frédéric roger - Academia.edu (original) (raw)
Papers by frédéric roger
Revue européenne de mécanique numérique
Therapeutic Laser Applications and Laser-Tissue Interactions IV, 2009
Journal of Materials Processing Technology, 2013
A simplified 2D axisymmetric model and a comprehensive 3D weld pool model, accounting for the fre... more A simplified 2D axisymmetric model and a comprehensive 3D weld pool model, accounting for the free surface deformation and the filler metal addition, have been developed to investigate the factors that lead to asymmetric bead shapes in horizontal GTA welding of stainless steels. Buoyancy-induced flow and the sagging of the pool free surface, under the action of gravity, are found to be responsible for the weld asymmetry and the decrease in the weld penetration at the bottom sidewall. The numerical results clearly emphasized the beneficial role of the Marangoni shear stress in limiting the asymmetry of horizontal GTA welds. An additional experimental investigation showed that the asymmetry in the weld shape can be reduced when placing the lowest sulfur content component at the bottom side.
Journal of Materials Processing Technology, 2008
... transfer is more important at the backing plate, a higher heat transfer coefficient is used a... more ... transfer is more important at the backing plate, a higher heat transfer coefficient is used at the bottom surface in order to consider the effect of the ... (2) Concerning metallurgical modelling offriction stir welding, most papers deal with the metallurgical evolutions occurring in ...
Journal of Materials Processing Technology, 2011
A transient arc and weld pool model is developed, to study the effect of helium addition on the w... more A transient arc and weld pool model is developed, to study the effect of helium addition on the weld pool properties. Supplying mixtures of argon-helium, and alternate supply of pure argon and pure helium, are both studied. The arc characteristics are found to be highly dependent on the shielding gas composition. The addition of helium to argon increases the main governing forces in the weld pool, and more particularly the electromagnetic forces. This leads to the appearing of an electromagnetically induced vortex in the molten pool, which itself leads to an increase in the weld penetration by a factor that goes up to 3. The comparison between the numerical predictions and the experimental macrographs shows a good agreement as well as shape as dimensions. The numerical results reveal two main advantages of alternate supply of shielding gases; compared to the conventional mixtures supplying, the alternate method is more cost saving, and reduces the heat transfer to the workpiece for an equivalent weld penetration.
International Journal of Thermal Sciences, 2010
In the present paper, a numerical model of spot pulsed current GTA welding for partially and full... more In the present paper, a numerical model of spot pulsed current GTA welding for partially and fully penetrated weld pools is presented. Heat transfer and fluid flow in the weld pool driven by the combination of electromagnetic force, buoyancy force, surface tension gradient and latent heat are included in our model. A new formulation of the electromagnetic problem is introduced to take into account eddy current in the weld pool. The shape of the free deformable surface under the action of pulsed arc force is also handled after the magneto-hydrodynamic calculation. The numerical model was applied to 304 stainless steel welding. We compare the influence of various pulsed welding parameters such as pulse frequency and current ratio on the weld quality. Experimental study is conducted to compare our numerical prediction with welding macrographies. It shows a good agreement of the model.
International Journal of Heat and Mass Transfer, 2012
A hybrid 2D-3D model for the numerical simulation of Gas Tungsten Arc welding is proposed in this... more A hybrid 2D-3D model for the numerical simulation of Gas Tungsten Arc welding is proposed in this paper. It offers the possibility to predict the temperature field as well as the shape of the solidified weld joint for different operating parameters, with relatively good accuracy and reasonable computational cost. Also, an original approach to simulate the effect of immersing a cold filler wire in the weld pool is presented. The simulation results reveal two important observations. First, the weld pool depth is locally decreased in the presence of filler metal, which is due to the energy absorption by the cold feeding wire from the hot molten pool. In addition, the weld shape, maximum temperature and thermal cycles in the workpiece are relatively well predicted even when a 2D model for the arc plasma region is used.
