SAM
https://sam.ensam.eu:443
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http://hdl.handle.net/10985/10754
On the Model Order Reduction of Confined Plasticity
NASRI, Mohamed Aziz; AMMAR, Amine; CHINESTA, Francisco; ROBERT, Camille; EL AREM, Saber; MOREL, Franck
Forming processes usually involve irreversible plastic transformations. The calculation in that case becomes cumbersome when large parts and processes are considered. Recently Model Order Reduction techniques opened new perspectives for an accurate and fast simulation of mechanical systems. In some processes, plastic deformations remain very localized, for example in the immediate neighborhood of the surface. In that case, the in-plane characteristic dimension is several orders of magnitude higher than the one related to the deepness in which plasticity localizes. In those situations the use of standard mesh-based 3D discretization is challenging because the extremely different characteristic dimensions that to capture all the information requires the use of millions of nodes.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10985/107542016-01-01T00:00:00ZNASRI, Mohamed AzizAMMAR, AmineCHINESTA, FranciscoROBERT, CamilleEL AREM, SaberMOREL, FranckForming processes usually involve irreversible plastic transformations. The calculation in that case becomes cumbersome when large parts and processes are considered. Recently Model Order Reduction techniques opened new perspectives for an accurate and fast simulation of mechanical systems. In some processes, plastic deformations remain very localized, for example in the immediate neighborhood of the surface. In that case, the in-plane characteristic dimension is several orders of magnitude higher than the one related to the deepness in which plasticity localizes. In those situations the use of standard mesh-based 3D discretization is challenging because the extremely different characteristic dimensions that to capture all the information requires the use of millions of nodes.Simplified numerical approach for incremental sheet metal forming process
http://hdl.handle.net/10985/8600
Simplified numerical approach for incremental sheet metal forming process
BEN AYED, Lanouar; ROBERT, Camille; DELAMEZIERE, Arnaud; NOUARI, Mohammed; BATOZ, Jean-Louis
The current work presents a finite element approach for numerical simulation of the incremental sheet metal forming (ISF) process, called here ‘‘ISF-SAM’’ (for ISF-Simplified Analysis Modelling). The main goal of the study is to develop a simplified FE model sufficiently accurate to simulate the ISF process and quite efficient in terms of CPU time. Some assumptions have been adopted regarding the constitutive strains/stresses equations and the tool/sheet contact conditions. A simplified contact procedure was proposed to predict nodes in contact with the tool and to estimate their imposed displacements. A Discrete Kirchhoff Triangle shell element called DKT12, taking into account membrane and bending effects, has been used to mesh the sheet. An elasto-plastic constitutive model with isotropic hardening behaviour and a static scheme have been adopted to solve the nonlinear equilibrium equations. Satisfactory results have been obtained on two applications and a good correlation has been shown compared to experimental and numerical results, and at the same time a reduction of CPU time more than 60% has been observed. The bending phenomenon studied through the second application and the obtained results show the reliability of the DKT12 element.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/86002014-01-01T00:00:00ZBEN AYED, LanouarROBERT, CamilleDELAMEZIERE, ArnaudNOUARI, MohammedBATOZ, Jean-LouisThe current work presents a finite element approach for numerical simulation of the incremental sheet metal forming (ISF) process, called here ‘‘ISF-SAM’’ (for ISF-Simplified Analysis Modelling). The main goal of the study is to develop a simplified FE model sufficiently accurate to simulate the ISF process and quite efficient in terms of CPU time. Some assumptions have been adopted regarding the constitutive strains/stresses equations and the tool/sheet contact conditions. A simplified contact procedure was proposed to predict nodes in contact with the tool and to estimate their imposed displacements. A Discrete Kirchhoff Triangle shell element called DKT12, taking into account membrane and bending effects, has been used to mesh the sheet. An elasto-plastic constitutive model with isotropic hardening behaviour and a static scheme have been adopted to solve the nonlinear equilibrium equations. Satisfactory results have been obtained on two applications and a good correlation has been shown compared to experimental and numerical results, and at the same time a reduction of CPU time more than 60% has been observed. The bending phenomenon studied through the second application and the obtained results show the reliability of the DKT12 element.Micro-mechanical modelling of high cycle fatigue behaviour of metals under multiaxial loads
