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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.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.Modélisation autocohérente des matériaux hétérogènes élasto-viscoplastiques: une approche à champs translatés
http://hdl.handle.net/10985/10844
Modélisation autocohérente des matériaux hétérogènes élasto-viscoplastiques: une approche à champs translatés
MAREAU, Charles; BERBENNI, Stéphane
La méthode autocohérente [1] est un des outils permettant de faire le lien entre les mécanismes de déformation à l'échelle locale et le comportement macroscopique effectif. Si la méthode autocohérente a été initialement développée pour des comportements locaux linéaires, des extensions ont été proposées pour différentes classes de comportements non-linéaires : élastoplasticité [2] et viscoplasticité [3]. (...)
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/108442014-01-01T00:00:00ZMAREAU, CharlesBERBENNI, StéphaneLa méthode autocohérente [1] est un des outils permettant de faire le lien entre les mécanismes de déformation à l'échelle locale et le comportement macroscopique effectif. Si la méthode autocohérente a été initialement développée pour des comportements locaux linéaires, des extensions ont été proposées pour différentes classes de comportements non-linéaires : élastoplasticité [2] et viscoplasticité [3]. (...)Experimental and numerical study of the evolution of stored energy in metallic materials under cyclic loading
http://hdl.handle.net/10985/10763
Experimental and numerical study of the evolution of stored energy in metallic materials under cyclic loading
MAREAU, Charles; MOREL, Franck
In-service loading conditions usually generate complex cyclic stress states. As such, the choice of an appropriate multiaxial fatigue criterion plays a crucial role in obtaining correct fatigue predictions. In the case of high cycle fatigue, the observation of the stabilized behavior is generally required to build either stress-based criteria or energy-based criteria. ....
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/107632014-01-01T00:00:00ZMAREAU, CharlesMOREL, FranckIn-service loading conditions usually generate complex cyclic stress states. As such, the choice of an appropriate multiaxial fatigue criterion plays a crucial role in obtaining correct fatigue predictions. In the case of high cycle fatigue, the observation of the stabilized behavior is generally required to build either stress-based criteria or energy-based criteria. ....Surface versus internal fatigue crack initiation in steel : Influence of mean stress
http://hdl.handle.net/10985/10759
Surface versus internal fatigue crack initiation in steel : Influence of mean stress
GAUR, Vidit; DOQUET, Véronique; PERSENT, Emmanuel; MAREAU, Charles; ROGUET, Eléonore; KITTEL, Jean
Stress-controlled fatigue tests were run at different R ratios (= sigma min / sigma max) up to at most 3 million cycles on a 2.5%Cr–1%Mo steel (ASTM A182 F22) used in riser tubes connectors for offshore oil drilling. The fatigue lives, as well as the slope of the S – N curves were found to decrease with increasing R and the endurance limit to follow Gerber’s parabola. Surface crack initiation without any defect involved, was most often observed for R=-1, 0.5 and 0, while an R ratio of 0.25 triggered crack initiation from either surface or internal pores or chemically inhomogeneous areas, leading, in the latter case, to fish-eye patterns for relatively low numbers of cycles. A further increase in R ratio to 0.5 promoted only defect-initiated surface cracks, while no fatigue fracture was observed within 10 million cycles above R=0.6. These transitions in crack initiation mode are discussed based on X-ray diffraction analyses of residual stresses, elastic–plastic F.E. computations on a unit cell model containing a pore and some fracture mechanics analyses, with a particular attention to environmental effects.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10985/107592016-01-01T00:00:00ZGAUR, ViditDOQUET, VéroniquePERSENT, EmmanuelMAREAU, CharlesROGUET, EléonoreKITTEL, JeanStress-controlled fatigue tests were run at different R ratios (= sigma min / sigma max) up to at most 3 million cycles on a 2.5%Cr–1%Mo steel (ASTM A182 F22) used in riser tubes connectors for offshore oil drilling. The fatigue lives, as well as the slope of the S – N curves were found to decrease with increasing R and the endurance limit to follow Gerber’s parabola. Surface crack initiation without any defect involved, was most often observed for R=-1, 0.5 and 0, while an R ratio of 0.25 triggered crack initiation from either surface or internal pores or chemically inhomogeneous areas, leading, in the latter case, to fish-eye patterns for relatively low numbers of cycles. A further increase in R ratio to 0.5 promoted only defect-initiated surface cracks, while no fatigue fracture was observed within 10 million cycles above R=0.6. These transitions in crack initiation mode are discussed based on X-ray diffraction analyses of residual stresses, elastic–plastic F.E. computations on a unit cell model containing a pore and some fracture mechanics analyses, with a particular attention to environmental effects.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.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).(...)Development of a polycrystalline approach for the modelling of high cycle fatigue damage: Application to a HSLA steel
http://hdl.handle.net/10985/10379
Development of a polycrystalline approach for the modelling of high cycle fatigue damage: Application to a HSLA steel
ZGHAL, Jihed; MAREAU, Charles; MOREL, Franck
For many metallic alloys, fatigue crack initiation is governed by the development of a localized plastic activity at the grain scale. Because of the irreversible nature of plasticity, a significant proportion of the total work is dissipated into heat during a cyclic loading. As a consequence, one may expect some correlation between heat dissipation and high cycle fatigue damage as both phenomena are closely related. The purpose of the present work is to study such correlation for a ferritic high strength low alloyed steel subjected to various cyclic loading conditions. For several uniaxial fatigue tests carried out under different load ratios and stress levels, an experimental dataset consisting of stress, strain and temperature measurements is used to estimate the evolution of the amount of dissipated energy. A clear correlation between dissipated energy and the number of cycles to failure is observed.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10985/103792015-01-01T00:00:00ZZGHAL, JihedMAREAU, CharlesMOREL, FranckFor many metallic alloys, fatigue crack initiation is governed by the development of a localized plastic activity at the grain scale. Because of the irreversible nature of plasticity, a significant proportion of the total work is dissipated into heat during a cyclic loading. As a consequence, one may expect some correlation between heat dissipation and high cycle fatigue damage as both phenomena are closely related. The purpose of the present work is to study such correlation for a ferritic high strength low alloyed steel subjected to various cyclic loading conditions. For several uniaxial fatigue tests carried out under different load ratios and stress levels, an experimental dataset consisting of stress, strain and temperature measurements is used to estimate the evolution of the amount of dissipated energy. A clear correlation between dissipated energy and the number of cycles to failure is observed.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.