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Dantas C.C.,Institute Aeronautica e Espaco IAE
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2011

We report a full (3D) micromagnetic simulation of a set of 100 ferrite (Fe 3O 4) cylindrical dots, arranged in a 10 by 10 square (planar) array of side 3.27μm, excited by an external in-plane magnetic field. The resulting power spectrum of magnetic excitations and the dynamical magnetization field at the resulting resonance modes were investigated. The absorption spectrum deviates considerably from that of a single particle reference simulation, presenting a mode-shifting and splitting effect. We found an inversion symmetry through the center of the array, in the sense that each particle and its inversion counterpart share approximately the same magnetization mode behavior. Magnonic designs aiming at synchronous or coherent tunings of spin-wave excitations at given spatially separated points within a regular square array may benefit from the new effects here described. © 2011 Elsevier B.V.

Gama A.M.,Institute Aeronautica e Espaco IAE | Rezende M.C.,Institute Aeronautica e Espaco IAE | Dantas C.C.,Institute Aeronautica e Espaco IAE
Journal of Magnetism and Magnetic Materials | Year: 2011

We report the analysis of measurements of the complex magnetic permeability (μr) and dielectric permittivity (εr) spectra of a rubber radar absorbing material (RAM) with various MnZn ferrite volume fractions. The transmission/reflection measurements were carried out in a vector network analyzer. Optimum conditions for the maximum microwave absorption were determined by substituting the complex permeability and permittivity in the impedance matching equation. Both the MnZn ferrite content and the RAM thickness effects on the microwave absorption properties, in the frequency range of 218 GHz, were evaluated. The results show that the complex permeability and permittivity spectra of the RAM increase directly with the ferrite volume fraction. Reflection loss calculations by the impedance matching degree (reflection coefficient) show the dependence of this parameter on both thickness and composition of RAM. © 2011 Elsevier B.V. All rights reserved.

Avelar A.C.,Institute Aeronautica E Espaco IAE | Basso E.,Institute Aeronautica E Espaco IAE | Filho J.B.P.F.,Institute Aeronautica E Espaco IAE | Romero P.G.M.,Instituto Tecnologico Of Aeronautica Ita | Hsu J.J.L.,Institute Aeronautica E Espaco IAE
29th Congress of the International Council of the Aeronautical Sciences, ICAS 2014 | Year: 2014

An investigation of flow patterns in the fore-body section of a sounding rocket is presented. Wind tunnel tests on a 1:34 scaled model were carried out for Mach numbers varying from 0.4 to 1.1 using the techniques of Pressure Sensitive Paint (PSP), Schlieren and Pressure Taps. Additionally, a numerical analysis was carried out, using a commercial package, in the same range of Mach numbers. All measurements and simulations were carried out for zero angle of attack. The results obtained allowed the identification of complex physical phenomena as shock waves, boundary layer detachment, and expansion waves. Good agreements between numerical and experimental results were observed and the flow fields obtained with PSP, Schlieren and CFD were reasonably coherent.

Bojowald M.,Pennsylvania State University | Chinchilli A.L.,Pennsylvania State University | Simpson D.,Pennsylvania State University | Dantas C.C.,Institute Aeronautica e Espaco IAE | Jaffe M.,University of California at Berkeley
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

Inhomogeneous quantum cosmology is modeled as a dynamical system of discrete patches, whose interacting many-body equations can be mapped to a nonlinear minisuperspace equation by methods analogous to Bose-Einstein condensation. Complicated gravitational dynamics can therefore be described by more-manageable equations for finitely many degrees of freedom, for which powerful solution procedures are available, including effective equations. The specific form of nonlinear and nonlocal equations suggests new questions for mathematical and computational investigations, and general properties of nonlinear wave equations lead to several new options for physical effects and tests of the consistency of loop quantum gravity. In particular, our quantum cosmological methods show how sizeable quantum corrections in a low-curvature Universe can arise from tiny local contributions adding up coherently in large regions. © 2012 American Physical Society.

