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Research Papers

# Studies of Mechanical Properties of Multiwall Nanotube Based Polymer CompositesOPEN ACCESS

[+] Author and Article Information
A. K. Gupta

Vibration and Noise Control Laboratory,
Department of Mechanical and
Industrial Engineering,
Indian Institute of Technology Roorkee,
Roorkee 247667, India;
Instruments Research and
Development Establishment,
e-mail: anandmechiitr@gmail.com

S. P. Harsha

Vibration and Noise Control Laboratory,
Department of Mechanical and
Industrial Engineering,
Indian Institute of Technology Roorkee,
Roorkee 247667, India
e-mail: spharsha@gmail.com

1 Corresponding author.

Manuscript received October 14, 2014; final manuscript received December 16, 2014; published online January 13, 2015. Assoc. Editor: Roger Narayan.

J. Nanotechnol. Eng. Med 5(3), 031006 (Aug 01, 2014) (5 pages) Paper No: NANO-14-1066; doi: 10.1115/1.4029414 History: Received October 14, 2014; Revised December 16, 2014; Online January 13, 2015

## Abstract

The two phase polymer composites have been extensively used in various structural applications; however, there is need to further enhance the strength and stiffness of these polymer composites. Carbon nanotubes (CNTs) can be effectively used as secondary reinforcement material in polymer based composites due to their superlative mechanical properties. In this paper, effects of multiwall nanotubes (MWNTs) reinforcement on epoxy–carbon polymer composites are investigated using experiments. MWNTs synthesized by chemical vapor deposition (CVD) technique and amino-functionalization are achieved through acid-thionyl chloride route. Diglycidyl ether of bisphenol-A (DGEBA) epoxy resin with diethyl toluene diamine (DETDA) hardener has been used as matrix. T-300 carbon fabric is used as the primary reinforcement. Three types of test specimen of epoxy–carbon composite are prepared with MWNT reinforcement as 0%, 1%, and 2% MWNT (by weight). The resultant three phase nanocomposites are subjected to tensile test. It has been found that both tensile strength and strain at failure are substantially enhanced with the small addition of MWNT. The analytical results obtained from rule of mixture theory (ROM) shows good agreement with the experimental results. The proposed three phase polymer nanocomposites can find applications in composite structures, ballistic missiles, unmanned arial vehicles, helicopters, and aircrafts.

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## Introduction

CNTs are among the most exciting new material which has been discovered in the last three decades. Since their discovery of CNT [1], CNTs have generated huge activity in most areas of science and engineering due to their superlative mechanical, thermal, and electronic properties [2,3]. Polymer matrix composites are being utilized in an increasing number of industrial applications including transportation, automotive, aerospace, defense, sporting goods, energy, and infrastructure sectors [4]. This is due to their high durability, high strength, light weight, and process flexibility. The two phase epoxy–carbon composites have been extensively used in last few decades [5]. Traditional fiber-reinforced composite materials made of oriented fiber stacks embedded in a polymer have excellent in-plane properties but have poor through-thickness properties. The CNT reinforcement can improve the through-thickness mechanical properties and resultant nanocomposite can provide high elastic modulus, tensile strength, and fracture toughness [6].

In the recent years, CNTs reinforcement in polymer composites has shown great potential [7]. The mechanical load carrying capacities of CNTs in nanocomposites have been demonstrated using experiments [8,9]. The CNT has exceptionally high thermal conductivity and it has been reported that graphene layer coating on silicon wafer can result in highly efficient heating film [10]. Despite the fact that the polymer materials are found most suitable for reinforcement with CNTs, only relatively low concentrations (<∼5 wt.%) of nanotubes can easily be incorporated in thermosetting composites, due to rapidly increasing viscosity and subsequent processing difficulties. Even well-dispersed, shortened nanotubes can form a stiff gel, simply in solvent, due to their high aspect ratio and resulting network forming ability [11]. MWNTs are generally entangled in the form of curved agglomerates and CNTs are produced as bundles. In order to achieve optimal enhancement in properties of CNTs/polymer composites, there are several key issues to be resolved, i.e., improved dispersion of CNTs, alignment of CNTs in the polymer resin and functionalization of CNTs surface for good adhesion [12]. Chemical functionalization does improve covalent coupling between the CNTs and the matrix [13]. The use of amino-functionalized MWNTs in epoxy systems resulted in improved mechanical properties [14]. Recent studies suggests that interfacial bonding in the interphase region between embedded CNT and its surrounding polymer plays a crucial role in load transferring [15]. The interfacial interaction between CNTs and polymer matrix can be controlled to improve the mechanical performance of structural and functional nanocomposites [16]. A good CNT/matrix interfacial bonding and a perceptible reinforcement of the matrix with the nanotubes can bring improvement to the fracture strength of the composite by ensuring a shear stress transfer to the reinforcement [17].

