Artigos Científicos - FEM/ITEC

URI Permanente para esta coleçãohttps://repositorio.ufpa.br/handle/2011/2552

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Agora exibindo 1 - 19 de 19

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Influência dos procedimentos e modos de transferência no processo MAG na redução de deformações em painéis de estruturas navais
(Associação Brasileira de Soldagem, 2013-11) CABRAL, Tarcio dos Santos; BRAGA, Eduardo de Magalhães; MENDONÇA, Everton Augusto Maciel; SCOTTI, Américo
The Growth in the Brazilian shipbuilding industry brought on numerous problems in the production line. Some of these problems are related to the manufacturing process, welding process, due to residual stress and distortions. In the present paper, the influence of the welding procedure (sequence and direction of welding and the use of back weld) was studied. Different welding processes with different transfer modes (GMAW-CC, GMAW-TT and GMAW-CW) were also used. These changes were made to observe the influences on the amplitude of the distortions. All the welds were made using the ER70S-6 electrode and pure CO2 as a shielding gas with the short circuit transfer mode. The results showed that the most important variable is the direction of welding, which is related to the level of restriction of the panels welded. The effect of the welding sequence presented on the values of distortion produced were minor. The panels produced using the back welding procedure presented small values of distortion however, the procedure showed to be inefficient. It was also observed that the level of distortion for the processes GMAW-CC and GMAW-STT showed similar values. On the other hand the values of distortion in the panel welded using the GMAW-CW process presented the lowest values.
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Efeitos do comprimento de reversão e do ângulo de ataque sobre a estrutura de solidificação do cordão em soldagem MIG/MAG com "Switch Back"
(Universidade Federal do Pará, 2012-06) ALMEIDA, Hélio Antônio Lameira de; MOTA, Carlos Alberto Mendes da; SCOTTI, Américo
The welding technique denominated switch-back technique consists in a torch oscillation in the welding direction rather than transversally. However, there is not much information in literature about the solidification structure of the bead when this technique is applied. Therefore, in this work is presented a study on the effect of the torch leading angle and of the reversion course length over the bead solidification structure. Welds were carried out with Pulsed MIG/MAG Process on plain carbon steel plates. The results showed that the parameters under analysis modify the solidification mode of the bead. In general, when the angle of torch leads to pushing-pulling movement, equiaxial grains near the fusion line is favored. In relation to the course length, its increase leads to finer solidification structure.
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Revestimento de níquel depositado pela soldagem MIG e MIG com arame frio
(Universidade Federal do Pará, 2016-12) MOTA, Carlos Alberto Mendes da; NASCIMENTO, Alexandre Saldanha do; GARCIA, Douglas Neves; SILVA, Diego Almir Silva da; TEIXEIRA, Felipe Ribeiro; FERRARESI, Valtair Antônio
This paper presents a study about the operational, geometrical and microstructural characteristics of GMAW and GMAW-CW (GMAW Cold Wire) welds applied on a coating of steel AISI 1020 plate, with a nickel superalloy ER NiCrMo-4, Hastelloy 276C type. The welding was automated in flat position, and executed with an electronic source on DC+ and having instantaneous acquisition of the welding voltage and current oscillograms. The input variables were the speeds of the electrode and cold wires and the welding speed. It was evaluated the operational processes and the effect of heat input on the geometrical characteristics (reinforcement and width), dilution, microstructure and microhardness of the coating. The results indicated a good operating performance, the absence of defects in single passes and in the GMAW-CW coatings. Furthermore, it has been found the lowest level of dilution.
