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Design, analysis, manufacture and test of carbon fiber composite cylindrical carbon fiber cloth for space

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  • Save International Journal of Composite Materials 2015, 5(5): 102-128 DOI: 10.5923/j.cmaterials.20150505.03 Design, Analysis, Fabrication and Testing of CFRP with CNF Composite Cylinder for Space Applications S. Sankar Reddy1,*, C. Yuvraj2, K. Prahlada Rao3 1Department of Metro Production, M/s BEML Ltd., Bangalore, India 2Department of Mechanical Engineering, Madanapalli Institute of Technology & Science, Andhra Pradesh, India 3Department of Mechanical Engineering, JNTU College of Engineering, Andhra Pradesh, India Abstract Carbon Fiber Reinforced Polymers (CFRPs) have been widely used in numerous applications where high specific stiffness and strength offer structural weight reduction and fuel efficiency. RVS (re-entry vehicle system) structural protection to the weapon system during re-entry. These kinds of structures are realized using filament winding process. In this paper mechanical characterization of CFRP with Carbon Nano-fiber has been prented. Studies are carried out to characterize the strength and Young‟s modulus of the composite structure. Carbon Nano-fibers are among the greatly potential reinforcing additives for polymeric composites due to their high axial Young‟s modulus, high aspect ratio, large surface area, and excellent thermal and electrical properties. Various studies can be found in the literature regarding the incorporation of CNFs in polymeric matrices and the final mechanical and/or electrical properties of these materials. To prove the technology a composite cylinder having size Length of 600mm, Diameter 300mm and thickness 1.5mm is considered for experimental study. In the present work a method has been developed to analyze composite shell using Layered 46. In addition, 3D layered analysis of composite cylinder with end metallic plates have been performed to predict the Buckling behavior of the Composite shell. Composite shell were fabricated & tested with buckling load condition to verify the design and analysis procedure. It has been observed that the experimental results are in close agreement with the finite element analysis results, also the design stresses were within safe limits. Based on test results, the Longitudinal Strength of CFRP with CNF is achieved 1860 MPa, Young‟s modulus is 118 GPa and improvement against CFRP with epoxy resin (LY556). Keywords CFRP, Carbon Nano-fibers (CNF), Buckling of Cylinder, Filament Winding, FE Analysis, Composite cylinder, Tensile strength, Young‟s Modulus, Epoxy resin 1. Introduction 1.1. Filament Wound Rocket Motor Case The filament winding technique offers high speed and precision for placing composite fibers. Continuous fibers can be oriented to match the direction and magnitude of stresses in a laminated structure, allowing optimal reinforcement loading. Since this fabrication technique provides the production of strong, lightweight, corrosion and chemical resistant parts, it has proved particularly useful for components of aerospace, hydrospace and military applications such as pressure vessels, pipe lines, rocket motor casings, helicopter blades, large storage tanks, etc. Typical pressure vessels consist of a cylindrical section and two quasi-spherical domes. Since the dome regions undergo the highest stress levels and are the most critical * Corresponding author: (S. Sankar Reddy) Published online at Copyright © 2015 Scientific & Academic Publishing. All Rights Reserved locations with regard to failure of the structures, the optimal design of the domes is one of the most important issues in the design of composite pressure vessels. Rocket motor casing is basically a pressure vessel with specially designed end fittings namely polar bosses and skirts. The end fittings are configured to suit to the fore end and aft end systems. Composite casings are popular as rocket motor casing as they provide high strength with low weight. Given a free hand, the rocket motor can be designed as a complete system and the casing can be designed to achieve the absolute maximum efficiency. However, when the designs of fore / aft end systems and that of casing are carried out in isolation keeping only the interfaces in mind, limited efficiency as depicted by weight saving, performance factor and cycle time, can still be achieved. The CFRP material is used for filament wound rocket motor