International Journal of Heat and Mass Transfer, 2011
A finite element model is introduced in this paper to describe the coupling between the welding a... more A finite element model is introduced in this paper to describe the coupling between the welding arc and the weld pool dynamic in pulsed gas tungsten arc welding. The cathode, arc-plasma and melting anode regions are taken into account. The unified time-dependent model describes the heat transfer, fluid flow and electromagnetic fields in the three regions. The originality of the numerical model is its ability to treat the arc and weld pool time evolution under pulsed current welding in a unified formalism, taking into account eddy current in the weld pool. The case of thin plates with fully penetrated weld pools is also handled. To validate the predictions of the model, an Infra-Red camera is used to film the dynamic of the weld pool surface. Then an image processing algorithm permits to get the time evolution of the weld pool width directly from the film. The numerical model is applied to the 304 stainless steel welding, and the computed results show that the predictions are in fair agreement with the experimental results.
Engineering Fracture Mechanics, 2009
A comprehensive approach is developed for studying the fatigue phenomena (crack initiation and pr... more A comprehensive approach is developed for studying the fatigue phenomena (crack initiation and propagation) induced by repeated rolling or rolling–sliding contacts between wheel and rail. Cracks initiate and propagate in the rail head in a complex varying multiaxial stress regime due to Hertzian or non-Hertzian contacts generating 3D residual stress pattern. This paper presents the main steps of such an approach devoted to the modeling of defects induced in the rails by the traffic. Special attention is paid to some of the principal difficulties met as well as to the proposed solutions. Examples of applications for the prediction of initiation as well as propagation of some defects are presented. It is shown that numerical simulations predict very well the locus of crack initiation as well as its propagation in the rail. Our approach presents at least three main originalities: first, it is a global approach starting from the evaluation of the initial state of the rail to the simulation of the crack propagation under complex loading including multiaxial residual stresses. Second, special and original numerical methods for the evaluation of the initial states, the overloads and the elastoplastic state under service loading have been developed. Third, a new concept based on a “structural Paris law” has been developed and used in the crack propagation simulations.
HAL (Le Centre pour la Communication Scientifique Directe), Aug 28, 2017
Le polyuréthane thermoplastique à mémoire de forme est un matériau dit ''intelligent'', réactif, ... more Le polyuréthane thermoplastique à mémoire de forme est un matériau dit ''intelligent'', réactif, capable de répondre à un stimulus thermique en déployant de grandes déformations et de retrouver ensuite sa forme initiale lors d'un cycle thermomécanique. Cette réversibilité totale est possible sur plusieurs cycles. Afin de dimensionner un composant à mémoire de forme dans un système mécanique, un modèle de simulation numérique thermo-viscoélastique en grandes déformations de l'effet mémoire de forme est proposé. L'identification des paramètres de ce modèle est réalisée sur la base d'essais thermomécaniques (analyse mécanique dynamique DMA, traction-relaxation en température, recouvrements libres et contraints). La loi de comportement ainsi formulée, qui découple la contrainte hyperélastique et la contrainte viscoélastique, est programmée dans le logiciel de simulation numérique Comsol Multiphysics. Les résultats de la simulation montrent une très bonne concordance avec la réponse expérimentale du matériau au cours de plusieurs cycles de mémoire de forme. Mots clés : polyuréthane à mémoire de forme, loi de comportement viscohyperélastique, cycle thermomécanique, grandes déformations.
HAL (Le Centre pour la Communication Scientifique Directe), Apr 26, 2017
A transient finite element model has been developed to study the heat transfer and fluid flow dur... more A transient finite element model has been developed to study the heat transfer and fluid flow during spot Gas Tungsten Arc Welding (GTAW) on stainless steel. Temperature field, fluid velocity and electromagnetic fields are computed inside the cathode, arc-plasma and anode using a unified MHD formulation. The developed model is then used to study the influence of different helium-argon gas mixtures on both the energy transferred to the workpiece and the time evolution of the weld pool dimensions. It is found that the addition of helium to argon increases the heat flux density on the weld axis by a factor that can reach 6.5. This induces an increase in the weld pool depth by a factor of 3. It is also found that the addition of only 10% of argon to helium decreases considerably the weld pool depth, which is due to the electrical conductivity of the mixture that increases significantly when argon is added to helium.