The CNT reinforced polymer composites can find applications in biosensors, actuators, and electromagnetic shielding. It can be very well used in industrial applications including composite structures, replication, foaming, molding, and ballistic protection. The studies revealed that the nanophase biomaterials had higher biocompatibility than similar micron-sized materials [18] and can be used as biosensor for reverse inotophoresis-based glucose monitoring system [19]. It has been reported that nanochannel electroporation biochips can precisely deliver plasmid for nonviral gene transfection [20]. In polymer nanocomposites, the large surface area to volume ratio of CNTs makes it a suitable candidate for micro-electromechanical systems and nano-electromechanical systems [21]. The recent studies show that CNTs can be effectively used as conductive adhesives for aerospace applications [22].

The present work focuses on prediction of tensile strength and failure strain of the multiwall nanotube reinforced epoxy–carbon composites using experimental and analytical approach. For the nanocomposite fabrication, DGEBA epoxy resin with DETDA hardener has been used as matrix system. T-300 carbon fabric having 8-H satin weave (woven with 3 K tows) is used as the main reinforcement. High pure MWNTs synthesized by CVD method and these MWNTs are amino-functionalized through acid—thionyl chloride route [23]. Initially, MWNTs are mixed with resin and uniform dispersion of CNTs is achieved by sonication followed by ball milling. The MWNT-epoxy is then applied on carbon fabrics and layers are stacked to achieve the desired thickness. The samples of three phase epoxy–carbon fiber with MWNTs have been developed in the form of sheet. The TEM studies show that MWNTs has typically 20–30 walls having diameter in the range of 20–30 nm. The volume fractions of fibers are kept as 60% (±1%). The 2D nanocomposite samples are prepared with 0%, 1%, and 2% MWNT (by weight), respectively. For tensile test of the nanocomposite, the test samples are prepared as per ASTM D-638 standard. An electronic tensometer with load cell of 20 KN is used for tensile test of the nanocomposites. The test specimen was held in a quick grip chuck, which is specially designed for sheet and the load is varied at the rate of 5 kg/s. The experimental studies show that there are substantial improvements in the tensile strength and plastic strain of the polymer nanocomposites.

Analytical approach has already been used for estimation of mechanical properties when the deformation is within the elastic region [24]. In the present study, ROM theory is used to estimate the strength of polymer composite with MWNT reinforcement considering axial tensile failure of long fiber composites. The composite laminate has two-dimensional arrays with randomly distributed MWNT. Although it is difficult to simulate the test sample of nanocomposites in our analytical studies, the effect of MWNT reinforcement on tensile strength of the nanocomposites can be estimated with ROM theory. The tensile strength obtained from ROM shows good agreement with the test results.

## Experimental Methods

###### Preparation of Test Sample.

The test specimens of the nanocomposites are prepared according to ASTM D-638 standard, which is applicable for tensile testing of composites. Two types of specimen, i.e., type I and type IV, is prepared with 0%, 1%, and 2% MWNT reinforcement. The drawings of type I and type IV specimen are shown in Figs. 1(a) and 1(b), respectively. The dimensional details and nomenclature of type I and type IV specimen are given in Table 1.

