1,720,961 research outputs found
Hypervelocity Impact on Satellite Sandwich Structures: Development of a Simulation Model and Investigation of Projectile Shape and Honeycomb Core Effects
Get PDFNumerous Earth observations, communications, and scientific satellites have been developed in Canada or with significant Canadian participation over the last few decades, and many are currently being developed. To ensure mission success goals, space satellites in Earth orbit must be analyzed for their ability to survive hypervelocity impacts (HVI) by orbital debris, as collision of a functional satellite with even a millimeter-sized object traveling at typical orbital speed (7 km/s and higher) that can be detrimental for the Earth’s orbit environment generating new orbital debris which may damage other spacecraft.These collisions can also result in damage of components vital for satellite functioning (e.g., electronics units or connecting cables) or bursting of pressurized containers, such as satellite propellant tanks. In a typical unmanned satellite, this impact-sensitive equipment is usually situated in the enclosure of the honeycomb-core sandwich panels. These panels form the satellite’s shape and are primarily designed to resist launching loads and provide attachment points for satellite subsystems. With low additional weight penalties, their intrinsic ballistic performance can often be upgraded to the level required for orbital debris protection. This study aims to develop and validate simulation models for HVI on honeycomb-core sandwich panels to enable accurate assessment of orbital debris impact survivability of space satellites. The developed and validated model will be then used to conduct parametric studies and investigate different impact conditions (spherical vs. non-spherical projectile impacts), and effects of panel design parameters, such as honeycomb core cell size and foil (wall) thickness, on ballistic performance of sandwich panels
Special Issue: Advanced Modeling and Design for Composite Materials and Structures
No full textGreen Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Structural Integrity & Composite
An Investigation of the Mechanical Properties of Aircraft Engine Fan Casing Abradable Materials at Different Temperatures and Strain Rates
Get PDFCertification of an aircraft turbofan engine requires the demonstration of its ability to contain a fan blade should the blade accidentally separate under critical operating conditions. Significant efforts have been made by the industry in creating high-fidelity full-engine numerical models for pre-certification simulations of blade-off scenarios to ensure engine certification via only one physical test, thus enabling multimillion-dollar cost avoidance. In the areas adjacent to the rotating fan blades, a fan blade containment system of an engine is usually supplemented with a lightweight abradable rub strip material. The abradable’s main function is to minimize the clearance between blade tips and the fan case. However, the interaction between the released blade and the layer of abradable material during the fan blade-off event can significantly influence blade orientation and trajectory and, therefore, may have a pronounced effect on all subsequent phases of the process and resulting damage to engine components. Therefore, the availability of a physics-based constitutive material model for abradable materials and its representation in the full-engine numerical models is highly important for the accuracy and reliability of predictions of the fan blade-off simulations. This study focused on the very first and the most critical step in the development of such a constitutive material model, namely the physical characterization of two distinct abradable systems currently used in turbofan engines. Compositional analysis of both abradables was conducted using scanning electron microscopy, which enabled formulation and development of a test program; manufacturing procedures for test specimens were developed and fine-tuned. Both abradable materials were tested under quasi-static (tension, uniaxial and confined compression), elevated temperatures (tension and compression), and high strain-rate (tension and compression) conditions. Despite compositional differences, both studied materials exhibited unequal resistance to tensile and compressive loading (compression strength higher than tensile), as well as significant temperature softening in the range of temperatures between 20 and 120°C. Abradable 1 was found to be strain-rate sensitive in compression, while Abradable 2 did not demonstrate such sensitivity, as follows from a comparison of quasi-static and ~1000/s strain rate test results. In addition, Abradable 1 demonstrated foam-like behaviour (stress plateau on the stress-strain diagram) when subjected to confined compression loading. Modelling implications following the test results were formulated and future work was discussed
Design and analysis of orbital debris protection for spacecraft composite pressure vessels
No full textBeing parts of spacecraft systems, composite overwrapped pressure vessels (COPVs) are exposed to orbital debris environment. In the case of impact of orbital debris on a composite vessel, the vessel may fail non-catastrophically, possibly resulting in the loss of spacecraft, or catastrophically, producing numerous non-trackable fragments, which may result in the loss of spacecraft and also affect and destroy other active and future spacecraft in neighbor orbits. Consequences of orbital debris impacts, therefore, must be minimized with the use of an appropriate design strategy. For a weight-efficient design providing high level of protection for spacecraft composite pressure vessels, the following design strategy is suggested in this study:
• Exclude any involvement of the pressure wall in resisting orbital debris impacts by means of an external shielding designed for the same tolerable risk of penetration as the shielding of any other critical subsystem of the spacecraft (R1tol; typically, 1-5%);
• Ensure that the shielded COPV will not fail catastrophically under conditions corresponding to even stricter tolerable risk of penetration (R2tol), such that R2tol < R1tol, which can correspond to the tolerable risk of accidental explosion during mission operations in Orbit (typically, 0.1%).
Implementation of the proposed design paradigm required 1) weight-efficient shielding systems to be designed against highly probable impacts of small-size orbital debris; and 2) a procedure capable of predicting the behavior of a shielded COPV subjected to perforating orbital debris impacts to be developed. Correspondingly, this study focused on these two aspects. First, five different external shielding systems were analysed for their weight efficiency when designed against small-size (1 mm) orbital debris impacts, including a novel orbital debris shield with ceramo-metallic bumper. Conducted evaluation made it possible to identify and recommend weight-efficient shielding designs in such categories as “Single purpose orbital debris shields” and “Multipurpose structural panels”. In this part, the results are mainly applicable to the spacecraft in low Earth Orbit. Second, a two-step modeling procedure was proposed to simulate behavior of shielded composite overwrapped pressure vessels when subjected to perforating impacts by large-size hypervelocity projectiles. The procedure can be used to evaluate vulnerability of a shielded vessel to catastrophic failure.February 201
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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