1,720,964 research outputs found
Computational mechanics modelling of carbon nanotube-based nanocomposites
Get PDFComposites are engineered materials that consist of two or more insoluble phases combined together; a continuous phase, known as the matrix, as well as interdispersed component known as the reinforcing phases. If at least one of the constituent phases of a composite material is less than 100 nm in size, e.g. the reinforcing phase, this composite is commonly termed nanocomposite. Among all the variety of different fillers that can be used as a nanocomposite’s reinforcing phase, carbon nanotubes (CNTs), have shown to be promising candidates for their very specific and remarkable mechanical and physical properties. Carbon nanotube–based nanocomposites, i.e. composite materials in which carbon nanotubes are used as the composite’s reinforcing phase, are therefore very much interesting for scientists and scholars, for the many outstanding applications that they can contribute to the world of science and industry. This study uses a computational mechanics approach to numerically characterise the properties of single– and multi–walled carbon nanotubes by simulating their molecular structure, by the finite element method, at the first stage. Special emphasis is given to investigate the effect of some imperfections in the structure of both single– and multi–walled CNTs on their mechanical properties, namely perturbation, missing atoms and silicon doping in the structure of CNTs. Later on, a unit cell of a composite material, consisting of a single CNT and its surrounding matrix is simulated and studied and finally, parallel CNTs, as reinforcement fibres in a macroscopic polymer matrix, are randomly distributed and modelled to obtain the mechanical properties of the structure and observe how random distribution of short fibres influences the properties of nanocomposites. Based on the results of this research, any type of imperfection in the structure of carbon nanotubes and carbon nanotube-based nanocomposites leads to a Young's modulus value of less than 1TPa
On finite element modeling of single- and multi-walled carbon nanotubes
No full textIn this study, Single-Walled and Multi-Walled Carbon Nanotubes in their perfect forms were investigated by the Finite Element Method. Details on the modeling of the structure are provided in this paper, including the appropriate elements, the element properties that should be defined based on the atomic structure of Carbon Nanotubes and the corresponding chemical bonds. Non-covalent van der Waals interactions between two neighbor atoms as well as the required approximations for the modeling of the structures with this kind of interaction are also presented. Specific attention was dedicated to the necessity of using some time- and energy-consuming steps in the simulation process. First, the effect of simulating only a single ring of the whole structure is studied to find out if it would represent the same mechanical behavior as the long structure. Results show that by applying an appropriate set of boundary conditions, the stiffness of the shortened structure is practically equal to the long perfect structure. Furthermore, Multi-Walled Carbon Nanotube structures with and without defining the van der Waals force are studied. Based on the observations, applying the van der Waals force does not significantly influence the obtained Young's modulus of the structure in the case of a uniaxial tensile test
Young's modulus variation of carbon nanotubes due to defects associated with atomic reconstruction of random vacancies
No full textThis paper studies the effect of three different types of defects on the Young’s modulus of zigzag and armchair single-walled carbon nanotubes. The defects are randomly introduced into the structure with a maximum distribution density of 2%. The defects include monovacancies, before and after reconstruction of dangling bonds, resulting finally to the Stone-Wales defect. As the length of model effects computation time significantly, finite element models are created in pristine and very short tube lengths to investigate the effect of model length on the results obtained. The investigation shows that the introduction of defects generally weakens the elastic strength of tubes but to rather different degrees. However, the structure is capable of restoring its elastic strength by rearranging its atoms in form of the Stone-Wales defect. The use of shorter nanotube models on the other hand can lead to accurate results if appropriate cylindrical boundary conditions are defined.Griffith Sciences, Griffith School of EngineeringNo Full Tex
Buckling behaviour and natural frequency of zigzag and armchair single-walled carbon nanotubes
Get PDFIn this study, single-walled carbon nanotubes were generated in their perfect state as finite element models in the MSC.Marc software. The buckling behaviour and resonant frequency modes of the two limiting cases of carbon nanotubes, i.e. the armchair and zigzag models, were studied. The obtained results were compared with the classical analytical solutions related to a similar continuum structure of a hollow cylinder. The buckling behaviour of single-walled carbon nanotubes under cantilever boundary conditions proved to be almost identical to the prediction of the classical Euler equation. Furthermore, there was very good agreement between the analytical and finite element results of the studied single-walled carbon nanotubes; though the achieved value of the first mode of frequency, obtained from the finite element results, was more accurate than the higher modes
Defects: Defects in Carbon Nanotubes
No full textCarbon nanotubes (CNTs) have shown to be promising candidates as outstanding engineering materials, for their remarkable mechanical, thermal, optical, and electrical properties. Therefore, they are expected to contribute in many outstanding applications in the world of science and industry. Nonetheless, there are several types of imperfections in the structure of CNTs, which may occur during the process of manufacturing. Defects are an inevitable part of all devices. Although in the macro world, the existence of defect does not inuence the functionality of devices extensively, in the world of nano, even minor defects can alter the basic properties of the device signicantly. Hence, the study of the defects is a major topic that should be investigated very carefully in nanoscience and technology.Griffith Sciences, Griffith School of EngineeringNo Full Tex
Characterization of Carbon Nanotube Based Composites under Consideration of Defects
No full textThis volume presents the characterization methods involved with carbon nanotubes and carbon nanotube-based composites, with a more detailed look at computational mechanics approaches, namely the finite element method. Special emphasis is placed on studies that consider the extent to which imperfections in the structure of the nanomaterials affect their mechanical properties. These defects may include random distribution of fibers in the composite structure, as well as atom vacancies, perturbation and doping in the structure of individual carbon nanotubes.Griffith Sciences, School of Engineering and Built EnvironmentNo Full Tex
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
A numerical evaluation of the influence of defects on the elastic modulus of single and multi-walled carbon nanotubes
No full textFinite element models of single-walled and multi-walled carbon nanotubes in their perfect and fundamental forms (zigzag and armchair) were constructed. Then, after obtaining the mechanical properties of perfect carbon nanotubes, three types of imperfections, i.e., doping with Si atoms, carbon vacancy and perturbation of the ideal location of the carbon atom were introduced in different amounts to the perfect models to make them imperfect. Finally, the mechanical properties of the imperfect carbon nanotubes were numerically simulated and compared with those of perfect ones. Simple relations which predict the change of Young’s modulus as a function of the imperfection percentage were derived. The results show that the existence of any kind of imperfection in the perfect models leads to lower stiffness values. This study allows to realistically judge any simulation based on perfect structures and gives for the first time a good estimate to which extend the values based on perfect structures must be lowered in order to account for common imperfections to predict the mechanical properties of carbon nanotubes which are nowadays used in the production of advanced nanocomposites and reinforced materials
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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