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Estimativa de vida útil do pbx (plastic-bonded explosive) com envelhecimento acelerado
(Universidade Federal do Pará, 2016-07) KIRCHHOF, Edemar; ROCHA, Roberta Jachura; NAKAMURA, Nanci Miyeko; LAPA, Camila Maria; PINHEIRO, Glaci Ferreira Martins; GONÇALVES, Rene Francisco Boschi; ROCCO, José Atílio Fritz Fidel; ILHA, Koshun
This article aims to estimate the shelf life of the PBX by thermal analysis estimated by the Arrhenius equation, equivalent to the time of storage at accelerated aging. The PBX was subjected to accelerated aging in an oven at controlled temperature 60 ºC for periods of 5, 10, 15 and 25 weeks, which are equivalent to 5, 10, 15 and 25 of natural aging, respectively, at a temperature of 25 ºC. The curves of thermal decomposition of the samples were obtained by the DSC (Differential Scanning Calorimetry) technique. The kinetic parameters, such as the activation energy and pre-exponential factor, were determined by the Ozawa method and the Kissinger method. Initial results of this study indicated that, for a period of 25 years of storage in the cargo hold, the material did not change this aging significantly. To study the life of PBX analyzes, vacuum chemical stability were also conducted to verify the safety of explosive handling.
Acesso aberto (Open Access)
On the Natural Convection in the Columnar to Equiaxed Transition in Directionally Solidified Aluminum-based Binary and Multicomponent Alloys
(Universidade Federal do Pará, 2015-12) GOMES, Carlos Henrique Ursolino; KIKUCHI, Rafael Hideo Lopes; BARROS, André dos Santos; SILVA, José Nazareno Santos da; SILVA, Maria Adrina Paixão de Souza da; MOREIRA, Antonio Luciano Seabra; ROCHA, Otávio Fernandes Lima da
In order to investigate the effect of natural convection in columnar to equiaxed transition (CET), Al-3.0wt.%Cu and Al-3.0wt.%Cu-5.5wt.%Si alloys ingots were obtained during the transient horizontal directional solidification (THDS). Aiming to analyze the effect of superheat in the formation of the macrostructure in ternary Al-Cu-Si alloy, the experiments were conducted with three superheat temperatures above the liquidus temperature of the ternary alloy. A water-cooled solidification experimental device was used. Continuous temperature measurements were made during solidification at different positions in the casting and the data were automatically acquired. Thermal analysis has been applied to determine the thermal parameters such as growth rate (VL), cooling rate (TR) and temperature gradient (GL), whose values have been interrelated with the CET. The observation of the macrostructures has indicated that the resulting thermosolutal convection combined with superheat seem to favor the transition, which did not occur in a single plane, for all ingots obtained, i.e., it has been seen in a range of positions in ingots. The addition of Si element in binary Al-Cu alloy anticipates the CET. A comparison with experimental results for CET occurrence in different growth directions has been carried out.
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Use of green composites for manufacturing small boats in the Amazon: numerical and experimental evaluations
(Universidade Federal do Pará, 2017) CARVALHO, Mateus Fortes; VALENTE, João Carlos; XAVIER, Mário Américo; SILVA, Filipe Renan Benicio da; RAIOL, José Alan; RODRIGUES, Leonardo Dantas; FUJIYAMA, Roberto Tetsuo
The Amazon has a great potential of natural resources. There is a wide diversity of plant specimens and many of them can be extracted and processed such as jute, sisal and mauve fibers. It is known that usualy small communities from Amazon build their boats using a rudimentary and ecologically incorrect method, which comes from brazilian natives. This method consists in cut of trees with large trunks, which are burned and scraped until they get the desired shape. This process is not viable due to the long time spent and also it is environmentally unacceptable nowadays. Considering these facts, it was created a project at UFPA aiming to evaluate the building viability of small boats adapted to the Amazon region. These boats have been made with composite material, polymeric resin reinforced with natural fiber fabric. Hence, this paper brings the first stage of this project, treating on the build of a small boat with reduced dimensions. This prototype was experimentally studied, using strain gages, and evaluated numerically by finite element method through the software ANSYS¨. This stage was very important to optimize the parameters used in the finite element model, which was employed to analyse the model with real dimensions. As a result, the numerical models showed a good compatibility with real tests. Additionally, the designed boat demonstrated to be able to hold the imposed loads.
