Vibration Analysis of Hybrid Composite Leaf Spring

Vibration Analysis of Hybrid Composite Leaf Spring S.B. Jadhav 1, Prof. A.V. Karande 2 1 DGOI, FOE, Bhigvan, Pune, Maharashtra India, 2 Prof., DGOI, FOE, Bhigvan, Pune, Maharashtra India ABSTRACT This Project Vibration analysis plays a very important role in the design of composite leaf spring, since the failure due to vibration is more prominent rather than material failure. The heavy & light vehicles need a good suspension system that can deliver a good ride and handling. At the same time, it needs to be lightweight and have an excellent fatigue life. Springs are crucial suspension elements in cars necessary to minimize the vertical vibrations, impacts and bumps due to road irregularities and create a comfortable ride. Vertical vibrations and impacts are buffered by variations in the spring deflection so that potential energy is stored in spring as strain energy and then releases slowly. So increasing the strain energy capacity of the leaf spring ensures a more compliant suspension system. Therefore, material with maximum strength and minimum modulus of elasticity in the longitudinal direction is the most suitable material for a leaf spring. Composite materials are now used extensively in the automotive industry to take the place of metal parts. So it is essential to provide hybrid composite leaf spring with reduced spring rate, which evenly distributes glass fibers and carbon fibers, graphite fiber throughout resin matrix. The hybrid composite materials offer the various advantages like maximum strength, minimum modulus of elasticity in the longitudinal direction, weight & vibration reduction, improved packaging, strain energy capacity, improved durability & fatigue life and cost reduction due to the use of glass fibers & carbon fibers over the conventional composites materials. This research work an attempt has been made to predict the vibration behavior of Hybrid composite leaf spring which is the combination of epoxy glass fiber and carbon fiber under the analysis of FFT and ANSYS and then comparison of these results. KEY WORDS- Hybrid composite leaf spring, vibrations, epoxy glass fiber carbon fiber. 1. INTRODUCTION Leaf spring (also known as flat plate) is made up of plat plate. Leaf spring can be designed in two ways mono leaf spring or multi leaf spring. Mono leaf spring is used for the lighter vehicle which consists of a single steel plate. While in the multi leaf spring a leaf spring can be made from several leaves stacked on top of each other in several layers, often with progressively shorter leaves. Leaf springs can serve locating and to some extent damping as well as springing functions. While the inter leaf friction provides a damping action. A leaf spring can either be attached directly to the frame at both ends or attached directly at one end, usually the front, with the other end attached through a shackle, a short swinging arm. The shackle takes up the tendency of the leaf spring to elongate when compressed and thus makes for softer springiness. Spring is crucial suspension elements in car necessary to minimize the vertical vibration, Impact and bumps due to road irregularities and create a comfortable ride. Composite materials are ideal for structural application where high strength to weight and stiffness to weight ratio are required. These materials are basically hybrid materials formed of multiple materials in order to utilize their individual structural advantages in a single structural material. The composite material then has the properties of the two materials that have been combined. The advantage of composite materials is that, if well designed, they usually exhibit the best qualities of their components or constituents and often some qualities that neither constituent possesses. Some of the properties that can be improved by forming a composite material are Strength, Fatigue life, Stiffness, Corrosion resistance, Thermal insulation, Weight, Wear resistance, Attractiveness, Thermal conductivity, Acoustical insulation. Naturally, not all of these properties are improved at the same time nor is there usually any requirement to do so. In fact, some of the properties are in conflict with one another, e.g., thermal insulation versus thermal conductivity. Modern composites using fiberreinforced matrices of various types have created a revolution in high-performance structures in recent years. Advanced composite materials offer significant advantages in strength and stiffness coupled with light weight, relative to conventional metallic materials. 2. THE MAIN OBJECTIVE OF THIS PAPER 16