case (CRMC). Generally realization of CRMC is observed with carbon fiber and epoxy resin by wet filament winding process. This composite having a longitudinal tensile strength of 1200MPa and modulus of 110GPa. Efforts are made for improving these properties by Formulating resin system. International Journal of Composite Materials 2015, 5(5): 102-128 103 1.2. Back Ground It has been proved that the optimal shape profile for a filament wound dome is a isotensoid [1, 6], on the basis of the netting theory [2]. The isotensoid, which provides the dome structure with the minimum weight and maximum carrying capacity, implies that all the rovings show uniform tensions throughout their length. It can be designed in such a way that the major stresses are carried only by the fibers of the laminate [3]. A number of studies have been conducted on the design of such structures. de Jong [4] presented the geometry and structural properties for isotensoid pressure vessels with the aid of the continuum theory, in which the behaviour of matrix in composites has been taken into account. The primary aim of this paper is to manufacture a composite cylinder with conductive polymer layer for Solid Rocket Motor Casing. Studies are carried out to characterize the conductive polymer properties and studied in different material like CFRP with Carbon Nanotube and Copper Nano-powder and their enhancement of properties. 2. Material Characterization 2.1. Introduction Composite material in the form of towpreg is the state of the art of technology. Towpreg find wide application in composite manufacture, especially, where components are manufactured by filament winding process. Handling point of view towpreg makes its easy and simple. Towpreg has consistent and uniform resin content and high friction factor to carry out non geodesic winding than wet winding material. Tensile strength and modulus of composite depends on fibre volume fraction of composite. Towpreg composite has high fibre volume fraction (6- 65%) than wet winding processed composite material. Percentage of Translation of carbon fibre strength in composite is higher in towpreg than that of filament wet winding process. Towpreg systems deliver more of fiber strand tensile strength, compared with wet wind systems, and the finished parts exhibit smaller variation in properties. The net result is that less material can be used for towpreg vessels of equal performance. The experimental characterization of carbon fibre T-700/epoxy towpreg composite material is necessary required for generation of mechanical properties data for analysis, design, and fabrication of structural components using that material and for quality control of the material. The testing of composite material offers unique surprises because of the special characteristics of composites, factrors not considered important in metals testing are very important in testing composites. In order to design composite products, a through experimental characterization of carbon fibre T-700/ Epoxy towpreg composite material and its behaviour is necessary. 2.2. Evaluation of Carbon Fibre T700/Epoxy Towpreg for Physical Parameters Indigenous developed Carbon fibre T700/Epoxy Towpreg was received from M/s Chemapol industries, Mumbai for characterization purpose. The specifications of the carbon fiber T700/Epoxy Towpreg are given below. The Towpreg must be evaluated for their respective properties before processing of laminates by filament winding process. 2.3. Experimental Characterization of Towpreg 700 / Epoxy Composite Characterisation means determination of all effective Properties over sufficiently large volumes to represent composite and which are statistically reproducible. The main purpose of Experimental characterization data are  for checking micromechanical analysis  for design and analysis of practical structures  for Fabrication Process QA / Product QC  for Comparison of properties between candidate materials When selecting a material for a specific product application like Composite Rocket Motor Casing for a missile system, the relevant properties of proposed composite material need to be determined experimentally designing a particular product to meet a specific structural requirement of the composite product. Experimental characterization of carbon fibre T700/ Epoxy towpreg composite was carried out for generation of design input data for design and analysis of composite rocket motor casings and other composite products. The mechanical and thermal tests for