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An Investigation of a Mathematical Model for the Internal Velocity Profile of Conical Diffusers Applied to DAWTs
(Universidade Federal do Pará, 2015-06) BARBOSA, Disterfano Lima Martins; VAZ, Jerson Rogério Pinheiro; FIGUEIREDO, Sávio W.O. ; SILVA, Marcelo de Oliveira e; LINS, Erb Ferreira; MESQUITA, André Luiz Amarante
The Diffuser Augmented Wind Turbines (DAWTs) have been widely studied, since the diffusers improve the power coefficient of the wind turbine, particularly of small systems. The diffuser is a device which has the function of causing an increase on the flow velocity through the wind rotor plane due to pressure drop downstream, therefore resulting in an increase of the rotor power coefficient. This technology aids the turbine to exceed the Betz limit, which states that the maximum kinetic energy extracted from the flow is 59.26%. Thus, the present study proposes a mathematical model describing the behavior of the internal velocity for three conical diffusers, taking into account the characteristics of flow around them. The proposed model is based on the Biot-Savart's Law, in which the vortex filament induces a velocity field at an arbitrary point on the axis of symmetry of the diffusers. The results are compared with experimental data obtained for the three diffusers, and present good agreement.
Acesso aberto (Open Access)
Numerical Study of Wake Characteristics in a Horizontal-Axis Hydrokinetic Turbine
(Universidade Federal do Pará, 2016-12) SILVA, Paulo Augusto Strobel de Freitas e; OLIVEIRA, Taygoara Felamingo de; BRASIL JUNIOR, Antonio Cesar Pinho; VAZ, Jerson Rogério Pinheiro
Over the years most studies on wake characteristics have been devoted to wind turbines, while few works are related to hydrokinetic turbines. Among studies applied to rivers, depth and width are important parameters for a suitable design. In this work, a numerical study of the wake in a horizontal-axis hydrokinetic turbine is performed, where the main objective is an investigation on the wake structure, which can be a constraining factor in rivers. The present paper uses the Reynolds Averaged Navier Stokes (RANS) flow simulation technique, in which the Shear-Stress Transport (SST) turbulent model is considered, in order to simulate a free hydrokinetic runner in a typical river flow. The NREL-PHASE VI wind turbine was used to validate the numerical approach. Simulations for a 3-bladed axial hydrokinetic turbine with 10 m diameter were carried out, depicting the expanded helical behavior of the wake. The axial velocity, in this case, is fully recovered at 12 diameters downstream in the wake. The results are compared with others available in the literature and also a study of the turbulence kinetic energy and mean axial velocity is presented so as to assess the influence of proximity of river surface from rotor in the wake geometry. Hence, even for a single turbine facility it is still necessary to consider the propagation of the wake over the spatial domain.
Acesso aberto (Open Access)
Contribution to the marine propeller hydrodynamic design for small boats in the Amazon region
(Instituto Nacional de Pesquisas da Amazônia, 2016-03) FAVACHO, Breno Inglis; VAZ, Jerson Rogério Pinheiro; MESQUITA, André Luiz Amarante; LOPES, Fábio; MOREIRA, Antonio Luciano Seabra; SOEIRO, Newton Sure; ROCHA, Otávio Fernandes Lima da
In the Amazon, river navigation is very important due to the length of navigable rivers and the lack of alternative road networks. Boats usually operate in unfavorable conditions, since there is no hydrodynamic relation among propellers, geometry, and the dimensions of the boat hull. Currently, there is no methodology for propeller hydrodynamic optimization with low computational cost and easy implementation in the region. The aim of this work was to develop a mathematical approach for marine propeller design applied to boats typically found on Amazon rivers. We developed an optimized formulation for the chord and pitch angle distributions, taking into account the classical model of Glauert. A theoretical analysis for the thrust and torque relationships on an annular control volume was performed. The mathematical model used was based on the Blade Element Momentum Theory (BEMT). We concluded that the new methodology proposed in this work demonstrates a good physical behavior when compared with the theory of Glauert and the experimental data of the Wageningen B3-50 propeller.