This project work focuses on using composite material for leaf spring of heavy vehicle for weight reduction without losing strength. The objective of present dissertation is to carry out finite element analysis of composite leaf spring and experimental validation of it. To compare between conventional steel leaf & Hybrid composite leaf spring vibration characteristics by FEM. The main aim of the project is to determine the vibration frequency in Hz with displacement mechanical loading and suggest the minimum design changes in the hybrid composite leaf spring. This research work an attempt has been made to predict the vibration behavior of leaf spring under dynamic forces and to check the suitability of composite materials combination like E-Glass/ Epoxy, & Carbon/Epoxy vehicle leaf spring. 3. LITERATURE SURVEY W. J. Yu and H. C. Kim [01] have introduced Double Tapered FRP Beam for Automotive Suspension Leaf Spring. Fundamental properties of the dimensioning of the double tapered FRP leaf spring were investigated. The optimal taper ratio was proved to be 0.5. Prototype longitudinal type double tapered leaf springs to replace four leaf steel springs were made from glass fiber and epoxy. A new device for attachment of the longitudinal type double tapered GRP leaf spring to the vehicle was prepared. Prototype GRP leaf springs showed a superior endurance and fail-safe characteristics, and the device or vehicle attachment was proved to have a sufficient strength. Erol Sancaktar and Mathieu Gratton [02] have investigated Design, analysis, and optimization of composite leaf springs for light vehicle applications. Design and manufacture of a functional composite spring for a solar powered light vehicle is described. The objective is to provide an understanding of the manufacture, use, and capabilities of composite leaf springs produced by using unidirectional Eglass roving impregnated by an epoxy resin for light vehicle applications where the vehicle weight is of primary concern. The current design application involves a solar powered car. I. Rajendra and S. Vijayarangam [03] have investigated Optimal design of a composite leaf spring using genetic algorithms. A formulation and solution technique using genetic algorithms for design optimization of composite leaf springs is presented here. The suspension system in automobile significantly affects the behavior of the vehicle i.e. vibration characteristics including ride comfort, directional stability, etc. Leaf springs are commonly used in suspensions systems of automobile and subjected to millions of varying stress cycles leading to fatigue failure. If the unsprung wait is reduced, then the fatigue stress induced in the leaf spring is also reduced. Leaf spring contributes for about 10-20% 0f unsprung wait. A composite material offers minimum wait. A reduction of 75.8% weight is achieved when several steel leaf springs is replaced with a mono-leaf composite spring under the identical conditions of design parameters and optimization. H.A. Al-Qureshi [04] has introduced Automobile leaf spring from composite materials. A single leaf variable thickness spring of glass fiber reinforced plastic with similar mechanical and geometric properties to the multi leaf steel spring. Mahmood M. Shokrieh and Davood Rezaei [05] have investigated Analysis and optimization of a composite leaf spring. A four-leaf steel spring used in the rear suspension system of light vehicles is analyzed using ANSYS V5.4 software. The finite element results showing stresses and deflections verified the existing analytical and experimental solutions. Using the results of the steel leaf spring, a composite one made from fiberglass with epoxy resin is designed and optimized using ANSYS. Main consideration is given to the optimization of the spring geometry. The objective was to obtain a spring with minimum weight that is capable of carrying given static external forces without failure. The design constraints were stresses (Tsai Wu failure criterion) and displacements. The results showed that an optimum spring width decreases hyperbolically and the thickness increases linearly from the spring eyes towards the axle seat. Compared to the steel spring, the optimized composite spring has stresses that are much lower, the natural frequency is higher and the spring weight without eye units is nearly 80% lower. J.P. Hou et.al. [06] have investigated Evolution of the eye-end design of a composite leaf spring for heavy axle loads. This paper presents the design evolution process of a composite leaf spring for freight rail applications. Three designs of eye-end attachment for composite leaf springs are described. The material used is glass fibre reinforced polyester. Static testing and finite element analysis have been 17

carried out to obtain the characteristics of the spring. Load deflection curves and strain measurement as a function of load for the three designs tested have been plotted for comparison with FEA predicted values. The main concern associated with the first design is the delamination failure at the interface of the fibres that have passed around the eye and the spring body, even though the design can withstand 150 kn static proof load and one million cycles fatigue load. FEA results confirmed that there is a high interlaminar shear stress concentration in that region. The second design feature is an additional transverse bandage around the region prone to delamination. Delamination was contained but not completely prevented. The third design overcomes the problem by ending the fibres at the end of the eye section. Hiroyuki Sugiyama et.al. [07] have conducted Development of nonlinear elastic leaf spring model for multi body vehicle systems. In this investigation, a nonlinear elastic model of leaf springs is developed for use in the computer simulation of multibody vehicle systems. In the leaf spring model developed in this investigation, the distributed inertia and stiffness of the leaves of the spring are modeled using the finite element floating frame of reference formulation that accounts for the effect of the nonlinear dynamic coupling between the finite rotations and the leaf deformation. The leaf spring geometry and deformations are modeled using nodal degrees of freedom defined with respect to the spring body coordinate system. By assuming that the leaf deformation can be large but the leaf deformed shape remains simple, component mode synthesis techniques can be used to significantly reduce the number of deformation coordinates. The nonlinear stiffness matrix is first developed for the finite element of each leaf and is used to determine the overall leaf spring stiffness matrix. The pre-stresses, the contact and friction that characterize the nonlinear behavior of leaf springs are discussed. Using the nonlinear leaf spring formulation presented in this study, a detailed multibody model for a sport utility vehicle is developed. It is shown that the proposed leaf spring model that accounts for the effect of windup, contact and friction between the spring leaves can be effectively used for assessing the dynamic stability of sports utility vehicles. 4. EXPERIMENTAL SETUP USING FFT Fig. 4.1 Experimental setup The basic experimental modal setup is shown in fig 4.1. The frequency response function (FRP) in terms of reacceptance ratio of displacement to forces was measured using the experimental setup. The Hybrid composite leaf spring was fixed to the rigid fixture and tested by using two fixed end conditions. An impact with a force transducer is used as an excitation source (channel 1) and an accelerometer is used as the output (channel 2).The point of impact and position of the accelerometer are chosen such a way that the natural frequencies of the system can be easily determined by locating peaks of transfer function. Test would be conducted as follows: 1. Mount an accelerometer on the composite leaf spring and connect it to channel 2 of the analyzer. 2. Connect an instrumented force hammer to channel 1. 3. Set the analysers trigger level (channel 1). Set the input attenuation of channel 1 and channel 2 to avoid overload. 4. Choose a time window which shows preparing down of time domain output of system. 5. View transfer function magnitude and phase. 6. View the coherence display. A value near 1.0 indicates a good test. 7. The FRF data then transferred to modal analysis software to estimate modal parameters (Natural frequencies and damping ratios) 8. Use single degree of freedom form curve fitting routine over each modal peak to obtain modal parameters for that mode. This procedure is repeated for the remaining next natural frequencies. Fig. 4.1 shows the experimental set up. 5. Result and Discussion FFT Results of composite leaf spring 1) For 1 st mode 18