experimental characterization of carbon fibre T700/Epoxy towpreg composite are given in the following table 1. Table 1. Sl. no Property ASTM No. of No Specimen’s MECHANICAL / DESIGN PROPERTIES 1 L. Tensile Strength( T11), MPa 2 L. Tensile Modulus (E11), GPa, 9 3 Major Poison‟s ratio, 12 D3039 4 T. Tensile Strength(T22), MPa 6 5 T.Tensile Modulus (E22 ), GPa 6 Inplane shear strength (12), MPa D3518 7 7 Inplane shear modulus(G12), GPa 8 L. Compressive strength (C11), MPa D3410 6 9 T. Compressive strength(C22), MPa 10 NOL Ring Tensile Strength, MPa D2290 10 11 Interlaminar shear Strength, MPa D2344 10 THERMAL PROPERTIES 1 Glass Transition Temp. Tg, C E1256 3 104 S. Sankar Reddy et al.: Design, Analysis, Fabrication and Testing of CFRP with CNF Composite Cylinder for Space Applications 2.4. Manufacturing Process of UD Laminates and NOL Rings 2.4.1. Fabrication of Unidirectional (UD) Laminates Flat UD laminates can be fabricated by filament winding in order to provide the stock from which flat test specimens can be prepared. One process for doing this involves winding a unidirectional mat over a large mandrel, cutting and removing the fibers, as wound material, from the mandrel, then plying, consolidating and curing (in an autoclave) to the flat configuration. The material resulting from the process can be quite different from the material in a filament wound composite structure. Towpreg was winding to a flat rectangular plate by filament winding by heating towpreg to temperature about 60°C by hot air gun at pay out eye and also heating at winding surface by IR lamps to temperature about 60°C to get good inter layer bonding during winding. 2 kg Tension was maintained per spool during winding. This flat shaped mandrel was specially designed and fabricated to prepare UD laminate as shown in the Fig. 1, 2. 2.4.2. Curing After Filament winding, the laminate is cured in an oven having accurate temperature control. The flat mandrel is placed inside the oven on metal stands. The following cure cycle (as shown in Fig. 3) was followed  Raise temperature of the oven from room temperature to 120°C in 3minutes with heating rate of 2 to 4°C per minute  Hold the temperature at 120°C ±5°C for 2hours.  Raise temperature of the oven from 120°C to 150°C in 3 minutes with heating rate of 2 to 4°C per minute.  Hold the temperature at 150°C ±5°C for 4 hours  Switch off the oven and allow the component to cool naturally.  Open the door and remove mandrel when it is below 40°C Figure 1. Mounted Towpreg spools Figure 3. Cure Cycle for Carbon Fibre T-700 / Epoxy Towpreg Composite 2.4.3. Fabrication of NOL Ring Specimens Figure 2. Filament winding Process using Towpreg on flat Mandrel Figure 4. NOL Ring Test Specimen (ASTM D 2290) NOL (Naval ordnance laboratory) Ring specimens that simulate the cylindrical geometry of composite over wrap pressure vessel (COPV). NOL ring specimens are prepared by Carbon fibre T700/Epoxy towpreg by filament winding technique on NOL ring mandrel as shown in the figure 4. NOL ring mandrel was specially designed and fabricated to prepare a laminate simulating the real filament wound. Hoop winding is carried out on the mandrel and followed International Journal of Composite Materials 2015, 5(5): 102-128 105 above process parameter of towpreg mentioned in the preparation of UD laminates. Curing of NOL ring winding was carried out in oven with cure cycle. After curing, NOL Ring winding was machined on lathe to remove accumulated resin on winding during curing to get uniform thickness of ring sand winding was partitioned into standard width as ASTM 229 to get NOL Rings. The dimensions of NOL ring specimen is shown in the Fig.NOL winding and partition of winding into rings as shown in the Fig. 2.4.4. Specimen‟s Preparation from UD Laminates When selecting the type of test specimen to use in an experimental characterization, one of the most important point is to use a type of specimen which has been made in the same manner as the full scale end product structure. In the characterization programme described herein, the end product is carbon-epoxy filament wound rocket motor casing. It is desirable to characterize experimentally the properties of a single ply of the composite material for design purpose. However, practical considerations often prevent their construction. Thus, it becomes necessary to conduct tests on multi-layered specimens and use appropriate laminate theory to reduce the results in terms of single-ply properties. The dimensions of different types test