14-05-2012, 01:15 PM
Mono Composite Leaf Spring for Light Weight Vehicle
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INTRODUCTION
In order to conserve natural resources and economize
energy, weight reduction has been the main focus of
automobile manufacturer in the present scenario. Weight
reduction can be achieved primarily by the introduction of
better material, design optimization and better
manufacturing processes.
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. This helps in
achieving the vehicle with improved riding qualities. It is
well known that springs, are designed to absorb and store
energy and then release it. Hence, the strain energy of the
material becomes a major factor in designing the springs.
DESIGNS AND FABRICATION OF COMPOSITE MONO LEAF SPRING
Considering several types of vehicles that have leaf
springs and different loading on them, various kinds of
composite leaf spring have been developed. In multi-leaf
composite leaf spring, the interleaf spring friction plays a
spoil spot in damage tolerance. It has to be studied
carefully.
The following cross-sections of mono-leaf composite
leaf spring for manufacturing easiness are considered.
1. Constant thickness, constant width design.
2. Constant thickness, varying width design.
3. Varying width, varying thickness design.
Lay up Selection
The amount of elastic energy that can be stored by a
leaf spring varies directly with the square of maximum
allowable stress and inversely with the modulus of
elasticity both in the longitudinal direction. Composite
materials like the E-Glass/Epoxy in the direction of fibers
have good characteristics for storing strain energy. So, the
lay up is selected to be unidirectional along the
longitudinal direction of the spring. The unidirectional lay
up may weaken the spring at the mechanical joint area and
require strengthening the spring in this region.
Fabrication Process
The constant cross section design is selected due to its
capability for mass production, and to accommodate continuous
reinforcement of fibers and also it is quite suitable
for hand lay-up technique.
Many techniques can be suggested for the fabrication
of composite leaf spring from unidirectional GERP. Composite
leaf spring was fabricated using wet filamentwinding
technique [1]. In the present work, the hand lay-up
process was employed.
THREE-DIMENSIONAL FINITE ELEMENT ANALYSIS
To design composite leaf spring, a stress analysis was
performed using the finite element method done using
ANSYS software. Modeling was done for every leaf with
eight-node 3D brick element (solid 45) and five-node 3D
contact element (contact 49) used to represent contact and
sliding between adjacent surfaces of leaves. Also, analysis
carried out for composite leaf spring with bonded end
joints for Glass/Epoxy, Graphite/Epoxy and Carbon/Epoxy
composite materials and the results were compared with
steel leaf spring with eye end.