Yogi L.M.,Brazilian Technological Institute of Aeronautics | Sugahara T.,Brazilian Technological Institute of Aeronautics | Reis D.A.P.,Brazilian Technological Institute of Aeronautics | De Moura Neto C.,Brazilian Technological Institute of Aeronautics | And 2 more authors.
65th ABM International Congress, 18th IFHTSE Congress and 1st TMS/ABM International Materials Congress 2010 | Year: 2010

Currently, materials with proper behavior at high temperatures and aggressive environments have become a technical necessity, scientific and economic. In this context, titanium alloys have applications in service conditions that require resistance to high temperatures, such as components of gas turbines. It is important to understand the mechanisms of strain at high temperature and the relationship among the variables of processing, microstructure and properties. This study aims to evaluate the creep life of Ti-6Al-4V alloy heat treated at 600°C. The alloy was received in the condition forged and annealed at 190°C for 6 hours and cooled in air. The analysis involves four structural conditions: equiaxed, bimodal, martensite and Widmanstätten. The alloy with Widmanstätten structure shows the longest life time in creep with a lower rate of deformation. Copyright © (2010) by Associação Brasileira de Metalurgia Materiais e Mineração (ABM).

Do Nascimento Filho E.,Brazilian Technological Institute of Aeronautics | Henriques V.A.R.,Institute Aeronautica e Espaco IAe | De Oliveira J.L.,Institute Aeronautica e Espaco IAe | Diniz E.F.,Institute Aeronautica e Espaco IAe
SAE Technical Papers | Year: 2012

In the aerospace industry, 80-90% of the titanium used in airframes has been from Ti-6Al-4V. This alloy is used throughout the section of an aircraft - fuselage, nacelles, landing gear, wing and empennage. In gas turbine engines Ti-6Al-4V is used in static and rotating components. Castings are used for the manufacture of more complex static components; forgings are typically used for moving parts. Conventional methods for obtaining titanium alloys require special conditions of controlled atmosphere that culminates in a high production cost. In this paper it was investigated the peculiarities of the typical microstructure of Ti-6Al-4V produced by powder metallurgy using TiH2 powder. Samples were produced from the initial mixture of Al, V and TiH 2 powders, followed by cold uniaxial and isostatic pressing with subsequent densification by sintering in temperatures between 800-1400°C, in vacuum. Sintered samples were characterized by means of x-ray diffraction, Vickers micro hardness, scanning electron microscopy and density analysis. Due to the complete dissolution of the alloying elements in the titanium matrix and the presence of hydrogen during the sintering stage, an improved combination of homogenous microstructure, densification and mechanical properties could be achieved. Copyright © 2012 SAE International.

Dos Reis Luz T.,University of Sao Paulo | De Camargo E.N.,Brazilian Technological Institute of Aeronautics | Henriques V.A.R.,Institute Aeronautica e Espaco IAE | De Oliveira J.L.,Institute Aeronautica e Espaco IAE | Diniz E.F.,Institute Aeronautica e Espaco IAE
SAE Technical Papers | Year: 2012

Shape Memory Alloys (SMA) are novel materials which have the ability to return to a predetermined shape when heated. SMA are useful as actuators which are materials that change shape, stiffness, position, natural frequency, and other mechanical characteristics in response to temperature or electromagnetic fields. Applications include engines in cars and airplanes, electrical generators and surgical implants that make use of the mechanical energy resulting from the shape transformations. Powder metallurgy allows the SMA production with savings of energy and time and with higher microstructural homogeneity than those obtained by conventional processes. In this work a new nickel-free titanium alloy Ti-22Nb-6Zr (%at) was produced in order to expand the application field of SMA. Samples were produced by mixing of initial metallic powders followed by uniaxial and cold isostatic pressing with subsequent densification by sintering between 800-1600 °C, in vacuum. Sintered samples were characterized for phase composition, microstructure and microhardness by X-ray diffraction, scanning electron microscopy and Vickers indentation, respectively. Density was measured by Archimedes method. It was shown that the samples were sintered to high densities and presented homogeneous microstructure with complete dissolution of alloying elements in the titanium matrix. Copyright © 2012 SAE International.