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Influence of thermal parameters on the dendritic arm spacing and the microhardness of Al-5.5wt.%Sn alloy directionally solidified
(2014-06) VASCONCELOS, Angela de Jesus; SILVA, Cibele Vieira Arão da; MOREIRA, Antonio Luciano Seabra; SILVA, Maria Adrina Paixão de Souza da; ROCHA, Otávio Fernandes Lima da
Al-Sn alloys are widely used in tribological applications. In this study, thermal, microstructural and microhardness (HV) analysis were carried out with an Al-5.5wt.%Sn alloy ingot produced by horizontal directional transient solidification. The main parameters analyzed include the growth rate (VL) and cooling rate (TR).These thermal parameters play a key role in the microstructural formation. The dendritic microstructure has been characterized by primary dendritic arm spacing (λ1) which was experimentally determined and correlated with VL, and TR. The behavior presented by the Al-5.5wt.%Sn alloy during solidification was similar to that of other aluminum alloys, i.e., the dendritic network became coarser with decreasing cooling rates, indicating that the immiscibility between aluminum and tin does not have a significant effect on the relationship between primary dendritic arm spacing and the cooling rate. The dependence of the microhardness on VL, TR and λ1 was also analyzed. It was found that for increasing values of TR, the values of HV decrease. On the other hand, the values of HV increase with increasing values of λ1.
Acesso aberto (Open Access)
Solidification thermal parameters and dendritic growth during the horizontal directional solidification of Al-7wt.%Si alloy
(2014-09) CARVALHO, Diego de Leon Brito; COSTA, Thiago Antônio Paixão de Sousa; MOREIRA, Antonio Luciano Seabra; SILVA, Maria Adrina Paixão de Souza da; DIAS FILHO, José Marcelino da Silva; MOUTINHO, Daniel Joaquim da Conceição; ROCHA, Otávio Fernandes Lima da
The main purpose of this work is to investigate the influence of thermal parameters such as growth rate (VL) and cooling rate (TR) on the primary dendrite arm spacings (λ1) during the horizontal transient directional solidification of Al-7wt.%Si hypoeutectic alloy. The primary dendrite spacings were measured along the length of the samples and correlated with these thermal parameters. The variation of dendrite spacings is expressed as a power law function of VL and TR given by the formulas λ1 = 55(VL)-1.1 and λ1 = 212 (TR)-0.55, respectively. A comparative study between the results of this work and those from the literature proposed to investigate these dendrite spacings during the upward and downward vertical directional solidification of Al-7wt.%Si alloy is also conducted. Finally, the experimental data are compared with some predictive dendritic models from the literature.
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Production and evaluation of recycled polymers from açaí fibers
(2010-06) CASTRO, Clívia Danúbia Pinho da Costa; DIAS, Carmen Gilda Barroso Tavares; FARIA, José de Assis Fonseca
The possibility of recycling and the favorable mechanical properties of the products have encouraged the study and production of thermoplastic composites from natural fibrous waste. Açaí (cabbage palm) fiber, which is removed from the seed, has been slightly investigated, as compared to what is already known about the fruit pulp. In this study, the influence of açaí fiber as an element of reinforcement in recycled everyday usage thermoplastics using simple, low cost methodology was evaluated. Recycled matrixes of high impact polystyrene and polypropylene were molded by hot compression from which the fiber composites were obtained. The FTIR technique showed that the process was efficient in preventing degradation of the açaí fibers. The influence of the fiber on the mechanical behavior of the recycled matrixes was investigated by microscopic images of compression and impact tests. The results showed better impact performance for the fiber combined with the polymeric matrixes.