###### Experimental Setup.

The tensile testing of nanocomposite samples is carried out using electronic tensometer model PC 2000 (courtesy: M/s Kudale Instruments Pvt. Ltd., Pune, India). The equipment is driven by DC motor (with encoder) and the true stress strain graphs are plotted on digital readout unit. The various parts of the equipment are shown in Fig. 2(a). A load cell of 20 KN is selected for the test and quick grip chuck is used to hold the test specimen. The specimen under test is shown in Fig. 2(b). The load is varied at the rate of 5 kg/s.

## Analytical Approach for Estimation of Tensile Strength of Nanocomposites

Analytical equations based on ROM are used to estimate the tensile failure of the nanocomposites. Figure 3 refers to a system in which the fiber has a higher strain to failure than the matrix. The stress train relationship is shown in Fig. 3(a), where Fig. 3(b) shows dependence of composite failure stress on volume fraction of fiber. In case, the matrix lower failure strain ($ɛmu<ɛfu$), for strain up to $ɛmu$, the composite stresses $σ1$ given by the simple ROMs can be written as

where $σf$ represents stresses of the fiber, $σm$ represents stresses in the matrix, and f is the volume fraction of the fiber. Above strain $ɛmu$, however, the matrix starts to undergo microcracking. The composite extends with further increase in applied stress. The load is progressively transferred to the fiber with the increase in matrix cracking and the final fracture takes place when the strain reaches $ɛfu$. If the matrix fracture takes place while the fibers are still bearing some load, then the composite failure stress $σ1u$ is given in Ref. [25] Display Formula

(2)$σ1u=fσfmu+(1-f)σmu$

where $σfmu$ is the fiber stress at the onset of matrix cracking ($ɛ1$ = $ɛmu)$ and $σmu$ is the failure stress corresponding to matrix. The composite failure stress therefore depends on the fiber volume fraction. The fiber volume fraction above which the fiber can sustain a fully transferred load is obtained by setting the Eq. (2) to $fσfu$Display Formula

(3)$f'=σmuσfu-σfmu+σmu$

where $σfu$ is the failure stress corresponding to fiber.

For the three phase polymer composite Eq. (2) can be written as Display Formula

(4)$σ1u=f1σfmu+f2σtmu+(1-f1-f2)σmu$

where $σtmu$ is the stress in the nanotube at the onset of matrix cracking. $f1$ and $f2$ are the volume fractions of fiber and nanotube, respectively.

## Results and Discussion

###### Experimental Results.

The tensile testing of three phase epoxy–carbon nanocomposite is carried out in order to investigate the effect of MWNT reinforcement on the epoxy–carbon composites. Both type I and type IV specimens are subjected to test. The load is continuously varied till the specimen failed. The failure pattern in type IV specimen was found to be inconsistent. This could be due to the fact the cross-sectional area is smaller compared to type I specimen. The true stress strain results of type I specimen, for 1% and 2% MWNT reinforcement, are shown in Figs. 4(a) and 4(b), respectively. The fractured sample of nanocomposite is shown in Figs. 5(a) and 5(b). The stress strain curve and failure of test specimen clearly indicates the brittle nature of the nanocomposites.

The values of tensile strength and failure strain of 0%, 1%, and 2% MWNT reinforced nanocomposites are given in Table 2. It can be seen that there is substantial increase in tensile strength and strain at failure due to addition of MWNT in epoxy–carbon fiber composite. The percentage increase in tensile strength and failure strain of the polymer composite, due to MWNT reinforcement, is shown in Fig. 6. It can be seen that 1% MWNT reinforcement results in 23.6% and 10.8% increase in tensile strength and failure strain, respectively. Also, 2% MWNT reinforcement results in 40.2% and 16.2% increase in tensile strength and failure strain, respectively.

###### Analytical Results.

The tensile strength of the three phase nanocomposite is estimated using Eq. (4). As the density of MWNT is close to the epoxy–carbon composite, the volume fraction of MWNT is taken as 1% and 2% instead of weight fraction. It has been assumed that matrix cracking takes place when the stresses in the carbon fiber and MWNT are reached to ∼60% value of the ultimate tensile strength. The tensile strength of the carbon fiber and epoxy matrix has been taken as 2500 MPa and 100 MPa, respectively. The tensile strength of MWNT is taken as 40 GPa [26]. The volume fraction of the primary reinforcement, i.e., carbon fiber is kept as 60%. The percentage increase in the tensile strength of nanocomposites obtained from ROM is shown in Fig. 7. It can be seen that for 1% reinforcement of MWNT, the tensile strength of the nanocomposite is increased by 25.4%. Also, 2% reinforcement results in 50.8% increase in the tensile strength.

