References of "Ponthot, Jean-Philippe"
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See detailAn overview of nonintrusive characterization, propagation, and sensitivity analysis of uncertainties in computational mechanics
Arnst, Maarten ULiege; Ponthot, Jean-Philippe ULiege

in International Journal for Uncertainty Quantification (2014), 4

In this paper, we offer a short overview of a number of methods that have been reported in the computational-mechanics literature for quantifying uncertainties in engineering applications. Within a ... [more ▼]

In this paper, we offer a short overview of a number of methods that have been reported in the computational-mechanics literature for quantifying uncertainties in engineering applications. Within a probabilistic framework, we describe the characterization of uncertainties using mathematical statistics methods, the propagation of uncertainties through computational models using either Monte Carlo sampling or stochastic expansion methods, and the sensitivity analysis of uncertainties using variance- and differentiation-based methods. We restrict our attention to nonintrusive methods that can be implemented as wrappers around existing computer programs, thus requiring no modification of the source code. We include some recent advances in the propagation and sensitivity analysis of uncertainties that are characterized by arbitrary probability distributions that may exhibit statistical dependence. Finally, we demonstrate the methods integrated in the proposed overview through a nonlinear engineering application relevant to metal forming. [less ▲]

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See detailThe influence of equivalent contact area computation in extended node to surface contact elements
Wautelet, Gaëtan ULiege; Ponthot, Jean-Philippe ULiege

in Key Engineering Materials [=KEM] (2014), 618

This article aims at extending the node to surface formulation for contact problems with an area regularization as proposed by [1]. For that purpose, two methods are proposed to compute the equivalent ... [more ▼]

This article aims at extending the node to surface formulation for contact problems with an area regularization as proposed by [1]. For that purpose, two methods are proposed to compute the equivalent contact area attributed to each slave node. The first method, which is based on a geometrical approach through force equivalence, is an original extension of the one proposed in [1] for two-dimensional contact problems, i.e. plane stress and plane strain state, to the axisymmetric modelling context. The second method relies on an energy consistent way obtained through the virtual work principle and the same expression for the equivalent contact area as the one originally cited in [2] is then recovered. First, the node to surface strategy with area regularization is introduced and the aforementioned methods for the equivalent contact area are presented in detail and compared. Afterwards a consistent linearization technique is applied to achieve a quadratic convergence rate in the Newton Raphson iterative procedure used to solve the non-linear equilibrium equations of the underlying finite element model. Finally, two axisymmetric numerical examples are provided in order to compare the aforementioned equivalent contact area evaluations and to demonstrate the performance and the robustness of the consistent approach especially in the neighbourhood the revolution axis. [less ▲]

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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 ULiege; Dialami, Narges; Boman, Romain ULiege et al

in Steel Research International (2014), 85(6), 968-979

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 neighborhood 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 behavior of the material in the neighborhood 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 detailEffect of the kinematic hardening in the simulations of the straightening of long rolled profiles
Bouffioux, Chantal ULiege; Boman, Romain ULiege; Caillet, Nicolas et al

in Key Engineering Materials [=KEM] (2014), 611-612

Residual stresses and lack of straightness appear during the cooling of sheet piles where the initial temperature field is not homogeneous. To meet the standards, the long hot rolled pieces are ... [more ▼]

Residual stresses and lack of straightness appear during the cooling of sheet piles where the initial temperature field is not homogeneous. To meet the standards, the long hot rolled pieces are straightened using a series of rollers placed alternately above and below the pieces with shifts which create a succession of bendings. The process is modeled to study the impact of the industrial parameters ( the duration of the cooling and the rollers positions), to improve the final geometry and to reduce the residual stresses.Tests are carried out on this structural steel to observe the material behavior, then material laws are chosen and parameters of these laws are defined using and inverse method. Two sets of material data are obtained: for the first one, the hardening is supposed to be isotropic, and for the second one, additional tests are performed to describe isotropic and kinematic hardenings.The cooling followed by the straightening is then simulated by the finite element with these two sets of date. The comparison of the rollers forces, the deformation and the residual stresses show the impact of the kinematic hardening on such a process where the material undergoes a sucession of the tensions and compressions. The real forces applied by the rollers,the real curvature of the interlocks at the end of the straightening process and the distribution of the residual longitudinal stresses measured on the web using the ring core method are used to validate the numerical model. [less ▲]

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See detailA one phase thermomechanical model for the numerical simulation of semi-solid material behavior. Application to thixoforming
Koeune, Roxane; Ponthot, Jean-Philippe ULiege

in International Journal of Plasticity (2014), 58

This work deals with the development of an appropriate constitutive model for semi-solid thixoforming processes of metallic alloys. These processes rely on a very specific material behavior called ... [more ▼]

