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Search Results: 1 - 10 of 11302 matches for " Monteiro Waldemar Alfredo "
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Characterization of Nickel Alloy 600 with Ultra-Fine Structure Processed by Severe Plastic Deformation Technique (SPD)  [PDF]
Waldemar Alfredo Monteiro, Silvio Luis Ventavele da Silva, Luciana Ventavele da Silva, Arnaldo Homobono Paes de Andrade, Luis Carlos Elias da Silva
Journal of Materials Science and Chemical Engineering (MSCE) , 2017, DOI: 10.4236/msce.2017.54004
Abstract: High strength nickel based alloys are used in a multitude of advanced systems where lightweight, high power density mechanical power transmission systems are required. Components such as gears, bearings and shafts could be made significantly smaller and more durable if a major improvement in nickel based alloy mechanical properties could be achieved. An important refinement in grain size (includes nanometric level) is thought to be a promising method for achieving fundamental improvements in mechanical properties. Grain size is known to have a significant effect on the mechanical behavior of materials. One of the most favorable methods of achieving extreme grain refinement is by subjecting the materials to severe plastic deformation (SPD). The principal micro-structural variations in superalloys are the precipitation amount and morphology, grain size and the distribution of carbide precipitation that could reduce the mechanical properties of the alloys. This work shows optical and transmission electron microscopy analysis and also hardness data after severe plastic deformation (pure shear stress).
Mathematical model predicts the elastic behavior of composite materials
Boari, Zoroastro de Miranda;Monteiro, Waldemar Alfredo;Miranda, Carlos Alexandre de Jesus;
Materials Research , 2005, DOI: 10.1590/S1516-14392005000100017
Abstract: several studies have found that the non-uniform distribution of reinforcing elements in a composite material can markedly influence its characteristics of elastic and plastic deformation and that a composite's overall response is influenced by the physical and geometrical properties of its reinforcing phases. the finite element method, eshelby's method and dislocation mechanisms are usually employed in formulating a composite's constitutive response. this paper discusses a composite material containing sic particles in an aluminum matrix. the purpose of this study was to find the correlation between a composite material's particle distribution and its resistance, and to come up with a mathematical model to predict the material's elastic behavior. the proposed formulation was applied to establish the thermal stress field in the aluminum-sic composite resulting from its fabrication process, whereby the mixture is prepared at 600 °c and the composite material is used at room temperature. the analytical results, which are presented as stress probabilities, were obtained from the mathematical model proposed herein. these results were compared with the numerical ones obtained by the fem method. a comparison of the results of the two methods, analytical and numerical, reveals very similar average thermal stress values. it is also shown that maxwell-boltzmann's distribution law can be applied to identify the correlation between the material's particle distribution and its resistance, using eshelby's thermal stresses.
The effect of cyclic torsion on the dislocation structure of drawn mild steel
Aguilar, Maria Teresa Paulino;Corrêa, Elaine Carballo Siqueira;Monteiro, Waldemar Alfredo;Cetlin, Paulo Roberto;
Materials Research , 2006, DOI: 10.1590/S1516-14392006000300016
Abstract: cold forming is usually associated with the "work hardening" of the material being formed. the work hardening behavior of metals subject to complex processing paths is different from that in monotonic deformation. the results show that, after some initial hardening, there is a possibility that further deformation will cause softening in the material ("work softening"). recent work showed that cyclic torsion applied to drawn products causes changes in the subsequent tensile behavior of low carbon steel, and that the effect will depend on the previous "history" of the material. for annealed samples, the cyclic torsion leads to an increase in the yield strength, but does not affect the tensile strength and elongation. for the case of previously drawn bars, the cyclic deformation caused a decrease in the yield and tensile strength and an increase in the total elongation. the present paper discusses the dislocation structure changes associated with different strain paths in mild steel.