http://hdl.handle.net/10985/6796
Micro-mechanical modelling of high cycle fatigue behaviour of metals under multiaxial loads
ROBERT, Camille; SAINTIER, Nicolas; PALIN-LUC, Thierry; MOREL, Franck
An analysis of high cycle multiaxial fatigue behaviour is conducted through the numerical simulation of polycrystalline aggregates using the finite elementmethod. The metallicmaterial chosen for investigation is pure copper, which has a Face Centred Cubic (FCC) crystalline microstructure. The elementary volumes are modelled in 2D using an hypothesis of generalised plane strain and consist of 300 equi-probability, randomly oriented grains with equiaxed geometry. The aggregates are loaded at levels equivalent to the average macroscopic fatigue strength at 107 cycles. The goal is to compute the mechanical quantities at the mesoscopic scale (i.e. average within the grain) after stabilization of the local cyclic behaviour. The results show that the mesoscopic mechanical variables are characterised by high dispersion. A statistical analysis of the response of the aggregates is undertaken for different loading modes: fully reversed tensile loads, torsion and combined in-phase tension-torsion. Via the calculation of the local mechanical quantities for a sufficiently large number of different microstructures, a critical analysis of certain multiaxial endurance criteria (Crossland, Dang Van and Matake) is conducted. In terms of material behaviour models, it is shown that elastic anisotropy strongly affects the scatter of the mechanical parameters used in the different criteria and that its role is predominant compared to that of crystal plasticity. The analysis of multiaxial endurance criteria at both the macroscopic and mesoscopic scales clearly show that the critical plane type criteria (Dang Van and Matake) give an adequate estimation of the shear stress but badly reflect the scatter of the normal stress or the hydrostatic stress.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10985/67962012-01-01T00:00:00ZROBERT, CamilleSAINTIER, NicolasPALIN-LUC, ThierryMOREL, FranckAn analysis of high cycle multiaxial fatigue behaviour is conducted through the numerical simulation of polycrystalline aggregates using the finite elementmethod. The metallicmaterial chosen for investigation is pure copper, which has a Face Centred Cubic (FCC) crystalline microstructure. The elementary volumes are modelled in 2D using an hypothesis of generalised plane strain and consist of 300 equi-probability, randomly oriented grains with equiaxed geometry. The aggregates are loaded at levels equivalent to the average macroscopic fatigue strength at 107 cycles. The goal is to compute the mechanical quantities at the mesoscopic scale (i.e. average within the grain) after stabilization of the local cyclic behaviour. The results show that the mesoscopic mechanical variables are characterised by high dispersion. A statistical analysis of the response of the aggregates is undertaken for different loading modes: fully reversed tensile loads, torsion and combined in-phase tension-torsion. Via the calculation of the local mechanical quantities for a sufficiently large number of different microstructures, a critical analysis of certain multiaxial endurance criteria (Crossland, Dang Van and Matake) is conducted. In terms of material behaviour models, it is shown that elastic anisotropy strongly affects the scatter of the mechanical parameters used in the different criteria and that its role is predominant compared to that of crystal plasticity. The analysis of multiaxial endurance criteria at both the macroscopic and mesoscopic scales clearly show that the critical plane type criteria (Dang Van and Matake) give an adequate estimation of the shear stress but badly reflect the scatter of the normal stress or the hydrostatic stress.Simulation of Metal Forming Processes with a 3D Adaptive Remeshing Procedure
http://hdl.handle.net/10985/10775
Simulation of Metal Forming Processes with a 3D Adaptive Remeshing Procedure
ZERAMDINI, Bessam; ROBERT, Camille; GERMAIN, Guénaël; POTTIER, Thomas
In this paper, a fully adaptive 3D numerical methodology based on a tetrahedral element was proposed in order to rove the finite element simulation of any metal forming process. This automatic methodology was implemented in a computational platform which integrates a finite element solver, 3D mesh generation and a field transfer algorithm. The proposed remeshing method was developed in order to solve problems associated with the severe distortion of elements subject to large deformations, to concentrate the elements where the error is large and to coarsen the mesh where the error is small. This leads to a significant reduction in the computation times while maintaining simulation accuracy . In addition, in order to enhance the contact conditions, this method has been coupled with a specific operator to maintain the initial contact between the workpiece nodes and the rigid tool after each remeshing step. In this paper special attention is paid to the data transfer methods and the necessary adaptive remeshing steps are given. Finally, a numerical example is detailed to demonstrate the efficiency of the approach and to compare the results for the different field transfer strategies
