bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sol‐gel derived C‐SiC composites for re‐entry structures
Authors: Haruvy Y. , Liedtke V. 
Published: April 2003

AbstractComposites of carbon fibers, fabrics, or their precursors as reinforcement, and sol‐gel‐derived silicon carbide as matrix, have been developed, aiming at high‐temperature stable ceramics that can be utilized for re‐entry structures. These composites are produced via the sol‐gel process, starting with a sol‐gel reaction of a mixture of silane precursors.The sol‐gel‐derived resin is cast onto the reinforcement fibers/fabrics mat (carbon or its precursors) to produce a ‘green’ composite that is being cured. The ‘green’ composite is converted into a C‐SiC composite via a gradual heat‐pressure process under inert atmosphere, during which the organic substituents on the silicon atoms undergo internal oxidative pyrolysis via the schematic reaction: (SiRO3/2)n → SiC + CO2 + H2OThe composition of the resultant silicon‐oxi‐carbide is tailorable via modifying the composition of the sol‐gel reactants. The reinforcement, when made of carbon precursors, is converted into carbon during the heat‐and‐pressure processing as well.The C‐SiC composites thus derived exhibit superior thermal stability and comparable thermal conductivity, combined with good mechanical strength features and failure resistance, which render them greatly applicable for re‐entry shielding, heat‐exchange pipes, and the like.
Investigation of the Tribological Behaviour of Si3N4 Based Ceramics
Authors: Babcsán Kiss J. , Berkes M. M. 
Published: April 2003

AbstractDifferently prepared Si3N4 based ceramics were examined from different aspects of the tribological behaviour: Mechanical and microstructural characteristics have been studied investigating the possible effect of a post heat‐treatment process on the wearing properties. Vacuum tribometer was used for measuring the wear resistance and friction coefficient of the ceramics. The worn volume of the samples was measured by profilometer. The possible microstructural changes induced by the post heat treatment processes were investigated by scanning electron microscopy. Micro‐hardness measurements have been executed for studying the correlation between the wear resistance and the hardness of the material. Transmission electron microscopy was used for structural examination of ion‐implanted layer of the samples. The results of the complex testing procedure provide facilities for evaluating the effect of the applied post heat‐treatment on the tribological behaviour.
Investigation of the Effect of Fe3O4 Particles on the Interface of Gf‐Pr‐Fa Magnetic Composites
Authors: Dima D. , Andrei G. 
Published: April 2003

AbstractThe aim of this study is to characterize and to assess the quality and performances of a new class of soft magnetic composites, with ferrite additive, used for aircraft‐type instruments as well as in electronic and chemical industries. The ferrite additive introduced in the structure of the composite induces desired magnetic properties and thus improve the quality of the interface. A major structural defect of the organic matrix composite is recognized by the presence of void space, which must be reduced. It was found that the paramagnetic behaviour of the molecules of oxygen could control the scattering of the air bubbles in the mass of the organic matrix. Thus, the ferrite particles introduced in the material mixture play the role of a “vacuum cleaner” which “aspirates” the voids raised on the interface. Moreover, if when producing the composite, an external vibrating magnetic field is active, it could be possible to obtain the scattering of this void space in the mass of the organic matrix. Therefore, it is expected an enhancement of the interface fitness.
Thermal cycling under vacuum and CME evaluation of carbon/epoxy laminates
Authors: Rouquié S. , Lafarie‐Frenot M. C. , Pönninger A. , Costin W. 
Published: April 2003

AbstractDealing with the « French Supersonic Aircraft Research Program», thermal cycling tests in four environments, neutral (vacuum, nitrogen) and oxidative (air, oxygen), were performed on carbon/epoxy cross ply laminates [03/903]S. This experimental study was conducted following a local approach through optical and scanning electron microscopy observations and X radiographs and showed a significant effect of the oxygen level on the damage development. Moreover, coefficient of moisture expansion (CME) tests were performed on the same material to characterize the influence of moisture on the sample expansion.
Outgassing Kinetics Testing of Spacecraft Materials
Authors: Rampini R. , Grizzaffi L. , Lobascio C. 
Published: April 2003

