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Title: Modelling the hyper-viscoelastic behaviour of synthetic rubbers applied to rubber pad forming
Other Titles: Modelação do comportamento hiper-viscoelástico de borrachas sintéticas aplicado ao processo de conformação com borracha
Authors: Mota, Henrique 
Orientador: Neto, Diogo
Keywords: Metallic bipolar plates; Rubber pad forming; Numerical simulation; Synthetic rubber; Hyper-viscoelastic behaviour
Issue Date: Jul-2018
Abstract: Fuel cells are a promising alternative to the combustion engines in the automotive industry, allowing to reduce significantly the air pollution generated by cars. However, this new technology still presents some economic issues due to the cost involved in the production of the bipolar plates (main component of fuel cells). In order to reduce the production costs, the rubber pad forming has been adopted in the manufacturing of thin stamped bipolar plates. Since the plastic deformation of the sheet is induced by a pad of rubber like material, the numerical modelling of this manufacturing process requires a deep knowledge about the mechanical behaviour of rubber materials. The main objective of this study is the numerical modelling of rubber-like materials, which typically present a hyper-viscoelastic behaviour. Accordingly, the constitutive law currently implemented in the V-Biomech finite element code, used to describe the mechanical behaviour of rubbers, is presented in detail. Hence, the hyperelastic behaviour is described by the Mooney-Rivlin model, while the viscoelasticity is modelled by a series of Maxwell elements. Considering the case of uniaxial compression stress state, the closed-form solution is derived for the hyper-viscoelastic behaviour, which is posteriorly used in the procedure to identify the material parameters involved in the constitutive model. Two different polyurethane materials are experimentally evaluated by means of uniaxial compression tests and relaxation tests, allowing to identify the material parameters by fitting the numerical model to the experimental data. Then, these rubber materials are adopted in the numerical simulation of the rubber pad forming process, using the Abaqus software to study numerically the forming of metallic bipolar plates. Taking into account the experimental results from both the uniaxial compression tests and relaxations tests performed on two different polyurethanes, the viscosity effect is small considering the range of velocity applied, particularly for the rubber with lower hardness value. Moreover, the predicted mechanical behaviour of both rubbers is in good agreement with the experimental values. The numerical results of the rubber pad forming process show that the final thickness of the stamped bipolar plate is not significantly influenced by the rubber hardness. However, the predicted final thickness distribution is more uniform in comparison with the one obtained with the conventional stamping process.
Rights: openAccess
Appears in Collections:FCTUC Eng.Mecânica - Teses de Mestrado

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