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10985/107752016-01-01T00:00:00ZZERAMDINI, BessamROBERT, CamilleGERMAIN, GuénaëlPOTTIER, ThomasIn this paper, a fully adaptive 3D numerical methodology based on a tetrahedral element was proposed in order to rove the finite element simulation of any metal forming process. This automatic methodology was implemented in a computational platform which integrates a finite element solver, 3D mesh generation and a field transfer algorithm. The proposed remeshing method was developed in order to solve problems associated with the severe distortion of elements subject to large deformations, to concentrate the elements where the error is large and to coarsen the mesh where the error is small. This leads to a significant reduction in the computation times while maintaining simulation accuracy . In addition, in order to enhance the contact conditions, this method has been coupled with a specific operator to maintain the initial contact between the workpiece nodes and the rigid tool after each remeshing step. In this paper special attention is paid to the data transfer methods and the necessary adaptive remeshing steps are given. Finally, a numerical example is detailed to demonstrate the efficiency of the approach and to compare the results for the different field transfer strategiesA comparison between different numerical methods for the modeling of polycrystalline materials with an elastic-viscoplastic behavior
http://hdl.handle.net/10985/9493
A comparison between different numerical methods for the modeling of polycrystalline materials with an elastic-viscoplastic behavior
ROBERT, Camille; MAREAU, Charles
The macroscopic behavior of polycrystalline materials is largely influenced by the shape, the arrangement and the orientation of crystallites. Different methods have thus been developed to determine the effective behavior of such materials as a function of their microstructural features. In this work, which focuses on polycrystalline materials with an elastic-viscoplastic behavior, the self-consistent, finite element and spectral methods are compared. These common methods are used to determine the effective behavior of \textit{different 316L polycrystalline aggregates} subjected to various loading conditions. Though no major difference is observed at the macroscopic scale, the hardening rate is found to be slightly overestimated with the finite element method. Indeed, spatial convergence cannot be guaranteed for finite element calculations, even when fine mesh resolutions, for which the computational cost is important, are used. Also, as the self-consistent method does not explicitly account for neighborhood effects, important discrepancies between the self-consistent method and the other methods exist regarding the mechanical response of a specific grain. The self-consistent method nevertheless provides a reasonable description of the average response obtained for a group of grains with identical features (e.g. shape, orientation).
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10985/94932015-01-01T00:00:00ZROBERT, CamilleMAREAU, CharlesThe macroscopic behavior of polycrystalline materials is largely influenced by the shape, the arrangement and the orientation of crystallites. Different methods have thus been developed to determine the effective behavior of such materials as a function of their microstructural features. In this work, which focuses on polycrystalline materials with an elastic-viscoplastic behavior, the self-consistent, finite element and spectral methods are compared. These common methods are used to determine the effective behavior of \textit{different 316L polycrystalline aggregates} subjected to various loading conditions. Though no major difference is observed at the macroscopic scale, the hardening rate is found to be slightly overestimated with the finite element method. Indeed, spatial convergence cannot be guaranteed for finite element calculations, even when fine mesh resolutions, for which the computational cost is important, are used. Also, as the self-consistent method does not explicitly account for neighborhood effects, important discrepancies between the self-consistent method and the other methods exist regarding the mechanical response of a specific grain. The self-consistent method nevertheless provides a reasonable description of the average response obtained for a group of grains with identical features (e.g. shape, orientation).Effet de surface libre dans les agrégats polycristallins en fatigue à grand nombre de cycles.