This work deals with the development of an appropriate constitutive model for semi-solid thixoforming processes of metallic alloys. These processes rely on a very specific material behavior called thixotropy that can be displayed by some metallic alloys heated up to their semi-solid state. It is a particular evolutionary behavior which is characterized by a solidlike behavior at rest and a liquid flow during shearing, thus by a decrease of the viscosity and of the resistance to deformation while sheared. An original one-phase thermo-elasto-viscoplastic constitutive model has been developed. The basic idea is to extend the classical isotropic hardening and viscosity models beyond the solid state by considering two more non-dimensional internal scalar parameters. The semi-solid state is treated as a particular case, and one of the main features of the proposed constitutive model is that it remains valid over a wide range of temperatures, starting from room temperature to above the liquidus in a continuous manner, thus allowing a continuous transition between classical solid and fluid behavior. Another feature is that, after the forming step, it is possible to simulate the cooling down of the component back to room temperature using the elastic–viscoplastic model. So it is possible to estimate residual stresses, something that is definitely impossible while using a fluid-like model or a rigid viscoplastic approach. The presented model is illustrated and validated by means of representative numerical applications, as two different extrusion tests are carried out and the computed predictions are compared to experimental results. [less ▲]

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See detailNumerical simulation and Visualization of Material Flow in Friction Stir Welding via Particle Tracing
Dialami, Narges; Chiumenti, Michele; Cervera, Miguel et al

in Idelsohn, Sergio (Ed.) Numerical Simulations of Coupled Problems in Engineering (2014)

This work deals with the numerical simulation and material flow visualization of Friction Stir Welding (FSW) processes. The fourth order Runge- Kutta (RK4) integration method is used for the computation ... [more ▼]

This work deals with the numerical simulation and material flow visualization of Friction Stir Welding (FSW) processes. The fourth order Runge- Kutta (RK4) integration method is used for the computation of particle trajectories. The particle tracing method is used to study the effect of input process parameters and pin shapes on the weld quality. The results show that the proposed method is suitable for the optimization of the FSW process. [less ▲]

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See detailThermoviscoplasticity at Finite Strains: A Thermoelastic Predictor-Viscoplastic Corrector Algorithm
Ponthot, Jean-Philippe ULiege; Papeleux, Luc ULiege

in Hetnarski, Richard B. (Ed.) Encyclopedia of Thermal Stresses (2014)

This contribution aims at describing the numerical background associated to an efficient time integration procedure for thermomechanical elastic-viscoplastic constitutive model in a large deformation ... [more ▼]

This contribution aims at describing the numerical background associated to an efficient time integration procedure for thermomechanical elastic-viscoplastic constitutive model in a large deformation context. First, from the continuum mechanics point of view, the constitutive model is established. Within the framework of viscoplasticity, we have tried to remain as general as possible and the presented model encompasses under the same unified format, both {\it Perzyna-Chaboche} model of viscoplasticity which is well suited for moderate strain rates, as well as {\it Johnson-Cook} model which is a reference for metals submitted to high strain rates. Both incorporate nonlinear isotropic and kinematic hardening models. The classical rate-independent elastic-plastic model can then be easily recovered by setting the viscous terms to zero. Second, as the resulting continuum model is a stiff first order ordinary differential system in time, an integration algorithm is presented. This algorithm generalizes the classical "radial return algorithm", well established for elasto-plasticity, to thermo-elastic-viscoplastic models. The differential equations are numerically integrated using a thermoelastic predictor-viscoplastic corrector algorithm. The resulting algorithm is once again quite general and contains as special cases isothermal viscoplastic cases as well as classical rate-independent plasticity. Thanks to that generality, only one unified algorithm can be used both for plastic (rate-independent) as well as viscoplastic (rate-dependent) material models. Besides, in the formulation, a special care has also been taken so that all material parameters, including thermal dilatation, can be temperature dependent. As a consequence, it is also possible to model a continuous transition from elevated temperatures (that require the use of a viscoplastic model) to room temperature where rate-independent models are sometimes better suited by using a temperature-dependent viscosity that goes to zero as the room temperature is approached. [less ▲]

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

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 ULiege; Boman, Romain ULiege; Jeunechamps, Pierre-Paul et al

in Proceedings of the 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 ULiege; Ponthot, Jean-Philippe ULiege

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 ULiege; Boman, Romain ULiege; 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 ULiege; Koeune, Roxane; Ponthot, Jean-Philippe ULiege

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 ULiege; Dialami, Narges; Boman, Romain ULiege 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 ULiege; Ponthot, Jean-Philippe ULiege

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 detailA bone remodeling model for long term orthodontic tooth movement.
Mengoni, Marlène ULiege; Ponthot, Jean-Philippe ULiege

Conference (2013, January)

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

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

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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