https://sam.ensam.eu:443 The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material. Thu, 05 Mar 2026 20:48:25 GMT 2026-03-05T20:48:25Z 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; PALIN-LUC, Thierry; MAREAU, Charles; KOECHLIN, Samuel; BRUGGER, Charles 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 GMT http://hdl.handle.net/10985/10762 2016-01-01T00:00:00Z DEHMANI, Helmi PALIN-LUC, Thierry MAREAU, Charles KOECHLIN, Samuel BRUGGER, Charles 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. 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 GMT http://hdl.handle.net/10985/10844 2014-01-01T00:00:00Z 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]. (...) 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 GMT http://hdl.handle.net/10985/9494 2015-01-01T00:00:00Z 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. 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 GMT http://hdl.handle.net/10985/9493 2015-01-01T00:00:00Z 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). http://hdl.handle.net/10985/16562 On the formation of adiabatic shear bands in titanium alloy Ti17 under severe loading conditions BEN BOUBAKER, Houssem; AYED, Yessine; MAREAU, Charles; GERMAIN, Guénaël For metallic materials, fabrication processes (e.g. machining and forging) may involve important strain rates and high temperatures. For such severe loading conditions, the development of damage is often associated with the formation of Adiabatic Shear Bands (ASB). In this work, the impact of loading conditions (strain rate, temperature) on the formation of ASB in a beta rich titanium alloy (Ti17) is investigated. In this perspective, uniaxial compression tests have been conducted on cylindrical samples with a Gleeble-3500 thermo-mechanical simulator at temperatures ranging from 25◦C to 800◦C and strain rates ranging from 0.1 to 50 s−1 with axial strains of approximately 50 %. According to the experimental results, the flow curves exhibit hardening from 25◦C to 550◦C and softening from 600◦C to 800◦C. When looking at the evolution of flow stress, the strain rate sensitivity is found to increase significantly with increasing temperatures. Also, adiabatic shear bands are preferably observed for high strain rates and low temperatures. The formation of ASB thus seems to be quite dependent on the evolution of the strain rate sensitivity of Ti17. Finally, metallographic observations have been carried out to better understand the process leading to the formation of ASB. Such observations demonstrate that the average width of ASB increases with increasing temperatures and decreasing strain rates. However, such observations do not allow for identifying whether some specific microstructural transformations (e.g. recrystallization or phase transformation) could explain the formation of ASB or not. Mon, 01 Jan 2018 00:00:00 GMT http://hdl.handle.net/10985/16562 2018-01-01T00:00:00Z BEN BOUBAKER, Houssem AYED, Yessine MAREAU, Charles GERMAIN, Guénaël For metallic materials, fabrication processes (e.g. machining and forging) may involve important strain rates and high temperatures. For such severe loading conditions, the development of damage is often associated with the formation of Adiabatic Shear Bands (ASB). In this work, the impact of loading conditions (strain rate, temperature) on the formation of ASB in a beta rich titanium alloy (Ti17) is investigated. In this perspective, uniaxial compression tests have been conducted on cylindrical samples with a Gleeble-3500 thermo-mechanical simulator at temperatures ranging from 25◦C to 800◦C and strain rates ranging from 0.1 to 50 s−1 with axial strains of approximately 50 %. According to the experimental results, the flow curves exhibit hardening from 25◦C to 550◦C and softening from 600◦C to 800◦C. When looking at the evolution of flow stress, the strain rate sensitivity is found to increase significantly with increasing temperatures. Also, adiabatic shear bands are preferably observed for high strain rates and low temperatures. The formation of ASB thus seems to be quite dependent on the evolution of the strain rate sensitivity of Ti17. Finally, metallographic observations have been carried out to better understand the process leading to the formation of ASB. Such observations demonstrate that the average width of ASB increases with increasing temperatures and decreasing strain rates. However, such observations do not allow for identifying whether some specific microstructural transformations (e.g. recrystallization or phase transformation) could explain the formation of ASB or not. http://hdl.handle.net/10985/17253 High cycle fatigue strength assessment methodology considering punching effects DEHMANI, Helmi; PALIN-LUC, Thierry; MAREAU, Charles; KOECHLIN, Samuel; BRUGGER, Charles Since a decrease of the fatigue strength may result from punching operations, this study proposes a methodology for designing punched parts against high cycle fatigue crack initiation. To reach this goal, high cycle fatigue tests are performed on different specimens configurations with either punched or polished edges. Due to punching effects, the fatigue strength of punched specimens is significantly decreased. Fracture surfaces observations reveal that crack initiation occurs always on a punch defect. Additional investigations are combined to characterize how the edges are altered by the punching operations. High tensile residual stress levels along the loading direction are quantified using X-Ray diffraction techniques. Furthermore, micro-hardness measurements and X-Ray diffraction results reveals a strong hardness gradient due to punching operation. For a better understanding of crack initiation mechanisms, the edge geometries have been scanned with 3D optical microscopy, allowing us to identify the most