Work softening of drawn low carbon steel bars
Aguilar Maria Teresa Paulino,Corrêa Elaine Carballo Siqueira,Monteiro Waldemar Alfredo,Ferreira Nildemar Aparecido Messias
Materials Research , 2001,
Abstract: The work hardening of metals subjected to complex processing paths is different from that in monotonic deformation. Changes in the deformation mode can promote transients in the strain-hardening rate, leading to anomalous softening or hardening of the material. This paper investigates the influence of strain path changes on the tensile behavior of drawn 0.12% steel rods. Annealed or predrawn specimens were submitted to cyclic twisting and then tested in tension. The results show that the cyclic deformation causes changes in the mechanical behavior of the metal, and the effect will depend on the previous "history" of the material. Cyclic twisting causes hardening in annealed samples, but leads to softening of the drawn bars. These phenomena are in line with the corresponding substructural aspects.
Work softening of drawn low carbon steel bars
Aguilar, Maria Teresa Paulino;Corrêa, Elaine Carballo Siqueira;Monteiro, Waldemar Alfredo;Ferreira, Nildemar Aparecido Messias;Cetlin, Paulo Roberto;
Materials Research , 2001, DOI: 10.1590/S1516-14392001000200008
Abstract: the work hardening of metals subjected to complex processing paths is different from that in monotonic deformation. changes in the deformation mode can promote transients in the strain-hardening rate, leading to anomalous softening or hardening of the material. this paper investigates the influence of strain path changes on the tensile behavior of drawn 0.12% steel rods. annealed or predrawn specimens were submitted to cyclic twisting and then tested in tension. the results show that the cyclic deformation causes changes in the mechanical behavior of the metal, and the effect will depend on the previous "history" of the material. cyclic twisting causes hardening in annealed samples, but leads to softening of the drawn bars. these phenomena are in line with the corresponding substructural aspects.
Microstructural and Mechanical Characterization after Thermomechanical Treatments in 6063 Aluminum Alloy  [PDF]
Waldemar A. Monteiro, Iara M. Espósito, Ricardo B. Ferrari, Sidnei J. Buso
Materials Sciences and Applications (MSA) , 2011, DOI: 10.4236/msa.2011.211206
Abstract: The aim of this work is the mechanical and microstructural characterization by optical and electron microscopy as well as microhardness of Al 6063 alloy after mechanical and thermal treatment. Al-Mg based alloys have special attention due to the lightness of the material and certain mechanical properties and recyclability. Such alloys produce good mechanical properties in moderate mechanical efforts (up to 700 MPa) and good resistance to the corrosion. Cold rolling steps (30%, 60% and 90% in area reduction) in Al 6063 alloy were employed for the recrystallization studies, followed by thermal treatment using four isothermal heating (423K, 523K, 623K and 723K) during 1800, 3600, 5400 and 7200s. The direct observation and chemical microanalysis were made in a JEOL200C and JEOL2010 transmission electron microscopes combined with mechanical characterization utilizing Vickers microhardness measurements. Normally classified as non-heat-treatable these alloys obtain higher strength either by strain-hardening or by solid solution. The nucleation of new grains is a non stability of the deformed microstructure, depending on subgrain size heterogeneities present as potential embryos in the deformed state adjacent to high local misorientation. The results indicate a significant effect of second-phase particles on recrystallization and how to control the resulting microstructure and texture by the use of particles. It may be a preferential growth in the early stage due to their local environment or a selection of certain orientations from among those produced by particles stimulated nucleation or a preferential nucleation at particles in favored sites such as grain boundaries.
Literature and Difference: A Conversation with Alfredo Bosi
Monteiro, Pedro Meira,Bosi, Alfredo
Ellipsis , 2006,
Abstract: Alfredo Bosi was born in 1936 and is today one of Brazil's most important intellectuals. Professor of literature at the University of S o Paulo and member of the Brazilian Academy of Letters, he is the author of História Concisa da Literatura Brasileira as well as of a number of books of essays, including O Ser e o Tempo da Poesia and Dialética da Coloniza o. The interview published in ellipsis brings together two moments in a long series of interviews conducted with Bosi in S o Paulo in August and September 2005.