Factories of the Future (FoF) are expected to implement new integrated design-manufacturing appro... more Factories of the Future (FoF) are expected to implement new integrated design-manufacturing approaches to go towards so-called 'advanced manufacturing'. Actually, combination of additive manufacturing (AM, or 3D-printing) and topological optimization offer new opportunities to produce lighter products with lower environmental footprint. Fused Deposition Modeling (FDM) is a widely used AM process which is affordable with a free control of process parameters. This paper aims at improving the design of 3D-printed structures using topological optimization to define the external geometry and then either heterogeneous internal filling or multimaterials to achieve targeted usage properties. 22 ème Congrès Français de Mécanique Lyon, 24 au 28 Août 2015 2 Based on structural mechanics simulation, parts of the structures where stresses field is high are printed with high density internal filling, or alternatively a new material with improved mechanical properties is added. In the pres...
Physics of Fluids, 2021
Air purifiers are limited to small polluting airborne particles and poor air circulation (fan) fo... more Air purifiers are limited to small polluting airborne particles and poor air circulation (fan) for bringing airborne particles inside the device. Thus, the optimal utility of domestic air purifiers (DAPs) for eliminating airborne viruses is still ambiguous. This paper addresses the above limitations using computational fluid dynamics modeling and simulations to investigate the optimal local design of a DAP in an indoor space. We also investigate the integrated fan system and the local transport of airborne viruses. Three different scenarios of using standard DAP equipment (144 m3/h) are explored in an indoor space comprising a furnished living room 6×6×2.5 m3. We show that the local positioning of a purifier indoors and the fan system embedded inside it can significantly alter the indoor airborne virus transmission risk. Finally, we propose a new indoor air circulation system that better ensures indoor airborne viruses' local orientation more efficiently than a fan embedded in...
Mechanics of Advanced Materials and Structures, 2018
In this paper, we propose to improve static and dynamic mechanical performance of thermoplastic p... more In this paper, we propose to improve static and dynamic mechanical performance of thermoplastic polyurethane (TPU) shape memory polymer by the addition of halloysite nanotubes (HNTs). In addition, we propose a finite element simulation of neat TPU and its nanocomposites. HNT/TPU nanocomposites as shape memory polymers with different weight percentages of nanotubes contents were prepared by melt extrusion with thermoplastic polyurethane. This process induced a homogeneous distribution and a good dispersion of nanotubes throughout the TPU matrix. Mechanical tests in tension demonstrated that strength and modulus of the nanocomposites significantly increase with addition of halloysites without significant loss of ductility. Moreover, cyclic shape memory tests under large strain showed that shape memory properties, mainly the recovery speed, were also enhanced. Using a thermo-visco-hyperelastic model for shape memory polymers, we have investigated the effect of nanotubes addition on the mechanical parameters. This model showed a good prediction of the mechanical behavior during shape memory tests.
Journal of Materials Science, 2017
This study aims at implementing an interfacial model to capture the role of interfaces in polyest... more This study aims at implementing an interfacial model to capture the role of interfaces in polyester-based composites reinforced by metallic fibres. A pull-out test of single aluminium and steel fibres embedded in unsaturated polyester matrix is performed. Finite element computation is performed to simulate the typical response of the pull-out test based on an interfacial model. The implemented model relies on a nonlinear relationship assumed between the interfacial shear and interfacial separation. A sensitivity analysis is conducted to reveal the effect of each parameter of the interfacial model. The identification of these parameters with respect to the experimental conditions is also attempted. The predictions show a perfect matching with the experimental trends if a two-term expression is accounted for as an interfacial response. The model outcome reveals superior interfacial performance of the aluminium/unsaturated polyester composite.
