References of "Ponthot, Jean-Philippe"
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See detailUltrasonic roll bite measurements in cold rolling - roll stress and deformation
Carretta, Yves; Hunter, Andrew; Boman, Romain ULg et al

in Journal of Materials Processing Technology (2017), 249

In cold rolling of thin metal strip, contact conditions between the work rolls and the strip are of great importance: roll deformations and their effect on strip thickness variation may lead to strip ... [more ▼]

In cold rolling of thin metal strip, contact conditions between the work rolls and the strip are of great importance: roll deformations and their effect on strip thickness variation may lead to strip flatness defects and thickness inhomogeneity. To control the process, several online measurements are usually carried out such as the rolling load, forward slip and strip tensions at each stand. Shape defects of the strip are usually evaluated after the last stand of a rolling mill thanks to a flatness measuring roll. However, none of these measurements is made within the roll bite itself due to the harsh conditions taking place in that area. This paper presents a sensor capable of monitoring roll deformations as well as roll radial stresses in situ and in real time. The sensor emits ultrasonic pulses that reflect from the roll surface. The time-of-flight (ToF) of the pulses is recorded during the testing. The sensor system was incorporated into a work roll and tested on a pilot rolling mill. Measurements were taken as steel strips were rolled under different strip elongation. Roll deformation and radial stresses obtained from the experimental data are in good agreement with numerical results computed with a cold rolling model developed in non-linear Finite Element software. [less ▲]

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See detailFATIGUE CRACK PROPAGATION IN HSS S690QL WELDED CONNECTIONS IN BRIDGES
Bouffioux, Chantal ULg; Canales Cardenas, Cristian ULg; Duchene, Laurent ULg et al

Conference (2017, June)

The fatigue and crack study of HSS S690QL steel welded pieces is first experimentally analyzed by fatigue tests on small samples of Base Material (BM), Heat Affected Zone (HAZ) and Weld Metal (WM ... [more ▼]

The fatigue and crack study of HSS S690QL steel welded pieces is first experimentally analyzed by fatigue tests on small samples of Base Material (BM), Heat Affected Zone (HAZ) and Weld Metal (WM) separately for several stress ratios, stress levels, on smooth and notched samples. The Lemaître-Chaboche fatigue model combined with the stress gradient method and the three sets of parameters are found to accurately describe the behavior of each material. Another experimental campaign with larger pieces (closer to the scale of the bridge connections) called "small scale samples", with/without welded stiffeners, with several geometries and with/without post-treatment has shown each effect separately: the scale and machining effects, residual stresses due to the welding, geometrical and post-treatments effects. Numerical simulations of these experiments are used to improve and validate the material data, with a study in real context and size. Then, the characterized fatigue damage model is coupled with the element deletion method to model the propagation of cracks along the welded samples and the numerical predictions are compared with experimental results in order to validate the approach. [less ▲]

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See detailNumerical modelling of micro-plasto-hydrodynamic lubrication in plane strip drawing
Carretta, Yves ULg; Bech, Jakob; Legrand, Nicolas et al

in Tribology International (2017), 110

This paper presents a new finite element model capable of predicting the onset of micro-plasto-hydrodynamic (MPH) lubrication and the amount of lubricant escaping from surface pockets in metal forming ... [more ▼]

This paper presents a new finite element model capable of predicting the onset of micro-plasto-hydrodynamic (MPH) lubrication and the amount of lubricant escaping from surface pockets in metal forming. The present approach is divided in two steps. First, a simulation at the macroscopic level is conducted. Then, a second simulation highlighting microscopic liquid lubrication mechanisms is achieved using boundary conditions provided by the first model. These fluid-structure interaction computations are made possible through the use of the Arbitrary Lagrangian Eulerian (ALE) formalism. The developed methodology is validated by comparison to experimental measurements conducted in plane strip drawing. The effect of physical parameters like the drawing speed, the die angle and the strip thickness reduction is investigated. The numerical results show good agreement with experiments. [less ▲]

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See detailUltrasonic roll bite measurements in cold rolling: Contact length and strip thickness
Carretta, Yves; Hunter, Andrew; Boman, Romain ULg et al

in Proceedings of the Institution of Mechanical Engineers - Part J - Journal of Engineering Tribology (2017)

In cold rolling of thin metal strip, contact conditions between the work rolls and the strip are of great importance: roll deformations and their effect on strip thickness variation may lead to strip ... [more ▼]

In cold rolling of thin metal strip, contact conditions between the work rolls and the strip are of great importance: roll deformations and their effect on strip thickness variation may lead to strip flatness defects and thickness inhomogeneity. To control the process, online process measurements are usually carried out; such as the rolling load, forward slip and strip tensions at each stand. Shape defects of the strip are usually evaluated after the last stand of a rolling mill thanks to a flatness measuring roll. However, none of these measurements is made within the roll bite itself due to the harsh conditions taking place in that area. This paper presents a sensor capable of monitoring strip thickness variations as well as roll bite length in situ and in real time. The sensor emits ultrasonic pulses that reflect from the interface between the roll and the strip. Both the time-of-flight of the pulses and the reflection coefficient (the ratio of the amplitude of the reflected signal to that of the incident signal) are recorded. The sensor system was incorporated into a work roll and tested on a pilot rolling mill. Measurements were taken as steel strips were rolled under several lubrication conditions. Strip thickness variation and roll-bite length obtained from the experimental data agree well with numerical results computed with a cold rolling model in the mixed lubrication regime. [less ▲]

