Investigation on the Feasibility of Composite Coil Spring for Automotive Applications

Transcription

1 International Journal o Mechanical and Mechatronics Engineering Investigation on the Feasibility o Composite Coil Spring or Automotive Applications D. Abdul Budan, T.S. Manjunatha Abstract This paper demonstrates the easibility o replacing the metal coil spring with the composite coil spring. Three dierent types o springs were made using glass iber, carbon iber and combination o glass iber and carbon iber. The objective o the study is to reduce the weight o the spring. According to the experimental results the spring rate o the carbon iber spring is 4% more than the glass iber spring and 45% more than the glass iber/carbon iber spring. The weight o the carbon iber spring is 18% less than the glass iber spring, 15% less than the Glass iber/carbon iber spring and 8% less than the steel spring. Keywords Carbon iber, Glass iber, Helical composite spring, spring rate. S I. INTRODUCTION prings are crucial suspension elements on automobiles which are necessary to minimize the vertical vibrations, impacts and bumps due to road irregularities and create a comortable ride. Coil springs are commonly used or automobile suspension and industrial applications. The uel eiciency and emission gas regulations o automobiles are two important issues in these days. The best way to increase the uel eiciency is to reduce the weight o the automobiles by employing composite materials in the structure o the automobiles. Metal coil springs can be replaced by composite springs because o weight reduction and corrosion resistance. Metal coil springs cannot withstand high temperature. At high temperature where it is required to operate composite springs are used. Metal springs have several advantages, they are very cheap to produce and can be produced in almost all kinds o measures and in a very broad range o stiness. Since the composite materials are anisotropic in nature, the design and manuacture o composite springs are diicult. Thereore the application o composite materials in springs is not yet popular. However they are used in the suspension system o the automobiles [1]. For the purpose o saving energy and improving the D. Abdul Budan, is Proessor in Department o Studies in Mechanical Engineering, University BDT college o Engineering, Davangere-5776, Karnataka State, India. (Phone: , mob: e- mail: abdul_budan@ redimail.com). T.S. Manjunatha is Assistant Proessor in Department o Mechanical Engineering, GM Institute o Technology, P.B.Road, Davangere-5776, Karnataka State, India. (Phone: , Fax: , tsmdvg@redimail.com). perormance o the shock absorbers, with light weight and high quality, composite materials have to be used or today s vehicles. ith the more no o electric vehicles and hybrid vehicles are entering into the market in the present scenario, it has become essential to go or the light components or improving the eiciency. Because composite springs have some advantages over the metal springs, many researchers are actively involved in the study o composite springs. Chang-Hsuan Chiu et al [2] have conducted the experiment on mechanical behavior o helical composite springs. They have made the springs with dierent material structures like, unidirectional laminates, rubber core unidirectional laminates, unidirectional laminates with a braided outer layer, and rubber core unidirectional laminate with a braided outer layer. Henry and c. Robert have tried to replace the metal coil spring o a Rover saloon car using carbon iber []. P.K. Mallick has abricated and conducted the perormance test on the composite elliptic springs [4]. The composite lea springs are successully used in the suspension o the light vehicles [5]. The ibers used in these are unidirectional E-glass due to their high extensibility, toughness and low cost. The composite lea spring is designed and analyzed using ansys [6]. The results showed that an optimum spring width decreases hyperbolically and the thickness increases linearly rom the spring eye towards the axle seat. Compare to steel springs the optimized composite spring has strength that are much lower, the natural requency is high and the spring weight is nearly 8% lower. The use o composite materials can be extended to conventional automotive parts [7] like, propeller shat, drive shats [8]-[9], bumper beam [1], side door impact beam [11], universal joints, bearings, brakes [12]. The literature survey has revealed that, only prototype composite springs were prepared and tested or the perormance. Since the time consumed or the manuacturing o the composite springs is more, the standard and simple method o mass production o composite coil springs is required rom the economical point o view. In this study a spring rom the two wheeler is taken or replacement. Glass iber and carbon ibers are used or the manuacture o composite coil springs. The principal advantage o iber reinorced polymer matrix composites or automobile parts is weight savings, part consolidation, and 15

