International Journal of Pure and Applied Mathematics Volume 118 No. 18 2018, 4199-4207 ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version) url: http://www.ijpam.eu Special Issue Material and Free Vibration Characterization of Carbon Nanotube Reinforced Composite Materials 1 Paul Praveen A, 2Vasudevan Rajamohan and 3Arun Tom Mathew 1,2,3 Center for Innovative Manufacturing Research, Vellore Institute of Technology (VIT), Vellore, India. Abstract In this study, the material and free vibration characterizations of Multi-Walled Carbon Nano Tube (MWCNT) reinforced hybrid composite material are investigated. The MWCNT Nano material is genuinely prepared by using the Chemical Vapour Deposition (CVD) method with 97% purity. The thermogravimetric analysis (TGA), Raman Spectroscopy, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) are used before and after Ultra sonication. The results obtained from the above analyses for with and without sonication process of MWCNT and the mixture of MWCNT and ly556 epoxy resin is presented. Key Words—Chemical Vapour Deposition, Multi-Walled Carbon nanotube, Raman Spectroscopy, Scanning Electron Microscopy, Transmission Electron Microscopy, Hybrid composites, vibration. 1.INTRODUCTION Fiber reinforced composite (FRC) materials are widely being used over a broad range of engineering applications, due to their high structural strength, less weight, extended service life and corrosive resistant properties. However, the applications of these materials are limited due to their poor damping and viscoelastic elastic nature of the composite fiber. In 1991, Iijima [1] discovered the Carbon nanotube (CNT) and their unique physical properties has brought a significant attention from many researchers to fabricate the MWCNT reinforced hybrid composite materials, in order to achieve the greater stiffness and damping properties. The MWCNT reinforcement of hybrid composite materials play an unique role in every field/areas especially in chemical field, mechanical field, electrical field, etc., Numerous investigation have shown that the addition of small quantity of MWCNT with 1 wt % in the composite film increases the thermal, mechanical (young’s modulus and break stress) and electrical properties of the polymeric composites [2]. The nano based hybrid structure has shown a greater potential in CNT for the reinforcement of composites [3]. The randomly oriented carbon nanotube has a good interaction with the polymeric materials and consequently the reliability, thermal and mechanical properties of the hybrid composites are improved significantly [4]. The properly aligned CNTs have five times higher ultimate and yield strength than the randomly aligned CNTs. It was shown that by adding the small quantity of Single walled nanotube (SWNT) in the composite polymer, the damping characteristics of the hybrid composite material was increases significantly [5]. Xie et al. [6] investigated several methods for dispersing the CNTs in a polymer matrix, to enhance the physical properties of the nanocomposites. It was shown that the ex-situ alignment was found to be an effective method than the optimal bending, in situ polymerization and chemical functionalization, to predict the accuracy of the hybrid composite. The structural stiffness, toughness and damping properties of the laminated reinforced composite fibers are increased tremendously by adding the small particles of CNT into the polymeric composites [7]. Thermal properties of the resin based are highly improved by the addition of limited particles of the carbon nanotube in polymer matrix. Also, the thermal conductivity of the material becomes more than the diamond material [8]. The electrophoresis technique has been carried out to distribute the CNT 4199 ijpam.eu International Journal of Pure and Applied Mathematics Special Issue uniformly on the surface of the carbon fabric. Due to this, the enhanced out-of-plane mechanical and electrical properties are acquired for the multiscale hybrid composites. Also, the interlaminar shear strength and electrical conductivity of the carbon fabric with CNT has been improved [9]. The CNT ratio and the interface type between the CNT and the polymer resin play a unique role in tailoring the stiffness of the reinforced hybrid composite. The interlaminar shear strength of the multifunctional 6 laminate increases about 69% and the in-plane is around 10 and the thickness direction laminate 8 increases upto 10 [10]. The mechanical properties of the light weight composite materials could be improved by the addition of CNTs with ~50% weight fractions. It was shown that the homogeneously aligned/embedded CNTs in the matrices could provide the excellent properties of the hybrid composite structures [11]. Khan et al. [12] investigated the damping characteristics of carbon nanotube (CNT) composite beams and Carbon fibers reinforced polymer (CFRP) beams embedded with and without CNTs. The CFRP composite has less damping ratio compared to the epoxy. The damping properties of the CFRP hybrid composite material are increased by the addition of MWCNT in the CFRP. The results obtained from the vibration analysis shows that the damping ratio of nanocomposites is greater than the CFRP hybrid composites. Whereas, the results from the DMA analysis shows that the loss modulus and loss factor of nanocomposite and CFRP composites have consistent increase with the reinforced of MWCNT. Zhu et al. [13] presented the dynamic responses of the thin and thick composite plates, reinforced by the Single walled carbon nanotubes (SWCNT). This SWCNT