specimens ((as shown in figure 5). Specimens are prepared from laminates with the help of a diamond wheel cutting machine (as shown in figure 6-10). Figure 7. Longitudinal Flat Compressive Test Specimen (ASTM D 3410) Figure 8. Transverse Flat Compressive Test Specimen (ASTM D 3410) Figure 5. Longitudinal Flat Tensile Test Specimen (ASTM D 3039) Figure 9. In plane Shear Test Specimen (ASTM D 3518) Figure 6. Transverse Flat Tensile Test Specimen (ASTM D 3039) Figure 10. Flexural specimens as per ASTM D 790 & ILSS Specimen as per ASTM D 2344 106 S. Sankar Reddy et al.: Design, Analysis, Fabrication and Testing of CFRP with CNF Composite Cylinder for Space Applications 2.5. Test Methods for Laminates 2.5.1. Mechanical Properties NOL Ring Tensile Test This method covers the determination of the comparative apparent tensile strength of ring or tubular composites. An apparent tensile strength rather than a true tensile strength is obtained in this test because of a bending moment imposed during test. The method is applicable to many types of tubular shaped specimens either parallel-fiber reinforced, extruded or molded. Parallel fiber reinforced specimen is prepared and tested as per ASTM D229 using split disc test fixture for determining the apparent hoop tensile strength of the composite. NOL ring specimens were tested using NOL test fixture (as shown in Fig). A plot Apparent Hoop tensile strength vs. displacement of NOL Ring test is shown in Figure. Failure modes of NOL Rings is shown in Figure. The test results of NOL ring are shown in the Table 2. Table 2. Sl. N0 1 2 3 4 5 6 7 8 9 10 AVERAGE Standard deviation % Coefficient of Variance NOL Ring TS (MPa) 1922 2125 2098 1897 2187 1874 2066 1793 2237 1944 2014 148 7.35 Failure Mode Splitting & delamination Splitting & delamination Splitting & delamination Splitting & delamination Splitting & delamination Splitting & delamination Splitting & delamination Splitting & delamination Hoop failure Splitting & delamination Figure 11. NOL Ring preparation stages and Testing International Journal of Composite Materials 2015, 5(5): 102-128 107 NOL Ring Tensile Strength (MPa) Figure 12. Plot for Tensile Strength Vs Displacement NOL Ring Tensile Strength of Carbon Fibre T700 ,6K/ Epoxy Resin (LY 556/ HY5200 Composite at different temperatures 2000 1750 1500 1250 1000 750 500 250 0 25 40 55 70 85 100 115 130 145 Temperature (°C) Figure 13. NOL Rings were failed in delamination and circumferential splitting failure modes 108 S. Sankar Reddy et al.: Design, Analysis, Fabrication and Testing of CFRP with CNF Composite Cylinder for Space Applications Tensile Test Tensile test on laminates will be performed in two directions namely  Tensile test in longitudinal direction  Tensile test in transverse direction Longitudinal Tensile Test The tension test on longitudinal specimens is conducted to determine longitudinal tensile strength (XT), Modulus (EL) and major Poisson‟s ratio (LT). In this method, the specimen with end tabs has been used. Rosette Strain gauge was bonded on specimens as per standard procedure of strain gauge bonding. Specimen preparation and testing is carried out as per the standard ASTM D3039.Rosette strain gauge was bonded on specimens for measurement of modulus and Poisson ration as shown in the fig. Longitudinal tensile strength is determined from the ultimate load and longitudinal tensile modulus is calculated from the stress-strain curve. The Tensile testing of UD laminate specimens in UTM with strain gauge data logger system is shown in the fig. Failure modes of specimens are shown in the fig. The plot of Tensile strength vs. strains is given in the Fig. for calculation of Ultimate tensile strength, tensile modulus, Poisson ratio. The values of the longitudinal strength, modulus, poisson ratio and ultimate failure strain are given in the Table. Figure 14. UD Tensile Specimens Figure 15. UTM - 100KN Capacity with strain data acquisition system Tensile test of CFT700/ Epoxy ED20 + Type 4 SR/ FH 5200 UD composite 2500 2000 Longitudinal Strain Transverse Strain Tensile Strength (MPa) 1500 1000 500 UTS (σ11) = 2074 Mpa TM (E11) = 132 Gpa Poisson Ratio (ν12)=0.29 Failure Strain : 15151 µε 0 0 5000 10000 15000 Strain ( µε ) 20000 Figure 16. Tensile stress vs. strains of longitudinal UD tensile specimen International Journal of Composite Materials 2015, 5(5): 102-128 109 Table 3. Test Results of Longitudinal Tensile Test of Carbon Fibre 700/ Epoxy towpreg Composite Compressive Test Results Compressive test on