Improved Damage Tolerance Properties of Aerospace Structures by the Addition of Carbon Nanotubes

This paper investigates the effect of multiwalled carbon nanotubes on the mechanical and electrical properties of epoxy resins and epoxy composites. The research concerns multiwalled carbon nanotubes obtained by catalytic chemical vapor deposition, subjected to purification processes and covalent functionalization by depositing functional groups on their surfaces. The study included the analysis of the change in DC resistivity, tensile strength, strain, and Young’s modulus with the addition of carbon nanotubes in the range of 0 to 2.5 wt.%. The effect of agents intended to increase the affinity of the nanomaterial to the polymer on the aforementioned properties was also investigated. The addition of functionalized multiwalled carbon nanotubes allowed us to obtain electrically conductive materials. For all materials, the percolation threshold was obtained with 1% addition of multiwalled carbon nanotubes, and filling the polymer with a higher content of carbon nanotubes increased its conductivity. The use of carbon nanotubes as polymer reinforcement allows higher values of tensile strength and a higher strain percentage to be achieved. In contrast, Young’s modulus values did not increase significantly, and higher nanofiller percentages resulted in a drastic decrease in the values of the abovementioned properties.

Carbon nanotubes (CNT) are highly versatile materials, with an enormous potential for biomedical applications. Their properties are dependent upon production process and may be modified by subsequent chemical treatment. Carbon nanotubes can be used to improve polymers’ composites mechanical properties. Its tailoring allows for the creation of anisotropic nanocomposites (Kanagaraj et al, 2007; Koerner et al, 2004; Pulskamp et al, 2007; Sen et al, 2004). Due to their semi conductive behaviour, its usage may provide electrical stimulation (Grunlan et al, 2004; Huang et al, 2003). The use of CNT as translocators in drug-delivery systems or in image diagnosis has also been suggested (Bianco et al, 2005; Cherukuri et al, 2004). High tumour accumulation of single-walled CNT (SWCNT) has been described, anticipating the possibility of further therapeutic uses (Liu et al, 2007). There are several studies on gas, temperature, pressure, glucose, chemical force and resonator mass sensors based on CNT (Barone et al, 2005; Barone et al, 2005b; Collins et al, 2000; Hrapovic et al, 2004; Kong et al, 2000; Lee et al, 2007; Lin et al, 2005; Perez et al, 2005; Wood et al, 1999; Yan et al, 2007; Yang et al, 2006; Yun et al, 2007). In face of recent studies, special attention has been drawn into promising orthopaedic use of CNT for improving tribological behaviour and material mechanical properties. However, and considering the conductive properties of CNT the range of orthopaedic application may broaden up, since it is known that electrical fields as small as 0,1 mV/cm may enhance osteoblastic proliferation locally (Brighton et al, 1992). CNT based electrodes could be considered for integrating implantable orthopaedic devices. CNT have been reported to have direct and distinct effects on osteoblasts and osteoclasts metabolic functions (Narita et al, 2009; Sirivisoot et al, 2007; Tutak et al, 2009). CNT have been discovered in 1991 (IIjima, 1991), but seem to have been around for quite a long time, since they were detected in gas combustion streams like the ones in normal households stoves (Murr et al, 2004). The fact that CNT are small enough to be inhaled has

Carbon nanotubes have a lot of applications in mechanical fields. This is because nanomaterials have many superior mechanical properties such as very high strength-to-weight ratio, high modulus-to-weight ratio, high corrosion resistance, and super intelligence properties, which make them as smart materials. One of these attractive applications is the use of carbon nanotubes in vehicle brake friction material. Therefore, the fabrication and testing processes of these nanomaterials should be performed carefully to evaluate their mechanical, tribological, and noise properties. In this paper, friction material mixed with carbon nanotubes have been fabricated with different carbon nanotube contents and the same fabrication parameters. The carbon nanotubes have been produced using the conventional submerged arc discharge technique. The produced friction materials have been cut into pieces with standard sizes and then tested mechanically and tribologically. The results of tests have illustrated that the addition of carbon nanotubes into the friction materials could improve their mechanical properties (hardness, strength, and modulus) and also could enhance their tribological properties (wear rate and friction coefficient). Moreover, the tests showed that the presence of carbon nanotubes in friction materials could reduce the noise, vibration of the friction materials, and reduce the temperature rise due to the effect of friction, which means that the carbon nanotubes could raise the thermal conductivity of friction material, while the friction coefficient has stayed within the allowable standard limits (0.35–0.45). Surface morphology shows that the presence of carbon nanotubes in the friction materials could help to avoid surface friction cracks or fins within the normal operating conditions. The good combination of mechanical and tribological properties was obtained at 0.5% carbon nanotubes.

The mechanical properties of a composite material with a matrix of aluminum alloy D16 reinforced with dispersed silicon carbide particles have been studied. The physicomechanical properties (density, elastic modulus, ultimate tensile strength, and limiting strains) of the composite material with various filler contents are determined experimentally. The experimental results are compared to the results of a theoretical simulation obtained using elastic and elastoplastic models of the composite material. The experimental and the calculated mechanical properties of the composite material with the volume content of the filler up to 30% agree well with each other.