AbstractSolid materials contain impurities from manufacturing/cleaning processes which diffuse (out‐gas) to the exterior during exposure to vacuum, especially at elevated temperature levels. Materials like plastics and resins tend to disintegrate under space conditions. In addition to the above mentioned diffusion process, contaminants adsorbed and absorbed from the environment encountered previously, e.g. during manufacturing, cleaning, integration, test and launch phases, might be desorbed from the surfaces. The released products represent a permanent source of potential contamination.This paper provides an overview of a research program carried out at the Austrian Research Centers Seibersdorf (ARCS), Aerospace Materials Technology Testhouse (AMTT), by means of the AMTT Sublimation Test Facility to acquire in‐depth knowledge of the outgassing kinetics characteristics of a set of non‐metallic materials, selected by Alenia on the basis of their usage on the International Space Station (ISS) and Scientific Satellites.
Room and high temperature tensile tests on the AA6061/10vol.%Al2O3p and AA7005/20vol.%Al2O3p composites
Authors: Ceschini L. , Morri A. , Cocomazzi R. , Troiani E. 
Published: April 2003

AbstractAluminium alloy based Metal Matrix Composites (MMCs), reinforced with ceramic particles such as Al2O3 or SiC, have a number of advantages over conventional aluminium alloys, primarily enhanced stiffness and increased wear resistance. In order to improve the fields of application, fundamental understanding of the relationship between microstructural features and mechanical properties is however required. In this work, the tensile behaviour of two composites based on 6061 and 7005 aluminium alloys, reinforced with Al2O3 particles, at room temperature, at 100°C and at 150°C was studied. The ductility of the composites was found to be much lower than that of the unreinforced alloys, while a significative increase of the elastic modulus and tensile strength was found. Both materials showed a slight decrease of the tensile strength with temperature, while elongation increased. Large particles and clusters of the reinforcement were found to be locations prone to failure in the composite, due to the high stress concentrations, mainly at room temperature. With increasing temperature, the fracture surfaces showed a dimpled appearance with a large amount of plastic deformation of the matrix, indicating that void nucleation, growth and coalescence is the main fracture mechanism.
Non‐destructive Investigation of AlSi7Mg/SiC70p MMCs by means of Acoustic Scanning Microscopy, X‐Ray and Neutron Diffraction
Authors: Göbel U. , Lefranc G. , Degischer H.‐P. 
Published: April 2003

AbstractParticulate silicon carbide reinforced aluminium matrix composites (Al‐SiC) have a high potential for advanced engineering materials beeing developed for use in traction, automotive, aviation and space applications. Especially high volume composites with up to 70 vol.% reinforcement of silicon carbide particles in a cast AlSi metal matrix (AlSi7Mg/SiC70p) show most interesting characteristics for application in high power electronics (IGBTs). To characterize such MMCs respectively reasons for failure, different non‐destructive material investigations were carried out among them Acoustic Scanning Microscopy, X‐Ray and Neutron Diffraction. Acoustic Scanning Microscopy delivers information about lateral density differences respectively material inhomogeneities integrated over sample thickness. Diffraction methods are used for a non‐destructive evaluation of absolute and phase specific residual stresses, whereas X‐Ray Diffraction provides near surface information (several tens of micrometers). High Energy Synchrotron and Neutron Diffraction on the contrary provide bulk information of several millimeters up to several centimeters. Important for the understanding of the deformation behaviour and dimensional stability is the understanding of the residual stress state and inhomogeneities in the composite and its change under operating conditions respectively under dynamic thermal load.
Spray‐Deposited Al‐Si (Osprey CE) Alloys and their Properties
Authors: Jacobson D. M. , Ogilvy A. J. W. 
Published: April 2003

