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http://hdl.handle.net/10985/7135
Micromechanical modeling if the interactions between the microstructure and the dissipative deformation mechanisms in steels under cyclic loading
MAREAU, Charles; FAVIER, Véronique; WEBER, Bastien; GALTIER, André; BERVEILLER, Marcel
A micromechanical model is proposed to describe the interactions between the microstructure and the dissipative deformation mechanisms in ferritic steels under cyclic loading. The model aims at optimizing the microstructure of steels since the dissipative mechanisms can be responsible for the initiation of microcracks. Therefore, a better understanding of the influence of the microstructure could lead to an improvement of fatigue properties. The dissipative mechanisms are assumed to be either anelastic (dislocation oscillations) or inelastic (plastic slip) and are described at the scale of the slip system using the framework of crystal plasticity. The macroscopic behavior is then deduced with a homogenization scheme. The model is validated by comparing the simulations with experimental results and is finally used to predict the impact of different microstructure parameters on the heat dissipation.
La version éditeur de cette publication est disponible à l'adresse suivante : http://www.sciencedirect.com/science/article/pii/S074964191100194X
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10985/71352012-01-01T00:00:00ZMAREAU, CharlesFAVIER, VéroniqueWEBER, BastienGALTIER, AndréBERVEILLER, MarcelA micromechanical model is proposed to describe the interactions between the microstructure and the dissipative deformation mechanisms in ferritic steels under cyclic loading. The model aims at optimizing the microstructure of steels since the dissipative mechanisms can be responsible for the initiation of microcracks. Therefore, a better understanding of the influence of the microstructure could lead to an improvement of fatigue properties. The dissipative mechanisms are assumed to be either anelastic (dislocation oscillations) or inelastic (plastic slip) and are described at the scale of the slip system using the framework of crystal plasticity. The macroscopic behavior is then deduced with a homogenization scheme. The model is validated by comparing the simulations with experimental results and is finally used to predict the impact of different microstructure parameters on the heat dissipation.Study of the contribution of different effects induced by the punching process on the high cycle fatigue strength of the M330-35A electrical steel
http://hdl.handle.net/10985/11188
Study of the contribution of different effects induced by the punching process on the high cycle fatigue strength of the M330-35A electrical steel
DEHMANI, Helmi; BRUGGER, Charles; PALIN-LUC, Thierry; MAREAU, Charles; KOECHLIN, Samuel
Because of their improved magnetic properties, Fe-Si alloys are widely used for new electric motor generations. The use of punching process to obtain these components specially affects their mechanical behavior and fatigue strength. This work aims at studying the influence of punching operations on the fatigue behavior of a Fe-Si alloy. High cycle fatigue tests are performed on different smooth specimen configurations with either punched or polished edges. Results show a significant decrease of the fatigue strength for punched specimens compared to polished ones. To understand the origin of the fatigue failure on punched specimens, SEM observations of the fracture surfaces are carried out. They reveal that crack initiation always occurs on a punch defect. Additional experimental techniques are combined to characterize how the edges are altered by punching. The impact of punching operations on residual stresses and hardening is then investigated. Residual stresses are quantified on punched edges using X-ray diffraction techniques. Important tensile residual stresses exist in the loading direction as a result of punching operations. Also, according to XRD analyses and micro-hardness measurements, teh hardened zone depht is about 200µm. To dissociate teh respective influences of strain hardening, residual stresses and geometrical defects, a heat tratment is applied to both punched and polished specimens in order to quantify the contribution of each parameter to the high cycle fatigue resistance. Results show that the geometry of defects is one of teh most influent parameters. Consequantly, a finite element model is developed to simulate teh influence of edge defects on the fatigue strength of punched components. A non-local high cycle fatigue criterion is finally used as a post-processing of FEA to consider the effect of defets and teh associated stress-strain gradients in the HCF strength assessment.