## Conclusions

The exceptional properties of carbon nanotube have attracted composite fraternity to use them as potential reinforcement material primarily in polymer based composites. The polymer based nanocomposites can find many potential applications. The low percolation threshold of CNTs makes it ideal for application in sensors and actuators. The recent development in chemical modification and biofunctionalization methods has made it possible to generate a new class of bioactive CNT, which are combined with proteins, carbohydrates, or nucleic acids. In this paper, the effects of MWNT reinforcement on two phase epoxy–carbon composites are studied. The properties of resultant three phase composites are studied using experiments as well as analytical method. The samples of epoxy–carbon composite with 0%, 1%, and 2% MWNT (by weight) are subjected to tensile test. It has been found that both tensile strength and strain at failure have been substantially enhanced due to the addition of MWNT. The experimental results shows that 1% MWNT reinforcement results in 23.6% and 10.8% increase in tensile strength and failure strain, respectively. Similarly, 2% MWNT reinforcement results in 40.2% and 16.2% increase in tensile strength and failure strain, respectively. The results clearly indicate that the load bearing capacity of the nanocomposites have been substantially improved due to proper dispersion and amino-functionalization of MWNTs. The analytical studies also suggest that the tensile strength of the nanocomposites are increased by 25.4% for 1% MWNT and 50.8% for 2% MWNT, respectively. Although large volume fractions of CNTs are difficult to achieve due to increasing viscosity and processing issues, three phase polymer composite with low volume fractions of CNTs has immense potential to be used specially in structural and aerospace applications.

## Acknowledgements

The authors would like to thank Mr. I. Srikanth, Advanced System Laboratory, Hyderabad, India, for providing the test sample and process details of nanocomposite. The authors would like to thank Mr. A. B. Khare, Mr. H. P. Agrahari, and Mr. Vinod Kumar, IRDE, Dehradun, India for providing their support in testing of nanocomposites.