critical defect (and its real geometry) by comparing the edges before and after fatigue failure. Finally, FEA are performed on identified defects. A non-local high cycle multiaxial fatigue strength criterion has been used as post-processing of FEA to take into account the effect on the HCF strength of defects and the strong stress-strain gradients around them. Mon, 01 Jan 2018 00:00:00 GMT http://hdl.handle.net/10985/17253 2018-01-01T00:00:00Z DEHMANI, Helmi PALIN-LUC, Thierry MAREAU, Charles KOECHLIN, Samuel BRUGGER, Charles Since a decrease of the fatigue strength may result from punching operations, this study proposes a methodology for designing punched parts against high cycle fatigue crack initiation. To reach this goal, high cycle fatigue tests are performed on different specimens configurations with either punched or polished edges. Due to punching effects, the fatigue strength of punched specimens is significantly decreased. Fracture surfaces observations reveal that crack initiation occurs always on a punch defect. Additional investigations are combined to characterize how the edges are altered by the punching operations. High tensile residual stress levels along the loading direction are quantified using X-Ray diffraction techniques. Furthermore, micro-hardness measurements and X-Ray diffraction results reveals a strong hardness gradient due to punching operation. For a better understanding of crack initiation mechanisms, the edge geometries have been scanned with 3D optical microscopy, allowing us to identify the most critical defect (and its real geometry) by comparing the edges before and after fatigue failure. Finally, FEA are performed on identified defects. A non-local high cycle multiaxial fatigue strength criterion has been used as post-processing of FEA to take into account the effect on the HCF strength of defects and the strong stress-strain gradients around them. http://hdl.handle.net/10985/17536 Impact of the initial microstructure and the loading conditions on the deformation behavior of the Ti17 titanium alloy BEN BOUBAKER, Houssem; MAREAU, Charles; AYED, Yessine; GERMAIN, Guénaël; TIDU, Albert In this work, the impact of the microstructure and the loading conditions on the mechanical behavior of a β-rich Ti17 titanium alloy is investigated. For this purpose, two different initial microstructures are considered : (i) a two-phase lamellar α + β microstructure and (ii) a single-phase equiaxed β-treated microstructure. First, compression tests are performed at different strain rates (from 10-1 to 10 s-1) and different temperatures (from 25 to 900°C) for both microstructures. Then, optical microscopy, scanning electron microscopy, EBSD and X-ray diffraction analyses of deformed specimens are carried out. Whatever the loading conditions are, the flow stress of the as-received α + β Ti17 is higher than that of the β-treated Ti17. Also, because of a higher strain-rate sensitivity, the β-treated Ti17 is less prone to shear banding. At low temperatures (i.e., T ≤ 450°C), the deformation behavior of both the as-received α + β and the β-treated Ti17 is controlled by strain hardening. For the β-treated Ti17 alloy, martensitic transformation is systematically detected in this temperature range. The softening behavior of the as-received α + β Ti17 observed at high temperatures is due to the joint effect of dynamic recrystallization, dynamic transformation, adiabatic heating and morphological texture evolution. For the β-treated Ti17 alloy, when the temperature exceeds 700°C, stress–strain curves display a yield drop phenomenon, which is explained by dynamic recrystallization. Tue, 01 Jan 2019 00:00:00 GMT http://hdl.handle.net/10985/17536 2019-01-01T00:00:00Z BEN BOUBAKER, Houssem MAREAU, Charles AYED, Yessine GERMAIN, Guénaël TIDU, Albert In this work, the impact of the microstructure and the loading conditions on the mechanical behavior of a β-rich Ti17 titanium alloy is investigated. For this purpose, two different initial microstructures are considered : (i) a two-phase lamellar α + β microstructure and (ii) a single-phase equiaxed β-treated microstructure. First, compression tests are performed at different strain rates (from 10-1 to 10 s-1) and different temperatures (from 25 to 900°C) for both microstructures. Then, optical microscopy, scanning electron microscopy, EBSD and X-ray diffraction analyses of deformed specimens are carried out. Whatever the loading conditions are, the flow stress of the as-received α + β Ti17 is higher than that of the β-treated Ti17. Also, because of a higher strain-rate sensitivity, the β-treated Ti17 is less prone to shear banding. At low temperatures (i.e., T ≤ 450°C), the deformation behavior of both the as-received α + β and the β-treated Ti17 is controlled by strain hardening. For the β-treated Ti17 alloy, martensitic transformation is systematically detected in this temperature range. The softening behavior of the as-received α + β Ti17 observed at high temperatures is due to the joint effect of dynamic recrystallization, dynamic transformation, adiabatic heating and morphological texture evolution. For the β-treated Ti17 alloy, when the temperature exceeds 700°C, stress–strain curves display a yield drop phenomenon, which is explained by dynamic recrystallization. http://hdl.handle.net/10985/11142 Micromechanical modelling of twinning in polycrystalline materials: Application to magnesium MAREAU, Charles; DAYMOND, Mark R In this work, a crystal plasticity constitutive model is proposed to describe the mechanical behavior of metallic materials for which twinning plays a significant role in the deformation process. Constitutive relations are obtained from a micromechanical approach that explicitly considers the interactions between twinned and untwinned domains. Then, based on a