This paper discusses the advantages of composite structures over conventional metallic structures and the replacement of steel spring with fiberglass composite leaf spring. It also covers the design and analysis of a Mono Composite leaf spring using E-Glass/Epoxy.
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International Journal of Mechanical and Industrial Engineering (IJMIE), ISSN No. 2231 –6477, Vol-2, Issue-1, 2012 97 Design and Analysis of Composite Leaf Spring Y. N. V. Santhosh Kumar & M. Vimal Teja Dept. of Mechanical Engineering, Nimra College of Engineering & Technology, Ibrahimpatnam, Vijayawada E-mail: santhosh.nagarjuna@gmail.com Abstract -In these paper, composite structures for conventional metallic structures has many advantages because of higher specific stiffness and strength of composite materials is discussed. The automobile industry has shown increased interest in the replacement of steel spring with fiberglass composite leaf spring due to high strength to weight ratio. This work deals with the replacement of conventional steel leaf spring with a Mono Composite leaf spring using E-Glass/Epoxy. The design parameters were selected and analyzed with the objective of minimizing weight of the composite leaf spring as compared to the steel leaf spring. The leaf spring was modeled in Pro/E and the analysis was done using ANSYS Metaphysics software. Keywords -Composite Material, Steel Leaf Spring, Pro-E, FEA, ANSYS. I.INTRODUCTION Originally called laminated or carriage spring, a leaf spring is a simple form of spring, commonly used for the suspension in wheeled vehicles. It is also one of the oldestformsofspringing,datingbacktomedieval times. Sometimes referred to as a semi-elliptical spring orcartspring,ittakestheformofaslender arcshaped length of spring steel of rectangular cross- section. The center of the arc provides location for the axle, while tie holes called eyes are provided at either end for attaching to the vehicle body. For very heavy vehicles, 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. A leaf spring can either be attached directly to the frame at both ends or attached directly at one end, usually the front, with theotherendattached throughashackle,ashort swinging arm. The shackle takes up the tendency of the leaf spring to elongate when compressed and thus makes for softer springiness. Theautomotiveindustryisexploringcomposite materialsforstructuralcomponentsconstructionin order to obtain the reduction of weight without decrease in vehicle quality and reliability. To conserve the natural resources and economize energy, weight reduction has been the main focus of automobile manufacturer in the presentscenario.Actually,thereisalmostadirect proportionalitybetween the weight of the vehicle and its fuel consumption, particularly in city driving. The advanced composite materials such as Graphite, Carbon, Kevlar and Glass with suitable resins are widely used because of their high specific strength (strength/density) and high specific modulus (modulus/density). Advanced composite materials seem ideally suited forsuspension(leafspring)applications.Their elastic properties can be tailored to increase the strength and reduce the stresses induced during application. Fig. 1 : Leaf Spring The objective of the present work is to design the E- Glass/Epoxy composite leaf spring without change in stiffness for automobile Suspension system and analyze it. This is done to achieve the following.
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Design and Analysis of Composite Leaf Spring International Journal of Mechanical and Industrial Engineering (IJMIE), ISSN No. 2231 –6477, Vol-2, Issue-1, 2012 98 •To the replace conventional steel leaf springs with Eglass/Epoxy composite leaf spring without change in stiffness. •Toachievesubstantialweightreductioninthe suspensionsystemby replacingsteelleafspring with composite leaf spring. II.PRINCIPLE OF LEAF SPRING The suspension leaf spring is one of the potential items for weight reduction in automobile as it accounts for ten to twenty percent of the unsprung weight. The introduction of composites helps in designing a better suspension system with better ride quality if it can be achieved without much increase in cost and decrease in quality and reliability. In the design of springs, strain energy becomes the major factor. The relationship of the specific strain energy can be expressed as 2/UEσρ= Whereσis the strength, ρis the density and E is the Young’s Modulus of the spring material It can be easily observed that material having lower modulus and density will have a greater specific strain energycapacity.Theintroductionof composite materialsmadeitpossibletoreducethe weightoftheleafspringwithoutreductionof load carrying capacityand stiffnessdue to the following factors of composite materials as compared to steel. Fig. 2 : Arrangement of leaf spring in a car Model An upturned spring eye is used to attach the front end of semi-elliptic leaf spring to the chassis frame, and a free end with a bracket constraining vertical motion to attach the back end of semi-elliptic leaf spring to the chassis frame. A Composite in engineering sense is any materials that have been physically assembled to form one single bulk without physical blending to foam a homogeneous material.Theresultingmaterialwouldstillhave components identifiableastheconstituentofthe different materials. One of the advantages of composite is that two or more materials could be combined to take advantage of the good characteristics of each. III. DESIGN OF LEAF SPRING Considering several types of vehicles that have leaf springs and different loads on them, various kinds of composite leaf spring have been developed. In the case of multi- leaf composite leaf spring, the interleaf spring friction plays a spoil spot in damage tolerance. It has to be studied carefully. In the present work, only a leaf spring with constant thickness, constant width design is analyzed. Fig.3 : Main Parts of Leaf Spring Thefollowingcross-sectionsofleaf springfor manufacturing easiness are considered. 1.Constant thickness, constant width design 2.Constant thickness, varying width design 3.Varying width, varying width design. Table 1 Design Specifications ParameterSpecification MaterialSteel(55Si2Mn90) Tensile Strength1962N/Sq. mm Yelid Strength1470N/Sq.mm Young's Modulus2.1e5 N/Sq.mm Spring Weigth16.4 Kg Thickness at the Center12mm Thickness at extreme ends9mm
