Strength Of Carbon Nanotubes Research Articles

Molecular Dynamics Simulations and Theoretical Model for Engineering Tensile Properties of Single-and Multi-Walled Carbon Nanotubes.

To apply carbon nanotubes (CNTs) as reinforcing agents in next-generation composites, it is essential to improve their nominal strength. However, since it is difficult to completely remove the defects, the synthesis guideline for improving nominal strength is still unclear, i.e., the effective strength and the number of nanotube layers required to improve the nominal strength has been undermined. In this study, molecular dynamics simulations were used to elucidate the effects of vacancies on the mechanical properties of CNTs. Additionally, the relationships between the number of layers and effective and nominal strengths of CNTs were discussed theoretically. The presence of extensive vacancies provides a possible explanation for the low nominal strengths obtained in previous experimental measurements of CNTs. This study indicates that the nominal strength can be increased from the experimentally obtained values of 10 GPa to approximately 20 GPa by using six to nine nanotube layers, even if the increase in effective strength of each layer is small. This has advantages over double-walled CNTs, because the effective strength of such CNTs must be approximately 60 GPa to achieve a nominal strength of 20 GPa.

Fabrication of Carbon Nanotube/Aluminum Matrix Composites by Ball Milling and Cold Press Processing

Carbon nanotube (CNT) has been one of promising candidates as a reinforcement in metal matrix composites (MMCs) for its variety of excellent properties such as lightweight, high strength etc. It is necessary to disperse CNT to the level of each one in order to lead to efficiently reflect the excellent essential physical properties of CNT in the composites. This research investigates fabrication processes linked with dry ball milling and cold pressing followed by sintering to uniformly disperse CNT in aluminum (Al) matrix. It was found that dispersibility of CNT were improved with increasing ball milling time based on observation of morphology of mixed powders and the composites using SEM. Vickers hardness and tensile strength of CNT/ Al composites increased with increasing ball milling time up to 24 hours, while they were constant or decreased because of increase of voids in case of longer than 24 hours of ball milling time.

On the low reinforcing efficiency of carbon nanotubes in high-performance polymer fibres

Driven by the exceptionally high mechanical properties of carbon nanotubes (CNTs), over the years an extensive research effort has been devoted to the reinforcement of high-performance polymer fibres with CNTs. However, to date, improvements in the strength of these fibres have been rather modest even for relatively high CNT contents. After a brief review of CNT reinforced polymer fibres, here, analytical and numerical finite element models will be used to show that these experimental findings are to be expected based on the intrinsic mechanical properties of these polymer fibres and CNTs, their aspect ratio and interfacial characteristics. Results show that for realistic CNT contents and aspect ratios, the extraordinary strength of CNTs cannot be easily fully exploited in high-performance polymer fibres like Dyneema®or Kevlar®. Even if CNTs are perfectly aligned, bonded and dispersed, the low intrinsic shear strength of these highly anisotropic polymer fibres limits effective stress transfer and nanotube reinforcement.

Effect of 1D carbon nano- tube and fiber reinforcement on the long-term creep performance of glass fiber/epoxy composite using the time-temperature superposition principle

In this article, one-dimensional (1D) carbon nanotube (CNT) and carbon nanofiber (CNF) is added to glass fiber/epoxy (GE) composite in an attempt to improve its life-long creep resistance. Accelerated deformation of GE and both nanofiller reinforced GE (CNT-GE and CNF-GE) composite were done in 30–120 °C temperature span, and the long-term creep behavior was evaluated by implementing time–temperature superposition principle at 30 °C and 90 °C reference temperature (RT). CNT-GE and CNF-GE composite showed positive creep compliance till ∼109.5 and ∼104.5 years, respectively, at RT of 30 °C as compared to GE composite. However, at a RT of 90 °C, positive creep compliance duration was reduced to ∼800 for CNT-GE and ∼8 days for CNF-GE composite. The creep resistance of both nanofiller reinforced GE composites was highly temperature-sensitive due to an increase in heterogeneity in the composite with second phase nano reinforcement addition. Higher specific surface area and strength of CNTs than CNFs produced better creep resistance in GE composite at lower temperatures.