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See detailBelgian National Committee for Theoretical and Applied Mechanics
Ponthot, Jean-Philippe ULg

Article for general public (2017)

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See detailA generic wear prediction procedure based on the Discrete Element Method for ball mill liners in the cement industry
Boemer, Dominik ULg; Ponthot, Jean-Philippe ULg

in Minerals Engineering (2017)

generic procedure to predict the wear evolution of lining surfaces, namely the spatial distribution of wear and the progressive modification of the geometry due to wear, is introduced in the context of ... [more ▼]

generic procedure to predict the wear evolution of lining surfaces, namely the spatial distribution of wear and the progressive modification of the geometry due to wear, is introduced in the context of shell liners in ball mills. The wear data is accumulated on the surface of the liner by 3D discrete element method (DEM) simulations of the ball charge in an axial slice of the mill, which is either closed by a periodic boundary condition or by frictionless end walls. The calibration of this wear data with the measured wear profiles of the shell liner in a 5.8 m diameter industrial cement tube mill shows that the tangential damping energy defined by the linear spring-slider-damper DEM contact law is the best fitting wear model of 6 different models. The gradual update of the liner shape delivers adequate results for liners without an axial height variation, while the accuracy of fully variable geometrical modifications is limited by the computation time. Nevertheless, detailed phenomena, like the creation of grooves in the liner, were for the first time numerically modeled. [less ▲]

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See detailComputational methods in manufacturing
Ponthot, Jean-Philippe ULg; Feulvarch, Eric; Drapier, Sylvain et al

in International Journal of Material Forming (2017), 10

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See detailPreliminary assessment of the possibilities of the Particle Finite Element Method in the numerical simulation of bird impact on aeronautical structures
Cerquaglia, Marco Lucio ULg; Deliège, Geoffrey ULg; Boman, Romain ULg et al

in Procedia Engineering (2017), 173

As well known, in the analysis of bird impact events the bird is often reduced, even experimentally, to a surrogate projectile modeled as a weakly compressible fluid (typically a mixture of water and air ... [more ▼]

As well known, in the analysis of bird impact events the bird is often reduced, even experimentally, to a surrogate projectile modeled as a weakly compressible fluid (typically a mixture of water and air). From a numerical standpoint, the presence of a free surface and the strong interaction with the aircraft structures represent a limit for traditional computational fluid dynamics methods based on an Eulerian grid. On the other hand, classical Lagrangian methods cannot cope with the extremely large deformations experienced by the projectile during the impact. The Particle Finite Element Method (PFEM) is a Lagrangian particle method that can account for very large deformations, preserving the robustness and generality of the finite element method, and thus owning a key advantage over other approaches, e.g. Smoothed Particle Hydrodynamics (SPH), usually cursed with consistency and stability issues. To assess the possibilities of the method in the context of bird impact, theoretical analyses are initially performed based on the impact of a water jet on a rigid surface. Then, the influence of the geometry of a more realistic projectile is analyzed and the capability of the method to take into account separation and fragmentation is highlighted. [less ▲]

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See detailNumerical modelling of microscopic lubricant flow in sheet metal forming. Application to plane strip drawing
Carretta, Yves; Bech, Jacob; Legrand, Nicolas et al

in International Journal for Numerical Methods in Engineering (2017)

This paper presents a numerical investigation of microscopic lubricant flows from the cavities to the plateaus of the surface roughness of metal sheets during forming processes. This phenomenon, called ... [more ▼]

This paper presents a numerical investigation of microscopic lubricant flows from the cavities to the plateaus of the surface roughness of metal sheets during forming processes. This phenomenon, called micro-plastohydrodynamic lubrication, was observed experimentally in various situations such as compression sliding tests, strip drawing and cold rolling. It leads to local friction drop and wear reduction. It is therefore critical to achieve a good understanding of this phenomenon. As to move towards that goal, a multiscale fluid–structure interaction model is developed to model lubricant flows at the microscopic scale. These simulations are made possible through the use of the Arbitrary Lagrangian Eulerian (ALE) formalism. In this paper, this methodology is used to study plane strip drawing. The numerical model is able to predict the onset of lubricant escape and the amount of lubricant flowing on the plateaus. Numerical results exhibit good agreement with experimental measurements. [less ▲]

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See detailOn the numerical simulation of sheet metal blanking process
Canales Cardenas, Cristian ULg; Bussetta, Philippe; Ponthot, Jean-Philippe ULg

in International Journal of Material Forming (2017), 10

The use of the blanking process has been widely spread in mass production industries. In this technique, the quality of the final product is directly related to the setting parameters of the process and ... [more ▼]

