References of "Ponthot, Jean-Philippe"
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See detailArbitrary Lagrangian Eulerian simulations of stationary and non-stationary metal forming processes
Boman, Romain ULg; Ponthot, Jean-Philippe ULg

in AIP Conference Proceedings (2013, December 16), 1567

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See detailAn implicit erosion algorithm for the numerical simulation of metallic and composite materials submitted to high strain rate.
Ponthot, Jean-Philippe ULg; Boman, Romain ULg; Jeunechamps, Pierre-Paul et al

in Proceedings Indian National Science Academy (2013), 79/4(Part A), 519-528

In this paper, we present a general consistent numerical formulation able to take into account strain rate, damage and thermal effects of the material behaviour. A thermomechanical implicit approach for ... [more ▼]

In this paper, we present a general consistent numerical formulation able to take into account strain rate, damage and thermal effects of the material behaviour. A thermomechanical implicit approach for element erosion to model material failure is also presented. This approach can be applied both to ductile fracture for metals, relying on a continuum damage mechanics approach, coupled to different fracture criteria, as well as composite material failure described with either a failure criterion or a progressive damage model. The numerical models will be illustrated by different quasi-static and high strain rate applications for both metallic alloys and composite materials. All these physical phenomena have been included in an implicit dynamic object-oriented finite element code (implemented at LTAS-MN²L, University of Liège, Belgium) named Metafor [1]. [less ▲]

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See detailA probabilistic characterization, propagation, and sensitivity analysis of uncertainties in a metal forming application
Arnst, Maarten ULg; Ponthot, Jean-Philippe ULg

Conference (2013, September 05)

In metal forming processes, after leaving the tooling, formed pieces of metal have a tendency to partially return to their original shape because of their elastic recovery. This phenomenon, referred to as ... [more ▼]

In metal forming processes, after leaving the tooling, formed pieces of metal have a tendency to partially return to their original shape because of their elastic recovery. This phenomenon, referred to as the springback, is quite complex and depends not only on material properties such as Young's modulus and yield stress but also on many process parameters such as sheet thickness and bending angles. The springback is difficult to predict and is a major quality concern in forming processes because when the springback is smaller or larger than expected, it can cause serious problems to subsequent assembly processes due to geometry mismatches. In this communication, we present a probabilistic analysis of a metal forming application. We consider the bending of a metal sheet with uncertain elastoplastic material properties. First, we use methods from mathematical statistics to obtain a probabilistic characterization of the elastoplastic material properties from data. Next, we map this probabilistic representation of the elastoplastic material properties into a probabilistic representation of the deformed shape of the metal sheet through a mechanical model implemented using the Metafor software. Finally, we conduct a stochastic sensitivity analysis to determine which elastoplastic material properties are most influential in driving uncertainty in the deformed shape after the springback. Our probabilistic analysis involves so called nonintrusive methods, that is, methods that can be implemented as wrappers around the Metafor software without requiring modification of its source code. Further, it includes recent methods for the propagation and sensitivity analysis of uncertainties characterized by arbitrary probability distributions that may exhibit statistical dependence. [less ▲]

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See detailNumerical simulations of asperity crushing using boundary conditions encountered in cold-rolling
Carretta, Yves ULg; Boman, Romain ULg; Legrand, Nicolas et al

in Key Engineering Materials [=KEM] (2013), 554-557

Asperity flattening has a huge influence on friction and wear in metal forming processes. Nevertheless, phenomena that occur at the microscopic scale are still not well understood. Since no experiment can ... [more ▼]

Asperity flattening has a huge influence on friction and wear in metal forming processes. Nevertheless, phenomena that occur at the microscopic scale are still not well understood. Since no experiment can be easily performed in real forming conditions, numerical models are essential to achieve a better knowledge of what happens in these contact regions. In this paper, two finite elements models are presented. The first one represents the flattening of a serrated asperity field in plane-strain conditions. The results are compared to the experiments published by Sutcliffe [1]. The second one is a tri-dimensional asperity model flattened by a rigid plane. The boundary conditions applied to this model correspond to the ones encountered in a real cold-rolling case. The results are compared to the relative contact area computed by a strip rolling model using the analytical laws proposed by Wilson & Sheu [2] and Marsault [3]. [less ▲]

