DESIGN AND ANALYSIS OF COMPOSITE HELICAL SPRING FOR TWO WHEELER SHOCK

ABSORBER

P.Dhanapal1, K.R. Mathevanan2, M. Rahul Krishnan3, R.Thennarasan3

1Professor,

Department of Mechanical Engineering

Karpagam College of Engineering, Coimbatore - 641 032, Tamilnadu, INDIA 2Assistant Professor,

Department of Mechanical Engineering,

Karpagam College of Engineering, Coimbatore - 641 032, Tamilnadu, INDIA 3Mechanical Student,

Department of Mechanical Engineering,

Karpagam College of Engineering, Coimbatore - 641 032, Tamilnadu, INDIA

Abstract: The automobile industry has shown

increased interest in the replacement of ferrous metals

using composite materials due to high strength to

weight ratio. The present study describes design and

comparative analysis using standard empherical

formula and ANSYS of steel spring with the glass and

carbon fibre epoxy materials. Carbon fibre has

maximum deflection. A maximum of 5% deviation

occurs in the carbon epoxy spring while comparing the

theoretical and experimental values and the other two

materials are low. Hence the usage of this analysis

software has an error of 5% only. Glass fibre epoxy

shows the maximum spring rate. The ultimate yield

stress of the carbon fiber epoxy is 216 % and 32%

compared with the steel.

AMS Subject Classification: 74E30

Keywords: Analysis, Design, Conventional materials,

Composite material, Stresses.

1. Introduction

Suspension systems have been applied to vehicles,

from the horse-drawn cart with flexible leaf springs, to

the modern automobile with complex control

algorithms. The suspension of a road vehicle is usually

designed with two objectives; to isolate the vehicle

body from road irregularities and to maintain the wheel

control with the roadway. Leaf spring, coil spring and

their combination are used as suspension systems in

automobiles.

Pro-Engineer is a parametric, feature-based

modeling architecture incorporated into a single

database philosophy with advanced rule-based design

capabilities. This data is then documented in a standard

2D production drawing or the 3D drawing standard

ASME Y14.41-2003. ANSYS is standard FEA tool

used to solve problems in various disciplines like civil

and electrical engineering, as well as the physics and

chemistry. ANSYS provides a cost-effective way to

explore the performance of products. The multifaceted

nature of ANSYS also provides a means to ensure that

users are able to see the effect of a design on the whole

behavior of the product, be it electromagnetic, thermal,

mechanical etc.

Generic steps to solving any problem in ANSYS

are Define the solution domain, Create the physical

model, Fix boundary conditions and add the physical

properties. Solve the problem and present the results. In

numerical methods, the main difference is an extra step

called mesh generation. This is the step that divides the

complex model into small elements that become

solvable in an otherwise too complex situation. Below

describes the processes in terminology slightly more

attune to the software.

Multi leaf spring is designed by finite element

approach using CAE tools (i.e CATIA, ANSYS) and

analysed the stress-deflection. When the leaf spring is

fully loaded, a variation of 0.632 % in deflection is

observed between the experimental and FEA result (1).

The oscillatory behavior of stresses is also responsible

for causing rotational movement of springs in slots,

observed in experimental analysis. The failure locations

matched with considerable amount of failures occurred

in experiment (2). Numerical results have been

compared with theoretical results and found to be in

good agreement three different composite helical

springs. Compared to steel spring, the composite helical

spring has been found to have lesser stress. Weight of

spring has been reduced and has been shown that

changing percentage of fiber, especially at

Carbon/Epoxy composite, does not affect spring weight

(3). Composite mono leaf spring reduces the weight by

International Journal of Pure and Applied MathematicsVolume 118 No. 11 2018, 549-555ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version)url: http://www.ijpam.eudoi: 10.12732/ijpam.v118i11.70Special Issue ijpam.eu

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85% for E-Glass/Epoxy, 91% for Graphite/Epoxy, 90%

for Carbon/Epoxy over conventional leaf spring (4).

