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Analyse numérique des tests expérimentaux à grande vitesse de déformation Jeunechamps, Pierre-Paul ; Ponthot, Jean-Philippe ; et al in 7ème Colloque National en calcul des Structures (2005) Detailed reference viewed: 21 (4 ULg)A variational framework for nonlinear viscoelastic and viscoplastic models in finite deformation regime Stainier, Laurent ; ; Ponthot, Jean-Philippe in MECOM 2005, , Mecanica Computational (2005) Detailed reference viewed: 24 (2 ULg)Heat generation due to friction and plastic dissipation – a coupled thermomechanical approach for impact and metal forming simulation ; Ponthot, Jean-Philippe in Proceedings of Int. Conf. on Computational Methods for Coupled Problems in Science and Engineering – COUPLED PROBLEMS 2005 (2005) Detailed reference viewed: 81 (1 ULg)Finite element simulation of cold roll-forming processes ; Ponthot, Jean-Philippe in ACOMEN 2005 (2005) Detailed reference viewed: 29 (1 ULg)Numerical simulation of mixed lubrication in cold rolling using an object-oriented philosophy ; Ponthot, Jean-Philippe in ACOMEN 2005 (2005) Detailed reference viewed: 22 (1 ULg)Numerical simulation of springback using enhanced assumed strain elements ; Papeleux, Luc ; Ponthot, Jean-Philippe 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 ▲] Detailed reference viewed: 73 (14 ULg)Efficient algorithmic approach for mixed-lubrication in cold rolling ; Ponthot, Jean-Philippe ; et al in Journal of Materials Processing Technology (2004), 153(1), 307-313 A model of cold rolling taking into account lubrication in mixed mode was developed. The main objective is to obtain a numerical tool that permits us to optimise a mill configuration from the lubrication ... [more ▼] A model of cold rolling taking into account lubrication in mixed mode was developed. The main objective is to obtain a numerical tool that permits us to optimise a mill configuration from the lubrication point of view. It means that lubricant viscosity but also roll diameter and roughness, rolling diagrams, etc could be modified to improve stability and efficiency of the mill. A modified slab method is solved iteratively and is coupled with a sophisticated tribological model. A general calculation of the modified Reynolds equation is presented in order to evaluate the fluid pressure for any piezoviscosity law. The coupling is made through the calculation of fluid thickness and friction along the roll bite. The evolution of the cylinder/strip contact area due to the asperity crushing along the roll bite is also considered. A parametric study has been undertaken in order to determine the influence of various process parameters on friction and lubricant flow. Applications to industrial cases obtained from Cockerill Sambre plant will show the applicability of the method. (C) 2004 Elsevier B.V. All rights reserved. [less ▲] Detailed reference viewed: 43 (4 ULg)Finite Element Simulation of Lubricated Contact in Rolling using the Arbitrary Lagrangian-Eulerian Formulation Boman, Romain ; Ponthot, Jean-Philippe in Computer Methods in Applied Mechanics and Engineering (2004), 193(39-41), 4323-4353 In this paper, the lubrication problem in numerical simulation of forming processes is considered. Two efficient convection algorithms are presented in order to update the value stored at the Gauss points ... [more ▼] In this paper, the lubrication problem in numerical simulation of forming processes is considered. Two efficient convection algorithms are presented in order to update the value stored at the Gauss points during the Eulerian step of an arbitrary Lagrangian Eulerian computation in solid mechanics. They are based on the finite volume method and on the streamline upwind Petrov Galerkin method. After enumerating the difficulties encountered when trying to solve the lubrication problem with the finite element method, a generalization of the formulation introduced by Liu [Simulation of Ring Rolling Process by Arbitrary Lagrangian Eulerian Finite Element Method, vol. 20, p. 225; ASME Winter Meeting, Dallas, Tx, 1990, Int. J. Numer. Methods Engrg. 36 (1993) 855; Numerical Methods in Industrial Forming Processes, Valbonne, France, 1992, p. 731] for the thin film hydrodynamic lubrication regime is presented. This method is then applied to a strip rolling simulation, using the arbitrary Lagrangian Eulerian formalism. (C) 2004 Elsevier B.V. All rights reserved. [less ▲] Detailed reference viewed: 64 (11 ULg)Prédiction numérique de l’angle de surformage en profilage à froid Boman, Romain ; Papeleux, Luc ; Ponthot, Jean-Philippe Report (2004) Detailed reference viewed: 10 (3 ULg)Simulation of complex impact problems with implicit time algorithms: Application to a turbo - engine blade loss problem Noels, Ludovic ; ; Ponthot, Jean-Philippe Poster (2004, July) Detailed reference viewed: 13 (0 ULg)Combined implicit/explicit time-integration algorithms for the numerical simulation of sheet metal forming Noels, Ludovic ; Stainier, Laurent ; Ponthot, Jean-Philippe in Journal of Computational & Applied Mathematics (2004), 168(1-2, Sp. Iss. SI), 331-339 In order to simulate stamping processes, an explicit method, which is conditionally stable, is generally thought to be the most adapted. Such an algorithm presents the advantage of being noniterative ... [more ▼] In order to simulate stamping processes, an explicit method, which is conditionally stable, is generally thought to be the most adapted. Such an algorithm presents the advantage of being noniterative while, the contact configuration evolves rapidly, and the conditional stability is not a disadvantage since time steps must be small enough anyway for an accurate computation. But during the springback simulation, an implicit method, which is iterative, presents the advantage of unconditional stability. The optimal solution is then to have both implicit and explicit methods readily available in the same code and to be able to switch automatically from one to the other. Criteria that decide to switch from a method to another, depending on the current dynamic, have been developed. Implicit restarting conditions are also proposed that annihilate numerical oscillations resulting from an explicit calculation. (C) 2003 Elsevier B.V. All rights reserved. [less ▲] Detailed reference viewed: 54 (4 ULg)On the use of large time steps with an energy momentum conserving algorithm for non-linear hypoelastic constitutive models Noels, Ludovic ; Stainier, Laurent ; Ponthot, Jean-Philippe in International Journal of Solids and Structures (2004), 41(3-4), 663693 This paper presents an extension of the energy momentum conserving algorithm, developed by the authors for hypoelastic constitutive models. For such a material, contrarily to hyperelastic models, no ... [more ▼] This paper presents an extension of the energy momentum conserving algorithm, developed by the authors for hypoelastic constitutive models. For such a material, contrarily to hyperelastic models, no potential can be defined, and thus the conservation of the energy is ensured only if the elastic work of deformation can be restored by the scheme. In a previous paper, we proposed a new expression of internal forces at the finite element level which is shown to verify this property. We also demonstrated that the work of plastic deformation is positive and consistent with the material model. In this paper, the second order terms that were neglected in the previous work are now taken into account. Several numerical applications are presented to demonstrate the necessity of taking these terms into account once large time step sizes are used. The limitations of the Newmark algorithm in the non-linear range are also illustrated. (C) 2003 Elsevier Ltd. All rights reserved. [less ▲] Detailed reference viewed: 31 (2 ULg)Combined implicit/explicit algorithms for crashworthiness analysis Noels, Ludovic ; Stainier, Laurent ; Ponthot, Jean-Philippe in International Journal of Impact Engineering (2004), 30(8-9, SEP-OCT), 1161-1177 In order to simulate an industrial process, an explicit method, which is conditionally stable, is the most adapted while the non-linearities evolve rapidly (impact phase, stamping process, etc.). But when ... [more ▼] In order to simulate an industrial process, an explicit method, which is conditionally stable, is the most adapted while the non-linearities evolve rapidly (impact phase, stamping process, etc.). But when the dynamics becomes quasi-linear (post-impact analysis, springback simulation, etc.), an implicit method, which is iterative, presents the advantage of unconditional stability. The optimal solution is then to have both implicit and explicit methods readily available in the same code and to be able to switch automatically from one to the other. Criteria that decide to switch from one method to another, depending on the current dynamics, have been developed. Implicit restarting conditions are also proposed that annihilate numerical oscillations resulting from an explicit calculation. (C) 2004 Elsevier Ltd. All rights reserved. [less ▲] Detailed reference viewed: 49 (7 ULg)An energy-momentum conserving algorithm for non-linear hypoelastic constitutive models Noels, Ludovic ; Stainier, Laurent ; Ponthot, Jean-Philippe in International Journal for Numerical Methods in Engineering (2004), 59(1), 83-114 This paper presents an extension of the energy momentum conserving algorithm, usually developed for hyperelastic constitutive models, to the hypoelastic constitutive models. For such a material no ... [more ▼] This paper presents an extension of the energy momentum conserving algorithm, usually developed for hyperelastic constitutive models, to the hypoelastic constitutive models. For such a material no potential can be defined, and thus the conservation of the energy is ensured only if the elastic work of the deformation can be restored by the scheme. We propose a new expression of internal forces at the element level