Design and Analysis of Composite Leaf Spring International Journal of Mechanical and Industrial Engineering (IJMIE), ISSN No. 2231 –6477, Vol-2, Issue-1, 2012 99 For steel leaf spring cross section is according to considereddesign andnotaltered. Due to manufacturing ease, a composite leaf spring with uniform rectangularcrosssectionisconsideredand analyzed. IV. PROBLEM DEFINITION Objective of present work is to consider an existing automobile leafspringmodelTATASUMOEZRR PARABOLICREARandtodesignand analyzea compositeleafspringwithupturnedeyewithout changing stiffness in order to replace the existing steel leaf spring with a composite leaf spring. A spring eye is essentially the end of a leaf spring bended into a circular shape to allow rotation about the spring eye. The main types of spring eye designs are upturned,militarywrapper,down turned, and Berlin eyesFig:4.TypesUpturnedeyesarethemost commonlyusedtypeofspringeyebecauseof their simple design and high durability. Upturned eyes are highly durable because they resist stress due to vertical forces on a suspension system. Fig. 4 : Types of Spring Eyes Unlike other spring eye designs, an upturned eye appliesvertical loadson thelinear leaf section that was not bent to form the eye. Therefore, upturned eyes have less of a tendency to unwrap as result of vertical forces than the other types of spring eyes. The Following Assumptions are made for this work. 1.The leaf spring has a uniform, rectangular cross section. 2.All non- linear effects are excluded. 3.The stress-strain relationship for composite material islinearandelastic;hence Hooke’slawis applicable for composite materials. 4.Acoustical fluid interactions are neglected, i.e., the leaf spring is assumed to be in vacuum. 5.The load is distributed uniformly at the middle of the leaf spring. V.STATIC ANALYSIS OF LEAF SPRING The leaf spring modeled in Pro/E was imported to ANSYS in IGES format. Since leaf spring was modeled as a solid, solid element named SOLID187 was used to mesh the model. SOLID187 element is a higher order 3-D,10-nodeelement. SOLID187hasaquadratic displacementbehaviorandiswellsuitedto modeling irregular meshes (such as those produced from various CAD/CAM systems). The element is defined by 10nodeshavingthreedegreesoffreedomateach node: translations in the nodal x, y, and z directions. The elementhasplasticity,hyper elasticity,creep,stress stiffening, large deflection, and large strain capabilities. The geometry, node locations, and the coordinate system for this element are shown in the figure 5. In addition to the nodes, the element input data includestheorthotropic oranisotropicmaterial properties.Orthotropicandanisotropicmaterial directionscorrespondingtotheelementcoordinate directions. Fig. 5 : Solid 187 3D 10 node tetra hydral structure VI. RESULTS AND CONCLUSIONS It was observed that the deflection in the composite leafspringwasalmost equalsowecansaythat composite spring had the same stiffness as that of steel spring. Itwasobservedthatthecompositeleafspring weighed only 39.4% of the steel leaf spring for the analyzed stresses. Hence the weight reduction obtained
Design and Analysis of Composite Leaf Spring International Journal of Mechanical and Industrial Engineering (IJMIE), ISSN No. 2231 –6477, Vol-2, Issue-1, 2012 100 by using composite leaf spring as compared to steel was 60.48 %. Fig.6 : Deflection of Master Leaf (Steel) By analyzing the design, it was found that all the stresses in the leaf spring were well within the allowable limits and with good factor of safety. It was found that thelongitudinalorientationsoffibersinthe laminate offered good strength to the leaf spring. Ride quality is generally quantified as the natural frequency of a suspension system. Fig. 7 : x Component of Stress in Master Leaf strings Suspension system natural frequencies less than 1 Hz will cause motion sickness in a vehicle’s passengers, and suspension system natural frequencies greater than 2.5 Hz will provide a “harsh” ride. Inthepresentwork,the2modeshapeofthe compositeleafspringhasa naturalfrequencyof 1.7444Hz and 1.7496 Hz which provides for good ride quality. Table 2 Normal Stresses in Shear Table 3 Deflection in Load String ACKNOWLEDGEMENTS The authors would like to thank the anonymous reviewers for their comments which were very helpful in improving the quality and presentation of this paper. REFERENCES: [1]J.Andreasson,M.Gavert.The VehicleDynamics LibraryOverviewand Applications Modelon.,Homepage:http:// www.modelon.se/. In Proceedings of Modelica’ 2006, Vienna, Sep. 2006. [2]Georg Rill,Norbert Kessing, Olav Lange and Jan Meier: Leaf Spring Modelling for Real Time Applications In the 18th IAVSD-Symposium in Atsugi, Japan 2003, 2003. [3]SAE:SpringDesignManualISBN:1-56091- 680-X, 1996. [4]A grimm, C. Winkler and ,R. Sweet Mechanics of HeavyDutyTruckSystems.Universityof Michigan transportation research institute, UK , 2004. [5]Chen, F. C., and Hsu, M. H., 2001, ‘‘On the TransmissionEfficiencyofSpring-Type OperatingMechanismforSF6GasInsulated Circuit Breakers,’’J. Mech. Eng. Sci., 215(10), pp. 1239–1249. [6]Fu-Chen Chen, “Dynamic response of spring-type operatingmechanismfor69KVSF6gas insulatedcircuitbreaker,”Mechanismand Machine Theory, Volume 38, 2003, Pages 119- 134. MaxMinMaxMinMaxMin Master79.73-89.324.36-25.6618.02-12.69 Second89.78-86.0540.45-26.0734.96-36.32 Composite18.28-23.265.25-5.423.37-3.28 σxy(Mpa)σyz(Mpa)σzx(Mpa) Leaf MaterialMax. AverageTotal Mater53.22 Second52.18 54.0354.03-Composite Leaf 52.755.21 Maximum Deflection Steel