## References

Iijima, S., 1991, “Helical Microtubules of Graphite Carbon,” Nature, 354, pp. 56–58.
Treacy, M. M. J., Ebbesen, T. W., and Gibson, J. M., 1996, “Exceptionally High Young's Modulus Observed for Individual Carbon Nanotubes,” Nature, 381(6584), pp. 678–680.
Krishnan, A., Dujardin, E., Ebbesen, T. W., Yianilos, P. N., and Treacy, M. M. J., 1998, “Young's Modulus of Single Walled Nanotubes,” Phys. Rev. B, 58(20), pp. 14013–14019.
Khare, R., and Bose, S., 2005, “Carbon Nanotube Based Composites—A Review,” J. Miner. Mater. Charact. Eng., 4(1), pp. 31–46.
Kurahatti, R. V., Surendranathan, A. O., Kori, S. A., Singh, N., Kumar, A. V. R., and Srivastava, S., 2010, “Defence Applications of Polymer Nanocomposites,” Def. Sci. J., 60(5), pp. 551–563.
Hu, K., Kulkarni, D. D., Choi, I., and Tsukruk, V. V., 2014, “Graphene-Polymer Nanocomposites for Structural and Functional Applications,” Prog. Polym. Sci., 39(11), pp. 1934–1972.
Bower, C., and Rosen, R., 1999, “Deformation of Carbon Nanotubes in Nanotube-Polymer Composites,” Appl. Phys. Lett., 74(22), pp. 3317–3319.
Qian, D., Dickey, E. C., Andrews, R., and Rantell, T., 2000, “Load Transfer and Deformation Mechanisms in Carbon Nanotube-Polystyrene Composites,” Appl. Phys. Lett., 76(20), pp. 2868–2870.
Coleman, J., Khan, U., Blau, J., and Gun'ko, Y., 2006, “Small But Strong: A Review of the Mechanical Properties of Carbon Nanotube–Polymer Composites,” Carbon, 44(9), pp. 1624–1652.
Xie, P., He, P., Yen, Y.-C., Kwak, K. J., Gallego-Perez, D., Chang, L., Lioa, W.-C., Yi, A., and Lee, L. J., 2014, “Rapid Hot Embossing of Polymer Microstructures Using Carbide-Bonded Graphene Coating on Silicon Stampers,” Surf. Coat. Technol., 258, pp. 174–180.
Shaffer, M. S. P., Fan, X., and Windle, A. H., 1998, “Dispersion and Packing of Carbon Nanotubes,” Carbon, 36(11), pp. 1603–1612.
Zhu, J., Peng, H., Rodriguez-Macias, F., Margrave, J., Khabashesku, V., Imam, A., Lozano, K., and Barrera, E., 2004, “Reinforcing Epoxy Polymer Composites Through Covalent Integration of Functionalized Nanotubes,” Adv. Funct. Mater., 14(7), pp. 643–648.
Peponi, L., Puglia, D., Torre, L., Valentini, L., and Kenny, J. M., 2014, “Processing of Nanostructured Polymers and Advanced Polymeric Based Nanocomposites,” Mater. Sci. Eng. R, 85, pp. 1–46.
Gojny, F. H., Nastalczyk, J., Roslaniec, Z., and Schulte, K., 2003, “Surface Modified Multi-Wall Carbon Nanotubes in CNT/Epoxy-Composites,” Chem. Phys. Lett., 370(5–6), pp. 820–824.
Rafiee, R., and Pourazizi, R., 2015, “Influence of CNT Functionalization on the Interphase Region Between CNT and Polymer,” Comput. Mater. Sci., 96(Part B), pp. 573–578.
Hu, K., Kulkarni, D. D., Choi, I., and Tsukruk, V. V., 2014, “Graphene-Polymer Nanocomposites for Structural and Functional Applications,” Prog. Polym. Sci., 39(11), pp. 1934–1972.
Odegard, G. M., Frankland, S. J. V., and Gates, T. S., 2005, “The Effect of Chemical Functionalization on Mechanical Properties of Nanotube/Polymer Composites,” AIAA J., 43(8), pp. 1828–1835.
Li, X. M., Feng, Q., Liu, X., Dong, W., and Cui, F., 2013, “The Use of Nanoscaled Fibers or Tubes to Improve Biocompatibility and Bioactivity of Biomedical Materials,” J. Nanomater., 3, pp. 1–16.
Chang, L., Liu, C., He, Y., Xiao, H., and Cai, X., 2011, “Small-Volume Solution Current-Time Behavior Study for Application in Reverse Iontophoresis-Based Non-Invasive Blood Glucose Monitoring,” Sci. China Chem., 54(1), pp. 223–230.
Gao, K., Li, L., Hinkle, K., Wu, Y., Ma, J., Chang, L., Zhao, X., Perez, D. G., Eckardt, S., McLaughlin, J., Liu, B., Farson, D. F., and Lee, L. J., 2014, “Design of Microchannel—Nanochannel Array Based Nanoelectroporation System for Precise Gene Transfection,” Small, 10(5), pp. 1015–1023. [PubMed]
Zang, X., Zhou, Q., Chang, J., Liu, Y., and Lin, L., “Graphene and Carbon Nanotubes in MEMS/NEMS Applications, Microelectronic Engineering,” Micoelectron. Eng. (in press).
Jakubinek, M. B., Ashrafi, B., Zhang, Y., Martinez-Rubi, Y., Kingston, C. T., Johnston, A., and Simard, B., 2015, “Single-Walled Carbon Nanotube–Epoxy Composites for Structural and Conductive Aerospace Adhesives,” Compos.: Part B, 69, pp. 87–93.
Cassell, A. M., Raymakers, J. A., Kong, J., and Dai, H. J., 1999, “Large Scale CVD Synthesis of Single-Walled Carbon Nanotubes,” J. Phys. Chem. B, 103(31), pp. 6484–6492.
Joshi, U. A., Sharma, S. C., and Harsha, S. P., 2011, “Effect of Pinhole Defects on the Elasticity of Carbon Nanotube Based Nanocomposites,” ASME J. Nanotechnol. Eng. Med., 2(1), p. 011003.
Hull, D., and Clyne, T., 2008, “An Introduction to Composite Materials,” Cambridge University Press, Cambridge, UK, pp. 158–207.
Min-Feng, Y., Lourie, O., Dyer, M. J., Moloni, K., Kelly, T. F., and Ruoff, R. S., 2000, “Strength and Breaking Mechanism of Multiwalled Carbon Nanotubes Under Tensile Load,” Science, 287(5453), pp. 637–640. [PubMed]
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## References

