References of "Ponthot, Jean-Philippe"
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See detailA cascade optimization methodology for automatic parameter identification and shape/process optimization in metal forming simulation
Ponthot, Jean-Philippe ULg; Kleinermann, Jean-Pascal

in Computer Methods in Applied Mechanics & Engineering (2006), 195(41-43), 5472-5508

Computer simulations of metal forming processes using the finite element method (FEM) are, today, well established. This form of simulation uses an increasing number of sophisticated geometrical and ... [more ▼]

Computer simulations of metal forming processes using the finite element method (FEM) are, today, well established. This form of simulation uses an increasing number of sophisticated geometrical and material models, relying on a certain number of input data, which are not always readily available. The aim of inverse problems, which will be considered here, is to determine one or more of the input data relating to these forming process simulations, thereby leading to a desired result. In this paper, we will focus on two categories of such inverse problems. The first category consists of parameter identification inverse problems. These involve evaluating the material parameters for material constitutive models that would lead to the most accurate results with respect to physical experiments, i.e. minimizing the difference between experimental results and FEM simulations. The second category consists of shape/process optimization inverse problems. These involve determining the initial geometry of the specimen and/or the shape of the forming tools, as well as some parameters of the process itself, in order to provide the desired final geometry after the forming process. These two categories of inverse problems can be formulated as optimization problems in a similar way, i.e. by using identical optimization algorithms. In this paper, we intend firstly to solve these two types of optimization problems by using different non-linear gradient based optimization methods and secondly to compare their efficiency and robustness in a variety of numerical applications. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

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See detailNumerical simulation in cold rolling using adiabatic strip model : application to large roll deformation
STEPHANY, A.; Ponthot, Jean-Philippe ULg; LEGRAND, N.

in AUSTRIB 06 (2006)

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See detailSimulation of complex impact problems with implicit time algorithms: Application to a turbo-engine blade loss problem
Noels, Ludovic ULg; Stainier, Laurent ULg; Ponthot, Jean-Philippe ULg

in International Journal of Impact Engineering (2005), 32(1-4), 358386

Recent developments, in non-linear structural dynamics, have led to a new kind of implicit algorithms: the energy-momentum conserving algorithm (EMCA) and the energy-dissipative, momentum-conserving ... [more ▼]

Recent developments, in non-linear structural dynamics, have led to a new kind of implicit algorithms: the energy-momentum conserving algorithm (EMCA) and the energy-dissipative, momentum-conserving algorithm. Contrarily to commonly used algorithms, such as the explicit central difference or the alpha-generalized method, the stability of those algorithms is always ensured in the non-linear range. Thanks to this unconditional stability the only requirement on the time step size is that it must be small enough to capture the physics. This requirement is less restrictive than a conditional stability. In previous works, we have developed a new formulation of the internal forces for a hypoelastic model, that leads to an EMCA. In this paper, we will extend this formulation to an energy-dissipative, momentum-conserving algorithm. We will prove with an academic example, that our algorithm is more accurate than the alpha-generalized method in the non-linear range. Then we will simulate a blade loss problem to demonstrate the efficiency of our developments on complex dynamics simulations. (c) 2005 Elsevier Ltd. All rights reserved. [less ▲]

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See detailThermomechanical modeling of metals at finite strains: First and mixed order finite elements
Adam, Laurent; Ponthot, Jean-Philippe ULg

in International Journal of Solids and Structures (2005), 42(21-22), 5615-5655

The aim of this paper is to describe an updated EAS (Enhanced Assumed Strain) finite element formalism developed to model the thermomechanical behavior of metals submitted to large strains. We will also ... [more ▼]

The aim of this paper is to describe an updated EAS (Enhanced Assumed Strain) finite element formalism developed to model the thermomechanical behavior of metals submitted to large strains. We will also expose the use of mixed order elements (first order mechanical elements strongly coupled with quadratic thermal elements) which, as we will show, is of particular interest for modeling fast processes inducing important temperature gradients. The features of this formalism, used jointly with an Updated Lagrangian approach and an hypoelastic anisothermal constitutive formulation, will be described. Three applications involving finite strains and important thermomechanical couplings will be studied. The results obtained will be compared with the results given by the now classical SRI (Selective Reduced Integration) formalism. (c) 2005 Elsevier Ltd. All rights reserved. [less ▲]

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See detailAn ALE Model for Numerical Simulation of Cold Roll Forming Process
Boman, Romain ULg; Papeleux, Luc ULg; Viet, B. Q. et al

in AIP Conference Proceedings (2005, August 05), 778

In this paper, the Arbitrary Lagrangian Eulerian formalism is used to compute the steady state of a 3D U-shaped cold roll forming process. Compared to the Lagrangian case, this method allows the use of a ... [more ▼]

In this paper, the Arbitrary Lagrangian Eulerian formalism is used to compute the steady state of a 3D U-shaped cold roll forming process. Compared to the Lagrangian case, this method allows the use of a refined mesh near the tools, leading to an accurate representation of the bending of the sheet with a limited computational time. The main problem of this kind of simulation is the rezoning of the nodes on the free surfaces of the sheet. A modified iterative isoparametric smoother is used to manage this geometrically complex and CPU expensive task. [less ▲]