Composite leaf springs of varying width and

thickness and constant cross section has been analyzed

in ANSYS software and observed that Boron

Aluminum is the best suitable material for replacing the

steel in manufacturing of mono leaf spring (5). The

weight of the composite spring was much lesser, this

can be justified by the amount of fuel saved and the

stiffness of springs. An optimum design of composite

springs is required to balance the weight and stiffness;

hence the application of composite springs is limited to

light commercial vehicles. In this study, advanced

composite materials are chosen as spring materials, the

dimensions of the springs are chosen as per the springs

available in the market. Their behavior is analyzed

using ANSYS software.

2. Materials and Methods

The suspension system of Yamaha RX100 is chosen for

the analysis. Figure 1 shows the assembled view of

solid modeling of the actual spring components. The

shock absorber is dismantled, sizes of individual

components are measured and reverse engineering is

applied to get this model.

Figure 1. Assembled View

A modal analysis is typically used to determine

the vibration characteristics (natural frequencies and

mode shapes) of a structure while it is being designed.

It can also serve as a starting point for detailed dynamic

analysis, such as a harmonic response or full transient

dynamic analysis. A reduced solver utilizing

automatically or manually selected master degrees of

freedom to drastically reduce the problem size and

solution time.

The actual spring contains 18 numbers of active

coils with 57 mm coil outer diameter, 220 mm length,

10.52 mm pitch and 7mm circular section wire.

Materials library of the necessary object being modeled

are defined. This includes thermal and mechanical

properties. The mesh type is defined. The last task is to

apply the constraints, such as physical loadings or

boundary conditions. The software provides a platform

for different type of loads like static, dynamic, shock

load etc. Obtain solution. After the solution has been

obtained, there are many ways to present the results

such as tables, graphs, and contour plots. The

theoretical values of stiffness, deflection and the

stresses are calculated with standard formulae and

standard design data book and compared with the

experimental value to conform the correctness.

Carbon-fiber reinforced thermoplastic (CFRP)

were commonly used in structural engineering

applications, in sports equipment such as racing

bicycles, in aerospace engineering for micro Air

vehicles and also used in high-end automobile racing.

2.1 Analysis Procedure

The following procedure is carried out in order to

analyze the springs differing in the material in ANSYS

workbench. First convert the spring model file which is

designed using Pro-E into IGES format. Select

geometry mode and change the input mode to ‘mm’.

Go to file→ import external geometry file and browse

for the IGES file (Figure 2a). Then generate the spring.

Discretization is the first and major step in the

successful analytical evaluation of any component in

FEM. This process of discretizing the solid part into

finite number of elements is called Meshing in ANSYS.

Select new mesh and change the reference center as

fine and select generate mesh. Fine’ should be selected

to get the nearest approximate results. The meshed

object should be moved to the simulation mode for

proceeding the analysis. Select convert to simulation

option, the window changes to simulation mode. Select

new analysis → static structural Apply fixed end and

give the load on the whole geometry of the spring, the

material properties are defined.

Figure 2a. spring solid model

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Figure 2b. Meshed view

Choose static structural → solution and choose

insert → deformation → total in order solve the

analysis for total deformation due to applied load.

Choose equivalent elastic strain and equivalent stress

(von- mises) for solving. Select new analysis → modal.

Analysis settings → options, enter value for maximum

modes to find, say 6. Add total deformation for 6

modes and for each consecutive total deformation,

under Definition, set the Mode value to corresponding

to respective mode number. Solve the modal analysis

by right clicking Modal Analysis in the left pane.

3. Results and Discussions

In this analysis circular cross-section is considered. The

load acting on the entire rear suspension system is 1000

N. The rear suspension system comprises of a pair of

shock absorbers. Hence the load on one suspension in

the rear is half of the entire load which is 500 N. This

load is applied on the spring in static structural analysis

for which the deflection, Von-Mises stress is studied.