AbstractOsprey Metals Ltd. has developed a new family of lightweight, low expansion aluminium‐silicon alloys to suit electronic applications, containing between 30 and 70 wt.% aluminium. They are produced using the Osprey spray deposition process, which achieves homogeneous and isotropic properties. Their advantageous physical characteristics, combining low thermal expansion, high thermal conductivity and low density are particularly suited for packaging electronic circuitry. These CE (controlled expansion) alloys are easy to machine to tight tolerances using standard machine tools and they can be electroplated with gold, silver or nickel finishes without difficulty. This paper focuses on the measurement of mechanical (flexural strength) and thermo‐mechanical properties (CTE, thermal diffusivity and specific heat) of these alloys, carried out in collaboration with AMTT. The property measurements were consistent with those measured previously elsewhere, apart from the CTE values, which deviated significantly and were at variance with values predicted from a rule of mixtures. This discrepancy was resolved in a short follow‐up series of measurements carried out under conditions corresponding more closely to temperature equilibrium.
Thermal and Electrical Conductivity Measurements on Aluminum Foams
Authors: Babcsán N. , Mészáros I. , Hegman N. 
Published: April 2003

AbstractMetal foams are one of the most interesting types of materials although there is limited information concerning their thermal and electrical conductivity. Closed cell different density Alporas foams are investigated, which has one of the most homogeneous cell size distribution recently. Comparative method has been chosen to determine the thermal conductivity of the samples in the function of the temperature at 30, 100, 200, 300, 400, 500 °C. For measuring the electrical conductivity of aluminium foams a special low frequency eddy current measuring apparatus was used. The ratio of thermal and electrical conductivity was calculated and shown an increasing function by the density of the foams.
Development of High Strength Magnesium Based MMC Reinforced with SiC Particles for Satellite Structure Applications
Authors: Landkof B. 
Published: April 2003

AbstractThe appearance of Metal Matrix Composites has opened a new area in structural design. The possibility of tailoring mechanical properties of structural metals reinforced with particles or fibers into specific spacecraft applications is very appealing. This paper deals with such a MMC, which is based on a magnesium alloy matrix and SiC reinforcement. The technology used is a commercial semi‐solid die‐casting, which promises a cost‐effective solution. The results of the first stage of this research are discussed with a focus on the satellite structure design application. The next steps of this investigation are also presented.
Thermal conductivity of zirconia‐based ceramics for thermal barrier coating
Authors: Leclercq B. , Mévrel R. , Liedtke V. , Hohenauer W. 
Published: April 2003

AbstractLowering the thermal conductivity of thermal barrier coatings used to protect blade and vane airfoils represents an important challenge for gas turbine designers and manufacturers. Dense zirconia‐based materials have been prepared by solid state reaction methods to determine their thermal properties up to 1000 °C. Partially stabilised zirconias having a thermal conductivity 40 % lower than the thermal conductivity of the most widely used system (ZrO2‐8wt.%Y2O3) have been obtained.
Microstructure control in precious metal coatings for high temperature applications, obtained by metallorganic chemical vapour deposition
Authors: Gimeno‐Fabra L. , Nizard H. , Benien H. , Vlcek J. , Redjaimia A. 
Published: April 2003

AbstractIn most high temperature applications, efficiency increases with service temperature of the component. Especially in combustion chambers, higher efficiency is translated into less propellant consumption and therefore a lower weight and a reduction of operational cost. In these components, the use of high performance coatings may simultaneously increase the service temperature and decrease its price. From the many available coating processes, Metal organic Chemical Vapour Deposition (MO‐CVD) is one of the few capable of producing coatings of most precious metals in internal surfaces with intricate geometry. Nevertheless the microstructure control of the films is extremely complicated and characterised by the formation of dendrite structures. This morphology eliminates the coating efficiency, as it is not compact. EADS has had the chance to use the research infrastructure of the AMTT in Seibersdorf to characterise the coatings and determine how the transformation from the compact to the non‐compact microstructure takes place. The understanding of this phenomenon should allow us to develop a process able to produce 100 % dense coatings independently of the coating thickness in an industrial scale.
TEM Studies of High Temperature Corrosion Behaviour of TiAl Intermetallics with Surface Modifications
Authors: Du H. L. , Rose S. R. , Xiang Z. D. , Datta P. K. , Li X. Y. 
Published: April 2003