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See detailNumerical Simulation of Cold Roll Forming Process
Bui, Quoc Viet; Papeleux, Luc ULg; Boman, Romain ULg et al

in Banabic, Dorel (Ed.) Proceedings of the 8th ESAFORM Conference on Material Forming (2005, April)

Cold roll-forming process of a U profile is modelled and simulated. The simulation is based on a 3D finite element analysis with the help of the home made Metafor code. The prediction on dimensions and ... [more ▼]

Cold roll-forming process of a U profile is modelled and simulated. The simulation is based on a 3D finite element analysis with the help of the home made Metafor code. The prediction on dimensions and deformed shape of the cold roll-formed sheet is in good agreement with the experimental results. Parametric study on roll forming parameters, such as the yield limit and the hardening property of materials, and the distance between stations is performed. [less ▲]

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See detailNumerical simulation of tribological devices used as a set of benchmarks for comparing contact algorithms
Chabrand, Patrick; Dubois, Frédéric; Graillet, Denis et al

in Finite Elements in Analysis & Design (2005), 41(6), 637-665

The aim of the present study was to carry out a numerical comparison of different frictional contact algorithms. Therefore three different contact algorithms (Lemke, penalty and Augmented Lagrangian) have ... [more ▼]

The aim of the present study was to carry out a numerical comparison of different frictional contact algorithms. Therefore three different contact algorithms (Lemke, penalty and Augmented Lagrangian) have been implemented into two. finite element codes. The correct implementation and behavior of these contact algorithms has been investigated by modeling four different tribological devices. It is shown that all these different methodologies lead to extremely similar results. Besides these four applications have been carefully described and detailed in such a way that the presented tests can be reproduced. The authors wish that they could serve as a benchmark set in order to allow comparison with other finite element software including frictional contact capabilities. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

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See detailSimulation of crashworthiness problems with implicit time integration methods for non-linear dynamics
Noels, Ludovic ULg; Stainier, Laurent; Ponthot, Jean-Philippe ULg

Scientific conference (2005, February)

When studying impact problems, time integration of the equations of evolution occurs in the non-linear range. Usually, explicit algorithms are used in such a context. Nevertheless, due to its lack of ... [more ▼]

When studying impact problems, time integration of the equations of evolution occurs in the non-linear range. Usually, explicit algorithms are used in such a context. Nevertheless, due to its lack of stability in the non-linear range, and its limitation in the time step size, an implicit scheme could advantageously be used. The most widely used implicit algorithm is the Newmark algorithm. Nevertheless, with this algorithm used in the non-linear range, the conservation of the energy is no longer satisfied. To avoid divergence due to the numerical instabilities, numerical damping was introduced, leading to the generalized- methods. But these schemes can exhibit instabilities in the non-linear range too. Therefore a new family of integration algorithms for problems in structural dynamics has appeared that satisfies the mechanical laws of conservation (i.e. conservation of linear momentum, angular momentum and total energy) and that remains stable in the non-linear range. The first algorithm verifying these properties was described by Simo and Tarnow. They called this algorithm Energy Momentum Conserving Algorithms or EMCA. It consists in a mid-point scheme with an adequate evaluation of the internal forces. This adequate evaluation was given for a Saint Venant-Kirchhoff hyperelastic material. A generalization to other hyperelastic models was given by Laursen, who iteratively solved a new equation for each Gauss point to determine the adequate second Piola-Kirchhoff stress tensor. Another solution that avoids this iterative procedure leads to a general formulation of the second Piola-Kirchhoff stress tensor, was given by Gonzalez. This formulation is valid for general hyperelastic materials. The EMCA was recently extended to dynamic finite deformation plasticity by Meng and Laursen. Armero and Romero also introduced numerical dissipation in these conserving algorithms. This dissipation only affects the total energy but preserves the angular momentum. Moreover, it is proved to be stable in the non-linear range, contrarily to the generalized-algorithms. It is called Energy Dissipative Momentum Conserving algorithm or EDMC. Besides, Armero and Petöcz proposed a treatment of contact interactions in a consistent way in the non-linear range. All the conserving methods described above were established for hyperelastic materials. We have recently established a new expression of the internal forces for the hypoelastic materials using the final rotation scheme. When associated with the mid-point scheme, this expression ensures the conservation laws of the mechanics for a hypoelastic constitutive model. Moreover, using the radial return mapping, we prove that this adaptation remains consistent with the Drucker postulate when plastic deformation occurs. In this work we introduce numerical dissipation in a consistent way for such hypoelastic constitutive models. Moreover, we propose a method to enhance the contact simulation proposed by Armero and Petöcz to surfaces with discontinuous normal as is the case when the two bodies in contact are deformable and are thus discretized by finite elements. With such improvements, we are able to simulate complex simulations of impact such as a blade-loss in a turbo engine. [less ▲]