which is shown to verify this property. We also demonstrate that the work of plastic deformation is positive and consistent with the material model. Finally several numerical applications are presented. Copyright (C) 2003 John Wiley Sons, Ltd. [less ▲] Detailed reference viewed: 37 (5 ULg)A trust region algorithm for automatic identification of elasto-viscoplastic model parameters in metallurgical finite element model Jeunechamps, Pierre-Paul ; ; Duysinx, Pierre et al in Steel Grips 2 (2004), Supplement Metal Forming 2004 Simulation of manufacturing processes, here metal forming, has made major progresses during the last years. The virtual simulation of the manufacturing process being now quite well established, a natural ... [more ▼] Simulation of manufacturing processes, here metal forming, has made major progresses during the last years. The virtual simulation of the manufacturing process being now quite well established, a natural step ahead consists in trying to find automatic procedures to optimize it. Another perspective is also to take care of the influence of the manufacturing constraints upon the design, which is the long term objective of the present research project. It aims at optimizing the design subject to both service constraints (stiffness and strength) and manufacturing constraints. A preliminary stage is to be able to build high fidelity digital models. Complex models require more and more material parameters for behavior laws (e.g. material constitutive and friction laws), which have to be identified numerically from experimental data. In this material parameter identification process, three steps can be identified. At first, an experimental testing is carried out. The second step consists in building a simulation model of the experiment. Finally, the unknown model parameters are determined to match the experimental data. A standard identification procedure consists in minimizing a given norm (here the Euclidean norm) of the error between the model predictions and the experimental results. Even if the identification problem is generally quasi-unconstrained, it has the same complexity as structural optimization problems because of the highly nonlinear and implicit character of the functions, which is especially amplified by the large deformation simulation analysis. In this paper, we use an approach of elastoplastic calculation by finite elements combined with two optimization algorithms: a Levenberg-Marquardt algorithm, which is rather classical in the literature for solving identification problems (see [2]) and a trust-region one (see [1]), which is a rather novel approach at least for structural problems. The results obtained with these two methods are then compared and discussed on two test cases. The first application is an academic test case to validate the identification method. The second one, the compression of a cylinder, takes into account an actual experiment. In this application, the material is assumed to be elasto-viscoplastic and described by a Norton-Hoff behavior law and an isotropic strain hardening law. The parameters to be identified are the coefficients of the Norton-Hoff law. [less ▲] Detailed reference viewed: 54 (9 ULg)A Consistent Dissipative Time Integration Scheme for Structural Dynamics. Application to Rotordynamics. Noels, Ludovic ; Stainier, Laurent ; Ponthot, Jean-Philippe (2004) Recently, robust implicit energy and momentum conserving algorithms have been developed in the non-linear range. In previous works, the authors extended these algorithms to hypoelasticity-based ... [more ▼] Recently, robust implicit energy and momentum conserving algorithms have been developed in the non-linear range. In previous works, the authors extended these algorithms to hypoelasticity-based constitutive models. In this paper we introduce numerical dissipation, opening the way to more complex simulations such as blade-loss in a turbofan. [less ▲] Detailed reference viewed: 24 (2 ULg)Thermo-elasto-plastic modeling of the behaviour of metals submitted to finite strains. A coupled thermo-mechanical approach Ponthot, Jean-Philippe ; in Proceedings of ENIEF 2004, XIV Congress on numerical methods and their applications (2004) Detailed reference viewed: 9 (1 ULg)Analyse numérique des tests expérimentaux à grande vitesse de déformation sur des aciers dual phase Jeunechamps, Pierre-Paul ; Ponthot, Jean-Philippe ; in Colloque national MECAMAT 2005 (2004) Detailed reference viewed: 20 (1 ULg)Modeling the elastic-plastic behavior of a rotor support structure under a large unbalance: numerical simulations Stainier, Laurent ; ; Ponthot, Jean-Philippe in Proceedings of ISMA 2004, International Conference on Noise & Vibration Engineering (2004) Detailed reference viewed: 17 (2 ULg)Modeling and experimental validation of an industrial sheet metal forming process ; ; et al in Computational Mechanics, WCCM VI (2004) Detailed reference viewed: 5 (1 ULg) |
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