http://hdl.handle.net/10985/7383
Effet de surface libre dans les agrégats polycristallins en fatigue à grand nombre de cycles.
ROBERT, Camille; HOR, Anis; MOREL, Franck; SAINTIER, Nicolas; PALIN-LUC, Thierry
An analysis of high cycle fatigue behavior is done via the numerical simulation of polycrystalline aggregates. Different metallic materials with a FCC crystalline structure, but different cubic elastic coefficients, are investigated. Several statistical elementary volumes (SEV), consisting of 300 grains with isotropic texture and equiaxed geometries, are loaded at the median macroscopic fatigue limit for 107 cycles. Three different models are studied: 2D generalized plane strain, 3D periodic and 3D periodic with a free surface. Different mesoscopic variables are analyzed using extreme value statistics. The results show a detrimental e ect on the fatigue strength of the modeled aggregates with a free surface, if the crystalline elastic anisotropy is sufficient.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/73832013-01-01T00:00:00ZROBERT, CamilleHOR, AnisMOREL, FranckSAINTIER, NicolasPALIN-LUC, ThierryAn analysis of high cycle fatigue behavior is done via the numerical simulation of polycrystalline aggregates. Different metallic materials with a FCC crystalline structure, but different cubic elastic coefficients, are investigated. Several statistical elementary volumes (SEV), consisting of 300 grains with isotropic texture and equiaxed geometries, are loaded at the median macroscopic fatigue limit for 107 cycles. Three different models are studied: 2D generalized plane strain, 3D periodic and 3D periodic with a free surface. Different mesoscopic variables are analyzed using extreme value statistics. The results show a detrimental e ect on the fatigue strength of the modeled aggregates with a free surface, if the crystalline elastic anisotropy is sufficient.Separated representation of incremental elastoplastic simulations
http://hdl.handle.net/10985/9514
Separated representation of incremental elastoplastic simulations
NASRI, Mohamed Aziz; AGUADO, Jose Vicente; AMMAR, Amine; CUETO, Elias; CHINESTA, Francisco; MOREL, Franck; ROBERT, Camille; EL AREM, Saber
Forming processes usually involve irreversible plastic transformations. The calculation in that case becomes cumbersome when large parts and processes are considered. Recently Model Order Reduction techniques opened new perspectives for an accurate and fast simulation of mechanical systems, however nonlinear history-dependent behaviors remain still today challenging scenarios for the application of these techniques. In this work we are proposing a quite simple non intrusive strategy able to address such behaviors by coupling a separated representation with a POD-based reduced basis within an incremental elastoplastic formulation.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10985/95142015-01-01T00:00:00ZNASRI, Mohamed AzizAGUADO, Jose VicenteAMMAR, AmineCUETO, EliasCHINESTA, FranciscoMOREL, FranckROBERT, CamilleEL AREM, SaberForming processes usually involve irreversible plastic transformations. The calculation in that case becomes cumbersome when large parts and processes are considered. Recently Model Order Reduction techniques opened new perspectives for an accurate and fast simulation of mechanical systems, however nonlinear history-dependent behaviors remain still today challenging scenarios for the application of these techniques. In this work we are proposing a quite simple non intrusive strategy able to address such behaviors by coupling a separated representation with a POD-based reduced basis within an incremental elastoplastic formulation.Statistical assessment of multiaxial HCF criteria at the grain scale
http://hdl.handle.net/10985/8394
Statistical assessment of multiaxial HCF criteria at the grain scale
HOR, Anis; SAINTIER, Nicolas; ROBERT, Camille; PALIN-LUC, Thierry; MOREL, Franck