Revue européenne de mécanique numérique
Therapeutic Laser Applications and Laser-Tissue Interactions IV, 2009
Journal of Materials Processing Technology, 2013
A simplified 2D axisymmetric model and a comprehensive 3D weld pool model, accounting for the fre... more A simplified 2D axisymmetric model and a comprehensive 3D weld pool model, accounting for the free surface deformation and the filler metal addition, have been developed to investigate the factors that lead to asymmetric bead shapes in horizontal GTA welding of stainless steels. Buoyancy-induced flow and the sagging of the pool free surface, under the action of gravity, are found to be responsible for the weld asymmetry and the decrease in the weld penetration at the bottom sidewall. The numerical results clearly emphasized the beneficial role of the Marangoni shear stress in limiting the asymmetry of horizontal GTA welds. An additional experimental investigation showed that the asymmetry in the weld shape can be reduced when placing the lowest sulfur content component at the bottom side.
Journal of Materials Processing Technology, 2008
... transfer is more important at the backing plate, a higher heat transfer coefficient is used a... more ... transfer is more important at the backing plate, a higher heat transfer coefficient is used at the bottom surface in order to consider the effect of the ... (2) Concerning metallurgical modelling offriction stir welding, most papers deal with the metallurgical evolutions occurring in ...
Journal of Materials Processing Technology, 2011
A transient arc and weld pool model is developed, to study the effect of helium addition on the w... more A transient arc and weld pool model is developed, to study the effect of helium addition on the weld pool properties. Supplying mixtures of argon-helium, and alternate supply of pure argon and pure helium, are both studied. The arc characteristics are found to be highly dependent on the shielding gas composition. The addition of helium to argon increases the main governing forces in the weld pool, and more particularly the electromagnetic forces. This leads to the appearing of an electromagnetically induced vortex in the molten pool, which itself leads to an increase in the weld penetration by a factor that goes up to 3. The comparison between the numerical predictions and the experimental macrographs shows a good agreement as well as shape as dimensions. The numerical results reveal two main advantages of alternate supply of shielding gases; compared to the conventional mixtures supplying, the alternate method is more cost saving, and reduces the heat transfer to the workpiece for an equivalent weld penetration.
International Journal of Thermal Sciences, 2010
In the present paper, a numerical model of spot pulsed current GTA welding for partially and full... more In the present paper, a numerical model of spot pulsed current GTA welding for partially and fully penetrated weld pools is presented. Heat transfer and fluid flow in the weld pool driven by the combination of electromagnetic force, buoyancy force, surface tension gradient and latent heat are included in our model. A new formulation of the electromagnetic problem is introduced to take into account eddy current in the weld pool. The shape of the free deformable surface under the action of pulsed arc force is also handled after the magneto-hydrodynamic calculation. The numerical model was applied to 304 stainless steel welding. We compare the influence of various pulsed welding parameters such as pulse frequency and current ratio on the weld quality. Experimental study is conducted to compare our numerical prediction with welding macrographies. It shows a good agreement of the model.
International Journal of Heat and Mass Transfer, 2012
A hybrid 2D-3D model for the numerical simulation of Gas Tungsten Arc welding is proposed in this... more A hybrid 2D-3D model for the numerical simulation of Gas Tungsten Arc welding is proposed in this paper. It offers the possibility to predict the temperature field as well as the shape of the solidified weld joint for different operating parameters, with relatively good accuracy and reasonable computational cost. Also, an original approach to simulate the effect of immersing a cold filler wire in the weld pool is presented. The simulation results reveal two important observations. First, the weld pool depth is locally decreased in the presence of filler metal, which is due to the energy absorption by the cold feeding wire from the hot molten pool. In addition, the weld shape, maximum temperature and thermal cycles in the workpiece are relatively well predicted even when a 2D model for the arc plasma region is used.