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See detailNumerical Simulation of Double Cup Extrusion Test using the Arbitrary Lagrangian Eulerian Formalism
Boman, Romain ULg; Koeune, Roxane; Ponthot, Jean-Philippe ULg

in Proceedings of Coupled Problems 2013 (2013, June)

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See detailComparison of a fluid and a solid approach for the numerical simulation of Friction Stir Welding with a non-cylindrical pin
Bussetta, Philippe ULg; Dialami, Narges; Boman, Romain ULg et al

in Proceedings of "V International Conference on Computational Methods for Coupled Problems in Science and Engineering" (2013, June)

Friction Stir Welding (FSW) process is a solid-state joining process during which materials to be joined are not melted. As a consequence, the heat-affected zone is smaller and the quality of the weld is ... [more ▼]

Friction Stir Welding (FSW) process is a solid-state joining process during which materials to be joined are not melted. As a consequence, the heat-affected zone is smaller and the quality of the weld is better with respect to more classical welding processes. Because of extremely high strains in the neighbourhood of the tool, classical numerical simulation techniques have to be extended in order to track the correct material deformations. The Arbitrary Lagrangian Eulerian (ALE) formulation is used to preserve a good mesh quality throughout the computation. With this formulation the mesh displacement is independent from the material displacement. Moreover, some advanced numerical techniques such as remeshing or a special computation of transition interface is needed to take into account non-cylindrical tools. During the FSW process, the behaviour of the material in the neighbourhood of the tool is at the interface between solid mechanics and fluid mechanics. Consequently, a numerical model of the FSW process based on a solid formulation is compared to another one based on a fluid formulation. It is shown that these two formulations essentially deliver the same results in terms of pressures and temperatures. [less ▲]

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See detailEnhanced ALE Data Transfer Strategy for Explicit and Implicit Thermomechanical Simulations of High-Speed Processes
Boman, Romain ULg; Ponthot, Jean-Philippe ULg

in International Journal of Impact Engineering (2013), 53

The Arbitrary Lagrangian Eulerian (ALE) formalism, which allows the computational grid to move regardless of thematerial deformation, is a convenient way to avoid distortedmeshes in finite element ... [more ▼]

The Arbitrary Lagrangian Eulerian (ALE) formalism, which allows the computational grid to move regardless of thematerial deformation, is a convenient way to avoid distortedmeshes in finite element simulations. One crucial step of the ALE algorithm is the data transfer between the Lagrangian and the Eulerian meshes. In this paper, an enhanced transfer method is presented. It can handle complex finite elements which are integrated with more than one Gauss point. This method can thus be used either with an explicit or with an implicit time integration scheme. Choosing the adequate order of accuracy and the most appropriate number of physical fields to be transferred is always a compromise between the speed and the precision of the model. For example, some variables may be sometimes ignored during the transfer in order to decrease the CPU time. Therefore, the most effective way to use such an algorithm is demonstrated in this work by revisiting a classical ALE benchmark, the Taylor impact. An implicit thermomechanical ALE simulation of a high-speed tensile test is also presented and is compared to experimental results from the literature. [less ▲]

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See detailThe Impact of Surface Higher Order Differentiability in Two-dimensional Contact Elements
Nguyen, Duc Tue ULg; RAUCHS, Gast; Ponthot, Jean-Philippe ULg

in Journal of Computational & Applied Mathematics (2013), 246

The aim of this work is to propose new contact elements of higher order of differentiability for analysing two-dimensional frictionless contact problems. Several methods were proposed in the literature to ... [more ▼]