A comprehensive review: Influence of the concentration of carbon nanotubes (CNT) on mechanical characteristics of aluminium metal matrix composites: Part 1

Carbon nanotubes (CNT) are an outstanding development in the field of nanostructure. Unique characteristics of Carbon Nanotubes (CNT) make them a suitable reinforcing agent in Aluminium Metal Matrix composites. These composites are being anticipated in aviation for their high explicit quality just as utilitarian materials for their energizing mechanical and warm attributes. The property of carbon nanotube strengthened aluminum network (Al-CNT) composites mainly depends on the percentage weight of reinforced material in the base material. Thus the main objective of this review paper to addresses the concentration of CNT on tensile strength, yield strength and compressive strength of CNT - Al matrix composites.

Dielectric and Mechanical Properties of Local Commercial Single Walled Carbon Nanotubes for Medical Applications: A Practical Approach

Owing to their exceptional electrical and mechanical properties, low weights and availability of their synthesis and purification carbon nanotubes (CNTs) became the focus of scientists in many medical and electronic applications, and reinforcement of various materials. A close understanding of structure-properties of (CNTs) will be necessary for the development of carbon-nanotube applications. High stiffness and tensile strength of CNTs provide mechanical stability for electric nano-circuits formed by CNTs. Meanwhile, at earlier time of their application, researchers main concern was dedicated for preparation methods of CNTs. Eventually the structural and physical characteristics of CNTs became more attractive for scientist proper applications. Herein the current work introduce a practical approach for screening the dielectric and mechanical properties of local commercial purchased single walled carbon nanotubes for medical applications. Dielectric properties of CNTS were expressed in term of electrical relative permittivity, and electrical conductivity. The dielectric relaxation obeys ordinary alpha and beta relaxation of dielectrics at current frequency range. Besides the mechanical properties in term of dimetral tensile and compression strength that are expressed by Young’s modulus that is closer to graphite. As a results, we highly recommend these commercial (SWCNTs) from our local suppliers for further medical applications.

Analysis of critical interfacial shear strength between polymer matrix and carbon nanotubes and its impact on the tensile strength of nanocomposites

This paper focuses on the critical interfacial shear strength (τc) and interfacial shear strength (τ) between polymer matrix and carbon nanotubes (CNT) in nanocomposites, which divide the interphase region to two zones: τ < τc near the polymer matrix and τ > τc beside the CNT. “τc” is defined by CNT properties and a model is developed to consider the roles of “τ” and “τc” in the tensile strength of nanocomposites. Numerous experimental data for various samples and the parametric examines are applied to approve the developed approach. The high aspect ratio of CNT (thin and long CNT) produces a low “τc”, but the CNT strength directly influences the “τc”. The suitable agreement between experimental data and calculations for all samples and the proper roles of all parameters in the tensile strength of nanocomposites confirm the developed model. Low “τc” and high “τ” cause a high nanocomposite strength, but the strength of nanocomposites largely increases when τ > 5 τc.

Effect of Air Oxidation Treatment of CNT on Tensile Strength of CNT / Polyamide 6 Nanofibres and their Dispersion

Carbon nanotube (CNT) is excellent in mechanical and thermal characteristics, and are expected to be used in various fields such as nanoelectronic devices and reinforcing nanofillers for composites. It is expected that mechanical properties can be improved by adding CNT into the polymer. However, since CNT exists in a state of aggregation due to van der Waals forces, it is necessary to uniformly disperse CNT in order to fully extract the properties of CNT. In this study, CNT/polyamide 6 (PA6) composite nanofibres were fabricated by the electrospinning method. In order to disperse CNT in the CNT/PA6 nanofibres, CNT were subjected to air oxidation treatment. As a result of evaluating the dispersibility of CNT by sedimentation test, the dispersibility in pure water and HFIP is improved by oxidizing the surface of CNT. By conducting tensile tests and SEM observation of the nanofibre non-woven fabric, the influence of the surface treatment on the tensile strength of CNT/PA6 nanofibres and the dispersion of CNT was clarified. Although the addition of untreated CNT to PA6 nanofibres reduces the displacement at break, air oxidized CNT/PA6 suppressed the formation of CNT aggregates, and showed higher tensile strength and larger displacement at break than untreated CNT/PA6.