Ribeiro B.,São Paulo State University | Botelho E.C.,São Paulo State University | Rezende M.C.,São Paulo State University | Costa M.L.,São Paulo State University | Costa M.L.,Institute Aeronautica e Espaco IAE
Journal of Advanced Materials | Year: 2011

The hygrothermal and UV radiation influences on shear properties and moisture diffusion aging in polyetherimide (PEI) reinforced with continuous fibers were systematically studied in this research, by using ILSS and losipescu shear tests. The moisture weight gain curves of the PEI composites reinforced with glass fiber and carbon fiber were compared in order to determine the interface effect on moisture absorption. Both composites display similar anomalous diffusion behavior; the PEI reinforced with glass fiber presented higher diffusion and water absorption values. The mechanical results Indicate that moisture associated with temperature and UV radiation degrades the shear properties by about 20%, giving evidences of plasticization of PEI matrix.

Silva C.R.M.,University of Brasilia | Nono M.C.A.,National Institute for Space Research | Reis D.A.P.,Institute Aeronautica e Espaco IAE | Hwang M.K.,Institute Aeronautica e Espaco IAE
Materials Science and Engineering A | Year: 2010

Silicon carbide has a good match of chemical, mechanical and thermal properties and therefore is considered an excellent structural ceramic for high temperature applications. The aim of the present work is compressive creep evaluation of liquid phase sintered silicon carbide with aluminum and rare earth oxide as sintering aids. Rare earth oxides are possible additives considering their highly refractory remnant grain-boundary phase and lower synthesis costs compared to high purity rare earth. Samples were prepared with silicon carbide powder (90wt%) and aluminum oxide (5wt%) plus rare earth oxide (5wt%) additions. Powders were mixed, milled and hot pressed at 1800°C in argon atmosphere. Compressive creep tests were carried out under stress from 150 to 300MPa and temperatures from 1300 to 1400°C. At lower creep test temperatures, the obtained stress exponent values were correlated to mechanisms based on diffusion. At intermediate temperatures, grain-boundary sliding becomes operative, accommodated by diffusion. At higher temperatures cavities are discernible. Oxidation reactions and ionic diffusion result on surface oxidized layer, grain-boundary amorphous and intergranular crystalline Al6Si2O13, δ-Y2Si2O7 and YAG phases. In this case cavitation and amorphous phases redistribution enhance grain-boundary sliding, not accommodated by diffusion. Coalescence occurs at triple point and multigrain-junctions, with subsequent strain rate acceleration and cavitational creep. © 2010 Elsevier B.V.

Ferrari V.C.G.M.,University of Paraíba Valley | Azevedo M.F.P.,Institute Aeronautica e Espaco IAe | David L.H.,Institute Aeronautica e Espaco IAe | Lourenco V.L.,Institute Aeronautica e Espaco IAe
Polimeros | Year: 2014

This paper aims to determine the kinetics of a pre-impregnated ("prepreg") epoxy resin/carbon fiber using differential scanning calorimetry (DSC) with the isoconversional method. The latter method analyzes the cure kinetics through the dependence of activation energy during conversion (isothermal analysis) or temperature (non- isothermal analysis) and uses this dependence to calculate the kinetic parameters. The evaluation of reaction kinetics by DSC is based on the heat generating rate during an exothermic reaction. The hypothesis that a heat generated by a chemical reaction is proportional to the extension of cure allows one to obtain the kinetic parameters from the DSC curves obtained with the isothermal and nonisothermal modes. For the isoconversional isothermal method, the average activation energy ranged between 72 and 103 kJ/mol while in the non-isothermal method an average value of 80.5 kJ/mol was obtained. These results were compared with those obtained for ASTM E 2070 and ASTM E 698 methods, whose values were 89±5 kJ/mol and 77.5±2.5 kJ/mol, respectively, proving the efficiency of the method.

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