Design and Analysis of Composite Leaf Spring

This paper discusses the advantages of composite structures over conventional metallic structures and the replacement of steel spring with fiberglass composite leaf spring. It also covers the design and analysis of a Mono Composite leaf spring using E-Glass/Epoxy.

International Journal of Mechanical and Industrial Engineering (IJMIE), ISSN No. 2231 –6477, Vol-2, Issue-1, 2012
97
Design and Analysis of Composite Leaf Spring
Y. N. V. Santhosh Kumar & M. Vimal Teja
Dept. of Mechanical Engineering, Nimra College of Engineering & Technology, Ibrahimpatnam, Vijayawada
E-mail: [e-mail]
Abstract - In these paper, composite structures for conventional metallic structures has many advantages because of higher specific
stiffness and strength of composite materials is discussed. The automobile industry has shown increased interest in the replacement
of steel spring with fiberglass composite leaf spring due to high strength to weight ratio. This work deals with the replacement of
conventional steel leaf spring with a Mono Composite leaf spring using E-Glass/Epoxy. The design parameters were selected and
analyzed with the objective of minimizing weight of the composite leaf spring as compared to the steel leaf spring. The leaf spring
was modeled in Pro/E and the analysis was done using ANSYS Metaphysics software.
Keywords - Composite Material, Steel Leaf Spring, Pro-E, FEA, ANSYS.
I. INTRODUCTION
Originally called laminated or carriage spring, a leaf
spring is a simple form of spring, commonly used for
the suspension in wheeled vehicles. It is also one of the
oldest forms of springing, dating back to medieval
times. Sometimes referred to as a semi-elliptical spring
or cart spring, it takes the form of a slender
arcshaped length of spring steel of rectangular cross-
section. The center of the arc provides location for the
axle, while tie holes called eyes are provided at either
end for attaching to the vehicle body. For very heavy
vehicles, a leaf spring can be made from several leaves
stacked on top of each other in several layers, often with
progressively shorter leaves.
Leaf springs can serve locating and to some extent
damping as well as springing functions. A leaf spring
can either be attached directly to the frame at both ends
or attached directly at one end, usually the front, with
the other end attached through a shackle, a short
swinging arm. The shackle takes up the tendency of the
leaf spring to elongate when compressed and thus makes
for softer springiness.
The automotive industry is exploring composite
materials for structural components construction in
order to obtain the reduction of weight without decrease
in vehicle quality and reliability. To conserve the natural
resources and economize energy, weight reduction has
been the main focus of automobile manufacturer in the
present scenario. Actually, there is almost a direct
proportionality between the weight of the vehicle and
its fuel consumption, particularly in city driving. The
advanced composite materials such as Graphite, Carbon,
Kevlar and Glass with suitable resins are widely used
because of their high specific strength (strength/density)
and high specific modulus (modulus/density).
Advanced composite materials seem ideally suited
for suspension (leaf spring) applications. Their
elastic properties can be tailored to increase the strength
and reduce the stresses induced during application.
Fig. 1 : Leaf Spring
The objective of the present work is to design the E-
Glass/Epoxy composite leaf spring without change in
stiffness for automobile Suspension system and analyze
it. This is done to achieve the following.

Design and Analysis of Composite Leaf Spring
International Journal of Mechanical and Industrial Engineering (IJMIE), ISSN No. 2231 –6477, Vol-2, Issue-1, 2012
98
• To the replace conventional steel leaf springs with
Eglass/Epoxy composite leaf spring without change
in stiffness.
• To achieve substantial weight reduction in the
suspension system by replacing steel leaf spring
with composite leaf spring.
II. PRINCIPLE OF LEAF SPRING
The suspension leaf spring is one of the potential
items for weight reduction in automobile as it accounts
for ten to twenty percent of the unsprung weight. The
introduction of composites helps in designing a better
suspension system with better ride quality if it can be
achieved without much increase in cost and decrease in
quality and reliability. In the design of springs, strain
energy becomes the major factor. The relationship of the
specific strain energy can be expressed as
2 /U Eσ ρ=
Where σ is the strength,
ρ is the density and E is the Young’s Modulus of the
spring material
It can be easily observed that material having lower
modulus and density will have a greater specific strain
energy capacity. The introduction of
composite materials made it possible to reduce the
weight of the leaf spring without reduction of load
carrying capacity and stiffness due to the following
factors of composite materials as compared to steel.
Fig. 2 : Arrangement of leaf spring in a car Model
An upturned spring eye is used to attach the front
end of semi-elliptic leaf spring to the chassis frame, and
a free end with a bracket constraining vertical motion to
attach the back end of semi-elliptic leaf spring to the
chassis frame.
A Composite in engineering sense is any materials
that have been physically assembled to form one single
bulk without physical blending to foam a homogeneous
material. The resulting material would still have
components identifiable as the constituent of the
different materials. One of the advantages of composite
is that two or more materials could be combined to take
advantage of the good characteristics of each.
III. DESIGN OF LEAF SPRING
Considering several types of vehicles that have leaf
springs and different loads on them, various kinds of
composite leaf spring have been developed. In the case
of multi- leaf composite leaf spring, the interleaf spring
friction plays a spoil spot in damage tolerance. It has to
be studied carefully.
In the present work, only a leaf spring with constant
thickness, constant width design is analyzed.
Fig.3 : Main Parts of Leaf Spring
The following cross-sections of leaf spring for
manufacturing easiness are considered.
1. Constant thickness, constant width design
2. Constant thickness, varying width design
3. Varying width, varying width design.
Table 1 Design Specifications
Parameter Specification
Material Steel(55Si2Mn90)
Tensile Strength 1962N/Sq. mm
Yelid Strength 1470N/Sq.mm
Young's Modulus 2.1e5 N/Sq.mm
Spring Weigth 16.4 Kg
Thickness at the Center 12mm
Thickness at extreme ends 9mm