International Journal of Heat and Mass Transfer, 2011
A finite element model is introduced in this paper to describe the coupling between the welding a... more A finite element model is introduced in this paper to describe the coupling between the welding arc and the weld pool dynamic in pulsed gas tungsten arc welding. The cathode, arc-plasma and melting anode regions are taken into account. The unified time-dependent model describes the heat transfer, fluid flow and electromagnetic fields in the three regions. The originality of the numerical model is its ability to treat the arc and weld pool time evolution under pulsed current welding in a unified formalism, taking into account eddy current in the weld pool. The case of thin plates with fully penetrated weld pools is also handled. To validate the predictions of the model, an Infra-Red camera is used to film the dynamic of the weld pool surface. Then an image processing algorithm permits to get the time evolution of the weld pool width directly from the film. The numerical model is applied to the 304 stainless steel welding, and the computed results show that the predictions are in fair agreement with the experimental results.
Engineering Fracture Mechanics, 2009
A comprehensive approach is developed for studying the fatigue phenomena (crack initiation and pr... more A comprehensive approach is developed for studying the fatigue phenomena (crack initiation and propagation) induced by repeated rolling or rolling–sliding contacts between wheel and rail. Cracks initiate and propagate in the rail head in a complex varying multiaxial stress regime due to Hertzian or non-Hertzian contacts generating 3D residual stress pattern. This paper presents the main steps of such an approach devoted to the modeling of defects induced in the rails by the traffic. Special attention is paid to some of the principal difficulties met as well as to the proposed solutions. Examples of applications for the prediction of initiation as well as propagation of some defects are presented. It is shown that numerical simulations predict very well the locus of crack initiation as well as its propagation in the rail. Our approach presents at least three main originalities: first, it is a global approach starting from the evaluation of the initial state of the rail to the simulation of the crack propagation under complex loading including multiaxial residual stresses. Second, special and original numerical methods for the evaluation of the initial states, the overloads and the elastoplastic state under service loading have been developed. Third, a new concept based on a “structural Paris law” has been developed and used in the crack propagation simulations.
HAL (Le Centre pour la Communication Scientifique Directe), Aug 28, 2017
Le polyuréthane thermoplastique à mémoire de forme est un matériau dit ''intelligent'', réactif, ... more Le polyuréthane thermoplastique à mémoire de forme est un matériau dit ''intelligent'', réactif, capable de répondre à un stimulus thermique en déployant de grandes déformations et de retrouver ensuite sa forme initiale lors d'un cycle thermomécanique. Cette réversibilité totale est possible sur plusieurs cycles. Afin de dimensionner un composant à mémoire de forme dans un système mécanique, un modèle de simulation numérique thermo-viscoélastique en grandes déformations de l'effet mémoire de forme est proposé. L'identification des paramètres de ce modèle est réalisée sur la base d'essais thermomécaniques (analyse mécanique dynamique DMA, traction-relaxation en température, recouvrements libres et contraints). La loi de comportement ainsi formulée, qui découple la contrainte hyperélastique et la contrainte viscoélastique, est programmée dans le logiciel de simulation numérique Comsol Multiphysics. Les résultats de la simulation montrent une très bonne concordance avec la réponse expérimentale du matériau au cours de plusieurs cycles de mémoire de forme. Mots clés : polyuréthane à mémoire de forme, loi de comportement viscohyperélastique, cycle thermomécanique, grandes déformations.
HAL (Le Centre pour la Communication Scientifique Directe), Apr 26, 2017
A transient finite element model has been developed to study the heat transfer and fluid flow dur... more A transient finite element model has been developed to study the heat transfer and fluid flow during spot Gas Tungsten Arc Welding (GTAW) on stainless steel. Temperature field, fluid velocity and electromagnetic fields are computed inside the cathode, arc-plasma and anode using a unified MHD formulation. The developed model is then used to study the influence of different helium-argon gas mixtures on both the energy transferred to the workpiece and the time evolution of the weld pool dimensions. It is found that the addition of helium to argon increases the heat flux density on the weld axis by a factor that can reach 6.5. This induces an increase in the weld pool depth by a factor of 3. It is also found that the addition of only 10% of argon to helium decreases considerably the weld pool depth, which is due to the electrical conductivity of the mixture that increases significantly when argon is added to helium.