Fig.5.1 Frequency response graph for 1 st mode 2) For 2 nd mode 3) Third mode shape Fig.5.5 Second Mode Shape Fig.5.2 Frequency response graph for 2 st mode 3) For 3 rd mode Fig.5.3 Frequency response graph for 3 st mode 1 st mode shape the natural frequency hybrid composite leaf spring is 41Hz, for the 2 nd mode shape the natural frequency hybrid composite leaf spring is 87Hz, for the 3 rd mode shape the natural frequency hybrid composite leaf spring is 141Hz. So as the mode shapes changes the natural frequencies of composite leaf spring increases. FEA Results of composite leaf spring 1) First Mode Shape Fig.5.8 Third Mode Shape Table 1 Comparison of FEA Results with FFT of Hybrid composite leaf spring Mode No. Natural Frequency of Hybrid Composite Leaf Spring (Hz) by FEA Natural Frequency of Hybrid Composite Leaf Spring (Hz) by FFT 1 38.419 41 2 86.523 87 3 138.39 141 These are the natural frequencies of Hybrid Composite Leaf spring by using FFT analysis and ANSYS analysis. So both frequencies for different mode shapes are much closer. This shows the validations of natural frequencies of Hybrid Composite Leaf spring by ANSYS and FFT analysis. Fig. 5.4 First Mode Shape 2) Second mode shape Conclusion The natural frequencies of conventional leaf spring are obtained easily by using ANSYS Software at different mode numbers. From the results obtained by modified design of hybrid composite leaf spring we observed that the values of natural frequencies of leaf spring have been reduced. We have the natural frequencies of hybrid composite leaf spring from 19

modal analysis of spring and we have analyzed the spring experimentally with FFT Analyzer. With these results obtained we conclude that the natural frequencies of FEA for composite leaf spring are closer with natural frequencies of FFT analysis for composite leaf spring. Also the natural frequencies of hybrid composite leaf spring are less as compare to the convention steel leaf spring. So use of composite material in leaf spring reduces the range of natural frequencies in the leaf spring. References 1. W. J. Yu and H. C. Kim, Double Tapered FRP Beam for Automotive Suspension Leaf Spring, Composite Structures, 1988, pp. 279-300. 2. Erol Sancaktar and Mathieu Gratton, Design, analysis, and optimization of composite leaf springs for light vehicle applications, Composite Structures, 1999, pp. 195-204. 3. I. Rajendra and S. Vijayarangam, Optimal design of a composite leaf spring using genetic algorithms, Computers and structures, 2000, pp. 1121-1129. 4. H.A. Al-Qureshi, Automobile leaf spring from composite materials, Journal of materials processing technology, 2001, pp.58-61. 5. Mahmood M. Shokrieh and Davood Rezaei, Analysis and optimization of a composite leaf spring, Composite Structures, 2003, pp. 317 325. 6. J.P. Hou, J.Y. Cherruault, I. Nairne, G. Jeronimidis, R.M. Mayer, Evolution of the eye-end design of a composite leaf spring for heavy axle loads, Composite Structures, 2005, pp. 351-358. 7. Hiroyuki Sugiyama, Ahmed A. Shabana, Mohamed A. Omar, Wei-Yi Loh, Development of nonlinear elastic leaf spring model for multibody vehicle systems, Computer. Methods Appllied. Mechanics and. Engineering, 2006, pp. 6925 6941. 20