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Rio de Janeiro, Brazil

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. Source

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). Source

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. Source

Ribeiro B.,Sao Paulo State University | Botelho E.C.,Sao Paulo State University | Rezende M.C.,Sao Paulo State University | Costa M.L.,Sao 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. Source

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. Source

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