Factories of the Future (FoF) are expected to implement new integrated design-manufacturing appro... more Factories of the Future (FoF) are expected to implement new integrated design-manufacturing approaches to go towards so-called 'advanced manufacturing'. Actually, combination of additive manufacturing (AM, or 3D-printing) and topological optimization offer new opportunities to produce lighter products with lower environmental footprint. Fused Deposition Modeling (FDM) is a widely used AM process which is affordable with a free control of process parameters. This paper aims at improving the design of 3D-printed structures using topological optimization to define the external geometry and then either heterogeneous internal filling or multimaterials to achieve targeted usage properties. 22 ème Congrès Français de Mécanique Lyon, 24 au 28 Août 2015 2 Based on structural mechanics simulation, parts of the structures where stresses field is high are printed with high density internal filling, or alternatively a new material with improved mechanical properties is added. In the pres...
Physics of Fluids, 2021
Air purifiers are limited to small polluting airborne particles and poor air circulation (fan) fo... more Air purifiers are limited to small polluting airborne particles and poor air circulation (fan) for bringing airborne particles inside the device. Thus, the optimal utility of domestic air purifiers (DAPs) for eliminating airborne viruses is still ambiguous. This paper addresses the above limitations using computational fluid dynamics modeling and simulations to investigate the optimal local design of a DAP in an indoor space. We also investigate the integrated fan system and the local transport of airborne viruses. Three different scenarios of using standard DAP equipment (144 m3/h) are explored in an indoor space comprising a furnished living room 6×6×2.5 m3. We show that the local positioning of a purifier indoors and the fan system embedded inside it can significantly alter the indoor airborne virus transmission risk. Finally, we propose a new indoor air circulation system that better ensures indoor airborne viruses' local orientation more efficiently than a fan embedded in...
Mechanics of Advanced Materials and Structures, 2018
In this paper, we propose to improve static and dynamic mechanical performance of thermoplastic p... more In this paper, we propose to improve static and dynamic mechanical performance of thermoplastic polyurethane (TPU) shape memory polymer by the addition of halloysite nanotubes (HNTs). In addition, we propose a finite element simulation of neat TPU and its nanocomposites. HNT/TPU nanocomposites as shape memory polymers with different weight percentages of nanotubes contents were prepared by melt extrusion with thermoplastic polyurethane. This process induced a homogeneous distribution and a good dispersion of nanotubes throughout the TPU matrix. Mechanical tests in tension demonstrated that strength and modulus of the nanocomposites significantly increase with addition of halloysites without significant loss of ductility. Moreover, cyclic shape memory tests under large strain showed that shape memory properties, mainly the recovery speed, were also enhanced. Using a thermo-visco-hyperelastic model for shape memory polymers, we have investigated the effect of nanotubes addition on the mechanical parameters. This model showed a good prediction of the mechanical behavior during shape memory tests.
Journal of Materials Science, 2017
This study aims at implementing an interfacial model to capture the role of interfaces in polyest... more This study aims at implementing an interfacial model to capture the role of interfaces in polyester-based composites reinforced by metallic fibres. A pull-out test of single aluminium and steel fibres embedded in unsaturated polyester matrix is performed. Finite element computation is performed to simulate the typical response of the pull-out test based on an interfacial model. The implemented model relies on a nonlinear relationship assumed between the interfacial shear and interfacial separation. A sensitivity analysis is conducted to reveal the effect of each parameter of the interfacial model. The identification of these parameters with respect to the experimental conditions is also attempted. The predictions show a perfect matching with the experimental trends if a two-term expression is accounted for as an interfacial response. The model outcome reveals superior interfacial performance of the aluminium/unsaturated polyester composite.