**1. Introduction**

18 Will-be-set-by-IN-TECH

58 Materials Science and Technology

Yang, B. & Chen, G. (2003). Partially coherent phonon heat conduction in superlattices, *Phys.*

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complex aggregates of monodispersed colloids with well-defined sizes, shapes, and

URL: *http://link.aps.org/doi/10.1103/PhysRevB.67.195311*

URL: *http://dx.doi.org/doi/10.1063/1.98526*

URL: *http://dx.doi.org/10.1021/ja011048v*

*Rev. B* 67: 195311.

51(22): 1798–1800.

Weight reduction has been the main/primary focus of automobile manufactures. Suspension leaf spring, a potential item for weight reduction in automobiles, accounts for 10-25 percent of unsprung weight, (which is considered to be the mass not supported by leaf spring). Application of composite materials reduces the weight of leaf spring without any reduction on the load carrying capacity and stiffness in automobile suspension system(Daugherty,1981;Breadmore,1986;Morris,1986). A double tapered beam for automotive suspension leaf spring has been designed and optimized(Yu & Kim,1988). Composite mono leaf spring(Rajendran & Vijayarangan,2001) has also been analyzed and optimized.

Leaf spring should absorb vertical vibrations due to road irregularities by means of variations in the spring deflection so that potential energy is stored in the spring as strain energy and then released slowly. So, increasing energy storage capability of a leaf spring ensures a more compliant suspension system. A material with maximum strength and minimum modulus of elasticity in longitudinal direction is the most suitable material(Corvi,1990) for a leaf spring. Important characteristics of composites(Springer & Kollar,2003) that make them excellent for leaf spring instead of steel are higher strength-toweight ratio, superior fatigue strength, excellent corrosion resistance, smoother ride, higher natural frequency, etc. Fatigue failure is the predominant mode of in-service failure of many automobile components, especially the springs used in automobile suspension systems. Fatigue behaviour of Glass Fiber Reinforced Plastic epoxy (GFRP) composite materials has been studied(Hawang & Han,1986). A composite mono-leaf spring has been designed and their end joints are anlysed and tested for a light weight vehicle (Shivasankar & Vijayarangan, 2006). Experimental and numerical analysis are carried out on a single leaf constant cross section composite leaf spring (Jadhao & Dalu, 2011). Theoretical equation for predicting fatigue life, formulated using fatigue modulus and its degrading rate, is simplified by strain failure criterion for practical application. A prediction method for

Design, Manufacturing and Testing

using spring design SAE manual.

**2.2 Static testing** 

of Polymer Composite Multi-Leaf Spring for Light Passenger Automobiles - A Review 61

elements themselves overlay the solid elements describing the boundary of a deformable body and are potentially in contact with the target surface, defined by TARGE170. This target surface is discretized by a set of target segment elements (TARGE170) and is paired with its associated contact surface via a shared real constant set. An average coefficient of friction 0.03 is taken between surfaces(SAE manual). Also, analytical solution is carried out

The static testing on existing steel leaf spring was carried out using an electro-hydraulic test rig which is depicted in Fig.1. The rig has the ability to apply a maximum static load of 10 kN. It has a display unit to show both load and corresponding deflection. The loading was gradually from no load to full bump load of 3250 N. The strain gauges were employed to measure strain and to calculate stress. The experimental data corresponding to steel leaf spring is given in Table 2. Maximum normal stress, 11 from FEM is compared to the experimental solution under full bump loading (error, 8.63%). There is a good correlation for

**Parameters Experiment Analytical FEM** 

Load, N 3250 3250 3250 Maximum stress, MPa 680.05 982.05 744.32 Maximum deflection, mm 155 133.03 134.67 Maximum stiffness, N/mm 20.96 24.43 24.13 Table 2. Stress analysis of steel leaf spring using experimental, analytical and FEM.

**3. Composite Leaf Spring (CLS) (Senthilkumar & Vijayarangan,2007)** 

Applicability of CLS in automobiles is evaluated by considering the types of vehicles and different loading on them. Theoretical details of composite mono-leaf spring are reported (Ryan,1985; Richrad et al., 1990). In some designs, width is fixed and in each section the thickness is varied hyperbolically so that thickness is minimum at two edges and is maximum in the middle (Nickel,1986). Another design, in which width and thickness are fixed from eyes to middle of spring and towards the axle seat width decreases hyperbolically and thickness increases linearly, has been presented (Yu & Kim, 1988). In this design, curvature of spring and fiber misalignment in the width and thickness direction are neglected. A double tapered CLS has been designed and tested with optimizing its size for minimum weight(Rajendran & Vijayarangan,2002). A composite mono-leaf spring has also been designed and optimized with joint design(Mahmood & Davood,2003). The mono-leaf spring is not easily replaceable on its catastrophic failure. Hence, in this work, a composite multi leaf spring is designed and tested for its load carrying capacity, stiffness and fatigue

Material selected should be capable of storing more strain energy in leaf spring. Specific

stiffness in experimental, analytical and FEM methods (Table 2).

life prediction using a more realistic situation.

elastic strain energy can be written as:

**3.1 Material selection** 

fatigue strength of composite structures at an arbitrary combination of frequency, stress ratio and temperature has been presented (Yasushi,1997).

In the present work, a 7-leaf steel spring used in a passenger car is replaced with a composite multi leaf spring made of glass/epoxy composites. Dimensions and number of leaves of steel leaf spring (SLS) and composite leaf spring (CLS) are considered to be same. Primary objective is to compare their load carrying capacity, stiffness and weight savings of CLS. Ride comfort of both SLS and CLS is found and compared. Also, fatigue life of SLS and CLS is also predicted. This chapter of the book explores the work done on design optimisation, finite element analysis, analytical & experimental studies and life data analysis of steel and composite leaf springs (Senthilkumar & Vijayarangan,2007).