Design and Analysis of Composite Leaf Spring
International Journal of Mechanical and Industrial Engineering (IJMIE), ISSN No. 2231 –6477, Vol-2, Issue-1, 2012
99
For steel leaf spring cross section is according to
considered design and not altered.
Due to manufacturing ease, a composite leaf spring with
uniform rectangular cross section is considered and
analyzed.
IV. PROBLEM DEFINITION
Objective of present work is to consider an existing
automobile leaf spring model TATA SUMO EZRR
PARABOLIC REAR and to design and analyze a
composite leaf spring with upturned eye without
changing stiffness in order to replace the existing steel
leaf spring with a composite leaf spring.
A spring eye is essentially the end of a leaf spring
bended into a circular shape to allow rotation about the
spring eye. The main types of spring eye designs are
upturned, military wrapper, down turned, and Berlin
eyes Fig: 4. Types Upturned eyes are the most
commonly used type of spring eye because of their
simple design and high durability. Upturned eyes are
highly durable because they resist stress due to vertical
forces on a suspension system.
Fig. 4 : Types of Spring Eyes
Unlike other spring eye designs, an upturned eye
applies vertical loads on the linear leaf section that
was not bent to form the eye. Therefore, upturned eyes
have less of a tendency to unwrap as result of vertical
forces than the other types of spring eyes.
The Following Assumptions are made for this work.
1. The leaf spring has a uniform, rectangular cross
section.
2. All non- linear effects are excluded.
3. The stress-strain relationship for composite material
is linear and elastic; hence Hooke’s law is
applicable for composite materials.
4. Acoustical fluid interactions are neglected, i.e., the
leaf spring is assumed to be in vacuum.
5. The load is distributed uniformly at the middle of
the leaf spring.
V. STATIC ANALYSIS OF LEAF SPRING
The leaf spring modeled in Pro/E was imported to
ANSYS in IGES format. Since leaf spring was modeled
as a solid, solid element named SOLID187 was used
to mesh the model. SOLID187 element is a higher order
3-D, 10-node element. SOLID187 has a quadratic
displacement behavior and is well suited to
modeling irregular meshes (such as those produced from
various CAD/CAM systems). The element is defined by
10 nodes having three degrees of freedom at each
node: translations in the nodal x, y, and z directions. The
element has plasticity, hyper elasticity, creep, stress
stiffening, large deflection, and large strain capabilities.
The geometry, node locations, and the coordinate
system for this element are shown in the figure 5.
In addition to the nodes, the element input data
includes the orthotropic or anisotropic material
properties. Orthotropic and anisotropic material
directions corresponding to the element coordinate
directions.
Fig. 5 : Solid 187 3D 10 node tetra hydral structure
VI. RESULTS AND CONCLUSIONS
It was observed that the deflection in the composite
leaf spring was almost equal so we can say that
composite spring had the same stiffness as that of steel
spring.
It was observed that the composite leaf spring
weighed only 39.4% of the steel leaf spring for the
analyzed stresses. Hence the weight reduction obtained

Design and Analysis of Composite Leaf Spring
International Journal of Mechanical and Industrial Engineering (IJMIE), ISSN No. 2231 –6477, Vol-2, Issue-1, 2012
100
by using composite leaf spring as compared to steel was
60.48 %.
Fig.6 : Deflection of Master Leaf (Steel)
By analyzing the design, it was found that all the
stresses in the leaf spring were well within the allowable
limits and with good factor of safety. It was found that
the longitudinal orientations of fibers in the
laminate offered good strength to the leaf spring. Ride
quality is generally quantified as the natural frequency
of a suspension system.
Fig. 7 : x Component of Stress in Master Leaf strings
Suspension system natural frequencies less than 1
Hz will cause motion sickness in a vehicle’s passengers,
and suspension system natural frequencies greater than
2.5 Hz will provide a “harsh” ride.
In the present work, the 2mode shape of the
composite leaf spring has a natural frequency of
1.7444Hz and 1.7496 Hz which provides for good ride
quality.
Table 2 Normal Stresses in Shear
Table 3 Deflection in Load String
ACKNOWLEDGEMENTS
The authors would like to thank the anonymous
reviewers for their comments which were very helpful
in improving the quality and presentation of this paper.
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[2] Georg Rill, Norbert Kessing, Olav Lange and
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Atsugi, Japan 2003, 2003.
[3] SAE: Spring Design Manual ISBN: 1-56091-
680-X, 1996.
[4] A grimm, C. Winkler and ,R. Sweet Mechanics
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134.
Max Min Max Min Max Min
Master 79.73 -89.3 24.36 -25.66 18.02 -12.69
Second 89.78 -86.05 40.45 -26.07 34.96 -36.32
Composite 18.28 -23.26 5.25 -5.42 3.37 -3.28
σxy(Mpa) σyz(Mpa) σzx(Mpa)
Leaf
Material Max. Average Total
Mater 53.22
Second 52.18
54.03 54.03 -Composite Leaf
52.7 55.21
Maximum Deflection
Steel