The aim of this work is to propose new contact elements of higher order of differentiability for analysing two-dimensional frictionless contact problems. Several methods were proposed in the literature to solve the problem caused by the lack of continuity resulting from the discretization. Among them are Bézier interpolation, Hermitian interpolation and splines. One of the difficulties in using Hermitian interpolation is to verify the partition of unity. Therefore, new elements that satisfy the C1 and C2 continuity at the interface are presented in this paper. These new contact elements are based on Hermitian polynomials for ensuring a higher order of continuity. The advantage is that this approach can be easily developed not only for linear elements but also for quadratic elements with higher order of differentiability. The performance of different surface representations is assessed through a comparison with a C0 surface discretization. Some numerical examples are used for assessing the accuracy and the convergence behaviour [less ▲]

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See detailNumerical simulation of finite strain viscoplastic problems
Garcia-Garino, Carlos; Andia fages, Susana; Mirasso, Anibal et al

in Journal of Computational & Applied Mathematics (2013), 246

A large strain elastoplastic constitutive model based on hyperelasticity and multiplicative decomposition of deformation gradient tensor is extended to viscous case, in a framework similar to the one that ... [more ▼]

A large strain elastoplastic constitutive model based on hyperelasticity and multiplicative decomposition of deformation gradient tensor is extended to viscous case, in a framework similar to the one that has been proposed by Ponthot in an hypoelastic context. In this way a very useful framework can be obtained, able to deal with both rate dependent and rate independent problems. In this work a review of theoretical details and numerical implementation of the model are discussed. Similarly to what is done in rate independent plasticity, a Newton–Raphson scheme has been used to solve the non linear consistency condition in order to compute the viscoplastic multiplier. A plane strain plate with a central circular hole under tension is simulated in order to test the proposed model. Large deformation effects are considered in all the simulations carried out. Different parameters of the constitutive model are varied in order to study the sensitivity of the proposed algorithm. [less ▲]

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See detailSubject-specific finite element modelling of canine long bones up to fracture
Laurent, Cédric; Bohme, Béatrice; d'Otreppe de Bouvette, Vinciane et al

in Computer Methods in Biomechanics and Biomedical Engineering. Imaging & Visualization (2013), 16

Long bone fracture constitutes a common reason for medical consultation within veterinary orthopaedic services. Owing to the specificities of the veterinary field, post-operative complications after a ... [more ▼]

Long bone fracture constitutes a common reason for medical consultation within veterinary orthopaedic services. Owing to the specificities of the veterinary field, post-operative complications after a fracture osteosynthesis are usually more numerous than those in human medicine, and therefore, there is a need to better understand which orthopaedic device(s) should be preferred for a given fracture. The interest of subjectspecific finite element (FE) simulations in the understanding of long bone mechanics has been largely emphasised (Helgason et al. 2008; Schileo et al. 2008). However, available studies are often limited by the many assumptions made throughout the procedure of creating a validated subject-specific FE model of a long bone, including geometry acquisition and modelling, assignment of realistic material properties and accurate validation of FE results based on ex vivo experiments. Particularly, fracture prediction has often been limited to the fracture onset prediction based on arbitrary criteria. Based on these previous studies, the objective of the present contribution is to propose and compare different subject-specific FE models of long bones that could accurately predict long bone response and failure. [less ▲]

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See detailAn efficient 3D implicit approach for the thermomechanical simulation of elastic–viscoplastic materials submitted to high strain rate and damage
Jeunechamps, Pierre-Paul; Ponthot, Jean-Philippe ULg

in International Journal for Numerical Methods in Engineering (2013), 94

This paper aims at presenting a general consistent numerical formulation able to take into account, in a coupled way, strain rate, thermal and damage effects on the behavior of materials submitted to ... [more ▼]

