1,721,017 research outputs found
Ballistic characterization of nanostructured composite materials for aerospace applications
No full textThe manuscript is arranged in three main parts.
In the first chapter the nanocomposite manufacturing is described. As far as the CNTfilled
polymeric composites are concerned, a carbon nanotube functionalization process
by thermal and chemical treatments has been performed, and Scanning Electron
Microscopy (SEM) analysis, as well as Raman and FT-IR spectroscopies were used to
verify the surface modifications of the CNTs by the added radical groups. Then, the
manufacturing of the CNT-reinforced epoxy composite has been carried out, and
Differential Scanning Calorimetry (DSC) was used to analyze the polymerization
process for the nano-reinforced thermosetting polymer systems. SEM investigations
were also performed to assess the nanocomposites quality in terms of nanoparticle
dispersion and material homogeneity. Regarding the STF-reinforced materials, STFs
have been synthesized in a single step reaction through high power ultrasound
technique, and characterized in terms of their rheological properties. The shear
thickening fluid is prepared by ultrasound irradiation of silica nanoparticles dispersed in
liquid polyethylene glycol polymer. Then, STF-reinforced fabrics have been realized by
soaking layers of several types of Kevlar in STF/ethanol solution; the morphology of
the as-realized fabrics, in particular for what concerns the STF/fibers interaction, has
been deeply investigated by SEM analysis.
In the second chapter the realization and the characterization of the in-house built Coil
Gun device for ballistic applications is presented. The realization of such experimental
apparatus, and mostly the optimization with a view to space debris testing plane, is quite
complex since the fundamental machine parameters have high non-linearity behavior.
With the aim to perform an as accurate as possible ballistic characterization, both
theoretical issues and experimental preliminary results of the prototypal device are
widely presented and discussed.
In the third chapter the results of the ballistic characterization of the realized
nanocomposite materials are reported. The response of the manufactured materials to
several levels of impact energy is widely investigated. Charpy impact and weight drop
tests were performed to obtain a preliminary ballistic characterization of the CNTVI
reinforced epoxy composites in the low energy impact range. In order to assess the
influence of the nanoparticles content as well as the effectiveness of the nano-filler itself
and after chemical treatments, samples with different percentages of functionalized
CNTs embedded in two different epoxy resins were tested and compared with samples
reinforced by pristine CNTs and micrometric graphite powder. Finally, the response of
CNT-reinforced epoxy materials and STF-reinforced Kevlar fabrics was experimentally
investigated by Coil Gun ballistic tests at different impact energy: the effects of the
nanoparticles on the penetration failure and the impact absorbing mechanism is
analyzed and discussed
ELECTROMAGNETIC WAVE ABSORPTION DEVICE WITH ADJUSTABLE FREQUENCY OF ABSORPTION
No full textElectromagnetic wave absorbing device (10), and related manufacturing process, comprising an absorber element (20) made of a composite material comprising a polymeric matrix wherein electrically conductive and/or semiconductive microstructured and/or nanostructured fillers are dispersed, wherein one or more electrode layers comprising at least two electrodes (1A, 1B, 2A, 2B, 3A, 3B, 4A, 4B, 5C, 5D) are embedded, said at least two electrodes being physically separated from each other in at least one internal portion of the composite material, at least one generator of control electrical signals being connected to two electrodes (1A, 1B, 2A, 2B, 3A, 3B) selected from said at least two electrodes (1A, 1B, 2A, 2B, 3A, 3B, 4A, 4B, 5C, 5D)
Modeling of Radar Absorbing Materials using Winning Particle Optimization applied on Electrically Conductive Nanostructured Composite material.
No full textModelling and manufacturing of radar absorbing material are proposed using multilayer composite nanostructured materials and recent introduced winning particle optimization algorithm. The study concerns tile with dimensions of 0.3m×0.3m made by nanostructured composite materials, which consist on epoxy-resin and industrial grade carbon nanotube (CNTs) fillers. The industrial grade CNTs were appositely chosen for their low costs, in order to be applied in great amount to build large tile of composite materials. Here modelling takes into account for an extended frequency band (5-18 GHz) for several incidence angles of the electromagnetic field, and for the minimization of electromagnetic reflection coefficient. At least, simulations were compared with measurements of reflection coefficient of the manufactured radar absorbing material tile. Despite some error, probably due to the manufacturing process, simulations are in good agreement with measurements, showing an interesting approach to design multilayer radar absorbing materials
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
Mimic materials electromagnetic reflection and transmission coefficient
No full textThe paper is focused on a design method to build layered materials able to mimic the reflection and transmission coefficient profile of really existing or even invented dielectric materials. The design method is based on particle swarm optimization algorithm and electromagnetic matrix formalism which allows the minimization of an objective function. Goal of the procedure is to obtain a layered materials mimicking the target reflection and transmission coefficient profile a priori established. The design algorithm is coded in Matlab and it selects the best material for each layer by accessing to a database of dielectrically characterized materials. Materials in the database are made using different species and amount of carbon nanomaterials dispersed epoxy matrix. Thickness and the number of layers of final layered structures are optimized by the iterative design procedure. In the paper some interesting example of mimic optimization are shown. The numerical finite element method analysis complete the electromagnetic discussion showing how each layer of the optimized layered structures takes part in the final goal of mimicking the target electromagnetic profile
X-Band microwave chracterization of carbon-based nanocomposite material, absorption capability and RAS design simulation
No full textThis paper presents a microwave characterization of several carbon-based composite materials interesting the future aircraft/aerospace systems. They consist in epoxy resin reinforced with five different carbon species: micro-sized granular graphite, fullerenes, carbon nanofibers, single- and multi-walled carbon nanotubes. Main goal of this work is to show how carbon inclusions size and geometry are able to significantly modify the electromagnetic properties at microwave frequencies. Microwave characterization is performed in terms of microwave permittivity and intrinsic wave impedance evaluation; all the computations are based on microwave scattering parameters measured in the X-band (8.2/12.4 GHz) by waveguide method. A theoretical analysis of the microwave absorbing capability is then performed assuming that a multilayer of nanocomposite material was backed on a conductor plate (such a structure is typically called Radar Absorbing Material). The results obtained for the reflection coefficient indicate that nanoparticles give better absorption properties to the matrix than micro-sized ones: nanocomposite materials could thus be used successfully as microwave absorbers, not only for their absorption performances but also for their light weight