The behavior of the spring due to its self-weight is also

studied under modal analysis.

3.1 Steel Spring

Under Geometry, choose material → import and

continue the above given procedure. Figure 3a shows

the maximum deflection of the steel spring as 21.154

mm for the static condition. Figure 3b shows that the

equivalent von-mises stress is 392.570 MPa. In figure

3c the equivalent von-mises strain is obtained as 0.0018

and the final deflection of the spring in modal analysis

is 36.11mm from figure 3d.

Figure (3a). Total Deflection

Figure (3b). Von-Mises stress

Figure (3c). Von-Mises strain

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Figure (3d). Total Deflection (Modal)

3.2 Carbon Epoxy

Figure (4a). Total Deflection

Figure (4b). Von-Mises stress

Figure (4c). Von-Mises strain

Figure (4d).Total Deflection (Modal)

Carbon epoxy spring material analysis, under

geometry, choose Material → Import, if the material is

predefined just choose the material after verifying the

properties and continue the procedure. The maximum

deflection of the Carbon Epoxy spring (Figure 4a) is

22.264 mm for the static condition but for the steel

spring as 21.154 mm. Figure 4b shows that the

equivalent von-mises stress as 392.80 MPa whereas for

steel spring is 392.570 MPa. The Equivalent von-mises

strain is obtained as 0.0020 in figure 4c but for steel

spring it is 0.0018. The final deflection of the spring in

modal analysis is 45.826 mm but for the steel spring is

36.11 mm.

3.3 Comparison Charts

The ANSYS software results show varieties of output

values for different spring materials. Some of the

performances are described in table 2. Bar charts are

drawn to compare and discuss the important parameters

like deflection, spring rate and von-mises stress.

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Table 2. Comparison table for results

Material Steel Carbon Epoxy

Modal

Results

Deflection

(mm)

Frequenc

y (Hz)

Deflection

(mm)

Freque

ncy

(Hz)

Mode 1 27.973 8.492e-4

41.469 2.435 e-3

Mode 2 27.973 1.727e-3

41.469 2.875e

-

3

Mode 3 27.973 3.718e-3

41.469 6.22 e-3

Mode 4 35.42 13.961 45.51 17.86

Mode 5 35.37 14.942 45.46 17.97

Strain 1.88 e-3 2.10123 e-3

Densit

y (x10-

6

kg/mm3)

7.8 1.6

Figure 5. Deflection

The theoretical and experimental deflection is

expressed in figure 5, carbon fiber has maximum

deflection. Comparing the theoretical and experimental

values, a maximum of 5% error occurs in the carbon

epoxy spring and the other two materials are low.

Hence the usage of this analysis software has an error

of 5% only. The spring rate is compared in figure 6.

Glass fiber epoxy shows the maximum spring rate. The

higher stiffness and spring rate is the glass epoxy

springs because this fiber has high stiffness compared

to the carbon fiber of same size.

Von-mises and ultimate Yield Stress in the

springs are shown in figure 7, where the von-mises

stress is uniform in all the springs. The ultimate yield

stress of the carbon fiber epoxy is 216 % and 32 %

compared with the steel and glass fiber epoxy. Ultimate

yield stress of carbon is more compared to the glass

fiber gives higher this higher yield stress.

Figure 6. Spring Rate

Figure 7. Stress

4. Conclusion

The analysis has a maximum of only 5% variation with

the theoretical calculations. The analysis describes that

the use of glass fiber epoxy as a substitute for steel

spring would results in reduced yield stresses and

strain, also reduction in deflection for variation in

frequencies. Also it is found that the weight of the

spring is reduced, and the factor of safety of the

composites is found to be high. The glass fiber epoxy is

an alternate for the shock absorber coil springs.

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International Journal of Pure and Applied Mathematics Special Issue

553

[3] G. Sidharamanna, S. Shankar, S. Vijayarangan,

Mono Composite Leaf Spring for Light Weight Vehicle

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