2 International Journal o Mechanical and Mechatronics Engineering improvement in NVH (noise, vibration and harshness). The absence o corrosion problems, which lowers maintenance cost or automobile parts, enables the use o iber reinorced polymeric composite. Three types o springs were manuactured in this study with glass ibers [GF], carbon ibers [CF], glass iber/carbon iber [GF/CF] roving. These springs were tested or spring rate and other parameters. The results show the easibility o composite springs or light vehicle applications. II. PRINCIPLES OF CYLINDRICAL HELICAL SPRINGS here and in Fig. 1, is the applied load on spring (N); the delection (mm); G, the modulus o rigidity (N/mm 2 ); n, the no o active coils in the spring; t, the side length o rectangular cross section (mm) parallel to the axis o the spring, b, the width o the spring perpendicular to the axis and c is D/t. It is ound rom (2) that the magnitude o the spring constant o the cylindrical helical spring with a rectangular cross section is related to the mean coil diameter, the no o active coils and the side length o rectangular crosssection, as well as the modulus o rigidity o the material used. A Speciic strain energy The main actor to be considered in the design o a spring is the strain energy o a material used. Speciic strain energy in the material can generally be expressed as 2 U (1) E This indicates that a material with lower young s modulus ]. Thus the composite materials oer high strength and light weight. B The spring constant o a cylindrical helical spring Fig.1 represents when a cylindrical helical spring with rectangular cross section is under the action o an applied compression orce, the primary reaction orce on the coil is torsion and thus induces shear stresses on the cross section. For homogeneous and isotropic materials, both the spring acilitate the wetting o ibers, epoxy resin with 2 h pot lie is rectangular wire spring can be approximately derived as [1]: Gb ( t.56b) K (2) 2.45nD K ' D(1.5t.9b) () 2 2 b t 4c K ' (4) 4c 4 c Fig. 1 Schematic diagram o the cylindrical helical spring with rectangular cross section. III. FABRICATION OF COMPOSITE COIL SPRINGS A. Selection o materials: The ibers chosen or the spring design are E-glass in the orm o roving and PAN based carbon iber roving due to their high extensibility, toughness and low cost. In order to selected. L-552/K-552 Lapox epoxy system or laminating applications is used. They exhibit good mechanical strength both static and dynamic. B. Properties o material. E-Glass Fibers: Shear modulus: 15 GPa Fiber strength:.45 GPa Elongation: 4.88% Tensile modulus: 81.4 GPa Density: 2.6g/cc Carbon Fiber: Shear modulus: GPa Fiber strength: 4.5GPa Tensile modulus: GPa Elongation: 1.7% Density: 1.8g/cc Epoxy Resin: Modulus o elasticity:.45 GPa 16

3 International Journal o Mechanical and Mechatronics Engineering Tensile strength: 69 Mpa Speciic strength : 6Mpa Ductility : 4% C. Fabrication o composite coil springs. Composite springs were manuactured by the ilament winding method. All the three types o springs were manuactured by the same method. A mandrel having the proile o the spring is prepared irst. (Fig 2). This mandrel is ixed in the lathe chuck. A mould release agent like silicone gel is applied on the mandrel. Glass iber roving/carbon iber roving is dipped in the measured quantity o resin and wound on the mandrel by rotating it on a lathe. Ater the complete winding o the roving in the proile o the mandrel a shrink tape is wound on the mandrel. This shrink tape applies the required pressure on the material. The mandrel along with the material and the shrink tape is cured in atmospheric temperature or 24 hours. Ater curing shrink tape is removed. The excess resin on the surace o the spring is removed by iling. The cured spring is removed rom the mandrel by rotating in the reverse direction. Fig shows the ibers wound on the mandrel. Fig 4 shows the cross sectional view o spring with mandrel. Fig 5 shows the abricated composite coil springs. The abricated spring is having the dimensions L=2mm, D=47mm, n=1, b=1mm, t=8mm and pitch=2mm. Fig. 2 Mandrel having the proile o the spring Fig. Fibers wound on the mandrel Fig. 4 Sectional view o the composite spring with the mandrel Fig. 5 The abricated springs IV. TESTING OF COMPOSITE SPRINGS A. Measurement o spring rate, ailure load and maximum compression. The spring constant o a helical spring can be determined at two measured points, corresponding to delection at both % and 7 % o the ull loading, on the load delection curve rom the compression test o a helical composite spring The ailure load and the maximum compression o a helical composite spring are also evaluated to ensure its sae use. In this study, a spring testing machine which automatically records the delection and load applied on the spring is used. The load delection curve can be drawn rom these data. The spring rate, maximum compression and ailure load can be evaluated rom the load delection curve. A special ixture is used to hold the spring in the machine. B. Measurement o iber volume raction. The iber volume raction o the spring is measured by the test conducted as per ASTM D 171. The iber weight raction and iber volume raction can be calculated rom the ormula: 17