Iijima, S., 1991, “Helical Microtubules of Graphite Carbon,” Nature, 354, pp. 56–58.
Treacy, M. M. J., Ebbesen, T. W., and Gibson, J. M., 1996, “Exceptionally High Young's Modulus Observed for Individual Carbon Nanotubes,” Nature, 381(6584), pp. 678–680.
Krishnan, A., Dujardin, E., Ebbesen, T. W., Yianilos, P. N., and Treacy, M. M. J., 1998, “Young's Modulus of Single Walled Nanotubes,” Phys. Rev. B, 58(20), pp. 14013–14019.
Khare, R., and Bose, S., 2005, “Carbon Nanotube Based Composites—A Review,” J. Miner. Mater. Charact. Eng., 4(1), pp. 31–46.
Kurahatti, R. V., Surendranathan, A. O., Kori, S. A., Singh, N., Kumar, A. V. R., and Srivastava, S., 2010, “Defence Applications of Polymer Nanocomposites,” Def. Sci. J., 60(5), pp. 551–563.
Hu, K., Kulkarni, D. D., Choi, I., and Tsukruk, V. V., 2014, “Graphene-Polymer Nanocomposites for Structural and Functional Applications,” Prog. Polym. Sci., 39(11), pp. 1934–1972.
Bower, C., and Rosen, R., 1999, “Deformation of Carbon Nanotubes in Nanotube-Polymer Composites,” Appl. Phys. Lett., 74(22), pp. 3317–3319.
Qian, D., Dickey, E. C., Andrews, R., and Rantell, T., 2000, “Load Transfer and Deformation Mechanisms in Carbon Nanotube-Polystyrene Composites,” Appl. Phys. Lett., 76(20), pp. 2868–2870.
Coleman, J., Khan, U., Blau, J., and Gun'ko, Y., 2006, “Small But Strong: A Review of the Mechanical Properties of Carbon Nanotube–Polymer Composites,” Carbon, 44(9), pp. 1624–1652.
Xie, P., He, P., Yen, Y.-C., Kwak, K. J., Gallego-Perez, D., Chang, L., Lioa, W.-C., Yi, A., and Lee, L. J., 2014, “Rapid Hot Embossing of Polymer Microstructures Using Carbide-Bonded Graphene Coating on Silicon Stampers,” Surf. Coat. Technol., 258, pp. 174–180.
Shaffer, M. S. P., Fan, X., and Windle, A. H., 1998, “Dispersion and Packing of Carbon Nanotubes,” Carbon, 36(11), pp. 1603–1612.
Zhu, J., Peng, H., Rodriguez-Macias, F., Margrave, J., Khabashesku, V., Imam, A., Lozano, K., and Barrera, E., 2004, “Reinforcing Epoxy Polymer Composites Through Covalent Integration of Functionalized Nanotubes,” Adv. Funct. Mater., 14(7), pp. 643–648.
Peponi, L., Puglia, D., Torre, L., Valentini, L., and Kenny, J. M., 2014, “Processing of Nanostructured Polymers and Advanced Polymeric Based Nanocomposites,” Mater. Sci. Eng. R, 85, pp. 1–46.
Gojny, F. H., Nastalczyk, J., Roslaniec, Z., and Schulte, K., 2003, “Surface Modified Multi-Wall Carbon Nanotubes in CNT/Epoxy-Composites,” Chem. Phys. Lett., 370(5–6), pp. 820–824.
Rafiee, R., and Pourazizi, R., 2015, “Influence of CNT Functionalization on the Interphase Region Between CNT and Polymer,” Comput. Mater. Sci., 96(Part B), pp. 573–578.
Hu, K., Kulkarni, D. D., Choi, I., and Tsukruk, V. V., 2014, “Graphene-Polymer Nanocomposites for Structural and Functional Applications,” Prog. Polym. Sci., 39(11), pp. 1934–1972.
Odegard, G. M., Frankland, S. J. V., and Gates, T. S., 2005, “The Effect of Chemical Functionalization on Mechanical Properties of Nanotube/Polymer Composites,” AIAA J., 43(8), pp. 1828–1835.
