Navegando por Autor "Oliveira, Cristiano Peres"

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Algebraic rectilinear model for multilayer resin transfer molding injection
(2013) Oliveira, Cristiano Peres; Souza, Jeferson Avila; Isoldi, Liércio André; Amico, Sandro Campos
An analytical model for the multilayer rectilinear injection applied to the RTM process has been developed. The model takes into account the permeability in both in-plane (Kxx and Kyy ) and transverse (Kzz ) directions of each layer of the reinforcement media and calculates the transverse permeability (Kt ) through adjacent layers. Porosity and thickness are set independent for each layer of the assembly. Mass balance of resin within the layers is used to develop an expression that estimates resin position (xi ) as a function of time (t) independently of each layer. The resulting equation was solved using: (i) Numerical integration and (ii) algebraic integration of the simplified expression resulting in a closed expression for x i = xi (t). Results of both proposed methods were compared with the calculations performed using the PAM-RTM software for cases with three, five and seven layers and the maximum calculated error in all cases was less than 12%.
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An original procedure to determine transverse permeability using a multilayer reinforcement in RTM
(2010) Oliveira, Cristiano Peres; Souza, Jeferson Avila; Isoldi, Liércio André; Rocha, Luiz Alberto Oliveira; Amico, Sandro Campos; Silva, Rafael Diego Sonaglio da
Resin Transfer Molding (RTM) is a manufacturing process for polymer composites parts for a variety of uses. The numerical simulation of the resin flow into the mold can be used to minimize costs related to mold design and the manufacturing process itself. However, to obtain realistic results, accurate information about the resin and the reinforcement media are necessary. In the multilayer RTM, distinct porous media layers are stacked to obtain a final composite with better performance. For the numerical simulation of the multilayer RTM, transverse permeability (Kzz) data are necessary. This work proposes an original methodology to determine the transverse permeability in multilayer RTM composites, assuming that the in-plane permeabilities (Kxx and Kyy) are known and using this information, combined with experimental data obtained during mold filling. The motivation of this study is the fact that the transverse permeability is usually not available in the literature, being referred to as a difficult parameter to be directly determined using experiments.
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Comparação dos métodos VOF e FE/CV aplicados à solução de problemas de RTM
(2011) Oliveira, Cristiano Peres; Souza, Jeferson Avila; Amico, Sandro Campos; Isoldi, Liércio André; Silva, Rafael Diego Sonaglio da
A moldagem por transferência de resina (RTM) é um processo amplamente utilizado na produção de compósitos poliméricos com as mais diferentes geometrias. É um processo de infusão de resina em um molde fechado e preenchido com um reforço fibroso e poroso. Existem algumas variantes do processo de RTM tradicional, como o RTM Light e o VARTM. No estudo desse processo, a simulação numérica desenvolve um papel fundamental, pois através dela pode-se determinar como se dá o avanço da resina no interior do molde e assim perceber possíveis falhas no preenchimento bem como determinar com precisão os pontos mais adequados para a entrada e a saída da resina. Estes fatores possibilitam que haja, por exemplo, uma considerável diminuição do número de ensaios, normalmente de custo elevado, necessários para a construção dos moldes. Para a modelagem numérica do processo RTM são utilizados métodos numéricos para a solução do conjunto de equações diferenciais que governam o problema físico. Nesse trabalho, são apresentados e discutidos os métodos VOF (Volume of Fluid) e FE/CV (Finite Element/Control Volume Method). Para comparação entre os métodos, foram utilizadas as soluções numéricas apresentadas pelo FLUENT® e pelo PAM-RTM®, onde se obteve uma boa concordância entre esses modelos e os resultados experimentais obtidos.
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Computational modeling of the resin transfer molding process
(2009) Oliveira, Cristiano Peres; Souza, Jeferson Avila; Isoldi, Liércio André; Rocha, Luiz Alberto de Oliveira; Amico, Sandro Campos
The Resin Transfer Molding, or RTM, process has recently become one of the most important processes of fiber reinforced composites manufacturing. The process consists essentially of three stages: “an arrangement of fiber mats in a mold cavity, a mold filling by a polymeric resin and a curing phase”. Most of the difficulties of incorporating RTM occur during the filling stage. To create an acceptable composite part the preform must be completely impregnated with resin. The conditions which most strongly influence the flow are mold geometry, resin rheology, preform permeability, and location of the injection ports and vents. There are different types of RTM process, e.g. RTM Light or VARTM, employed in accordance with the final desired characteristics and properties of composite components. Besides, RTM may also be carried out using multilayers, with distinct characteristics. The numerical simulation of the mold filling stage becomes an important tool which helps the mold designer to understand the process parameters. Considering the fibrous preform as a porous media, the phenomenon can be modeled by Darcy’s law to describe resin flow. This study used two commercial softwares, FLUENT® and PAM-RTM®. FLUENT® is a general Computational Fluid Dynamics (CFD) code, based on Finite Volume Method (FVM). It applies the Volume of Fluid (VOF) method to solve the filling problem because it does not have a specific RTM module. PAM-RTM® is a specific package for RTM problems, based on the Finite Element Method (FEM). These tools were applied to simulate numerically several RTM examples of the resin flow into the mold and the results for both softwares were compared with previous works.
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A numerical methodology for permeability determination of reinforcements for polymeric composites
(2012) Souza, Jeferson Avila; Isoldi, Liércio André; Santos, Elizaldo Domingues dos; Oliveira, Cristiano Peres; Amico, Sandro Campos
This work focus on developing a numerical methodology for the determination of permeability of RTM reinforcements. The method allows the calculation of the three permeability components (Kxx, Kyy and Kzz) from a set of time dependent flow front coordinates data; one coordinate for each permeability component. An initial guess is set for the permeabilities and the difference between numerical and experimental values of flow front position at a specific time is minimized with the solution of an algebraic system of equations. Newton-Raphson method was used to solve the non-linear system of equations. The results presented in this paper were obtained for a rectilinear (1D) and a radial 2D problem, both with analytical solutions for the flow front position as a function of time. For the 1D comparison between the numerically calculated Kxx and the analytical value agreed within 1.7% and, for the 2D radial problem, numerical and analytical values of Kxx and Kyy agreed within 1.3%.
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Three-dimensional numerical modeling of RTM and LRTM processes
(2012) Isoldi, Liércio André; Oliveira, Cristiano Peres; Rocha, Luiz Alberto Oliveira; Souza, Jeferson Avila; Amico, Sandro Campos
Resin Transfer Molding (RTM) is a manufacturing process in which a liquid resin is injected into a closed mold pre-loaded with a porous fibrous preform, producing complex composite parts with good surface finishing. Resin flow is a critical step in the process. In this work, the numerical study of the resin flow in RTM applications was performed employing a general Computational Fluid Dynamics software which does not have a specific RTM module, making it necessary to use the Volume of Fluid method for the filling problem solution. Examples were presented and compared with analytical, experimental and numerical results showing the validity and effectiveness of the present study, with maximum difference among these solutions of around 8%. Besides, based on the computational model for the RTM process, a new computational methodology was developed to simulate Light Resin Transfer Molding (LRTM). In this process, resin is injected into the mold through an empty injection channel (without porous medium) which runs all around the perimeter of the mold. The ability of FLUENT® package to simulate geometries which combine porous media regions with open (empty) regions was used. Two specific cases were simulated, showing the differences in time and behavior between RTM and LRTM processes.