AbstractThe oxidation/sulphidation behaviour of a Ti‐46.7Al‐1.9W‐0.5Si alloy with a TiAl3 diffusion coating was studied in an environment of H2/H2S/H2O at 850oC. The kinetic results demonstrate that the TiAl3 coating significantly increased the high temperature corrosion resistance of Ti‐46.7Al‐1.9W‐0.5Si. The SEM, EDX, XRD and TEM analysis reveals that the formation of an Al2O3 scale on the surface of the TiAl3‐coated sample was responsible for the enhancement of the corroison resistance. The Ti‐46.7Al‐1.9W‐0.5Si alloy was also modified by Nb ion implantation. The Nb ion implanted and as received sampels were subjected to cyclic oxidation in an open air at 800oC. The Nb ion implantation not only increased the oxidation resistance but also substantially improved the adhesion of scale to the substrate.
A phase transition model with the entropy balance
Authors: Bonetti Elena , Frémond Michel 
Published: April 2003

AbstractThis paper deals with a phase transition model in which the energy balance is equivalently rewritten in terms of the entropy balance. The thermodynamical consistence of the model is proved and also under physically meaningful assumptions on the data, existence of a solution is stated for the corresponding initial boundary values problem by a maximum principle. Hence, L1‐arguments yield the uniqueness of the solution and show that it evolves in accordance with thermodynamics and everyday practical properties. Copyright © 2003 John Wiley & Sons, Ltd.
Global and blow‐up solutions for non‐linear degenerate parabolic systems
Authors: Duan Zhi‐wen , Zhou Li 
Published: April 2003

AbstractIn this paper the degenerate parabolic system ut=u(uxx+av). vt=v(vxx+bu) with Dirichlet boundary condition is studied. For $a. b {&#60;} \lambda_{1} (\sqrt {ab} {&#60;} \lambda_{1} {\rm if}\, \alpha_{1} {\neq} \alpha_{2})$, the global existence and the asymptotic behaviour (α1=α2) of solution are analysed. For $a. b \,{&#62;}\, \lambda_{1}\ (\sqrt{ab} {&#62;} \lambda_{1} {\rm if}\, \alpha_{1} {\neq} \alpha_{2})$, the blow‐up time, blow‐up rate and blow‐up set of blow‐up solution are estimated and the asymptotic behaviour of solution near the blow‐up time is discussed by using the ‘energy’ method. Copyright © 2003 John Wiley & Sons, Ltd.
Powerful FE approaches for Pochhammer's dispersion modelling
Authors: Mazúch Tibor 
Published: April 2003

AbstractSimple and very effective finite element approaches for modelling of the dispersion of torsional, longitudinal and flexural waves propagated in infinite and elastic cylindrical bars (Pochhammer's problem) and hollow cylinders are presented. The approaches allow one to model given problems without using infinite elements and their usage is demonstrated by using dispersion curves, shapes of waves and tables of phase velocities. Comparison of finite element solutions (solved in one task from small‐sized models) with exact solutions shows an excellent agreement. The maximum relative differences among the 20 lowest FEM and analytical phase velocities was less than 0.000015%. The approaches and results hold also for cylinders with finite lengths, simply supported on both ends. Copyright © 2003 John Wiley & Sons, Ltd.
A wavelet‐based method for solving discrete first‐kind Fredholm equations with piecewise constant solutions
Authors: Sánchez‐Ávila C. , Sánchez‐Reíllo R. 
Published: April 2003