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Characterization of the Al-3wt.%Si alloy in unsteady-state horizontal directional solidification
(2013-08) CARVALHO, Diego de Leon Brito; GUIMARÃES, Emanuelle Casseb; MOREIRA, Antonio Luciano Seabra; MOUTINHO, Daniel Joaquim da Conceição; DIAS FILHO, José Marcelino da Silva; ROCHA, Otávio Fernandes Lima da
The main purpose of this paper is to investigate both the columnar to equiaxed transition and primary dendritic arm spacings of Al-3wt.%Si alloy during the horizontal directional solidification. The transient heat transfer coefficient at the metal-mold interface is calculated based on comparisons between the experimental thermal profiles in castings and the simulations provided by a finite difference heat flow program. Simulated curve of the interfacial heat transfer coefficient was used in another numerical solidification model to determine theoretical values of tip growth rates, cooling rates and thermal gradients that are associated with both columnar to equiaxed transition and primary dendritic arm spacings. A good agreement was observed between the experimental values of these thermal variables and those numerically simulated for the alloy examined. A comparative analysis is carried out between the experimental data of this work and theoretical models from the literature that have been proposed to predict the primary dendritic spacings. In this context, this study may contribute to the understanding of how to manage solidification operational parameters aiming at designing the microstructure of Al-Si alloys.
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The columnar to equiaxed transition of horizontal unsteady-state directionally solidified Al-Si alloys
(2014-04) CARVALHO, Diego de Leon Brito; MOREIRA, Antonio Luciano Seabra; MOUTINHO, Daniel Joaquim da Conceição; DIAS FILHO, José Marcelino da Silva; ROCHA, Otávio Fernandes Lima da; SPINELLI, José Eduardo
Experiments were conducted to investigate the influence of thermal parameters on the columnar to equiaxed transition during the horizontal unsteady-state directional solidification of Al-Si alloys. The parameters analyzed include the heat transfer coefficients, growth rates, cooling rates, temperature gradients and composition. A combined theoretical and experimental approach is developed to determine the solidification thermal variables considered. The increasing solute content in Al-Si alloys was not found to affect significantly the experimental position of the CET which occurred for cooling rates in the range between 0.35 and 0.64 K/s for any of three alloy compositions examined. A comparative analysis between the results of this work and those from the literature proposed to analyze the CET during upward vertical solidification of Al-Si alloys is reported and the results have shown that the end of the columnar region during horizontal directional solidification is abbreviated as a result of about six times higher thermal gradient than that verified during upward unidirectional solidification of alloys investigated.
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Influência das variáveis térmicas sobre os espaçamentos dendríticos terciários durante a solidificação direcional horizontal da liga Al-6%Cu
(2015-03) DIAS FILHO, José Marcelino da Silva; KIKUCHI, Rafael Hideo Lopes; COSTA, Thiago Antônio Paixão de Sousa; MOREIRA, Antonio Luciano Seabra; ROCHA, Otávio Fernandes Lima da
The Al-6wt%Cu alloy was directionally solidified and dendritic microstructure, solidification thermal variables, i.e., tip growth rate (VL), cooling rate (TR) and temperature gradient ahead of liquidus isotherm (GL) were characterized and correlated with tertiary dendritic spacings (λ3) determined experimentally. For this purpose, a horizontal solidification experimental apparatus was developed and specimens were solidified under unsteady state heat flow conditions. It was observed that power laws -1.1 and -0.55 characterize the tertiary spacing variations with tip growth rate (VL) and cooling rate (TR), respectively. Comparisons with other studies published in the literature for Al-Cu alloys solidified in upward and downward vertical directional conditions were performed.
