PROCEEDINGS OF THE 22ND INTERNATIONAL ESAFORM CONFERENCE ON MATERIAL FORMING: ESAFORM 2019, 2019
Bipolar plates (BPPs) are the main component in proton exchange membrane fuel cells. In the last ... more Bipolar plates (BPPs) are the main component in proton exchange membrane fuel cells. In the last years, different manufacturing processes have been proposed as alternative to the traditional graphite BPPs, including the manufacture of thin stamped BPPs using the rubber pad forming process. In this context, the numerical simulation of the forming process is used to optimize of the process parameters. Thus, in addition to the modelling of the elastoplastic behavior of the metallic sheet, it is also necessary to describe the hyper-viscoelastic behavior of the rubber pad. The main objective of this study is to evaluate the importance of the viscous effect on the global behavior of two different polyurethanes, since the modelling of the viscoelastic behavior is significantly more complex than the hyperelastic one. Uniaxial compression and stress relaxation tests are carried out both experimentally and numerically, considering three loading/unloading velocities. The hyperelastic behavior is described by the Mooney-Rivlin model, while the viscoelasticity is modelled by a series of Maxwell elements. The results show that the viscous effect can be neglected in the numerical modelling of the rubber pad forming, if the rubber hardness value is low.
Local Bifurcation and Instability Theory Applied to Formability Analysis
... model [2], MC Oliveira (*) :LF Menezes CEMUC, Department of Mechanical Engineering, Universit... more ... model [2], MC Oliveira (*) :LF Menezes CEMUC, Department of Mechanical Engineering, University of Coimbra, Polo II, Rua Lu??s Reis Santos, Pinhal de Marrocos, 3030-788 Coimbra, Portugal e-mail: [email protected] JL ...
Modelação tridimensional e simulação numérica dos processos de enformação por deformação plástica : aplicação à estampagem de chapas metálicas
Este trabalho apresenta o desenvolvimento de um modelo tridimensional e respectivo programa de cá... more Este trabalho apresenta o desenvolvimento de um modelo tridimensional e respectivo programa de cálculo para simular o processo de estampagem de chapas metálicas. A modelação aqui elaborada considera a estampagem como um processo de grandes deformações e ...
The main goal of this study is to evaluate the influence of work-hardening modeling in springback... more The main goal of this study is to evaluate the influence of work-hardening modeling in springback prediction in the first phase of the Numisheet'05 ''Benchmark 3'': the U-shape ''Channel Draw''. Several work-hardening constitutive models are used in order to allow the different materials' mechanical behavior to be better described: the Swift law (a power law) or a Voce type saturation law to describe the classical isotropic work-hardening; a Lemaître and Chaboche type law to model the non-linear kinematic hardening, which can be combined with the previous two; and Teodosiu's microstructural work-hardening model. This analysis was carried out using two steels currently used in the automotive industry: mild (DC06) and dual phase (DP600).
This paper seeks to present a new approach to reverse analysis in depth-sensing indentation which... more This paper seeks to present a new approach to reverse analysis in depth-sensing indentation which makes use of numerical simulation. This methodology allows the results of experimental hardness tests acquired with single indenter geometry to be used to determine the plastic properties of materials. Forward and reverse analyses of high deformation three-dimensional numerical simulations of Vickers indentation tests are used to determine different mechanical properties of materials: Young's modulus, yield stress and strain-hardening exponent. The Vickers indenter used in the numerical simulations is formulated as a rigid body and takes into account the presence of the most common imperfection of the tip, so-called offset. The contact friction between the Vickers indenter and the deformable body is also considered. The forward analysis uses materials with Young's modulus values from 50 to 600 GPa, yield stress values from 0.3 to 10 GPa and strain-hardening exponents from 0 to 0.6; the Poisson ratio did not vary from 0.3. The representative plastic strain e r and the correspondent stress r r , as previously defined by other authors [Dao M, Chollacoop N, Vliet KJ, Venkatesh TA, Suresh S. Acta Mater 2001;49:3899], were identified by an independent numerical method. The values of the representative plastic strain e r obtained for the Vickers indenter confirm those of the above-mentioned authors, despite showing a slight influence from the Young's modulus values. The forward study enables the production of a unique plot of the hardness H IT vs. representative stress r r , where both are normalized by the Young's modulus E. The proposed reverse analysis provides a unique solution to the representative stress r r and the strain-hardening exponent, n, given that the Young's modulus is predetermined from the experimental hardness test. Depending on the material properties, the value of n can be more or less sensitive to the scatter of the experimental results obtained using the depth-sensing equipment, particularly the stiffness of the unloading curve. The validity of the proposed reverse analysis method is checked using three real materials: stamping quality steel (DC 06), stainless AISI 304 steel and BK7 glass.
