optimized tie rod can be successfully implemented in the vehicle.

ACKNOWLEDGEMENT

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ABBREVIATIONS

Pcr – Critical or maximum axial Load on column just before it begin to buckle (N)

E - Young’s Modulus of elasticity (N/mm2)

I - Moment of inertia for column cross sectional area (mm4)

L - Unsupported Length of column (mm) D - Outer Diameter of column (mm) d - Inner Diameter of column (mm) M – Mass of tie rod (kg)

REFERENCES

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[2] Raghavendra K and Ravi K (2014) “Buckling analysis of tractor tie rod subjected to compressive load” International Journal of Mechanical and Industrial Technology, Vol. 2, Issue 1,pp: (125-129).

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