1,720,952 research outputs found
Buckling of 3D-Printed Cylindrical Shells with Corrugated Surface
No full text3D-printing technology opens broad possibilities to manufacture structural shapes which could not be always possible by other methods. In the field of lightweight shells it allows to investigate structures with higher buckling loads than conventional shells. The buckling behavior of 3D-printed shells is studied in this paper where the shape of the cylindrical shells is modified by adding corrugation in the axial or circumferential directions. The shells are characterized by the amplitude of the corrugation and the number of the sinusoidal waves. Their elastic mechanical behavior is analyzed up to the buckling load. The numerical analysis shows that the modified surface can significantly improve the buckling load and reduces the sensitivity towards geometric imperfections. Prototypes of the shells were manufactured and tested to validate the numerical model. Regardless the experimental scatter, the average buckling load of the optimized corrugated shell twice exceeds the buckling load of the reference circular shell. At the same time stiffness and mass of the shell remain the same.Aerospace Structures & Computational Mechanic
Buckling and free vibration study of variable and constant-stiffness cylindrical shells
No full textThe ability to steer carbon fibre tapes, varying the tow angle, can widen the designs possibilities of cylindrical shells that are one of the main components of aerospace structures. This research presents experimental and numerical investigation of two carbon fibre reinforced plastic cylindrical shells – a cylinder with conventional layup made of unidirectional prepreg and a variable-stiffness cylinder manufactured by applying fibre placement technology. The shells were tested in compression until buckling and later subjected to a vibration analysis. Load-shortening curves and buckling shapes were acquired during the compression tests, while the natural frequencies and the mode shapes were measured during the vibration tests. Both tests provide a useful data set of the mechanical response of the cylinders which can be applied for further validation of models. The acquired experimental results were compared to a simple, approximated numerical model of the variable-stiffness cylinder showing good correlation with the test results.Aerospace Structures & Computational Mechanic
Mechanical Response of Variable and Constant-Stiffness Cylindrical Shells for Launcher Structures
No full textThe ability to steer the carbon fibre tape, varying the tow angle can open new designs of cylindrical shells – the main structural component of the space launcher vehicles. This research presents experimental and numerical investigation of two carbon-epoxy cylindrical shells – a cylinder with conventional layup made of unidirectional prepreg and a variable-stiffness cylinder manufactured by applying advanced fibre placement technology. The shells were tested in compression until buckling, measuring load-shortening and capturing the buckling shape by digital image correlation systems. For the purpose of modelling the variable-stiffness cylinder, a simplified stiffness approximation approach was applied. The obtained load-shortening curves and buckling shapes demonstrated good correlation with non-linear numerical models. The results of the investigation contributes to the understanding the phenomenon of buckling of variable-stiffness cylindrical shells, and the influence of initial geometric imperfections and thickness variations.Aerospace Structures & Computational Mechanic
Analysis and testing of a thermoplastic composite stiffened panel under compression
No full textThis paper presents the numerical analysis of a thermoplastic composite stiffened panel subjected to compression load. The panel has three stringers with a non-symmetric design, with an artificial crack at the middle stringer interface and is made from a fast crystallizing polyetherketoneketone carbon composite. The finite element model includes an approximation of the geometrical imperfections which were measured using a digital image correlation system. The finite element analyses are discussed, where the crack propagation is modelled using the virtual crack closure technique. The results show that crack propagation starts rather early after buckling and the crack growth behaviour is heavily influenced by the buckling shape, which consists of three half-waves in longitudinal direction in each bay.Aerospace Structures & Computational Mechanic
Flexural behavior of sandwich panels with cellular wood, plywood stiffener/foam and thermoplastic composite core
No full textA series of experimental tests have been carried out on three types of novel sandwich panels mainly designed for application in lightweight mobile housing. Two types of the panels are manufactured entirely from wood-based materials while the third one presents a combination of plywood for surfaces and corrugated thermoplastic composite as a core part. All sandwich panels are designed to allow rapid one-shot manufacturing. Mechanical performance has been evaluated in four-point bending comparing the data to the reference plywood board. Additionally, finite element simulations were performed to evaluate global behavior, stress distribution and provide the basis for a reliable design tool. Obtained results show sufficient mechanical characteristics suitable for floor and wall units. Compared to a solid plywood board, sandwich alternative can reach up to 42% higher specific stiffness, at the same time maintaining sufficient strength characteristics.Aerospace Structures & Computational Mechanic
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
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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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