4 International Journal o Mechanical and Mechatronics Engineering 1 X1% (5) 2 / V x1% (6) / / here is the iber weight raction (%), 1, the weight o iber (g), 2, the weight o specimen (g), V, iber volume raction (%), r, the resin weight raction (%),, the density o iber (g/cm ) and r, is the density o resin, (g/cm ). The mechanical properties o the three types o composite springs are listed in Table. T THE MECHANICAL PROPERTIES OF THE THREE OF SPRINGS. Material type Spring rate (N/mm) Failure load (N) Maximum compression (mm) Fiber volume raction (%) eight o spring (g) V. EXPERIMENTAL RESULTS AND DISCUSSION The objective o this research is to ind the easibility o replacing metal coil springs with the composite coil springs. Three types o composite springs were manuactured to study the use o composite materials. In order to improve relative reliability o the experimental results three sets o springs were abricated in each type and tests were conducted on these springs. The average values o these test results were taken or analysis. The average values o the load and delection rates o the three types o springs are given in table II. the load delection curves o the three types o springs are shown in Fig 6. The spring rates are calculated rom the load delection curves and are shown in Fig 7. As observed rom the results the spring rates o the carbon iber springs are 4% more than the glass iber spring and 45% more than the CF/GF spring. This is due to the more strength o the carbon iber compared to glass iber. Due to imperect bonding o glass iber and carbon ibers, the spring rates obtained by GF/CF springs are less. The ailure loads and maximum compression o the three types o springs is shown in Fig 8 and Fig 9. Again the ailure load o the carbon iber spring is 5% more than the carbon iber spring and 45% more than the GF/CF spring. The maximum compression o the carbon iber spring is more than the other two types o springs due to its high strength. The weight o the carbon iber spring is 18% less than glass iber spring and 15% less than the GF/CF spring. eight o all three types o composite springs is approximately 8% less than the steel spring. r r It is evident rom the above results the spring rate, ailure load, maximum compression o the spring depends upon the material characteristics. Since the properties o carbon iber are high speciic tensile strength, high modulus, low density, low coeicient o thermal expansion, heat resistant, chemical stability, and sel lubricity the springs made rom these ibers exhibit better properties. TABLE II THE AVERAGE VALUES OF THE LOAD AND DEFLECTIONS OF THE THREE OF SPRINGS L O A Sl no Delection Load (N) (mm) DEFLECTION (MM) Fig. 6 The load delection curves o the three types o springs CF GF GF/CF 18

5 International Journal o Mechanical and Mechatronics Engineering SPRING RATE (N /M M ) FAILURE LOAD (N) MAX. DEFLECTION (M M) Fig. 7 Spring rates o the three types o springs Fig. 8 Failure loads o the three types o springs 8 9 Fig. 9 Maximum compression o the three types o springs VI. CONCLUSION Three types o composite coil springs have been developed in this study; they are lighter than steel spring and the stiness achieved in these springs are less than the steel spring. 7 (Spring rate o the same dimension steel spring is approximately 14 N /mm and weight o the steel spring is 1.78 kg). The ollowing conclusions can be drawn rom the analysis o experimental results o these springs. The weight o the springs manuactured rom carbon iber roving is less than the glass iber and glass iber/carbon iber roving springs. The stiness o the carbon iber springs is greater than the other two types o composite coil springs. The springs developed rom the glass iber/carbon iber rovings does not exhibit a avorable results compare to other two types o springs. The cost o the glass iber springs are 25% more than the steel springs and the cost o the carbon iber springs is 2% more than the steel springs. The selection o the glass iber or a carbon iber springs depends upon the cost and application o the spring which can be compensated by saving the uel rom weight reduction. As compared to steel springs o the same dimensions, the stiness o composite coil springs is less. In order to increase the stiness o the spring the dimensions o the composite spring is to be increased which in turn increases the weight o the spring. Hence the application o the composite coil springs can be limited to light vehicles, which requires less spring stiness, e.g. electric vehicles and hybrid vehicles. The manuacturing o the composite coil springs is also diicult and time consuming compare to steel spring, however with the use o CNC winding machine and automated process which can be made easy and also the manuacturing cost can be reduced i produced in mass. REFERENCES [1] C.J. Morris, Composite integrated rear suspension, Composite structures, 5 (1986), P [2] Chang-Hsuan Chiu, Chung-Li Hwan, Han-Shuin Tsai, ei-ping Lee, An experimental investigation into the mechanical behaviors o Helical composite springs, Composite structures 77 (27) 1-4. [] Hendry and C. Pobert. Carbon iber coil springs, Materials and Design Vol No. 6 Nov/Dec 1986, P -7. [4] P.K. Mallick. Static mechanical perormance o composite elliptic springs Transactions o ASME 22/vol.19. jan1987. [5] Erol Sancakkar, Mathieu Gratton, Design, Analysis and optimization o composite lea springs or light vehicle applications, Composite structures, 44 (1997), P [6] Mahmood M. Shokrieh, Davood Rezaei. Analysis and optimization o a composite lea spring, Composite structures 6 (2) [7] Dai Gilles, Chang Suplee, Novel Applications o Composite Structures to Robots, Machine Tools and automobiles Composite Structures: 66(24) [8] Dai Bill Lee, Hak Sung Kim, Jong oon Kim, Jin Kook Kim, Design and Manuacture o an Automotive Hybrid Aluminium / Composite Drive Shat Composite Structures 6(24) [9] Naveen Rastogi. Design o composite Drive shats or automotive applications SAE Technical paper series.24 SAE world congress. [1] Seong sik cheon, Jin Ho Choi, Dai Gil Lee. Development o the composite bumper beam or passenger cars Composite structures 2 (1995) [11] Seon Sik Cheon, Dai Gil Lee and Kwang Seop Jeong. Composite side door impact beams or passenger cars. Composite structures 8 (1997) [12] Chritophar Byrne, Modern Carbon Composite Brake Materials - Journal o Composite Materials, Vol. 8, No. 21/24. [1] ahl A. Mechanical springs, Mc Graw hill Book Company. Inc: