References of "Ponthot, Jean-Philippe"
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See detailA generic anisotropic continuum damage model integration scheme adaptable to both ductile damage and biological damage-like situations
Mengoni, Marlène ULg; Ponthot, Jean-Philippe ULg

in International Journal of Plasticity (in press)

This paper aims at presenting a general versatile time integration scheme applicable to anisotropic damage coupled to elastoplasticity, considering any damage rate and isotropic hardening formulations ... [more ▼]

This paper aims at presenting a general versatile time integration scheme applicable to anisotropic damage coupled to elastoplasticity, considering any damage rate and isotropic hardening formulations. For this purpose a staggered time integration scheme in a finite strain framework is presented, together with an analytical consistent tangent operator. The only restrictive hypothesis is to work with an undamaged isotropic material, assumed here to follow a J2 plasticity model. The only anisotropy considered is thus a damage-induced anisotropy. The possibility to couple any damage rate law with the present algorithm is illustrated with a classical ductile damage model for aluminium, and a biological damage-like application. The later proposes an original bone remodelling law coupled to trabecular bone plasticity for the simulation of orthodontic tooth movements. All the developments have been considered in the framework of the implicit non-linear finite element code Metafor (developed at the LTAS/MN2L, University of Liège, Belgium - www.metafor.ltas.ulg.ac.be). [less ▲]

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See detailAn enhanced version of a bone remodelling model based on the continuum damage mechanics theory.
Mengoni, Marlène ULg; Ponthot, Jean-Philippe ULg

in Computer Methods in Biomechanics & Biomedical Engineering (in press)

The purpose of this work is to propose an enhancement of Doblaré and García's internal bone remodelling model based on the continuum damage mechanics theory. In their paper, they stated that the evolution ... [more ▼]

The purpose of this work is to propose an enhancement of Doblaré and García's internal bone remodelling model based on the continuum damage mechanics theory. In their paper, they stated that the evolution of the internal variables of the bone microstructure, and its incidence on the modification of the elastic constitutive parameters, may be formulated following the principles of Continuum Damage Mechanics, although no actual damage was considered. The resorption and apposition criteria (similar to the damage criterion) were expressed in terms of a mechanical stimulus. However, the resorption criterion is lacking a dimensional consistency with the remodelling rate. We here propose an enhancement to this resorption criterion, insuring the dimensional consistency while retaining the physical properties of the original remodelling model. We then analyse the change in the resorption criterion hypersurface in the stress space for a 2D analysis. We finally apply the new formulation to analyse the structural evolution of a 2D femur. This analysis gives results consistent with the original model but with a faster and more stable convergence rate. [less ▲]

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See detailMicro-plasto-hydrodynamic lubrication: a fundamental mechanism in cold rolling
Laugier, Maxime; Boman, Romain ULg; Legrand, Nicolas et al

in Advanced Materials Research (2014), 966-967

Micro Plasto-Hydrodynamic (MPH) lubrication is a general mechanism in metal forming that consists in a re-lubrication of tool-piece solid contacts by an outflow of lubricant from pressurized “pockets” ... [more ▼]

Micro Plasto-Hydrodynamic (MPH) lubrication is a general mechanism in metal forming that consists in a re-lubrication of tool-piece solid contacts by an outflow of lubricant from pressurized “pockets” promoted by the plastic deformation. MPH lubrication is one of the main sources of friction variation (e.g. uncontrolled friction) in metal forming processes like strip drawing or cold rolling. This paper presents experimental results giving evidence of the MPH lubrication mechanism in cold rolling and a new lubrication model that predicts for strip drawing conditions MPH lubrication initiation and lubricant extension along the solid contacts initially in boundary condition. This MPH model could be implemented in a cold rolling model soon to help in high strength steels developments on cold rolling mills. [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 Idelsohn, Sergio R. (Ed.) Numerical Simulations of Coupled Problems in Engineering (2014)

In this chapter Double Cup Extrusion Test (DCET) is modelled using the finite element method with the help of the Arbitrary Lagrangian Eulerian (ALE) formalism. DCET is a tribological test involving very ... [more ▼]

In this chapter Double Cup Extrusion Test (DCET) is modelled using the finite element method with the help of the Arbitrary Lagrangian Eulerian (ALE) formalism. DCET is a tribological test involving very large deformations which are traditionally dealt with complicated and costly remeshing algorithms. Since the topology of ALE meshes should remain constant throughout the simulation, twovery thin layers of auxiliary elements are added to the initial mesh of the billet where the material is expected to flow. This numerical trick is combined with an original and efficient node relocation procedure which allows the model to take into account complex geometries of punches. The presented model is firstly validated for limited punch strokes thanks to a purely Lagrangian simulation. It is then compared with results from the literature. Eventually the general nature and the effectiveness of this numerical strategy is demonstrated by a fully-coupled thermomechanical simulation of thixoforming where the final shape of the billet is compared to experimental measurements. [less ▲]

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See detailAn implementation of the generalized Maxwell viscoelastic constitutive model
Careglio, Claudio; Canales Cardenas, Cristian ULg; Papeleux, Luc ULg et al

in Bertolino, Graciela; Cantero, Mariano; Storti, Mario (Eds.) et al Mecánica Computacional Vol XXXIII (2014)

Viscoelastic problems deserve great interest in Computational Mechanics literature. In the last years different approaches have been proposed in order to model viscoelastic problems, as in the case of the ... [more ▼]

Viscoelastic problems deserve great interest in Computational Mechanics literature. In the last years different approaches have been proposed in order to model viscoelastic problems, as in the case of the generalized Maxwell model and its numerical implementation. In particular Kaliske and Rothert (M. Kaliske and H. Rothert, Comput. Mech., 19(3): 228-239 (1997)) discussed basic reological models and the formulation of a generalized Maxwell model and the corresponding implementation of three dimensional viscoelastic model both for small and large strain cases. The numerical implementation addressed by Kaliske and Rothert is quite simple for small strain case and can be extended to a large strain format amenable to be included in finite element codes SOGDE and Metafor. The implementation of the discussed model in a 1D constitutive model, written in Matlab, is addressed. The well known relaxation and creep tests are simulated and compared with analytical results. Furthermore, the influence of constitutive parameters on the viscoelastic response is discussed. In addition, the model is implemented in Finite Element codes and the obtained results are compared with the 1D ones. [less ▲]

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

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 detailOn the numerical simulation of sheet metal blanking process
Canales Cardenas, Cristian ULg; Bussetta, Philippe ULg; Habraken, Anne ULg et al

Conference (2014)

One of the most widely used cutting techniques in sheet metal forming processes for mass production is the blanking process. In this process, a metallic sheet is placed between a die and a blankholder ... [more ▼]

One of the most widely used cutting techniques in sheet metal forming processes for mass production is the blanking process. In this process, a metallic sheet is placed between a die and a blankholder, and is then cut by the action of a punch which moves downward. The quality of the final product is directly linked to the resulting shape of the cut edge. Due to the complexity of the separation step, the set-up of the blanking process in practice is often driven by empirical knowledge. Thus, an accurate numerical tool is extremely desirable to optimize the setting parameters of this technique and will lead to a better understanding of the entire process. The numerical approach must be able to deal with three main issues involved in blanking: large and localized deformation, friction and contact, and ductile fracture. Furthermore, due to requirements of mass production the punch velocity is normally high and the effects of the strain rate must also be considered. Several approaches have been developed in order to model this cutting process but its accuracy still presents some numerical challenges. [less ▲]

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See detailEffect of viscosity on the robustness of the element deletion method for crack propagation modelling
Canales Cardenas, Cristian ULg; Ponthot, Jean-Philippe ULg

Conference (2014)

The numerical simulation of crack propagation in solids is of main importance in fracture mechanics and has been extensively studied over the years. Several approaches have been developed in order to ... [more ▼]

The numerical simulation of crack propagation in solids is of main importance in fracture mechanics and has been extensively studied over the years. Several approaches have been developed in order to describe the evolving geometry of a crack [1{6], but despite the research e orts some challenges are still present. A commonly used technique in Finite Element codes is the element deletion method due to the simplicity of its numerical implementation and possible extension to 3D. Furthermore, it is possible to couple this method with any failure criterion or damage model without additional considerations. This advantages are extremely desirable for numerical approaches involving high computational costs, e.g. the multi-scale computational homogenization [7, 8], where the element deletion method can be used at the micro-scale to simulate the nucleation, growth and coalescence of micro-voids [9]. [less ▲]

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

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 ULg; Dialami, Narges; Boman, Romain ULg 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 ULg; Boman, Romain ULg; 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 ULg

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 detailA LARGE STRAIN ELASTO-VISCOPLASTIC NUMERICAL MODEL
Careglio, Claudio; Canales Cardenas, Cristian ULg; Ribero, Melisa et al

in Bustamante, Roger (Ed.) Proceedings of PACAM XIV (2014)

A large strain elasto-viscoplastic Perzyna model was proposed by Ponthot. The resultant numerical model computes the elastic response using an hypoelastic model. A viscoplastic multiplier was proposed ... [more ▼]

A large strain elasto-viscoplastic Perzyna model was proposed by Ponthot. The resultant numerical model computes the elastic response using an hypoelastic model. A viscoplastic multiplier was proposed, then both inviscid (elastoplastic) and elastic limiting cases can be easily recovered. More recently the authors have included this viscoplastic model in a large strain constitutive model based on hyperelasticity and multiplicative decomposition of deformation gradient tensor. In this work a brief summary of both, hypoelastic and hyperelastic based large strain models of viscoplasticity is provided. Large strain examples are simulated in order to test the discussed models. Different parameters of the constitutive model are tested in order to study the sensitivity of the resultant algorithm. From the obtained results can be said that both models show a very good agree and represent very well the characteristic of the viscoplastic constitutive model. [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 ULg; Papeleux, Luc ULg

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 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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