This paper aims at presenting a general consistent numerical formulation able to take into account, in a coupled way, strain rate, thermal and damage effects on the behavior of materials submitted to quasistatic or dynamic loading conditions in a large deformation context. The main features of this algorithmic treatment are as follows: -A unified treatment for the analysis and implicit time integration of thermo-elasto-viscoplastic constitutive equations including damage that depends on the strain rate for dynamic loading conditions. This formalism enables us to use dynamic thermomechanically coupled damage laws in an implicit framework. -An implicit framework developed for time integration of the equations of motion. An efficient staggered solution procedure has been elaborated and implemented so that the inertia and heat conduction effects can be properly treated. - An operator split-based implementation, accompanied by a unified method to analytically evaluate the consistent tangent operator for the (implicit) coupled damage–thermo-elasto-viscoplastic problem. -The possibility to couple any hardening law, including rate-dependent models, with any damage model that fits into the present framework. All the developments have been considered in the framework of an implicit finite element code adapted to large strain problems. The numerical model will be illustrated by several applications issued from the impact andmetal-forming domains. All these physical phenomena have been included into an oriented object finite element code (implemented at LTAS-MN2L, University of Liège, Belgium) named Metafor. [less ▲]

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See detailModeling thixoforming process using the eXtended Finite Element Method and the Arbitrary Lagrangian Eulerian formulation
Biotteau, Ewen; Bussetta, Philippe ULg; Ponthot, Jean-Philippe ULg

in Key Engineering Materials [=KEM] (2013), 554-557

In this contribution, one proposes a new strategy to model forming processes involving non-linear phenomena. The contact between the tool and the structure is enforced using a penalty approach. To free ... [more ▼]

In this contribution, one proposes a new strategy to model forming processes involving non-linear phenomena. The contact between the tool and the structure is enforced using a penalty approach. To free the user from the strict conforming between the structure and the mesh boundaries, one uses the level set and the extended finite element method for material/void interfaces. However, even if the finite element mesh does not need to conform with the boundaries, it still deforms with the structure. Then, an Arbitrary Lagrangian Eulerian formulation is introduced to relocate the mesh in its initial configuration and avoid distortions. From a user point of view, the whole calculation is then performed on a fixed Eulerian mesh. [less ▲]

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See detailA continuous fluid/solid transition model for semi-solid material modeling. Application to thixoforging.
Ponthot, Jean-Philippe ULg; Koeune, Roxane; Boman, Romain ULg

in 33° SENAFOR (CD) (2013)

This paper deals with the simulation of two extrusion tests by thixoforming: a non stationary extrusion test and a double-cup extrusion test. The simulations are based on a thermo-mechanical one-phase ... [more ▼]

This paper deals with the simulation of two extrusion tests by thixoforming: a non stationary extrusion test and a double-cup extrusion test. The simulations are based on a thermo-mechanical one-phase constitutive law that has been presented in details in several previous papers. A campaign of experimental extrusion testing has been conducted on a steel alloy and the comparison between the numerical and experimental results will validate the model under study. A new feature that has been added to the model is also discussed: the introduction of the phase change thermal effects such as the fusion latent heat and the contraction of the material [less ▲]

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See detailA Thermomechanical Model Dedicated to Thixoforming. Application to Semi-Solid Forming
Koeune, Roxane; Ponthot, Jean-Philippe ULg

in Solid State Phenomena (2013), 192-193

This paper deals with the simulation of two extrusion tests by thixoforming: a non stationary extrusion test and a double-cup extrusion test. The simulations are based on a thermo-mechanical one-phase ... [more ▼]

This paper deals with the simulation of two extrusion tests by thixoforming: a non stationary extrusion test and a double-cup extrusion test. The simulations are based on a thermo-mechanical one-phase constitutive law that has been presented in details in previous papers. A campaign of experimental extrusion testing has been conducted on a steel alloy and the comparison between the numerical and experimental results will validate the model under study. A new feature that has been added to the model is also discussed: the introduction of the phase change thermal effects such as the fusion latent heat and the contraction of the material [less ▲]

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See detailImplicit 2D Numerical Simulation of Materials Submitetd to High Strain Rates including Fracture
Jeunechamps, Pierre-Paul; Ponthot, Jean-Philippe ULg

in Key Engineering Materials [=KEM] (2013), 535-536

In this paper, we present a general consistent numerical formulation able to take into account strain rate and thermal effects of the material behavior. A thermomechanical implicit approach for element ... [more ▼]

In this paper, we present a general consistent numerical formulation able to take into account strain rate and thermal effects of the material behavior. A thermomechanical implicit approach for element erosion to model material failure is also presented. The numerical model will be illustrated by applications both from the metal forming and the impact domain. All these physical phenomena have been included in an implicit dynamic oriented object finite element code (implemented at LTAS-MN²L, University of Liège, Belgium) named Metafor [less ▲]

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See detailEfficient ALE mesh management for 3D quasi-Eulerian problems
Boman, Romain ULg; Ponthot, Jean-Philippe ULg

in International Journal for Numerical Methods in Engineering (2012), 92(10), 857-890

In computational solid mechanics, the ALE formalism can be very useful to reduce the size of finite element models of continuous forming operations such as roll forming. The mesh of these ALE models is ... [more ▼]

In computational solid mechanics, the ALE formalism can be very useful to reduce the size of finite element models of continuous forming operations such as roll forming. The mesh of these ALE models is said to be quasi-Eulerian because the nodes remain almost fixed—or almost Eulerian—in the main process direction, although they are required to move in the orthogonal plane in order to follow the lateral displacements of the solid. This paper extensively presents a complete node relocation procedure dedicated to such ALE models. The discussion focusses on quadrangular and hexahedral meshes with local refinements. The main concern of this work is the preservation of the geometrical features and the shape of the free boundaries of the mesh. With this aim in view, each type of nodes (corner, edge, surface and volume) is treated sequentially with dedicated algorithms. A special care is given to highly curved 3D surfaces for which a CPU-efficient smoothing technique is proposed. This new method relies on a spline surface reconstruction, on a very fast weighted Laplacian smoother with original weights and on a robust reprojection algorithm. The overall consistency of this mesh management procedure is finally demonstrated in two numerical applications. The first one is a 2D ALE simulation of a drawbead, which provides similar results to an equivalent Lagrangian model yet is much faster. The second application is a 3D industrial ALE model of a 16-stand roll forming line. In this case, all attempts to perform the same simulation by using the Lagrangian formalism have been unsuccessful. [less ▲]

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See detailThree-dimensional Modelling of Asperity Crushing
Carretta, Yves ULg; Boman, Romain ULg; Legrand, Nicolas et al

Conference (2012, October)

Asperity flattening has a huge influence on friction and wear in metal forming processes. Nevertheless, phenomena that occur at the microscopic scale are still not well understood. Since no experiment can ... [more ▼]

Asperity flattening has a huge influence on friction and wear in metal forming processes. Nevertheless, phenomena that occur at the microscopic scale are still not well understood. Since no experiment can be easily performed in real forming conditions, numerical models are essential to achieve a better knowledge of what happens in these contact regions. In this paper, a threedimensional model of a rough strip flattened by a rigid rough tool is presented. The boundary conditions applied to this model correspond to the ones encountered in a real cold-rolling case. The results are compared to experimental measurements from the pilot mill of ArcelorMittal Maizières R&D. [less ▲]

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See detailArbitrary Lagrangian Eulerian Modelling of Tension Levelling
Boman, Romain ULg; Parrico, Anthony; Legrand, Nicolas et al

in Matériaux et Techniques (2012, October), 100(Hors série 2012), 40-42

This paper presents a two-dimensional model of tension levelling using the Arbitrary Lagrangian Eulerian (ALE) approach. During the simulation, the ALE mesh remains globally fixed along the rolling ... [more ▼]

This paper presents a two-dimensional model of tension levelling using the Arbitrary Lagrangian Eulerian (ALE) approach. During the simulation, the ALE mesh remains globally fixed along the rolling direction. Therefore, the required number of finite elements is much smaller than in the Lagrangian case and smaller CPU times are obtained for the same accuracy on the results. The ALE model is first validated against a classical equivalent Lagrangian model. Then, both sets of numerical results are compared to experimental measurements from the pilot mill of ArcelorMittal Maizières R&D. [less ▲]

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