Plant fiber-reinforced polylactic acid (PLA) exhibits excellent mechanical properties and environmental friendliness and, therefore, has a wide range of applications. This study investigated the mechanical properties of three short plant fiber-reinforced PLA composites (flax, jute, and ramie) using mechanical testing and material characterization techniques (SEM, FTIR, and DSC). Additionally, we propose a methodology for predicting the mechanical properties of high-content short plant fiber-reinforced composite materials. Results indicate that flax fibers provide the optimal reinforcement effect due to differences in fiber composition and microstructure. Surface pretreatment of the fibers using alkali and silane coupling agents increases the fiber-matrix interface contact area, improves interface performance, and effectively enhances the mechanical properties of the composite. The mechanical properties of the composites increase with increasing fiber content, reaching the highest value at 40%, which is 38.79% higher than pure PLA. However, further increases in content lead to fiber agglomeration and decreased composite properties. When the content is relatively low (10%), the mechanical properties are degraded because of internal defects in the material, which is 40.42% lower than pure PLA. Through Micro-CT technology, the fiber was reconstructed, and it was found that the fiber was distributed mainly along the direction of injection molding, and the twin-screw process changes the shape and length of the fiber. By introducing the fiber agglomeration factor function and correcting the Halpin-Tsai criterion, the mechanical properties of composite materials with different contents were successfully predicted. Considering the complex stress state of composite materials in actual service processes, a numerical simulation method was established based on transversely isotropic material using the finite element method combined with theoretical analysis. The mechanical properties of high-content short plant fiber-reinforced composite materials were successfully predicted, and the simulation results showed strong agreement with the experimental results.

Nanostructured materials gained great importance in the past decade, owing to their wide range of potential applications in many areas, e.g. mechanical, structura l, sensor devices, biomedical, electronics. A large interest is involved with carbon nanotubes, which can be used as a main constituent of composite materials characterized by exceptional mechanical and electrical properties, very suitable for aerospace ap plications, due to their light weight, mechanical strength and flexibility. Recent results obtained in our laboratories are presented, concerning measurements of the electrical and mechanical properties (resilience and Young Modulus, conductivity) of a po lymer matrix, reinforced with carbon nanotubes synthesized by arc discharge and other techniques. Stress and numerical analysis of aerospace structures using carbon nanotubes reinforced composite materials are presented. The evaluation of the reduction wei ght of a typical aerospace structure is discussed.

Cardiovascular disease is currently the top global cause of death, however, research into new therapies is in decline. Tissue engineering is a solution to this crisis and in combination with the use of carbon nanotubes (CNTs), which have drawn recent attention as a biomaterial, could facilitate the development of more dynamic and complex in vitro models. CNTs’ electrical conductivity and dimensional similarity to cardiac extracellular proteins provide a unique opportunity to deliver scaffolds with stimuli that mimic the native cardiac microenvironment in vitro more effectively. This systematic review aims to evaluate the use and efficacy of CNTs for cardiac tissue scaffolds and was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. Three databases were searched: PubMed, Scopus, and Web of Science. Papers resulting from these searches were then subjected to analysis against pre-determined inclusion and quality appraisal criteria. From 249 results, 27 manuscripts met the criteria and were included in this review. Neonatal rat cardiomyocytes were most commonly used in the experiments, with multi-walled CNTs being most common in tissue scaffolds. Immunofluorescence was the experimental technique most frequently used, which was employed for the staining of cardiac-specific proteins relating to contractile and electrophysiological function.

Effect of CNT surface functionalisation on the mechanical properties of multi-walled carbon nanotube/epoxy-composites

Νέα προσέγγιση στην παρακολούθηση της αναπτυσσόμενης βλάβης υπό μηχανική φόρτιση σε ινώδη σύνθετα υλικά με μήτρα ενισχυμένη με νανοσωληνίσκους άνθρακα

Some mechanical properties of composite material based on scrap tyres and polyurethane type polymer binder were investigated to underline the significance of binder reactivity on selected mechanical properties of the composite material. Compressive stress and compressive modulus of elasticity E at 10% deformation and Shore C hardness were investigated. Connection was observed between the above-mentioned selected mechanical properties of composite material and reactivity of the polymer binder. It was confirmed previously that the crosslinking degree of polyurethane type binder separately and therefore at the same time mechanical properties of binder were strongly connected with water as a significant factor during the hardening of the polymer. The special objective of this work is to investigate connection between selected mechanical properties of the composite material, content and reactivity of the polymer binder under invariable composite material moulding and hardening conditions.