was distributed along the uniform and thickness directions of the composite plates. The excellent properties of the nanocomposites are identified, based on the rule of mixture introducing with CNT. It was shown that, the volume fraction of CNT, width to thickness ratio and boundary conditions are the parameters significantly influence the natural frequencies, mode shapes and bending responses of the composite plate. The physical properties of the CNT (including the damping and stiffness properties) embedded matrix based composite structures have been studied by many researchers. Moreover, to study the effect of CNT embedded on the dynamic properties of the fiber reinforced composite (FRC) have not been attempted. In the present work, the material and free vibration characterization of the carbon nanotube reinforced hybrid composite materials are investigated. The MWCNT Nano material is genuinely prepared by using the Chemical Vapour Deposition (CVD) method with 97% purity. The dimensions, dispersion, distribution, alignment and material characterization of the MWCNT have been carried out by using the Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR), before and after ultra-sonication. The results obtained from the above analyses with and without sonication process of MWCNT and the mixture of MWCNT and ly556 epoxy resin are presented. Also, the comparative studies on natural frequencies of fiber reinforced hybrid composite beams without and with CNT are investigated. 2.FABRICATION OF SPECIMENS The high aspect ratio of the CNTs yields the strong Vander-Waals attraction forces between individual nanotubes. As a result, CNTs form agglomeration and consequently reduces the reinforcement effect of the nanocomposite. Hence, the potential usage of CNTs could be achieved only when they are mixed with polymer or other materials by using well dispersed reinforcing agent in polymer matrix of the composites leading to well-adhesion. Further, interface adhesion bwteeen CNT and polymer is generally improved by a surface modification of the nanotubes through functionalization and high power dispersion methods, such as ultrasounication and high-speed shearing. A calculated amount of MWCNTs were oxidized with 3:1 vol. sulfuric and nitric acid mixture o by refluxing at 70 C. The resulting MWCNT-COOH mixture were washed and dried in vacuum after obtaining the pH value to 7. To further improve the dispersion, ultra sonication was performed by dispersing CNTs in acetone mixed with surfactant (Triton X100) of 10CMC (equivalent to a Triton weight to acetone volume ratio of approximately 12.5 mg/1000 ml). The mixture was subjected to sonication in a bath for 60 min. After adding appropriate amount of epoxy to mixture, it is further sonicated for 60 min. The entire sample is then transferred to a larger diameter beaker to increase o the exposed surface area of the sample (Figure 1). The mixture is maintained at 70 C for 12 hours to evaporate acetone. Hardener is added to the resin sample and mixed with the prepared 0.5% weight 4200 International Journal of Pure and Applied Mathematics Special Issue of CNT using manual stirring for two minutes, resulting resin and CNT mixture. A hand-layup technique is used to fabricate the hybrind composite specimens without CNT and with CNT. A unidirectional glass fiber with a nominal thickness of 0.16mm was used to fabricate the o specimens. Each laminate consists of ten laminas with fiber angle orientation of [0 ] E-glass unidirectional fibers. Fig. 1 Sonicated mixture of MWCNT and Epoxy resin The CNT mixed epoxy resins are laid-up and a vacuums bag was used to remove the excess resin from the laminated plate. The composite laminates were cured under vacuum pressure for 2 hours to remove excess resin. Then the sample was maintained at 80°C for 2 hours. The mold was then cooled to room temperature for 15min and the cured composite specimen measuring 300 X 30 X 2 mm was cut and allowed to cure at room temperature for an additional 24 h before using for experimental testing. (a) (b) Fig. 2 and 3 Fiber reinforced composite beams (a) Without CNT (b)With CNT Figure 3 shows the specimens fabricated without CNT and CNT reinforced hybrid composite beams. 3.CHARACTERIZATION OF MWCNT A. Scanning Electron Microscopy (SEM) A scanning electron microscope is a kind of electronic equipment that uses a high energy electrons focused beam to obtain an infinite number of scattered electron signals from the surface of solid specimen with their composition and provides a three dimensional (3D) image of sample. The maximum level of magnification in the SEM is 2 million with the resolution of 0.4 nanometersso that it is capable of showing the images of the sample in form of bit by bit. Figure 4 shows the SEM image of the Multi walled carbon nanotube before the Ultra sonication process. The Pure MWCNT sample was focused with a magnification of 10.00KX and scaling was about 2µm (micrometer). The SEM image of MWCNT represents the accumulation of nanotubes entangled with each other. At this stage, the MWCNT could not mix homogeneous in the polymer matrices. Ultra-sonication technique was employed in this scenario, to separate the entangled nano particles accurately without damaging the nanotubes. 