21-12-2012, 04:56 PM
Comparison of Performance of Two Leaf Spring Steels Used For Light Passenger Vehicle
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ABSTRACT
This paper describes static and fatigue life analysis of to conventional leaf springs made of respectively SUP 9
& EN 45. These springs are comparing for maximum stress, deflection and stiffness as well as fatigue life. The
CAD models are prepared in CATIA and analyzed by using ANSYS 12.1. Computer algorithm using C++
language has been used in calculating maximum stress, deflection and stiffness. Calculated results are
comparing with FEA result. SUP 9 springs has lower value of maximum stress, deflection and stiffness in
compare to EN45 spring. Predicted fatigue life of SUP 9 spring is higher than EN45 spring. Although, market
price is much lower than Sup 9 spring.
INTRODUCTION
In order to conserve natural resources and economic, energy, weight reduction has been the main focus of
automobile manufactures. In the present scenario weight reduction can be achieved primarily by the introduction
on better material. Design specialization and better manufacturing process.[1]
Leaf spring should absorb vertical vibration and impacts due to load irregularities by means of variation in the
spring deflection show that potential energy is stored in spring as strain energy and then release slowly so,
increasing energy stored capability of a leaf spring insure a more complaint suspension system.[2]
The large vehicle needs a good suspension system that can be delivered a good ride and handling. At the same
time that component need to be light weight and had an excellent of fatigue life.
MATERIALS
The materials SUP 9 steel (equal grade5160 steel) behavior characteristics related to spring performance are first
determined. The effect of component processing on these characteristics is then documented followed by a
demonstration of the application of these concepts to component fatigue life. Of particulars concern in fatigue
problems is the tendency for material properties to change as a result of cyclic deformation. These
circumstances require the determinations cyclic stress –strain relation for fatigue analysis.[7]
Many industries are manufactured steel leaf spring by EN 45 material; these materials are widely used for
production of parabolic leaf spring and conventional multi leaf spring. Leaf spring absorbed the vertical
vibrations, shocks and bumps loads (induced due to road irregularities) by means of spring deflection, so that the
potential energy stored in the leaf spring and then relieved slowly[8]. Ability to store and absorb more amount of
strain energy insures the comfortable suspension system.
CAD MODELING
CAD Modeling any project is one of the most time consuming process. This model drawing can not shoot
directly from the sketch finite element model. Finite element software will consider shape, whatever is made in
CAD model the model of multi leaf spring structures also includes many complicated parts, which are difficult
to make by any of other CAD modeling as well as finite element software. The complete leaf spring structure
performed by using CATIA V5R16 model of leaf spring consists of total three parts which are assembled
together in an assembly design to make a complete spring model.
FATIGUE LIFE
The main factors that contribute fatigue failure include number of load cycles analytically, range of stress and
mean stress experiments in each load cycle and presence of local stress concentration. Testing of leaf spring
using the regular procedure consumes a lot of time. Hence SAE [9] suggests a procedure for accelerated which
give quick result, particularly for steel leaf spring. The result of the accelerated tests can be extra plotted to get
the actual fatigue life under normal fatigue life conditions. Following the procedure out lined by the references
[9, 10].
ANALYSIS USING ANSYS
The CAD model of leaf spring now imported into ANSYS 12.1 the boundary conditions and material properties
are specified as for the standards used in the practical application. The material used for the leaf spring for
analysis is structure steel, which have approximately similar isotropic behavior and properties as compared to
SUP 9 and EN 45.
BOUNDARY CONDITION
Model of parabolic spring was partition into small region for easier mashing process method is used patch
conforming method the boundary condition was set according to rear static load which is the front eye was
allowing on a rotational at y axis and rear eye was constrained in y and z translation and x and z rotations
alloying free x translation and y rotation. Contact from main to helper leaf also been defined helper leaf was
constant 2nd degree of freedom to represent the clip that holds that to spring together. Finally vertical load was
applied at the center of the leaf spring.
CONCLUSION
These work involves and comparison of conventional SUP9 and EN45 material leaf spring under static loading
conditions the model is preferred of in CATIA and then analysis is perform through computer programming in
C++and ANSYS 12.1 from the result obtained it will be concluded that.
1. Variation of 3.82% is observed in maximum stress among analytical and FEA values for SUP9
material.
2. Variation of 4.38% is observed in maximum stress among analytical and FEA values for EN45
material.