Multiaxial high cycle fatigue modeling of materials is an issue that concerns many industrial domains (automotive, aerospace, nuclear, etc.) and in which many progress still remains to be achieved. Several approaches exist in the literature: invariants, energy, integral and critical plane approaches all of them having their advantages and drawbacks. These different formulations are usually based on mechanical quantities at the micro or mesoscales using localization schemes and strong assumptions to propose simple analytical forms. This study aims to revisit these formulations using a numerical approach based on crystal plasticity modeling coupled with explicit description of microstructure (morphology and texture) and proposes a statistical procedure for the analyses of numerical results in the HCF context. This work has three steps: First, 2.5D periodic digital microstructures based on a random grain sizes distribution are generated. Second, multiaxial cyclic loading conditions corresponding to the fatigue strength at 106 cycles are applied to these microstructures. Third, the mesoscopic Fatigue Indicator Parameters (FIPs), formulated from the different criteria existing in the literature, are identified using the finite element calculations of the mechanical fields. These mesoscopic FIP show the limits of the original criteria when it comes to applying them at the grain scale. A statistical method based on extreme value probability is used to redefine the thresholds of these criteria. These new thresholds contain the sensitivity of the HCF behavior to microstructure attributes. Finally, the biaxiality and phase shift effects are discussed at the grain scale and the loading paths of some critical grains are analyzed.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/83942014-01-01T00:00:00ZHOR, AnisSAINTIER, NicolasROBERT, CamillePALIN-LUC, ThierryMOREL, FranckMultiaxial high cycle fatigue modeling of materials is an issue that concerns many industrial domains (automotive, aerospace, nuclear, etc.) and in which many progress still remains to be achieved. Several approaches exist in the literature: invariants, energy, integral and critical plane approaches all of them having their advantages and drawbacks. These different formulations are usually based on mechanical quantities at the micro or mesoscales using localization schemes and strong assumptions to propose simple analytical forms. This study aims to revisit these formulations using a numerical approach based on crystal plasticity modeling coupled with explicit description of microstructure (morphology and texture) and proposes a statistical procedure for the analyses of numerical results in the HCF context. This work has three steps: First, 2.5D periodic digital microstructures based on a random grain sizes distribution are generated. Second, multiaxial cyclic loading conditions corresponding to the fatigue strength at 106 cycles are applied to these microstructures. Third, the mesoscopic Fatigue Indicator Parameters (FIPs), formulated from the different criteria existing in the literature, are identified using the finite element calculations of the mechanical fields. These mesoscopic FIP show the limits of the original criteria when it comes to applying them at the grain scale. A statistical method based on extreme value probability is used to redefine the thresholds of these criteria. These new thresholds contain the sensitivity of the HCF behavior to microstructure attributes. Finally, the biaxiality and phase shift effects are discussed at the grain scale and the loading paths of some critical grains are analyzed.Different composite voxel methods for the numerical homogenization of heterogeneous inelastic materials with FFT-based techniques
http://hdl.handle.net/10985/11476
Different composite voxel methods for the numerical homogenization of heterogeneous inelastic materials with FFT-based techniques
MAREAU, Charles; ROBERT, Camille
FFT-based homogenization methods aim at calculating the effective behavior of heterogeneous materials with periodic microstructures. These methods operate on a regular grid of voxels, and hence require an appropriate spatial discretization of periodic microstructures. However, when different microstructural length scales are involved, it is not always possible to have sufficient spatial resolutions to explicitly consider the influence of fine microstructural features (e.g. voids, second-phase particles). To circumvent this difficulty, one solution consists of using composite voxel methods to define the effective properties and the effective internal variables of heterogeneous voxels. In this work, different composite voxel methods are proposed to deal with inelastic materials with mul- tiple length scales. These methods use simple homogenization rules to calculate the effective behavior of heterogeneous voxels. The first part of this paper is dedicated to the description of the composite voxel methods, which are based either on the Voigt, laminate structure or Mori–Tanaka approximations. In the second part, these methods are used to model the elasto-plastic behavior of a pearlitic steel poly- crystalline aggregate. According to the results, the Voigt approximation, which ignores morphological fea- tures, is not appropriate for treating heterogeneous voxels. When morphological information is accounted for, with either the laminate structure or Mori–Tanaka approximations, a better agreement with experi- mental observations is obtained. Though none of these methods is universal, they offer some possibilities to investigate the mechanical behavior of heterogeneous materials involving multiple length scales.