4201 International Journal of Pure and Applied Mathematics Special Issue Fig. 4 SEM image of MWCNT before Sonication The separated nanotubes from the ultrasonication process are again drawn to the SEM analysis. Figure 5 shows the SEM image of the MWCNT after the ultra-sonication process. The Sonicated MWCNT sample is focused with a magnification of 13.00KX and scaling is about 2µm (micrometer). Fig. 5 SEM image of MWCNT after Sonication It was clearly shown that the entangled nanoparticles of the CNTs are separated individually with random distribution. In this stage the MWCNT was able to mix homogeneously in the polymer matrices to enhance the mechanical properties of the nano and hybrid composites. B. Transmission Electron Microscopy (TEM) Transmission electron microscope is an advance electronic equipment than the SEM, that uses a very high energy electrons focused beam to acquire the transmitted electrons directly pointed on the sample, which passes the signals throughout the entire sample and provides a 2D image with detailed information. The maximum magnification in the TEM is about 50 million and has the resolution of 0.5 angstroms. Figure 6 shows the TEM image of MWCNT before the sonication process. The Pure MWCNT sample was focused with a magnification of 200Kx and scaling was about 10nm (nanometer). The TEM image of MWCNT represents the single nanotube with multi wall layered CNT. It was clearly shown that the nanoparticles of the CNTs drawn from the chemical vapor deposition process are not contaminated/damaged by any other materials, which shows the quality of the nanotube particles. C. Fourier transform infrared spectroscopy (FT-IR) The Fourier transform infrared spectroscopy is a modern sample analysis technique which is highly useful to acquire the absorption or emission infrared signal from the solid, gas and powder materials. It has the ability to collect the high resolution data signals continuously from the wide range of spectral or from the sample. 4202 International Journal of Pure and Applied Mathematics Special Issue Fig. 6 TEM image of MWCNT (a) Figure 7 (a) and (b) show the graphical representation of MWCNT before and after ultra sonication technique. The X-axis denotes the Wave numbers (1/cm) and the Y-axis denotes the Absorbance -1 (%T). The scaling range of the wave numbers lies between 4000-500 cm and for the absorbance begins from 0-100 %T. The FT-IR analysis were carriedout the MWCNT with before and after sonication. The results form the FT-IR in the graphical form represents the similar values for both wave numbers. The carbon content has been found to the absorbance material with 97%, predicted from the both test samples of MWCNT. (b) Fig. 7 FT-IR Graphical Representation of MWCNT (a) before ultra sonication (b) after ultra sonication 4203 International Journal of Pure and Applied Mathematics Special Issue II. DYNAMIC CHARACTERIZATION OF COMPOSITE BEAM WITHOUT AND WITH MWCNT The fibers reinforced laminated composite beams without and with CNT were clamped at the left edge using a steel fixture. The schematic of the experimental set-up is shown in Figure 8. Fig. 8 Schematic of free vibration test on CNT reinforced hybrid composite beams Roving hammer (Impulse Force Hammer-086C03) method was used to accelerate the composite beams. A single-axis accelerometer, oriented along the z-axis, was installed at the free end of the plate to measure the acceleration due to excitation. This acceleration signals were converted into frequency response function using 4 channels Data Acquisition System (Model No. ATADAQ042451). The natural frequencies of the composite beams were subsequently identified from the peaks in the frequency response function and the results are presented in Table 1. The performance of the Multi-walled carbon nanotube in the composite material is increases/decreases significantly due to the ultra-sonication time period. It can be seen that the addition of 0.5% of CNT in fiber reinforced composites beams yields 67% increase in natural frequency in the fundamental mode. This can be attributed to fact that addition of CNT increases the stiffness of the structure. TABLE I COMPARISON OF NATURAL FREQUENCIES OF FIBER REINFORCED COMPOSITE BEAMS WITHOUT AND WITH CNT Mode No. 1 2 3 4 Natural Frequencies (Hz) Without % With CNT CNT increase 15 25 67 40 85 160 62 100 175 55 18 9.4 4. CONCLUSION In the present study, the material and free vibration characterization of MWCNT reinforced hybrid composite materials are investigated. The MWCNT Nano material is genuinely prepared by using the Chemical Vapour Deposition (CVD) method with 97% purity. The thermogravimetric analysis (TGA), Raman Spectroscopy, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) are used before and after Ultra sonication. The results obtained from the above analyses for with and without sonication process of MWCNT and the mixture of MWCNT and ly556 epoxy resin were presented. It was shown that the addition of carbon nanotube in fiber reinforced composite beam increases the stiffness of the structure and consequently increases the natural frequencies and alter the mode shapes. 4204 International Journal of Pure and Applied Mathematics Special Issue Acknowledgements Authors are grateful to DST-SERB, India for providing financial support through the project entitled ‘A study of structural damping and forced vibration responses of carbon nanotube reinforced rotation tapered hybrid composite plates’ under the Grant No. ETA-0009-2014 to carry out this work. Authors are also grateful to VIT University for providing SEM, TEM and vibration laboratories facilities to carry out this work. References [1] S. Iijima. (1991, Nov.). Helical microtubules of graphite carbon. Nature. 354, pp. 56-58. Available: http://www.nature.com/physics/looking-back/iijima/index.html [2] D. Qian and E.C. Dickey. (2000, May). 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