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Espaçamentos dendríticos primários da liga Sn-5%Pb solidificada direcionalmente em um sistema horizontal
(2012) NOGUEIRA, Márcio Roberto Alves; CARVALHO, Diego de Leon Brito; MOREIRA, Antonio Luciano Seabra; DIAS FILHO, José Marcelino da Silva; ROCHA, Otávio Fernandes Lima da
In order to investigate the effect of thermal parameters on the primary dendritic spacings of Sn - 5%Pb alloy, horizontal directional solidification experiments have been carried out under unsteady state heat flow conditions. Thermocouples have been connected with the metal, and the time - temperature data have been recorded automatically. The results include metal/mold heat transfer coefficient determined from comparisons between the experimental thermal profiles and simulations provided by a numerical model. A combined theoretical and experimental approach is developed to determine the solidification thermal parameters: tip growth rates, and cooling rates. The experimental and calculated values have shown a good agreement. A comparative study between experimental data of this work and those from the literature proposed to predict the primary spacings during upward and downward vertical unsteady-state directional solidification of Sn - Pb alloys is presented. The observation of the microstructures has indicated that the primary dendritic spacings have been affected by the direction of growth, increasing in conditions of horizontal solidification when compared with those obtained during vertical solidification.
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Modelagem do tempo de execução de obras civis: estudo de caso na Universidade Federal do Pará
(2012-03) COUTINHO, Lêda Sílvia de Aguiar Lédo; DUARTE, André Augusto Azevedo Montenegro; NEVES, Renato Martins das; COUTINHO NETO, Benedito; MANESCHY, Carlos Edilson de Almeida; PINHEIRO, Ana Maria Guerra Seráfico
This article proposes the adoption of a numerical prognosis model to estimate the variable "execution time" for public projects in an objective way. The field work consisted of the application of statistical methods for analyzing data from projects that were bid and contracted by the Federal University of Pará (UFPA) between 2006 and 2009. Data analysis involved linear regression and transformed functions. After the stratification and initial treatment of the data, the evidence adopted for the construction of the final model was limited to 102 out of the 225 projects originally investigated, resulting in the following statistical parameters: correlation coefficient (R) of 0.899, coefficient of determination (R2) of 0.808, adjusted coefficient of determination (adjusted R2) of 0.796, and standard error (Se) of 0.41. These parameters show a strong linear correlation between the variables, indicating that 79.60% of the variability of the execution of a public project is jointly caused by variations in the gross floor area, the estimated cost, the operational technical capacity of the client organization; the operational capacity of the company; the type of service, and the season.
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A Law of the Wall Formulation for Recirculating Flows
(2000) CRUZ, Daniel Onofre de Almeida; BORTOLUS, Marcos Vinicius
This work presents a new law of the wall formulation for recirculating turbulent flows. An alternative expression for the internal length which can be applied in the separated region is also presented. The formulation is implemented in a numerical code which solves the k-e model through a finite volume method. The theoretical results are compared with the experimental data of Vogel and Eaton (J. of Heat Transfer, Transactions of ASME, vol.107, pp. 922-929, 1985). The paper shows that the present formulation furnishes better results than the standard k-e formulation.
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The carreau-yasuda fluids: a skin friction equation for turbulent flow in pipes and kolmogorov dissipative scales
(2007-06) ANDRADE, Luiz Claudio Fialho; PETRONÍLIO, Jamilson A.; MANESCHY, Carlos Edilson de Almeida; CRUZ, Daniel Onofre de Almeida; Associação Brasileira de Ciências Mecânicas
In this work the turbulent flow of the Non-Newtonian Carreau-Yasuda fluid will be studied. A skin friction equation for the turbulent flow of Carreau-Yasuda fluids will be derived assuming a logarithmic behavior of the turbulent mean velocity for the near wall flow out of the viscous sub layer. An alternative near wall characteristic length scale which takes into account the effects of the relaxation time will be introduced. The characteristic length will be obtained through the analysis of viscous region near the wall. The results compared with experimental data obtained with Tylose (methyl hydroxil cellulose) solutions showing good agreement. The relations between scales integral and dissipative obtained for length, time, velocity, kinetic energy, and vorticity will be derived for this type of fluid. When the power law index approach to unity the relations reduces to Newtonian case.

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