References of "Ponthot, Jean-Philippe"
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See detailApplication of the Arbitrary Lagrangian Eulerian Formulation to the Numerical Simulation of Cold Roll Forming Process
Boman, Romain ULg; Papeleux, Luc ULg; Bui, Quoc Viet et al

in Journal of Materials Processing Technology (2006), 177(1-3), 621-625

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 to keep 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 to keep a refined mesh near the tools, thus allowing accurate contact prediction all along the computation with a limited number of elements. Mesh can also be kept refined in the bending zone, thus leading to accurate representation of the sheet with a limited computational time. The main problem of this kind of simulation lies in 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. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

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See detailSpringback and Twist Prediction of Roll Formed Parts
Viet, Bui Quoc; Boman, Romain ULg; Papeleux, Luc ULg et al

in Santos, Abel D.; Barata da Rocha, A. (Eds.) Proceedings of the IDDRG 2006 International Deep Drawing Research Group, Drawing the things to come, Trends and Advances in Sheet Metal Forming (2006, June)

In the construction market, Roll Forming is the reference forming process. Numerous parts are achieved in such a way: purlins, steeldecks or suspended ceiling parts are examples of it. Roll Forming is ... [more ▼]

In the construction market, Roll Forming is the reference forming process. Numerous parts are achieved in such a way: purlins, steeldecks or suspended ceiling parts are examples of it. Roll Forming is also more and more used in the automotive industry, as it constitutes a good alternative to forming for High Strength Steels. Among the major requirements to obtain a defect-free product are outlined: the accurate geometry of the part, the taking into account of the springback as well as the prediction of twist. Furthermore, the roll forming operation could be only the first forming operation: the part could be curved or locally deep drawn afterwards. FE codes could allow fulfilling these requirements. However, they need significant advances in terms of material model description and numerical development. This paper presents the work done in order to predict the geometry and the behaviour of a roll formed part: First the material is characterized in complex strain paths in order to identify elaborated microstructural model like Teodosiu’s one. This model is able to take into account Bauschinger effect, orthogonal strain paths, isotropic/kinematic hardening. The METAFOR code is then used to have a better understanding of the mechanics of the deformation of the strip during the forming process. Several experimental campaigns were performed on the I-R&D ARCELOR roll forming machine to define a strong database in order to validate the numerical results. The geometry of machine as well as the shape of the channels inside and outside the RF machine were measured. Some experiments were even carried out in order to generate defects like twist in the roll formed profile. [less ▲]

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See detailA 3D Arbitrary Lagrangian Eulerian Formulation for the Numerical Simulation of Forming Processes. Application to cold roll forming and metal cutting
Boman, Romain ULg; Papeleux, Luc ULg; Viet, Bui Quoc et al

in Mota Soares, C. A. (Ed.) Proceedings of ECCM 2006, III European Conference on Computational Mechanics, Solids, Structures and Coupled Problems in Engineering (2006, June)

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See detailA closed form technique to predict springback in creep age-forming
Jeunechamps, Pierre-Paul ULg; Ho, K. C.; Lin, J. et al

in International Journal of Mechanical Sciences (2006), 48(6), 621-629

An efficient numerical method has been developed and programmed to predict springback in creep age-forming (CAF) of alummium shell components. Physically based unified creep-ageing constitutive equations ... [more ▼]

An efficient numerical method has been developed and programmed to predict springback in creep age-forming (CAF) of alummium shell components. Physically based unified creep-ageing constitutive equations determined for AA7010 at 150 degrees C are used to evaluate age-hardening and creep deformation in CAF processes. The studies are mainly concentrated on the pure bending of aluminium plates. Effects of plate thickness, single and double curvature bending, ageing time and stress relaxation features on springback are investigated. It is shown that the proposed algorithm can predict springback accurately and gives a relationship between geometrical data and springback. (c) 2006 Elsevier Ltd. All rights reserved. [less ▲]

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See detailA variational formulation of constitutive models and updates in non-linear finite viscoelasticity
Fancello, Eduardo; Ponthot, Jean-Philippe ULg; Stainier, Laurent ULg

in International Journal for Numerical Methods in Engineering (2006), 65(11), 1831-1864

The purpose of this article is to present a general framework for constitutive viscoelastic models in finite strain regime. The approach is qualified as variational since the constitutive updates obey a ... [more ▼]

The purpose of this article is to present a general framework for constitutive viscoelastic models in finite strain regime. The approach is qualified as variational since the constitutive updates obey a minimum principle within each load increment. The set of internal variables is strain-based and employs, according to the specific model chosen, a multiplicative decomposition of strain into elastic and viscous components. The present approach shares the same technical procedures used for analogous models of plasticity or viscoplasticity, such as the Solution of a minimization problem to identify inelastic updates and the use of exponential mapping for time integration. However. instead of using the classical decomposition of inelastic strains into amplitude and direction, we take advantage of a spectral decomposition that provides additional facilities to accommodate, into simple analytical expressions, a wide set of specific models. Moreover, appropriate choices of the constitutive potentials allow the reproduction of other formulations in the literature. The final part of the paper presents a set of numerical examples in order to explore the characteristics of the formulation as well as its applicability to usual large-scale FEM analyses. Copyright (c) 2005 John Wiley [less ▲]

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See detailNumerical modelling and experimental validation of steel deep drawing processes - Part I. Material characterization
Garcia, Claudio; Celentano, Diego; Flores, F. et al

in Journal of Materials Processing Technology (2006), 172(3), 451-460

This work presents an experimental characterization of the mechanical behaviour of the EK4 deep drawing steel. The experimental procedure encompasses spectrometry, rnetalography, tension testing and ... [more ▼]

This work presents an experimental characterization of the mechanical behaviour of the EK4 deep drawing steel. The experimental procedure encompasses spectrometry, rnetalography, tension testing and hardness measurements. Special attention is devoted to the derivation of the elastic and plastic parameters involved in the assumed constitutive model based on the anisotropic Hill-48 yield criterion. The simulation of the deformation process during the whole tensile test is subsequently performed with the aim of assessing the adequateness of the proposed methodology. It should be mentioned that the material parameters obtained with this procedure are the basic data for the modelling and experimental validation of different deep drawing applications presented in Part II of this work. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

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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 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 detailNumerical simulation in cold rolling using adiabatic strip model : application to large roll deformation
Stephany, Antoine; Ponthot, Jean-Philippe ULg; Legrand, N.

in AUSTRIB 06 (2006)

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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, Eduardo; Ponthot, Jean-Philippe ULg; Vigneron, Laura et al

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

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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 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 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 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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