Nanostructured Composite Material for Electromagnetic Interference Shielding Applications
No full textCurrently some aerospace application of composite materials is to substitute classical metal based structural element with composite based structural element and most current work deal with the importance of EMI shielding systems. This is particularly important as an example on board the satellite / space vehicle, where several electronic subsystems have to operate with different interference sensitivity close to each other e.g., telecommunication and telemetry subsystems at microwave frequencies, DC supplier subsystems, acquisition data subsystem, navigation subsystem attitude control subsystem and so on. In this paper we propose an advanced concept of composite structure which is simultaneously microwave shielding and microwave absorbing capable. The absorbing properties reduce the reflected electromagnetic field while the shielding properties reduce the transmitted electromagnetic field. Both properties are useful in all the scenarios where the requirements are contemporary to reduce as much as possible the microwave propagation in terms of reducing the traveling spurious microwave interfering signals, and in military applications in terms of radar absorbing and microwave shielding structure too. As far as structures proposed they are based on multilayer system made of nanostrucutred composite materials built using epoxy-resin and carbon nanopowders as carbon nanotube, carbon nanofiber, micrographite. Such materials have been first characterized in terms of electric permittivity in previous works and here are assumed to be ready in order to be properly chosen by optimization algorithms. The design of such multilayer structure is not trivial since they must respect structural mechanics and electrical properties, in this work we focused our research in optimizing microwave absorbing properties only. In particular the design algorithms have multiple tasks since they must determine an optimized multilayer structure based on carbon composite nanostrucutred materials available in the data base as a trade off between overall thickness and microwave reflection and transmission coefficient to be minimized as much as possible. With respect to the current literature the optimization task here is even more difficult since, the microwave absorbing requirements have to be satisfied for several incidence angles and in the entire frequency band considered. The algorithm proposed here for the design of structure is a new evolutionary algorithm in-house built and baptized by us as winning particle optimization. It is a very simple algorithm where at each time epoch of evolution, particle which best fit the objective function, is deputed to pilot the trajectory of the remaining particles within the multidimensional space of solutions. Winning particle optimization is easy to implement and run, in fact, each single particle acts with no any knowledge about other particles with exception of index of the best fitting particle, under this point of view winning particle optimization it's like a primordial non intelligent life form which tries to find the best place to grow and proliferate. Step by step this simple but quite effective method evolves toward the best solution; the iterations are stopped when all particles end to converge in a single point which represents the optimal solution. In the first part of the paper the winning particle optimization algorithm is described, in the second part the electromagnetic model of multilayer absorber is in detail presented, in the third part the winning particle optimization and in-house particle swarm optimization are compared in terms of overall thickness and electromagnetic performances of the optimized multilayer absorber
A new technology for production of high thickness carbon/carbon composites for launchers application
No full textCarbon–Carbon (C/C) composites are known for their extraordinary stability and excellent mechanical properties, almost unchanged at high temperatures. Among the several advanced applications, C/C based materials can be used in engines as nozzle throat section for launchers. In particular, the main feature for such employment is the material high resistance in extreme thermal environment. On the other hand, large-size items are required for this kind of purposes, thus introducing criticalities in terms of material uniformity and final overall properties. Up to now, there no standard for the production of high thickness C/C structures. In this paper a novel manufacturing method is analyzed, following each phase of the process, from the carbon fiber preform design and preparation to the carbon densification by chemical vapor infiltration method. Five preforms of large dimensions with different characteristics have been manufactured and infiltrated. The realized prototypes have been then analyzed by means of mechanical, physical and morphological tests. Aim of the results of this preliminary work is to establish a set of guidelines for a well-defined high thickness C/C production method
Synthesis and electromagnetic characterization of frequency selective radar absorbing materials using carbon nanopowders
No full textA new method for the synthesis of multilayered radar absorbing materials is analyzed by using carbon nanomaterials. With respect to the literature, a desired profile of reflection coefficient is a priori established as a function of the frequency. The goal of the synthesis is to follow this target profile by computing thickness and type of the material of each layer until the reflection coefficient of the electromagnetic-wave absorber best approximates the wanted reflection coefficient. The material available for each layer is epoxy-resin reinforced by different kind of carbon-based nano/micro powders: graphene nanoplatelets, carbon nanofibers, multi-walled carbon nanotubes and polyaniline. The dielectric characterization of the composite materials is performed in the frequency range 2÷18 GHz. The synthesis uses evolutionary computation by drawing on the electric permittivity of composite materials. Three square layered electromagnetic wave absorbers of 25 cm side are manufactured. The comparison between the target, the simulated and the measured reflection coefficients shows a good agreement thus confirming the scientific validity of the dielectric characterization and the proposed design method. Finally, a finite element analysis has been carried out to explain the mechanism of electromagnetic wave absorption by a multilayer and to simulate a low radar observable naval military gun
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