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10985/111882016-01-01T00:00:00ZDEHMANI, HelmiBRUGGER, CharlesPALIN-LUC, ThierryMAREAU, CharlesKOECHLIN, SamuelBecause of their improved magnetic properties, Fe-Si alloys are widely used for new electric motor generations. The use of punching process to obtain these components specially affects their mechanical behavior and fatigue strength. This work aims at studying the influence of punching operations on the fatigue behavior of a Fe-Si alloy. High cycle fatigue tests are performed on different smooth specimen configurations with either punched or polished edges. Results show a significant decrease of the fatigue strength for punched specimens compared to polished ones. To understand the origin of the fatigue failure on punched specimens, SEM observations of the fracture surfaces are carried out. They reveal that crack initiation always occurs on a punch defect. Additional experimental techniques are combined to characterize how the edges are altered by punching. The impact of punching operations on residual stresses and hardening is then investigated. Residual stresses are quantified on punched edges using X-ray diffraction techniques. Important tensile residual stresses exist in the loading direction as a result of punching operations. Also, according to XRD analyses and micro-hardness measurements, teh hardened zone depht is about 200µm. To dissociate teh respective influences of strain hardening, residual stresses and geometrical defects, a heat tratment is applied to both punched and polished specimens in order to quantify the contribution of each parameter to the high cycle fatigue resistance. Results show that the geometry of defects is one of teh most influent parameters. Consequantly, a finite element model is developed to simulate teh influence of edge defects on the fatigue strength of punched components. A non-local high cycle fatigue criterion is finally used as a post-processing of FEA to consider the effect of defets and teh associated stress-strain gradients in the HCF strength assessment.Experimental study of the impact of punching operations on the high cycle fatigue strength of Fe-Si thin sheets
http://hdl.handle.net/10985/10762
Experimental study of the impact of punching operations on the high cycle fatigue strength of Fe-Si thin sheets
DEHMANI, Helmi; BRUGGER, Charles; PALIN-LUC, Thierry; MAREAU, Charles; KOECHLIN, Samuel
In this paper, the impact of punching operations on the high cycle fatigue strength of Fe–Si thin sheets is investigated. High cycle fatigue tests are performed on both punched and polished edge specimens. Results show a significant decrease of the fatigue strength in the case of punched specimens. Different factors are found to be responsible for this degradation. First, according to SEM observations of fracture surfaces and to 3D surface topography, fatigue crack initiation is strongly governed by the geometrical defects resulting from punching operations. Second, important tensile residual stresses, which are analyzed using X-ray diffraction techniques, are observed on punched edges. Depending on the loading conditions, it is possible for the residual stress field to be redistributed as a result of cyclic plasticity. Third, punching operations are responsible for the introduction of a plastically hardened zone which, according to both micro-hardness measurements and diffraction data, is about 200 µm deep. Based upon this experimental dataset, the parameters of the Murakami criterion are identified. This criterion is found to provide a reasonable description of the experimental results when the residual stresses around punched edges are accounted for.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10985/107622016-01-01T00:00:00ZDEHMANI, HelmiBRUGGER, CharlesPALIN-LUC, ThierryMAREAU, CharlesKOECHLIN, SamuelIn this paper, the impact of punching operations on the high cycle fatigue strength of Fe–Si thin sheets is investigated. High cycle fatigue tests are performed on both punched and polished edge specimens. Results show a significant decrease of the fatigue strength in the case of punched specimens. Different factors are found to be responsible for this degradation. First, according to SEM observations of fracture surfaces and to 3D surface topography, fatigue crack initiation is strongly governed by the geometrical defects resulting from punching operations. Second, important tensile residual stresses, which are analyzed using X-ray diffraction techniques, are observed on punched edges. Depending on the loading conditions, it is possible for the residual stress field to be redistributed as a result of cyclic plasticity. Third, punching operations are responsible for the introduction of a plastically hardened zone which, according to both micro-hardness measurements and diffraction data, is about 200 µm deep. Based upon this experimental dataset, the parameters of the Murakami criterion are identified. This criterion is found to provide a reasonable description of the experimental results when the residual stresses around punched edges are accounted for.Self-consistent modelling of heterogeneous materials with an elastic-viscoplastic behavior: Application to polycrystalline agregates
http://hdl.handle.net/10985/10846
Self-consistent modelling of heterogeneous materials with an elastic-viscoplastic behavior: Application to polycrystalline agregates
MAREAU, Charles; BERBENNI, Stéphane
The self-consistent scheme is a common homogenization method that was developed to connect local deformation mechanisms to the overall behavior of heterogeneous disordered materials. In the past decades, many efforts have been made to obtain extensions of the self-consistent approximation to the non-linear case. This work focuses on the specific case of heterogeneous materials with an elastic-viscoplastic behavior. For such materials, the overall behavior is strongly dependent on the space-time couplings originating from the differential form of the local constitutive law. Different approaches have thus been developed to describe the impact of such complex couplings on the overall behavior. (...)