laminates will be performed in two directions namely  Compressive test in longitudinal direction  Compressive test in transverse direction Longitudinal (0) compressive Test and Transverse (90) compressive tests are carried out to determine longitudinal and transverse compressive strength. Specimen preparation and testing is done as per the test standard ASTM D341by using IITRI fixture as shown in the Fig. Gauge length12mm was used for compressive testing of composites. Figure 17. Failure mode s of longitudinal Tensile Specimens Tensile fail mode can be described using the three part failure mode code in ASTM D3039 Example: XGM First character indicates Failure Type: X means explosive Failure Second character indicates Failure Area: G means Gauge length Third character indicates Failure Location: M means Middle of gauge length Table 4. Test Results of Transverse Tensile Test of Carbon Fibre 700/ Epoxy towpreg Composite Figure 18. IITRI test fixture for compression Table 5. Longitudinal and Transverse compression test results 110 S. Sankar Reddy et al.: Design, Analysis, Fabrication and Testing of CFRP with CNF Composite Cylinder for Space Applications In plane Shear Test The properties that are determined through the tests are the shear strengths and shear modulus. In these tests the specimen is subjected to loads that produce a pure shear state of stress and the resulting strains are measured. The test in which shear distortion takes place entirely in the plane of the composite material laminate are termed in-plane shear tests. The in plane shear strength (() and in plane shear modulus (G) are determined by this test. In this characterization programme of carbon-epoxy composites, the in-plane shear properties are determined by the uniaxial tension test on 45 specimens as per the test standard ASTM D3518. Figure 19. Failure modes of specimens The stacking sequence chosen for the preparation of the laminate is +45,-45. The importance of a laminate with the stacking sequence is that, such a laminate is specially orthographic with respect to in-plane forces and strains, and the bending-stretching coupling effects and the in plane and bending anisotropic effects are avoided. Rosette Strain gauge is bonded on specimens to measure strains along the loading direction and perpendicular to it as shown in Fig. The in plane shear modulus is calculated from the stress versus strain curve. The plot of shear Tensile strength vs. strain is given in the Fig. Failure modes of transverse specimens are given in the Fig. Test results are shown in the Table. Table 6. S.No 1 2 3 4 5 6 7 8 9 10 Average Standard deviation % Coefficient of Variance In plane Shear Strength (MPa) 49 40 48 39 41 38 51 48 47 48 45 4.8 10.66 In plane shear Modulus (GPa) ---------2.80 2.90 3.20 2.98 3.20 3.0 0.18 6.0 Shear Strength (MPa) In Plane Shear Test of Carbon Fibre T700/ Epofine 1555/ FH 5200 Compoiste 50 45 40 35 30 25 20 15 10 5 0 0 5000 10000 15000 20000 Sheat strain ( µε) 25000 30000 Figure 20. Plot for Shear Strength vs. Shear Strain International Journal of Composite Materials 2015, 5(5): 102-128 111 3 Point Flexural Test The Flexural strength modulus are evaluated using a three-point test fixture. The specimen is prepared as per test method ASTM D790. Flat specimens, machined with same care and precision as previously described for tensile testing, are selected for measurements. The material direction under investigation must be oriented along the length dimension of the specimen. The test pieces require a span/depth (l/d) ratio high enough to achieve failure in bending rather than shear and minimize the influence of shear.l/d ratio 40:1 was used for testing. The Flexural strength (FS) is calculated as follows, FS = 3PL / 2bd2 where, p Maximum load L Support span length b width of specimen d thickness of specimen Flexural testing of UD specimens in UTM and failure modes are shown in the fig. A plot of Load vs. displacement of Flexural Test is shown in fig. The values of Flexural Strength and modulus are given in Table. Figure 21. 3 point flexural testing Figure 22. Specimens after flexural testing Table 7. Tests results of flexural test Specimen No. 1 2 3 4 5 6 7 8 9 10 11 Average Standard deviation % Coefficient of Variance Flexural Strength (MPa) 850 848 913 908 925 907 963 842 904 917 867 895 38.14 4.26 Flexural Modulus (GPa) 112 108 110 105 106 103 107 104 106 110 104 107 2.89 2.70 Figure 23. Load Vs deflection curve for Flexural Test

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