Effects of Temperature on the Fibre Matrix Interfacial Shear Strength of Carbon Nanotube Grafted Carbon Fibre Reinforced Heat Resistant Resin

Transportation sector is required to reduce CO2 emissions as environmental problems are becoming more serious. Carbon fibre reinforced thermoplastic (CFRTP) are expected to be applied to the structural parts of automobiles and aircrafts because of their superior mechanical properties such as high specific strength, high specific stiffness and high recyclability. One of the problems in using CFRTP for the structural parts is heat resistance, and it is necessary to clarify the mechanical properties under their service environmental temperature. The tensile strength of CFRTP at high temperatures decreases with temperature rise. The fibre matrix interfacial shear strength is reported to be improved by grafting of carbon nanotubes (CNTs) on the surface of carbon fibre. In this study, in order to clarify the effects of temperature on the fibre matrix interfacial shear strength of CNTs grafted carbon fibre reinforced PPS resin, single fibre pull-out test was conducted. While the interfacial shear strength of CNT grafted-CF/PPS is higher than that of As-received-CF/PPS at 25 °C, no significant difference was found in the interfacial shear strength of As-received-CF/PPS and CNT grafted-CF/PPS at 80 °C.

Ultrafast Bonding of Wafer Scale Vertical Aligned Carbon Nanotubes onto Gold Surface by Induction Heating

A room temperature bonding method was developed in this study to bond vertical allied carbon nanotubes (CNTs) onto gold surface within 5 seconds, and the contact electrical resistance between the CNTs and metal surface was reduced by up to 99%. Unlike traditional thermocompression bonding method, the non-contact induction selective heating occurred at CNT/metal interface, avoiding high temperature and pressure applied on the device. In particular, the atomic study indicated that surface charges induced by the induction heating could improve the wetting between metal atoms and the CNT surface. In addition, the contact configure modification effectively facilitated the surface melting due to increased anharmonicity at the interface. As a result, the welding occurred at much lower temperature than the metal melting point. This behavior provides more material choices for targeting metallic surface rather than using metals with excellent wetting properties to the carbon nanotube. Also, the debonding process also showed that the bonding strength was higher than the tensile strength of CNT itself. The process is promising for large-scale and wafer-level CNT-based devices and thermal interface material assembly.

Load-transfer and failure behaviors of crosslinked interfaces in collagen-mimic carbon nanotube bundles

Weak interface has been a long-standing bottleneck critically hindering the exploitation of the ultra-high stiffness and strength of carbon nanotubes (CNTs) as reinforcement materials. Inspired by the structure of collagen fibril, a covalently cross-linked interface design for ultra-strong CNT bundles has attracted a lot of attentions. In the present paper, molecular dynamics simulations were conducted to systematically study the load-transfer capacity and failure behaviors of the crosslinked interface, including the influence of crosslink type (length), density, and interface length. We found that a small number of covalent crosslinks can significantly enhance the interface stiffness and strength. The shorter crosslinks usually yield higher interface stiffness while the longer crosslinks generally produce higher interface strength. There are three major failure modes unveiled as the crosslink density and interface length vary, namely the abrupt interface failure, the gradual interface failure and the CNT break. A forth failure mode was also seen upon an optimal interface design, in which bond breaks propagate simultaneously and gradually in crosslinked interfaces and CNTs. The optimal design is highly desired in engineering applications since it can simultaneously provide superior stiffness, strength and toughness. These findings provide useful insights into the interface design of high-performance CNT fibers.

Hydration Phenomena of Functionalized Carbon Nanotubes (CNT)/Cement Composites

The exciting features of carbon nanotubes (CNTs), such as high elastic modulus, high thermal and electrical conductivities, robustness, and nanoscopic surface properties make them attractive candidates for the cement industry. They have the potential to significantly enhanceengineering properties. CNTs play an important and critical role as nano-anchors in concrete, which enhance the strength by bridging pores in the composite matrix, thereby ensuring robust mechanical strength. The diameter, dispersion, aspect ratio, and interfacial surface interaction of CNTs affect the physical and mechanical properties of concrete, if due care is not taken. In this paper, the usable amount of CNT is scaled down considerably from 0.5% to 0.025% by weight of the cement and the fluctuation caused by these phenomena is assessed. It is observed that the properties and exact quantities of incorporated CNTs influence the hydration and consistency of the composites. In order to address these issues, the surface functionalization of CNTs and rheological studies of the composites are performed. The hydration products and functional groups are carefully optimized and characterized by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and a Zeta potential analyzer. For Mixes 6 and 7, the compressive and tensile strength of CNTs incorporated in mortar specimens caused77% and 48% increases in split tensile strength, respectively, and 17% and 35% increases in compressive strength, respectively, after 28 days of curing and compared withthe control Mix.