Li, X. M., Feng, Q., Liu, X., Dong, W., and Cui, F., 2013, “The Use of Nanoscaled Fibers or Tubes to Improve Biocompatibility and Bioactivity of Biomedical Materials,” J. Nanomater., 3, pp. 1–16.
Chang, L., Liu, C., He, Y., Xiao, H., and Cai, X., 2011, “Small-Volume Solution Current-Time Behavior Study for Application in Reverse Iontophoresis-Based Non-Invasive Blood Glucose Monitoring,” Sci. China Chem., 54(1), pp. 223–230.
Gao, K., Li, L., Hinkle, K., Wu, Y., Ma, J., Chang, L., Zhao, X., Perez, D. G., Eckardt, S., McLaughlin, J., Liu, B., Farson, D. F., and Lee, L. J., 2014, “Design of Microchannel—Nanochannel Array Based Nanoelectroporation System for Precise Gene Transfection,” Small, 10(5), pp. 1015–1023. [PubMed]
Zang, X., Zhou, Q., Chang, J., Liu, Y., and Lin, L., “Graphene and Carbon Nanotubes in MEMS/NEMS Applications, Microelectronic Engineering,” Micoelectron. Eng. (in press).
Jakubinek, M. B., Ashrafi, B., Zhang, Y., Martinez-Rubi, Y., Kingston, C. T., Johnston, A., and Simard, B., 2015, “Single-Walled Carbon Nanotube–Epoxy Composites for Structural and Conductive Aerospace Adhesives,” Compos.: Part B, 69, pp. 87–93.
Cassell, A. M., Raymakers, J. A., Kong, J., and Dai, H. J., 1999, “Large Scale CVD Synthesis of Single-Walled Carbon Nanotubes,” J. Phys. Chem. B, 103(31), pp. 6484–6492.
Joshi, U. A., Sharma, S. C., and Harsha, S. P., 2011, “Effect of Pinhole Defects on the Elasticity of Carbon Nanotube Based Nanocomposites,” ASME J. Nanotechnol. Eng. Med., 2(1), p. 011003.
Hull, D., and Clyne, T., 2008, “An Introduction to Composite Materials,” Cambridge University Press, Cambridge, UK, pp. 158–207.
Min-Feng, Y., Lourie, O., Dyer, M. J., Moloni, K., Kelly, T. F., and Ruoff, R. S., 2000, “Strength and Breaking Mechanism of Multiwalled Carbon Nanotubes Under Tensile Load,” Science, 287(5453), pp. 637–640. [PubMed]

## Figures

Fig. 1

(a) Type I test specimen as per ASTM D-638 and (b) type IV test specimen as per ASTM D-638

Fig. 2

(a) Electronic tensometer and (b) specimen under test

Fig. 3

Tensile failure of composite wherein fiber has a higher strain to failure than the matrix: (a) stress strain relationship and (b) composite failure stress versus volume fraction of fiber

Fig. 4

(a) Stress strain diagram of epoxy–carbon fiber with 1% MWNT by wt. and (b) stress strain diagram of epoxy–carbon fiber with 2% MWNT by wt.

Fig. 5

Fractured sample of nanocomposites: (a) nanocomposite with 1% MWNT (by wt.) and (b) nanocomposite with 2% MWNT (by wt.)

Fig. 6

Percentage enhancement in tensile strength and failure strain (test results)

Fig. 7

Percentage enhancement in tensile strength (analytical results)

## Tables

Table 1 Dimensional details of tests specimen
Table 2 Tensile test results of nanocomposites

## Discussions

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