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10985/108462015-01-01T00:00:00ZMAREAU, CharlesBERBENNI, StéphaneThe self-consistent scheme is a common homogenization method that was developed to connect local deformation mechanisms to the overall behavior of heterogeneous disordered materials. In the past decades, many efforts have been made to obtain extensions of the self-consistent approximation to the non-linear case. This work focuses on the specific case of heterogeneous materials with an elastic-viscoplastic behavior. For such materials, the overall behavior is strongly dependent on the space-time couplings originating from the differential form of the local constitutive law. Different approaches have thus been developed to describe the impact of such complex couplings on the overall behavior. (...)A crystal plasticity based approach for the modelling of high cycle fatigue damage in metallic materials
http://hdl.handle.net/10985/11139
A crystal plasticity based approach for the modelling of high cycle fatigue damage in metallic materials
ZGHAL, Jihed; GMATI, Hela; MAREAU, Charles; MOREL, Franck
In this paper, a polycrystalline model is proposed to describe the fatigue behaviour of metallic materials in the high cycle fatigue regime. The model is based on a multiscale approach, which allows the connection of local deformation and damage mechanisms to macroscopic behaviour. To consider the anisotropy of plastic properties, the constitutive model is developed at the grain scale within a crystal plasticity framework. A phenomenological approach, which requires the introduction of a damage variable for each slip system, is used to account for the anisotropic nature of damage. The constitutive model is then integrated within a self-consistent formulation to consider the polycrystalline nature of metallic materials. Finally, the proposed model is used to describe the high cycle fatigue behaviour of a medium carbon steel (0.35% C). With a proper adjustment of material parameters, the model is capable of correctly reproducing fatigue test results, even for complex loading conditions (multiaxial, non-proportional). According to the model, damage is found to be highly localized in some specific grains. Also, while fatigue damage results in a progressive decrease in elastic stiffness at the crystal scale, the elastic properties are not significantly affected at the macroscopic scale. The model is used to study the correlation and fatigue damage. According to the numerical results, no evident correlation between fatigue damage and energy dissipation is observed.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10985/111392016-01-01T00:00:00ZZGHAL, JihedGMATI, HelaMAREAU, CharlesMOREL, FranckIn this paper, a polycrystalline model is proposed to describe the fatigue behaviour of metallic materials in the high cycle fatigue regime. The model is based on a multiscale approach, which allows the connection of local deformation and damage mechanisms to macroscopic behaviour. To consider the anisotropy of plastic properties, the constitutive model is developed at the grain scale within a crystal plasticity framework. A phenomenological approach, which requires the introduction of a damage variable for each slip system, is used to account for the anisotropic nature of damage. The constitutive model is then integrated within a self-consistent formulation to consider the polycrystalline nature of metallic materials. Finally, the proposed model is used to describe the high cycle fatigue behaviour of a medium carbon steel (0.35% C). With a proper adjustment of material parameters, the model is capable of correctly reproducing fatigue test results, even for complex loading conditions (multiaxial, non-proportional). According to the model, damage is found to be highly localized in some specific grains. Also, while fatigue damage results in a progressive decrease in elastic stiffness at the crystal scale, the elastic properties are not significantly affected at the macroscopic scale. The model is used to study the correlation and fatigue damage. According to the numerical results, no evident correlation between fatigue damage and energy dissipation is observed.Evolution du bilan énergétique dans les matériaux métalliques sous sollicitation cyclique.
http://hdl.handle.net/10985/7462
Evolution du bilan énergétique dans les matériaux métalliques sous sollicitation cyclique.
MAREAU, Charles; MOREL, Franck
In the case of cyclic plasticity, the validity of a constitutive model is usually assessed using stress-strain curves. However, this description can be enriched by adopting an energetic point of view. Thus, in the present work, a multiscale model is developed to estimate the amount of energy which is either dissipated into heat or stored in the material in a medium carbon steel under cyclic loading. The results emphasize the heterogeneous aspect of the stored and dissipated energy fields at a microscopic scale.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/74622013-01-01T00:00:00ZMAREAU, CharlesMOREL, FranckIn the case of cyclic plasticity, the validity of a constitutive model is usually assessed using stress-strain curves. However, this description can be enriched by adopting an energetic point of view. Thus, in the present work, a multiscale model is developed to estimate the amount of energy which is either dissipated into heat or stored in the material in a medium carbon steel under cyclic loading. The results emphasize the heterogeneous aspect of the stored and dissipated energy fields at a microscopic scale.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.A comparison between different methods for the numerical simulation of polycrystalline aggregates
http://hdl.handle.net/10985/10777
A comparison between different methods for the numerical simulation of polycrystalline aggregates
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 (SC) method [1], the finite element (FE) method and the spectral (FFT) method [2] are compared. These common methods are used to determine the effective behavior of different 316L polycrystalline aggregates subjected to various loading conditions (uniaxial tension, cyclic tension/compression).(...)