In this paper we present a methodology for trimming 3D solid finite element meshes using a non-un... more In this paper we present a methodology for trimming 3D solid finite element meshes using a non-uniform rational B-spline (NURBS) surfaces representation. The algorithms applied in the identification of the spatial position of the finite element (FE) nodes and elements relative to the trimming surface are described, as well as, the explanation of the correction methods adopted to geometrically rearrange the trimmed elements. Three different strategies are proposed to adjust, with greater or lesser accuracy, the trimmed FE mesh to the trimming surface. The first consists only of an element elimination strategy, while the other two are based on a nodal stretching strategy, aiming for more accurate adjustment of the finite elements boundary to the trimming surface. Finally, to highlight the capabilities of the developed program, a mesh generation example is given by trimming a mesh with the shape of a blank automotive panel.
This work aims to analyse the influence of temperature, strain-rate and aging time in the mechani... more This work aims to analyse the influence of temperature, strain-rate and aging time in the mechanical behaviour of an EN AW 6016-T4 alloy, naturally aged. This Aluminium Alloy was select since it is commonly used in the automotive industry. Uniaxial tensile tests were performed within a temperature range between room temperature and 300oC, for different strain rates and at different times after its production. The results collected constitute an experimental database for evaluating the potential application of warm forming processes to this alloy Mots clefs: Al-Mg-Si Alloys; Mechanical Characterization; Temperature; Strain rate; Aging
Computer Methods in Applied Mechanics and Engineering, 2016
Highlights • A new 3D contact surface smoothing approach for large deformation contact problems b... more Highlights • A new 3D contact surface smoothing approach for large deformation contact problems between deformable bodies is proposed. • The local Nagata patch interpolation is used to smooth arbitrary surface meshes. • The original curvature of the master surface is recovered using a relatively coarse mesh. • The non-physical contact force oscillations usual in the faceted surface representation are eliminated. • The accuracy, robustness and performance of the numerical simulations is improved adopting the surface smoothing method.
International Journal of Mechanical Sciences, 2017
The high-strength steel sheets currently used in the automotive industry are prone to non-traditi... more The high-strength steel sheets currently used in the automotive industry are prone to non-traditional behaviour during forming, being wrinkling and springback two of the most challenging geometrical predictions for numerical simulation. Thus, the finite element method requires accurate and reliable numerical models. This study presents the experimental and numerical analysis of a rail component with high tendency to develop wrinkling and 2D springback. Two different materials are used for the sheet blank, namely a mild steel (DC06) and a dual phase steel (DP600). The frictional behaviour between each metallic sheet and the forming tools is evaluated through the flat-die test, allowing the determination of a friction coefficient as a function of the normal pressure. The influence of the applied boundary conditions on the numerical results is evaluated by means of two distinct numerical models (full blank geometry and 1/4 of the blank with symmetry conditions). The results show that the wrinkling behaviour is strongly affected by the blank's material, as well as by the symmetry conditions defined in the numerical model. In fact, considering the full model of the blank, the numerical results are in better agreement with the experimental ones. However, the computational cost of the numerical simulation considering the full blank is substantially higher than using 1/4 of the blank.
Journal of Physics: Conference Series, Jul 1, 2018
Both the plastic deformation and the friction forces generate heat in sheet metal forming process... more Both the plastic deformation and the friction forces generate heat in sheet metal forming processes. This yields a temperature rise on the blank and tools, which is mainly dictated by the blank properties and the press speed. Although modest values of temperature rise yield negligible changes in the mechanical behavior of metals, the lubricant properties are rather influenced by the temperature. Thus, the deep drawing of an aluminum cylindrical cup was selected to evaluate, experimentally and numerically, the temperature variation of the forming tools and blank at room temperature. Different values of punch speed are compared to evaluate the impact of the heat losses to the environment. The experimental results show that the temperature rise on the die surface is higher than 9ºC when the punch speed is 10 mm/s. The temperature is underestimated by the finite element model due to the isothermal conditions imposed on the forming tools.
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