AbstractThe inverse problem of finding piecewise constant solutions to discrete Fredholm integral equations of the first kind arises in many applied fields, e.g. in geophysics. This equation is usually an ill‐posed problem when it is considered in a Hilbert space framework, requiring regularization techniques to control arbitrary error amplifications and to get adequate solutions. In this work, we describe an iterative regularizing method for computing piecewise constant solutions to first‐kind discrete Fredholm integral equations. The algorithm involves two main steps at each iteration: (1) approximating the solution using a new signal reconstruction algorithm from its wavelet maxima which involves a previous step of detecting discontinuities by estimation of its local Hölder exponents; and (2) obtaining a regularized solution of the original equation using the a priori knowledge and the above approximation. In order to check the behaviour of the proposed technique, we have carried out a statistical study from a high number of simulations obtaining excellent results. Their comparisons with the results coming from using classical Tikhonov regularization by the multiresolution support, total variation (TV) regularization and piecewise polynomial truncated singular value decomposition (PP‐TSVD) algorithm, serve to illustrate the advantages of the new method. Copyright © 2003 John Wiley & Sons, Ltd.
Steady‐state Kalman filtering with nonstationary noise
Authors: Mäkilä P. M. , Paattilammi J. 
Published: April 2003

AbstractInfinite‐horizon Kalman filtering is re‐examined for linear discrete‐time systems and generalized to include a class of non‐stationary and non‐ergodic disturbances. This revision is achieved by defining a generalized infinite‐horizon filtering problem using a flexible functional analytic signal description. It is shown that the solution to the generalized filtering problem is equivalent to the solution of the corresponding standard filtering problem with noise covariance matrices having in the generalized problem a different, more general, meaning than in the standard problem. In the generalized problem these covariance matrices are majorizing matrices that have a precise meaning even in the non‐stationary and non‐ergodic signal case. This result justifies in a nice way the wide practice of interpreting the noise covariance matrices in Kalman filtering as design variables. Copyright © 2003 John Wiley & Sons, Ltd.
Incomplete sensitivities and cost function reformulation leading to multi‐criteria investigation of inverse problems
Authors: Cabot A. , Mohammadi B. 
Published: April 2003

AbstractThis paper deals with the application of typical minimization methods based on dynamical systems to the solution of a characteristic inverse problem. The state equation is based on the Burgers equation. The control is meant to achieve a prescribed state distribution and a given shock location. We show how to use incomplete sensitivities during the minimization process. We also show through a redefinition of the cost function that a multi‐criteria problem needs to be considered in inverse problems. This example shows that a correct definition of the minimization problem is crucial and needs to be studied before a direct application of brute force minimization approaches. Copyright © 2003 John Wiley & Sons, Ltd.
Robust disturbance attenuation for discrete‐time active fault tolerant control systems with uncertainties
Authors: Shi Peng , Boukas El Kebir , Nguang Sing Kiong , Guo Xianping 
Published: April 2003

AbstractThe problems of stochastic stability and stochastic disturbance attenuation for a class of linear discrete‐time systems are considered in this paper. The system under study is a state space model possessing two Markovian jump parameters: one is failure process and another is failure detection and isolation scheme. A controller is designed to guarantee the stochastic stability and a disturbance attenuation level. Robustness problems for the above system with norm‐bounded parameter uncertainties are also investigated. It is shown that the uncertain system can be robustly stochastically stabilized and have a robust disturbance attenuation level for all admissible perturbations if a set of coupled Riccati inequalities has solutions. A numerical example is given to show the potential of the proposed technique. Copyright © 2003 John Wiley & Sons, Ltd.
Dynamic ‘back‐off’ analysis: use of piecewise linear approximations
Authors: Figueroa José L. , Desages Alfredo C. 
Published: April 2003

AbstractThe operating point of a process is usually computed by optimizing an objective function, e.g. the profit, subject to some plant characteristics. Typically, the resulting point lies on the boundary of the operating region. At this point, the presence of disturbances can easily cause constraint violations and make the process move to the unfeasible region. Then, it is necessary to move the operating point away into the feasible region by considering the effect that the expected disturbances will have on the operation of the plant. The purpose of this paper is to present an efficient algorithm to modify the operating point in order to keep feasibility (both in steady‐state and along transitory) in the process operation against the disturbances. Copyright © 2003 John Wiley & Sons, Ltd.