1,720,956 research outputs found
A Numerical Study on Carbon-Fiber-Reinforced Composite Cylindrical Skirts for Solid Propeller Rockets
Full text linkA solid rocket motor (SRM) is a rocket engine that uses a fuel/oxidizer mixture in a solid state; the most commonly employed propellants are Hydroxyl-Terminated Polybutadiene (HTPB) as the fuel and ammonium/potassium perchlorate as the oxidizer. To increase the flight range of this kind of vehicle, the weight has to be reduced as much as possible. A possible element that can be worked on is the coating of the combustion chamber: the skirt. The aim of this paper is to investigate the behavior of a cylindrical skirt subjected to internal pressure load and axial thrust and to compare the performance of a skirt made of a standard steel for aeronautics purposes with a carbon-fiber-reinforced composite skirt. The motor test case is taken from the ONERA C1xb and the flowfield is simulated with an axisymmetric k-ω turbulence model. The carbon-fiber-reinforced composite skirt is a cylindrical shell with a symmetric and balanced layup [90/0/45/−45]s. To check composite layer integrity, Hashin’s failure criteria were adopted while linearized buckling methods were used to assess the buckling behavior of the skirt. The composite layup was modeled by adopting the classical laminate theory
On the Crashworthiness Behaviour of Innovative Sandwich Shock Absorbers
No full textIncreasing the impact resistance properties of any transport vehicle is a real engineering challenge. This challenge is addressed in this paper by proposing a high-performing structural solution. Hence, the performance, in terms of improvement of the energy absorbing characteristics and the reduction of the peak accelerations, of highly efficient shock absorbers integrated in key locations of a minibus chassis have been assessed by means of numerical crash simulations. The high efficiency of the proposed damping system has been achieved by improving the current design and manufacturing process of the state-of-the-art shock absorbers. Indeed, the proposed passive safety system is composed of additive manufactured, hybrid polymer/composite (Polypropylene/Composite Fibres Reinforced Polymers—PP/CFRP) shock absorbers. The resulting hybrid component combines the high stiffness-to-mass and strength-to-mass ratios characteristic of the composites with the capability of the PP to dissipate energy by plastic deformation. Moreover, thanks to the Additive Manufacturing (AM) technique, low-mass and low-volume highly-efficient shock-absorbing sandwich structures can be designed and manufactured. The use of high-efficiency additively manufactured sandwich shock absorbers has been demonstrated as an effective way to improve the passive safety of passengers, achieving a reduction in the peak of the reaction force and energy absorbed in the safety cage of the chassis’ structure, respectively, up to up to 30 kN and 25%
On the Crashworthiness Behaviour of Additive Manufactured Sandwich Panels
No full textThis paper explores the advantage introduced, in terms of load dissipation during a crash test, of additive manufactured composite sandwich panels. A numerical investigation has been performed on a small electric bus by comparing the results obtained by explicit crash test simulations with and without composite sandwich panels as shock absorption systems. To assess the crashworthy behaviour of the investigated structures, detailed numerical simulations with 3D formulation based finite element models have been performed within the ABAQUS Explicit FEM environment. The proposed sandwich panels configuration has been obtained by combining carbon reinforced skins with a polymeric core. This kind of hybrid structure has been considered suitable to dissipate large amounts of impact energy both by plasticisation and by fibre and matrix breakage due to the interaction between the ductility of the polymeric core with the brittle behaviour of the CFRP skins. In addition, the proposed sandwich panels are expected to exhibit a considerably high absorbed energy to mass ratio due to use of the additive manufacturing technique to produce the polymeric core. This manufacturing technique allow the definition of complex microstructures, such as lattice microstructures, characterised by significant energy absorption capabilities with a considerable mass reduction. Hence, the research study presented in this paper is aimed to prove that, for the analysed small electric bus configuration, the considered combination of innovative materials and processes can help to develop compact and highly efficient shock absorber sandwich panels capable to reduce both stress and energy distribution on the chassis structure
Structural Evaluation of a Vertical Tail for a Supersonic Vehicle: Architecture, Boundary Conditions, and Material System Influence
No full textSupersonic aircraft is defined as aircraft that can travel at speeds above the speed of sound (M > 1). For these aircraft, correct dimensioning is essential to enable them to withstand the high aerodynamic loads they face. This study evaluates the impact of internal architecture, boundary conditions, and material on the dimensioning of the vertical tailplane when subjected to a gust load. The optimal configuration is the one that achieves a balance between weight and structural performance. Titanium alloy Ti 6AI-4 V and carbon/carbon composites are selected as the most suitable materials for this application due to their known high-temperature resistance. The best configuration, although it weighs 20% times more than the composite configuration, manages to achieve a reduction in tip displacement of 80%, significantly improving strength and instability performance
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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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