Mechanical Properties of Carbon Nanotubes Reinforced AZ91 Composites by Enhanced Interfacial Bonding

The aim of this study is to enhance the interfacial bonding strength of carbon nanotubes (CNTs)/AZ91 composites by heat treatment (HT). Ternary carbides (Al2MgC2) were in situ formed and uniformly dispersed between CNTs and AZ91 matrix by 823K heat treatment of CNTs/AZ91 composites for 12 h. In situ synthesized Al2MgC2 can strengthen the interfacial bonding of CNTs/AZ91 composites, and guarantee an effective load transfer between matrix and CNTs. The HT-CNTs/AZ91 composites showed outstanding mechanical properties due to the excellent interface enhancing effect of Al2MgC2. Compared with pure AZ91 alloy, HT-CNTs/AZ91 composites exhibit improved ultimate tensile strength and 0.2% yield strength by 7% and 22% respectively.

Influence of dispersants on the properties of CNTs reinforced cement-based materials

Carbon nanotubes (CNTs) have attracted great attention due to their remarkable mechanical and electrical properties. Incorporation of CNTs can significantly improve the properties of cement-based materials, especially the electrical conductivity. However, agglomeration of CNTs is frequently encountered which can largely weaken the functionality of composites. In this work, enhanced dispersion of carbon nanotubes in cement-based materials has been achieved by using three dispersants and in combination with ultrasonic vibration. The influence of dispersants on the electrical conductivity and mechanical properties of cement paste incorporated with CNTs has been investigated. It is shown that enhanced dispersion of CNTs achieved by the use of dispersants significantly improves the electrical conductivity through the formation of electrical networks in the cement-based composite at mature stage. Air bubbles introduced by the dispersant in cement-based composites reduces its electrical conductivity significantly. Moreover, the air bubbles also lead to a large decrease of the compressive strength of CNTs reinforced cement-based composites.

Bond strength of individual carbon nanotubes grown directly on carbon fibers

The performance of carbon nanotube (CNT)-based devices strongly depends on the adhesion of CNTs to the substrate on which they were directly grown. We report on the bond strength of CNTs grown on a carbon fiber (T700SC Toray), measured via in situ pulling of individual CNTs inside a transmission electron microscope. The bond strength of an individual CNT, obtained from the measured pulling force and CNT cross-section, was very high (∼200 MPa), 8–10 times higher than that of an adhesion model assuming only van der Waals interactions (25 MPa), presumably due to carbon–carbon interactions between the CNT (its bottom atoms) and the carbon substrate.

Ni foams decorated with carbon nanotubes as catalytic stirrers for aerobic oxidation of cumene

Carbon nanotubes (CNTs) have received intensive scientific interests as a metal-free catalyst for the oxidation reactions of hydrocarbons in the liquid phase. However, its application in the liquid reaction is limited by the costly catalyst filtration process. Herein, a structured CNT catalyst was fabricated via growing CNTs on Ni foams with a porous Al2O3 coating layer. The resultant structured CNTs were used both as catalysts and as stirrer in a rotating foam stirrer reactor. The catalytic performance was evaluated in the production of cumene hydroperoxide by the aerobic oxidation of cumene. Under optimized experimental conditions, the cumene conversion reached 25.1%, 14% higher than that of commercial CNTs in a slurry reactor. The excellent adhesion strength of CNTs on the foam and catalytic stability in 5 runs of recycling were demonstrated, opening a new way to employing CNTs as a metal-free catalyst in the liquid phase reactions.

Reversible Tuning of Individual Carbon Nanotube Mechanical Properties via Defect Engineering.

