References of "Ponthot, Jean-Philippe"
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See detailNumerical modelling and experimental validation of steel deep drawing processes - Part II. Applications
Garcia, Claudio; Celentano, Diego; Flores, Fernando et al

in Journal of Materials Processing Technology (2006), 172(3), 461-471

This paper presents the modelling and experimental validation of three different deep drawing applications: the Erichsen test, a cylindrical cup test and an industrial sheet metal forming process. The ... [more ▼]

This paper presents the modelling and experimental validation of three different deep drawing applications: the Erichsen test, a cylindrical cup test and an industrial sheet metal forming process. The sheet forrning material considered in the study is the EK4 steel characterized in Part I of this work. A finite element analysis of the deformation process is performed with a large strain hyperelastic shell formulation including the Hill-48 associate plasticity model. The experimental validation of the results provided by the simulation encompasses the punch force evolution together with the in-plane principal deformations and thickness distributions of the final deformed part. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

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See detailSimulation of crashworthiness problems with improved contact algorithms for implicit time integration
Noels, Ludovic ULg; Stainier, Laurent ULg; Ponthot, Jean-Philippe ULg

in International Journal of Impact Engineering (2006), 32(5), 799-825

When studying crashworthiness problems, contact simulation can be the source of a number of problems. A first one is the discontinuities in the normal evolution for a boundary discretized by finite ... [more ▼]

When studying crashworthiness problems, contact simulation can be the source of a number of problems. A first one is the discontinuities in the normal evolution for a boundary discretized by finite elements. Another problem is the treatment of the contact forces that can introduce numerical energy in the system. In this paper, we propose to combine a method of discontinuity smoothing with the energy-momentum consistent scheme that recently appeared in the literature. (c) 2005 Elsevier Ltd. All rights reserved. [less ▲]

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See detailAn energy momentum conserving algorithm using the variational formulation of visco-plastic updates
Noels, Ludovic ULg; Stainier, Laurent ULg; Ponthot, Jean-Philippe ULg

in International Journal for Numerical Methods in Engineering (2006), 65(6), 904942

In this paper we use the variational formulation of elasto-plastic updates proposed by Ortiz and Stainier (Comput. Methods Appl. Mech. Eng. 1999; 171:419-444) in the context of consistent time integration ... [more ▼]

In this paper we use the variational formulation of elasto-plastic updates proposed by Ortiz and Stainier (Comput. Methods Appl. Mech. Eng. 1999; 171:419-444) in the context of consistent time integration schemes. We show that such a formulation is well suited to obtain a general expression Of energy momentum conserving algorithms. Moreover, we present numerical examples that illustrate the efficiency of our developments. Copyright (c) 2005 John Wiley [less ▲]

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See detailEnergy conserving balance of explicit time steps to combine implicit and explicit algorithms in structural dynamics
Noels, Ludovic ULg; Stainier, Laurent ULg; Ponthot, Jean-Philippe ULg

in Computer Methods in Applied Mechanics & Engineering (2006), 195(19-22), 21692192

Recent developments have proved the advantage of combining both time implicit and time explicit integration algorithms in structural dynamics. A major problem is to define the initial conditions for the ... [more ▼]

Recent developments have proved the advantage of combining both time implicit and time explicit integration algorithms in structural dynamics. A major problem is to define the initial conditions for the implicit simulation on the basis of a solution obtained from an unbalanced explicit resolution. The unbalanced nature of the explicit algorithm leads to oscillations in the fields of interest. Therefore, the values obtained after an explicit computation cannot be used directly as initial conditions for an implicit simulation. In this paper, we develop such initial values that lead to a stable (no numerical creation of energy) and energy-conserving transition. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

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See detailProblem and challenges of image-guided neurosurgical navigation and intervention
Verly, Jacques ULg; Kavec, Martin; Vigneron, Lara M. et al

Conference (2006)

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See detailA viscoelastic formulation for finite strains: application to brain soft tissues
FANCELLO, E.; Ponthot, Jean-Philippe ULg; VIGNERON, L. et al

in Proceedings of XXVII CILAMCE – Iberian Latin American Congress on Computational Methods in Engineering (2006)

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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)

Detailed reference viewed: 32 (5 ULg)