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The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Fri, 06 Dec 2019 08:22:29 GMT2019-12-06T08:22:29ZSurface 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.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 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.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. ....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.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.Micromechanical modeling if the interactions between the microstructure and the dissipative deformation mechanisms in steels under cyclic loading
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.An affine formulation for the self-consistent modeling of elasto-viscoplastic heterogeneous materials based on the translated field method
http://hdl.handle.net/10985/9494
An affine formulation for the self-consistent modeling of elasto-viscoplastic heterogeneous materials based on the translated field method
MAREAU, Charles; BERBENNI, Stéphane
The modeling of heterogeneous materials with an elasto-viscoplastic behavior is generally complex because of the differential nature of the local constitutive law. Indeed, the resolution of the heterogeneous problem involves space-time couplings which are generally difficult to estimate. In the present paper, a new homogenization model based on an affine linearization of the viscoplastic flow rule is proposed. First, the heterogeneous problem is written in the form of an integral equation. The purely thermoelastic and purely viscoplastic heterogeneous problems are solved independently using the self-consistent approximation. Using translated field techniques, the solutions of the above problems are combined to obtain the final self-consistent formulation. Then, some applications concerning two-phase fibre-reinforced composites and polycrystalline materials are presented. When compared to the reference solutions obtained from a FFT spectral method, a good description of the overall response of heterogeneous materials is obtained with the proposed model even when the viscoplastic flow rule is highly non-linear. Thanks to this approach, which is entirely formulated in the real-time space, the present model can be used for studying the response of heterogeneous materials submitted to complex thermomechanical loading paths with a good numerical efficiency.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10985/94942015-01-01T00:00:00ZMAREAU, CharlesBERBENNI, StéphaneThe modeling of heterogeneous materials with an elasto-viscoplastic behavior is generally complex because of the differential nature of the local constitutive law. Indeed, the resolution of the heterogeneous problem involves space-time couplings which are generally difficult to estimate. In the present paper, a new homogenization model based on an affine linearization of the viscoplastic flow rule is proposed. First, the heterogeneous problem is written in the form of an integral equation. The purely thermoelastic and purely viscoplastic heterogeneous problems are solved independently using the self-consistent approximation. Using translated field techniques, the solutions of the above problems are combined to obtain the final self-consistent formulation. Then, some applications concerning two-phase fibre-reinforced composites and polycrystalline materials are presented. When compared to the reference solutions obtained from a FFT spectral method, a good description of the overall response of heterogeneous materials is obtained with the proposed model even when the viscoplastic flow rule is highly non-linear. Thanks to this approach, which is entirely formulated in the real-time space, the present model can be used for studying the response of heterogeneous materials submitted to complex thermomechanical loading paths with a good numerical efficiency.A 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).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.