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10985/107772016-01-01T00:00:00ZROBERT, 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 (SC) method [1], the finite element (FE) method and the spectral (FFT) method [2] are compared. These common methods are used to determine the effective behavior of different 316L polycrystalline aggregates subjected to various loading conditions (uniaxial tension, cyclic tension/compression).(...)High Cycle Fatigue Strength of Punched Thin Fe-Si Steel Sheets
http://hdl.handle.net/10985/11225
High Cycle Fatigue Strength of Punched Thin Fe-Si Steel Sheets
DEHMANI, Helmi; BRUGGER, Charles; PALIN-LUC, Thierry; MAREAU, Charles; KOECHLIN, Samuel
Some parts of electrical machines are built from stacks of thin steel sheets, for which the coarse grain microstructure allows for minimizing magnetic losses. The fabrication process of these parts usually involves punching operations that generate important defects on the edges. Since these alterations may result in a degradation of the fatigue strength, this study aims at elaborating on a fatigue design strategy for such punched parts. To reach this objective, high cycle fatigue tests are performed on different specimens with either punched or polished edges. The results show a significant decrease of the fatigue strength for punched specimens. Scanning electron microscope observations of specimen facture surfaces reveal that defects on punched edges are at the origin of the fatigue cracks. The influence of temperature is also investigated. Fatigue tests are performed at ambient temperature (20°C) and at 180°C. According to the experimental results, no significant influence on the median fatigue strength is observed. Since crack initiation always occur on the edges, additional investigations are performed to characterize how edges are altered by punching operations. Residual stresses are determined on punched edges using x-ray diffraction techniques. As a consequence of punching, important tensile residual stresses exist along the loading direction. In association with the stress concentration caused by geometrical defects, residual stresses promote crack initiation and fast crack propagation. For a better understanding of crack initiation, edge geometries are scanned with a 3D optical profilometer, allowing us to identify the critical defect. It is found that the typical defect size is comparable to the grain size.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10985/112252016-01-01T00:00:00ZDEHMANI, HelmiBRUGGER, CharlesPALIN-LUC, ThierryMAREAU, CharlesKOECHLIN, SamuelSome parts of electrical machines are built from stacks of thin steel sheets, for which the coarse grain microstructure allows for minimizing magnetic losses. The fabrication process of these parts usually involves punching operations that generate important defects on the edges. Since these alterations may result in a degradation of the fatigue strength, this study aims at elaborating on a fatigue design strategy for such punched parts. To reach this objective, high cycle fatigue tests are performed on different specimens with either punched or polished edges. The results show a significant decrease of the fatigue strength for punched specimens. Scanning electron microscope observations of specimen facture surfaces reveal that defects on punched edges are at the origin of the fatigue cracks. The influence of temperature is also investigated. Fatigue tests are performed at ambient temperature (20°C) and at 180°C. According to the experimental results, no significant influence on the median fatigue strength is observed. Since crack initiation always occur on the edges, additional investigations are performed to characterize how edges are altered by punching operations. Residual stresses are determined on punched edges using x-ray diffraction techniques. As a consequence of punching, important tensile residual stresses exist along the loading direction. In association with the stress concentration caused by geometrical defects, residual stresses promote crack initiation and fast crack propagation. For a better understanding of crack initiation, edge geometries are scanned with a 3D optical profilometer, allowing us to identify the critical defect. It is found that the typical defect size is comparable to the grain size.Experimental and numerical study of the evolution of stored and dissipated energies in a medium carbon steel under cyclic loading
http://hdl.handle.net/10985/7034
Experimental and numerical study of the evolution of stored and dissipated energies in a medium carbon steel under cyclic loading
MAREAU, Charles; CUILLERIER, Daniel; MOREL, Franck
To obtain robust estimations of the fatigue limit from energy-based fatigue criteria, constitutive laws must include a correct description of the energy balance when modeling the cyclic behavior. The present paper aims at providing a better understanding of the evolution of the energy balance at both microscopic and macroscopic scales in a medium carbon steel. First, an experimental procedure is used to estimate the amount of energy which is either stored in the material or dissipated into heat at a macroscopic scale. The energy balance is observed to be very dependent on the stress amplitude and the number of loading cycles. A model is then developed to investigate the energy balance at a microscopic scale. From the simulation results, both the stored energy and dissipated energy fields are found to be strongly scattered. The dispersion is mostly explained by the crystallographic orientation distribution and the two-phased microstructure.
Lien vers la version éditeur: http://www.sciencedirect.com/science/article/pii/S0167663613000288
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/70342013-01-01T00:00:00ZMAREAU, CharlesCUILLERIER, DanielMOREL, FranckTo obtain robust estimations of the fatigue limit from energy-based fatigue criteria, constitutive laws must include a correct description of the energy balance when modeling the cyclic behavior. The present paper aims at providing a better understanding of the evolution of the energy balance at both microscopic and macroscopic scales in a medium carbon steel. First, an experimental procedure is used to estimate the amount of energy which is either stored in the material or dissipated into heat at a macroscopic scale. The energy balance is observed to be very dependent on the stress amplitude and the number of loading cycles. A model is then developed to investigate the energy balance at a microscopic scale. From the simulation results, both the stored energy and dissipated energy fields are found to be strongly scattered. The dispersion is mostly explained by the crystallographic orientation distribution and the two-phased microstructure.