Correla??o entre a idade e a contagem dos folículos antrais em mulheres inférteis
Castro, Eduardo Camelo de;Florêncio, Rodopiano de Souza;Monteiro Filho, Gercino;Amaral, Waldemar Naves do;
Revista Brasileira de Ginecologia e Obstetrícia , 2012, DOI: 10.1590/S0100-72032012000400008
Abstract: purpose: to produce age-related nomograms for ovarian antral follicle count (afc) in infertile women. methods: it was done a cross-sectional study of patients attended in the center of assisted reproduction fêmina, from march 2010 to october 2011. the patients were submitted to transvaginal ultrasonography from day 2 to day 4 of their menstrual period. patients included were between 21 to 45 years old, with regular menses, two healthy ovaries, without any evidence of endocrinopathies and who gave written informed consent. patients excluded were smokers, with galactosemia or ovarian cysts, with antecedents of liver disease, ovarian surgeries or who were treated with chemotherapy or radiotherapy. in order to check the evolution of the afc in relation to patient age, we used the 5th, 25th, 50th, 75th and 95th percentiles. linear regression was carried out using these percentiles, permitting us to determine the effect of age on the cfa. results: a total of 172 patients with a mean age of 32.7 years were included in the trial. the male and tubal factors were the main causes of infertility, accounting for 65% of cases. the age-related nomogram for the 5th, 25th, 50th, 75th and 95th percentiles of afc revealed that changes were best fitted by a linear function. the percentiles that showed the highest correlations were 25 (r=-0.9; p<0.001), 50 (r=-0.9; p<0.001) and 75 (r=-0.9; p<0.001). conclusion: a nomogram was constructed correlating age with the different afc percentiles in infertile women without endocrinopathies. this showed a linear pattern of decline in afc with age in all percentiles. these nomograms could provide a reference guide for the clinician. however, future validation, with longitudinal data, still is needed.
The Quantum Oscillatory Modulated Potential - Part II - The Stability of the Hydrogen Atom  [PDF]
Waldemar Wolney Filho
Journal of Modern Physics (JMP) , 2012, DOI: 10.4236/jmp.2012.38090
Abstract: The purpose of this work is to show the stability of the hydrogen atom with the use the Quantum Oscillatory Modulated Potential and the Heisenberg equations of motion, postulating that the electron in the hydrogen atom is behaving as a quantum harmonic oscillator. With the electron confined between two potential barriers, created by the new potential function, we are considering that at absolute temperature the power absorbed or emitted by the electron per unit of time can be used to determine the zero point energy of the oscillator. Assuming that electron is only exchanging energy with the nucleus of the atom we are making use of the operators of creation and annihilation of a photon to explain how the energy between the proton and the electron can be exchanged to keep the atom a stable system.
The Quantum Oscillatory Modulated Potential Ⅰ- The Hydrogen Atom  [PDF]
Waldemar Wolney Filho
Journal of Modern Physics (JMP) , 2012, DOI: 10.4236/jmp.2012.37081
Abstract: In this work we are presenting a modified Coulomb potential function to describe the interaction between two micro-scopic electric charges. In particular, concerning the interaction between the proton and the electron in the hydrogen atom. The modified potential function is the product of the classical Coulomb potential and an oscillatory function dependent on a quantized phase factor. The oscillatory function picks up only selected points along the Coulomb potential, creating potential wells and barriers around the nucleus of the atom. The new potential reveals us new features of the hydrogen atom. Searching for a manner to determine the phase factor, we are using the concept of the de Broglie particle wavelike behavior and the quantum analogue of the virial theorem for describing the bound motion of a particle in a central force field. This procedure is a kind of feedback action, where we are making use of well established concepts of the quantum mechanics aiming to determine the phase factor of the new interaction potential.
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