Carbon nanotubes (CNTs) possess exceptional mechanical, thermal, and electrical properties, facilitating their use as reinforcements or additives in various materials to improve the properties of the materials. Furthermore, chemically modified CNTs can introduce novel functionalities. In the medical field, biomaterials are expected to be developed using CNTs for clinical use. Biomaterials often are placed adjacent to bone. The use of CNTs is anticipated in these biomaterials applied to bone mainly to improve their overall mechanical properties, for applications such as high-strength arthroplasty prostheses or fixation plates and screws that will not fail. In addition, CNTs are expected to be used as local drug delivery systems (DDS) and/or scaffolds to promote and guide bone tissue regeneration. However, studies examining the use of CNTs as biomaterials still are in the preliminary stages. In particular, the influence of CNTs on osteoblastic cells or bone tissue is extremely important for the use of CNTs in biomaterials placed in contact with bone, and some studies have explored this. This review paper clarifies the current state of knowledge in the context of the relationship between CNTs and bone to determine whether CNTs might perform in biomaterials in contact with bone, or as a DDS and/or scaffolding for bone regeneration.

Introduction: The need for biocompatible and bioactive scaffolds to accelerate the regeneration and repair of fractured bones has been considered for bone tissue engineering applications during recent decades. The new methods were developed to produce scaffolds to improve the tissue quality, size of cavities, control the porosity and increase the scaffold compressive strength under different loads. The presence of compounds such as hydroxyapatite (HA), which contains calcium and phosphorus ions, is essential for bone marrow transplantation. The use of carbon nanotubes can be considered to improve mechanical, chemical and biological properties, much like bone collagen. However, the construction of bio-nanocomposite scaffold which includes all of the above properties is very important in accelerating bone repair and also in reducing the problems of using other conventional scaffold methods. Materials and Methods: In this paper, the fabrication of a bio-nanocomposite scaffold with a three-dimensional printing method, digital light processing (DLP) has been investigated. The used compounds of photopolymer resin, carbon nanotubes and hydroxyapatite are solvent by ultrasonic and magnet stirrer, then a scaffold model designed in SOLIDWORKS software applied to the DLP 3D printer. Results: The addition of single wall carbon nanotubes (SWCNT) increases the compressive strength of the samples more than two times, beside it leads to an increase in the porosity of the samples due to the addition of SWCNTs. The scaffold porosity was recorded around 75 and 85%, which is associated with a proper compressive strength around 2 -4 MPa. Addition of 2.5 to 5 wt% SWCNT to HA and photopolymer resin can leads to a better mechanical performance compared to the pure sample. Conclusion: The results obtained from this work showed that the above process was successful methodology in preparation of novel scaffold bio-nanocomposites using DLP technique for using in bone tissue engineering.

The present work is to be considered as additional research to the authors' previous studies. It is dedicated to the specification of the significance and impact of certain selected technological parameters on mechanical properties of the composite material based on scrap tires. The special method what is known as the “Greece-Latin square” was applied to estimate significance of each technological parameter (input parameter) for selected properties (output parameters) of the material. Moulding pressure (P), formation time (x), polymer binder content (Cpol.) and the size of rubber particles (R) were selected as the input parameters. Compressive modulus of elasticity (Ec), compressive stress at 10% deformation (σ10%), permanent deformation after 10% deformation in compressive mode (ε) and apparent density (AD) were chosen as the output parameters. An analysis of the obtained dispersion diagrams confirms that composition of the composite material (polymer content) has a greater impact on selected mechanical properties of the material than any other technological input parameter, but apparent density of the composite material demonstrates higher sensitivity to the formation time and moulding pressure of the material than to other input parameters. The obtained results of the experiment enable further optimization of the composite material production technology and at the same time securing the predictable mechanical properties of the material.

A critical review of the recent progress on carbon nanotubes-based nanogenerators

In this study, 3D printed porous poly(lactide-co-glycolide) (PLGA) and its nanocomposites with 5 wt. % hydroxyapatite (HA) and 0.5, 1 and 2 wt. % carboxyl-functionalized multi-walled carbon nanotube (CNT) scaffolds were fabricated by using extrusion-based printing. The printing parameters were optimized by rheological studies. The rheological studies demonstrated shear thinning properties for all compositions and an increase in storage modulus was observed after the addition of CNT. Porous PLGA/HA/CNT scaffolds were printed by applying a pressure of 4.76 bar at 125 °C. The addition of 0.5 wt. % of CNT reduced the strut size and increased the porosity from 42% to 60%. The increase in storage modulus and decrease in strut size were related to hydrogen bonding between CNT, HA and PLGA which ultimately improved shape fidelity. The scaffolds were characterized by analysis of their chemical structure, water contact angle measurement, in vitro bioactivity test, biodegradation test, mechanical analysis, and in vitro cell studies. The scaffolds were found to be more hydrophilic by the incorporation of CNTs. Also, degradation studies showed that the microstructure of the scaffold became more stable with the addition of HA and CNT. The compressive modulus of PLGA/HA/CNT2 scaffold was found to be 548.5 MPa, which is found suitable to replace cancellous bone. The scaffolds were found to be highly biocompatible which is possibly due to alignment of CNT and PLGA during 3D printing process. Alizarin red staining indicated improvement of mineralization of MC3T3-E1 cells on the CNT incorporated porous 3D scaffolds. The results suggest that the produced porous 3D printed PLGA/HA/CNT scaffolds are promising for bone regeneration applications.