**2. Steel Leaf Spring (SLS)**

#### **2.1 Design and finite element analysis**

Design parameters of 7-leaf steel spring that exists in a light passenger car (available in India) are given in Table 1. The spring is assumed to be a double cantilever beam, even though the leaf spring is simply supported at the ends. Also, this spring is geometrically and materially symmetrical so that only one half is considered with cantilever beam boundary conditions for the analysis to save the calculation time. Axle seat is assumed to be fixed and loading is applied at free eye end.


Table 1. Parameters of steel leaf spring.

A stress analysis was performed using two-dimensional, plane strain finite element model (FEM). A plane strain solution is considered because of the high ratio of width to thickness of a leaf. Model is restrained to the right half part only because the spring is symmetric. The contact between leaves is emulated by interface elements and all the calculations are done using ANSYS (version 7.1) (Eliahu Zahavi,1992). Nodes are created based on the values of co-ordinates calculated and each pair of coincident nodes is joined by the interface elements that simulate action between neighboring leaves. Element selected for this analysis is SOLID42(Eliahu Zahavi,1992) which behaves as the spring having plasticity, creep, swelling, stress stiffening, large deflection, and large strain capabilities. Element is defined by four nodes having two degrees of freedom at each node: translations in the nodal x and y directions. Interface elements CONTA174 that is defined by eight nodes and TARGE170 are used to represent contact and sliding between adjacent surfaces of leaves. The contact 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 using spring design SAE manual.

#### **2.2 Static testing**

60 Materials Science and Technology

fatigue strength of composite structures at an arbitrary combination of frequency, stress

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

Design parameters of 7-leaf steel spring that exists in a light passenger car (available in India) are given in Table 1. The spring is assumed to be a double cantilever beam, even though the leaf spring is simply supported at the ends. Also, this spring is geometrically and materially symmetrical so that only one half is considered with cantilever beam boundary conditions for the analysis to save the calculation time. Axle seat is assumed to be fixed and

> Total length (eye-to-eye), mm 1150 Arc height at axle seat(Camber), mm 175 Spring rate, N/mm 20 Number of full length leaves 2 Number of graduated leaves 5 Width of the leaves, mm 34 Thickness of the leaves, mm 5.5 Full bump loading, N 3250 Spring weight, kg 13.5

A stress analysis was performed using two-dimensional, plane strain finite element model (FEM). A plane strain solution is considered because of the high ratio of width to thickness of a leaf. Model is restrained to the right half part only because the spring is symmetric. The contact between leaves is emulated by interface elements and all the calculations are done using ANSYS (version 7.1) (Eliahu Zahavi,1992). Nodes are created based on the values of co-ordinates calculated and each pair of coincident nodes is joined by the interface elements that simulate action between neighboring leaves. Element selected for this analysis is SOLID42(Eliahu Zahavi,1992) which behaves as the spring having plasticity, creep, swelling, stress stiffening, large deflection, and large strain capabilities. Element is defined by four nodes having two degrees of freedom at each node: translations in the nodal x and y directions. Interface elements CONTA174 that is defined by eight nodes and TARGE170 are used to represent contact and sliding between adjacent surfaces of leaves. The contact

**Parameters Values** 

ratio and temperature has been presented (Yasushi,1997).

**2. Steel Leaf Spring (SLS)** 

loading is applied at free eye end.

Table 1. Parameters of steel leaf spring.

**2.1 Design and finite element analysis** 

of steel and composite leaf springs (Senthilkumar & Vijayarangan,2007).

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


Table 2. Stress analysis of steel leaf spring using experimental, analytical and FEM.