The structural defects that inevitably exist in real-world carbon nanotubes (CNTs) are generally considered undesirable because they break the structural perfection and may result in drastically degraded CNT properties. On the other hand, the deliberate defect introduction can provide a possibility to tailor the tube mechanical properties. Herein, we present a fully controllable technique to handle defects by using in situ transmission electron microscopy (TEM). Young's modulus, quality factor of the resonation and tensile strength of CNTs can be controllably, reversibly, and repeatedly tuned. Parallel high-resolution visualizing of structural defects suggests that the property tuning cycles are primarily attributed to the reversible conversion of defects at the atomic scale: the defects are created in the form of vacancies and interstitials under electron irradiation, and they vanish through the recombination via current-induced annealing. For applications, such as reversible frequency-tuned CNT resonators, this defect-engineering technique is demonstrated to be uniquely precise; the frequency may be tuned with 0.1%/min accuracy, improved by 1 order of magnitude compared with the existing approaches. We believe that these results will be highly valuable in a variety of property-tunable CNT-based composites and devices.

Optimizing the manufacturing parameters of carbon nanotubes stiffened speaker diaphragm using Taguchi method

This study developed a thermal transfer printing (TTP) technique to fabricate a carbon nanotubes (CNTs) stiffened speaker diaphragm. The self-developed TTP stiffening technique does not require a high curing temperature that decreases the mechanical property of CNTs. Therefore, the inherent strength of CNTs was preserved. In addition to increasing the stiffness of diaphragm substrate, this technique alleviates the middle and high frequency attenuation associated with the sound pressure curve of a speaker, thereby smoothing the sound pressure curve and achieving a full sound range as well as reducing bass distortion and enhancing treble clarity. Furthermore, the TTP technique can stiffen a localized area on a diaphragm substrate, thus increasing diaphragm stiffness without markedly raising diaphragm weight. The Taguchi quality engineering method was applied to identify the optimal process parameters (i.e., transfer area, stiffening pattern, coating layers, and transfer temperature). Finally, the optimal process parameters were employed to fabricate a stiffened diaphragm, which was then assembled onto a speaker. The result indicated that the stiffened diaphragm improved the smoothness of the sound pressure curve for the speaker, which produced a mid-frequency dip difference (ΔdB) of 1.9dB and an attenuation peak frequency (fpeak) of 4220Hz.

The Great Reduction of a Carbon Nanotube’s Mechanical Performance by a Few Topological Defects

It is widely believed that carbon nanotubes (CNTs) can be employed to produce superstrong materials with tensile strengths of up to 50 GPa. Numerous efforts have, however, led to CNT fibers with maximum strengths of only a few GPa. Here we report that, due to different mechanical responses to the tensile loading of disclination topological defects in the CNT walls, a few of these topological defects are able to greatly decrease the strength of the CNTs, by up to an order of magnitude. This study reveals that even nearly perfect CNTs cannot be used to build exceptionally strong materials, and therefore synthesizing flawless CNTs is essential for utilizing the ideal strength of CNTs.

Morphology-dependent load transfer governs the strength and failure mechanism of carbon nanotube yarns

The outstanding properties of individual carbon nanotubes (CNTs) have motivated interest in CNT fibers and yarns for composite materials, high-strength conductors and multifunctional textiles. However, despite advances in manufacturing, the strength of CNT yarns remains 10–100 fold less than individual CNTs. In light of the complex, multi-scale load transfer in CNT yarns, a hierarchical model taking into consideration the morphology-dependent mechanics is necessary to understand this limitation. We present a coupled analytical and finite element model of three-dimensional morphology and the full tensile behavior of CNT yarns. By incorporating load-induced changes in morphology, simulations of yarns in tension show different load paths such as fracture-type or stick–slip failure depending on the waviness and number density of CNTs. The strength of untwisted pristine CNT yarns is shown to be limited to <10% of the intrinsic CNT strength, even at practical limits to CNT packing density and alignment. Load-induced changes in CNT morphology are verified by tensile testing of CNT yarns along with in-situ X-ray scattering. In addition, the nominal structure of the yarn is shown to strongly influence the improvement in strength achieved by densified and/or cross-linking, and a sublinear relationship between CNT contact enhancement and yarn strength is predicted. Thus, this work provides a means to investigate the complex load transfer mechanisms in CNT yarns and other assemblies, to further study their process–structure–property relationships, and to understand potential property limits.