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/10985/114762017-01-01T00:00:00ZMAREAU, CharlesROBERT, CamilleFFT-based homogenization methods aim at calculating the effective behavior of heterogeneous materials with periodic microstructures. These methods operate on a regular grid of voxels, and hence require an appropriate spatial discretization of periodic microstructures. However, when different microstructural length scales are involved, it is not always possible to have sufficient spatial resolutions to explicitly consider the influence of fine microstructural features (e.g. voids, second-phase particles). To circumvent this difficulty, one solution consists of using composite voxel methods to define the effective properties and the effective internal variables of heterogeneous voxels. In this work, different composite voxel methods are proposed to deal with inelastic materials with mul- tiple length scales. These methods use simple homogenization rules to calculate the effective behavior of heterogeneous voxels. The first part of this paper is dedicated to the description of the composite voxel methods, which are based either on the Voigt, laminate structure or Mori–Tanaka approximations. In the second part, these methods are used to model the elasto-plastic behavior of a pearlitic steel poly- crystalline aggregate. According to the results, the Voigt approximation, which ignores morphological fea- tures, is not appropriate for treating heterogeneous voxels. When morphological information is accounted for, with either the laminate structure or Mori–Tanaka approximations, a better agreement with experi- mental observations is obtained. Though none of these methods is universal, they offer some possibilities to investigate the mechanical behavior of heterogeneous materials involving multiple length scales.Development of a numerical model for the understanding of the chip formation in high-pressure water-jet assisted machining
http://hdl.handle.net/10985/10378
Development of a numerical model for the understanding of the chip formation in high-pressure water-jet assisted machining
AYED, Yessine; ROBERT, Camille; GERMAIN, Guénaël; AMMAR, Amine
The aim of this study is to develop a new numerical cutting model that includes fluid structure interaction and to take into account heat transfer between the water-jet, the workpiece and the chip. This has been achieved using a CEL (Coupled–Eulerian–Lagrangian) technique, an algorithm has been developed to ensure heat exchange between the fluid and the structure. This new model allows decoupling of the mechanical and the thermal effects of the water-jet on chip formation and fragmentation. It has been demonstrated that fragmentation of the chip is ensured by the combination of the thermal and the mechanical effects of the water-jet. Moreover, the tool rake temperature is reduced by more than 400 °C, the tool/chip contact length is also decreased by about 30%.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10985/103782016-01-01T00:00:00ZAYED, YessineROBERT, CamilleGERMAIN, GuénaëlAMMAR, AmineThe aim of this study is to develop a new numerical cutting model that includes fluid structure interaction and to take into account heat transfer between the water-jet, the workpiece and the chip. This has been achieved using a CEL (Coupled–Eulerian–Lagrangian) technique, an algorithm has been developed to ensure heat exchange between the fluid and the structure. This new model allows decoupling of the mechanical and the thermal effects of the water-jet on chip formation and fragmentation. It has been demonstrated that fragmentation of the chip is ensured by the combination of the thermal and the mechanical effects of the water-jet. Moreover, the tool rake temperature is reduced by more than 400 °C, the tool/chip contact length is also decreased by about 30%.