09-07-2012, 04:57 PM
Analysis and optimization of a composite leaf spring
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Introduction
Composite materials are now used extensively in the
automotive industry to take the place of metal parts.
Several papers were devoted to the application of com-
posite materials for automobiles. Some of these papers
are reviewed here, with emphasis on those papers that
involve composite leaf springs. Breadmore [1,2] studied
the application of composite structures for automobiles.
Moris [3] concentrated on using composites in the rear
suspension system. Daugherty [4] studied the applica-
tion of composite leaf spring in heavy trucks. Yu and
Kim [5] designed and optimized a double tapered beam
for automotive suspension leaf spring. Corvi [6] inves-
tigated a preliminary approach to composite beam de-
sign and used it for a composite leaf spring.
Steel leaf spring
Parameters of the four-leaf steel spring used in this
work are shown in Table 1. This spring is unsymmetrical
so that the length of the front half is 559 mm and the
rear half is 686 mm. Every leaf is 50 mm wide and 7 mm
thick.
Experimental results from testing the steel leaf spring
under static and full bump loading containing the
stresses and deflections are listed in the Table 2.
Composite 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 some
designs the thickness and width of the spring are fixed
along the longitudinal axis [10]. In some types, the width
is kept fixed and thickness is variable along the spring
[11]. In other types width is fixed and in each section the
thickness is varying hyperbolically so that at two edges
the thickness is minimum and in the middle is maximum
[12]. Another design is presented by Yu and Kim [5] so
that the width and thickness are fixed from eyes to the
middle of spring and towards the axle seat the width
decreases hyperbolically and thickness increases linearly.
In their design the curvature of spring and fiber mis-
alignment in the width and thickness direction are
neglected. Therefore, in this study the simplified assump-
tions are removed and the spring is designed using a
more realistic situation.
Summary and results
A steel leaf spring used in the rear suspension of light
passenger cars was analyzed by two analytical and finite
element methods. The experimental results verified the
analytical and the finite element solutions.
The steel leaf spring was replaced with an optimized
composite one. Main consideration was given to the
optimization of the leaf spring geometry. The objective
was to obtain a spring with minimum weight that is
capable of carrying given static external forces by con-
straints limiting stresses (Tsai–Wu criterion) and dis-
placements.