The use of the blanking process has been widely spread in mass production industries. In this technique, the quality of the final product is directly related to the setting parameters of the process and the material response of the sheet. In the present work, a general framework based on the finite element method for the simulation of the sheet metal blanking process is presented. The proposed approach properly addresses all the numerical challenges related to blanking. First, an extension of elasto-viscoplastic constitutive equations for the large strain regime is used to take into account the material strain-rate sensitivity. Then, the inertial effects coming from high velocity operations are considered by means of an implicit time integration scheme. Moreover, the frictional contact interactions are simulated with the classical Coulomb law and an energetically consistent formulation of area regularization. Finally, ductile fracture is modeled thanks to the element deletion method coupled with a fracture criterion. The blanking process is then simulated for different setting parameters. The accuracy of this approach is evaluated by comparing the numerical predictions to experimental results for both quasi-static and dynamic conditions. Good agreement is found between experimental and numerical results for all cases. [less ▲]

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See detailNumerical Methods
Agelet de Saracibar, Carlos; Boman, Romain ULg; Bussetta, Philippe et al

in Schmitz, Georg; Prahl, Ulrich (Eds.) Handbook of Software Solutions for ICME, (2017)

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See detailApplication of Uncoupled Damage Models to Predict Ductile Fracture in Sheet Metal Blanking
Canales Cardenas, Cristian ULg; Boman, Romain ULg; Ponthot, Jean-Philippe ULg

in Key Engineering Materials (2016), 725

The use of uncoupled damage models has been widely used over the years for the prediction of ductile fracture in engineering applications. Nevertheless, its applicability in the prediction of failure has ... [more ▼]

The use of uncoupled damage models has been widely used over the years for the prediction of ductile fracture in engineering applications. Nevertheless, its applicability in the prediction of failure has been shown to be limited in the wide range of loading conditions encountered in different manufacturing processes. In order to enhance the formulation of former damage models, the Lode angle has been recently used to characterize the stress states along with the stress triaxiality. This new family of damage models has been demonstrated to give excellent results when proportional loading paths are considered, but its efficiency in more complex applications still need further analysis. To this end, a comparative study of former and recently developed uncoupled damage models is performed in this work. The identification of material parameters is done considering simple mechanical tests under different conditions. Then, the models are used to predict the onset and propagation of cracks during blanking, where numerical predictions are compared with experimental results. Finally, the selected damage models presented a remarkable overall performance in the range of clearances under study. [less ▲]

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See detailDEM modeling of ball mills with experimental validation: influence of contact parameters on charge motion and power draw
Boemer, Dominik ULg; Ponthot, Jean-Philippe ULg

in Computational Particle Mechanics (2016), 4(1), 53-67

Discrete element method simulations of a 1:5-scale laboratory ball mill are presented in this paper to study the influence of the contact parameters on the charge motion and the power draw. The position ... [more ▼]

Discrete element method simulations of a 1:5-scale laboratory ball mill are presented in this paper to study the influence of the contact parameters on the charge motion and the power draw. The position density limit is introduced as an efficient mathematical tool to describe and to compare the macroscopic charge motion in different scenarios, i.a. with different values of the contact parameters. While the charge motion and the power draw are relatively insensitive to the stiffness and the damping coefficient of the linear spring-slider-damper contact law, the coefficient of friction has a strong influence since it controls the sliding propensity of the charge. Based on the experimental calibration and validation by charge motion photographs and power draw measurements, the descriptive and predictive capabilities of the position density limit and the discrete element method are demonstrated, i.e. the real position of the charge is precisely delimited by the respective position density limit and the power draw can be predicted with an accuracy of about 5 %. [less ▲]

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See detailTwo novel ways to impose free-slip boundary conditions in fluid-structure interaction problems using the Particle Finite Element Method
Cerquaglia, Marco Lucio ULg; Deliège, Geoffrey ULg; Boman, Romain ULg et al

Conference (2016, June 09)

As well known, the imposition of boundary conditions is, in many cases, the trickiest part in solving differential problems, both from a physical and numerical standpoint. This work focuses on the way ... [more ▼]

As well known, the imposition of boundary conditions is, in many cases, the trickiest part in solving differential problems, both from a physical and numerical standpoint. This work focuses on the way boundary conditions are accounted for in the solution of fluid-structure interaction problems using the Particle Finite Element Method (PFEM). In particular, the PFEM traditionally employs no-slip conditions on the fluid-solid interfaces. Our aim is twofold. On the one hand, we demonstrate that, in the framework of the PFEM, the no-slip hypothesis is too strong in some cases, leading to erroneous physical results, and that a free-slip condition is to be preferred instead; we therefore propose two novel ways to impose free-slip conditions, devoting special attention to generality, simplicity and robustness. On the other hand, we show how the use of free-slip boundary conditions can also be beneficial with regards to two major problems arising from the remeshing procedure employed by the PFEM: the violation of the mass conservation principle and the introduction of spurious pressure oscillations. [less ▲]

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