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See detailLarge strain elasto/viscoplastic constitutive model. Theory and numerical scheme
Ponthot, Jean-Philippe ULg; GARCIA-GARINO, C.; MIRASSO, A.

in MECOM 2005, Mecanica Computational (2005)

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See detailOptimisation methods for initial/tool shape optimisation in metal forming processes
Ponthot, Jean-Philippe ULg; Kleinermann, Jean-Pascal

in International Journal of Vehicle Design (2005), 39(1-2), 14-24

Nowadays, the computer simulations of metal forming processes using the finite element method (FEM), have reached some level of maturity. Inverse problems purpose is to determine one or more of these ... [more ▼]

Nowadays, the computer simulations of metal forming processes using the finite element method (FEM), have reached some level of maturity. Inverse problems purpose is to determine one or more of these forming processes simulations input data, leading to a desired result. A first example that has now become classical is called parameter identification. It consists in evaluating the material parameters for material behaviour laws that would lead to the most accurate model, minimising the difference between experimental and numerical results. Another example, which is much less extensively described in the literature is the initial geometry and tool shape design, which consists in determining the initial shape of the specimen and/or the shape of the forming tools, in order to provide the desired final geometry after forming process. In this paper, we will show how some optimisation methods are able to solve this shape optimisation problems. We will also compare the efficiency of the proposed numerical methods. [less ▲]

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See detailSimulation of Complex Crashworthiness Problems by Using a Combined Implicit/Explicit Time Integration.
Noels, Ludovic ULg; Stainier, Laurent ULg; Ponthot, Jean-Philippe ULg

(2005)

In this work we will combine the ®-generalized explicit time integration scheme with the Energy-Dissipating Momentum-Conserving (EDMC) implicit time-integration scheme.

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See detailA variational framework for nonlinear viscoelastic models in finite deformation regime
Fancello, E. A.; Ponthot, Jean-Philippe ULg; Stainier, Laurent ULg

in Journal of Computational & Applied Mathematics (2005), 215(2), 400-408

This work presents a general framework for constitutive viscoelastic models in the finite deformation regime. The approach is qualified as variational since the constitutive updates consist of a ... [more ▼]

This work presents a general framework for constitutive viscoelastic models in the finite deformation regime. The approach is qualified as variational since the constitutive updates consist of a minimization problem within each load increment. The set of internal variables is strain-based and uses a multiplicative decomposition of strain in elastic and viscous components. Spectral decomposition is explored in order to accommodate, into analytically tractable expressions, a wide set of specific models. Moreover, it is shown that, through appropriate choices of the constitutive potentials, the proposed formulation is able to reproduce results obtained elsewhere in the literature. Finally, numerical examples are included to illustrate the characteristics of the present formulation. (C) 2007 Elsevier B.V. All rights reserved. [less ▲]

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See detailA variational formulation of constitutive models and updates in nonlinear finite viscoelasticity
FANCELLO, E.; Stainier, Laurent ULg; Ponthot, Jean-Philippe ULg

in 7ème Colloque National en calcul des Structures (2005)

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See detailAnalyse numérique des tests expérimentaux à grande vitesse de déformation
Jeunechamps, Pierre-Paul ULg; Ponthot, Jean-Philippe ULg; BOUVIER, S. et al

in 7ème Colloque National en calcul des Structures (2005)

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See detailA variational framework for nonlinear viscoelastic and viscoplastic models in finite deformation regime
Stainier, Laurent ULg; FANCELLO, E.; Ponthot, Jean-Philippe ULg

in MECOM 2005, , Mecanica Computational (2005)

Detailed reference viewed: 29 (2 ULg)
See detailHeat generation due to friction and plastic dissipation – a coupled thermomechanical approach for impact and metal forming simulation
Adam, L.; Ponthot, Jean-Philippe ULg

in Proceedings of Int. Conf. on Computational Methods for Coupled Problems in Science and Engineering – COUPLED PROBLEMS 2005 (2005)

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See detailFinite element simulation of cold roll-forming processes
BUI, Q. V.; Ponthot, Jean-Philippe ULg

in ACOMEN 2005 (2005)

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See detailNumerical simulation of springback using enhanced assumed strain elements
Bui, Q. V.; Papeleux, Luc ULg; Ponthot, Jean-Philippe ULg

in Journal of Materials Processing Technology (2004), 153(1), 314-318

The quality of springback prediction for a sheet metal forming process depends on a precise estimate of the elasto-plastic stress distribution throughout the metal sheet. The use of low-order conventional ... [more ▼]

The quality of springback prediction for a sheet metal forming process depends on a precise estimate of the elasto-plastic stress distribution throughout the metal sheet. The use of low-order conventional finite elements may be, without any proper treatment, responsible for low quality prediction because of volumetric and shear lockings. In this study, the enhanced assumed strain technique will be exploited for locking removal. The quality of the numerical simulation is evaluated through a comparison with other popular techniques like selective and uniform reduced integration. In contrast to the latter, and thanks to a full numerical integration scheme, the enhanced assumed strain element is very efficient in accurately capturing the development of plastic flow. This enables a reliable prediction of springback even with a rather coarse mesh. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

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