thermodynamical analysis of the problem, a new expression for the driving force for the expansion of twinned domains is proposed. Finally, to account for the polycrystalline nature of metallic materials, the constitutive model is implemented in a FFT spectral solver. In the second part of this paper, the model is used to study the mechanical behavior of a AZ31 magnesium alloy under compression, for which a significant amount of experimental data is available in the literature. The comparison between numerical and experimental data allows for discussion of the influence of the different deformation modes on the development of both crystallographic texture and lattice strains. The evolution of lattice strains is found to be largely influenced by the internal stress redistribution process associated with the expansion of twinned domains. Also, the polycrystalline plasticity model provides a correct description of how the morphological texture is strongly altered during the deformation process due to the important activity of twinning systems. Fri, 01 Jan 2016 00:00:00 GMT http://hdl.handle.net/10985/11142 2016-01-01T00:00:00Z MAREAU, Charles DAYMOND, Mark R In this work, a crystal plasticity constitutive model is proposed to describe the mechanical behavior of metallic materials for which twinning plays a significant role in the deformation process. Constitutive relations are obtained from a micromechanical approach that explicitly considers the interactions between twinned and untwinned domains. Then, based on a thermodynamical analysis of the problem, a new expression for the driving force for the expansion of twinned domains is proposed. Finally, to account for the polycrystalline nature of metallic materials, the constitutive model is implemented in a FFT spectral solver. In the second part of this paper, the model is used to study the mechanical behavior of a AZ31 magnesium alloy under compression, for which a significant amount of experimental data is available in the literature. The comparison between numerical and experimental data allows for discussion of the influence of the different deformation modes on the development of both crystallographic texture and lattice strains. The evolution of lattice strains is found to be largely influenced by the internal stress redistribution process associated with the expansion of twinned domains. Also, the polycrystalline plasticity model provides a correct description of how the morphological texture is strongly altered during the deformation process due to the important activity of twinning systems. http://hdl.handle.net/10985/17964 Microstructure and self-heating for ferritic steels under cyclic loading at low stress magnitudes MAREAU, Charles; GALTIER, André; WEBER, Bastien; BERVEILLER, Marcel; FAVIER, Véronique A newmicromechanical modelling is proposed to correlate some microstructural parameters and dissipation in ferritic steels under cyclic loading.We assumed the occurrence of two dissipative mechanisms associated with anelastic and inelastic deformations, respectively. We showed that the modelling provides good qualitative prediction of the heating curves when changing the volume fraction of precipitates in ferritic steels. We highlighted the key role of the dispersion of the grain size on the local and global dissipation. Fri, 01 Jan 2010 00:00:00 GMT http://hdl.handle.net/10985/17964 2010-01-01T00:00:00Z MAREAU, Charles GALTIER, André WEBER, Bastien BERVEILLER, Marcel FAVIER, Véronique A newmicromechanical modelling is proposed to correlate some microstructural parameters and dissipation in ferritic steels under cyclic loading.We assumed the occurrence of two dissipative mechanisms associated with anelastic and inelastic deformations, respectively. We showed that the modelling provides good qualitative prediction of the heating curves when changing the volume fraction of precipitates in ferritic steels. We highlighted the key role of the dispersion of the grain size on the local and global dissipation. http://hdl.handle.net/10985/17254 Characterization and simulation of the effect of punching on the high cycle fatigue strength of thin electric steel sheets DEHMANI, Helmi; PALIN-LUC, Thierry; MAREAU, Charles; KOECHLIN, Samuel; BRUGGER, Charles Rotors of electric machines are built from stacks of thin steel sheets. The fabrication process of these components usually involves punching operations that generate defects on the steel sheet edges. In this study, high cycle fatigue tests are performed on punched and polished edges specimens to investigate the effect of the punching process on the fatigue behaviour of these thin sheets. Results show a significant decrease of the fatigue strength for punched specimens. SEM observations of fracture surfaces reveal that crack initiation always occurs on a punching defect. Residual stresses on punched edges are analysed using X-Ray diffraction techniques. High tensile residual stresses along the loading direction are found. Some specimens edges were scanned using 3D topography prior to the fatigue tests. This allows for identifying the real geometry of the most critical defect. Murakami criterion was then evaluated in order to take into account the effect of defects. The best trend of the experimental results is given when residual stresses are taken into account. Local elastic stresses for 3 defects geometries have been calculated using FEA. Crossland fatigue criterion has been evaluated to try accounting for the local stress state around defects. Results show that the assessed fatigue strength is overestimated using this criterion. 6th Fatigue Design conference, Fatigue Design 2015 Thu, 01 Jan 2015 00:00:00 GMT http://hdl.handle.net/10985/17254 2015-01-01T00:00:00Z DEHMANI, Helmi PALIN-LUC, Thierry MAREAU, Charles KOECHLIN, Samuel BRUGGER, Charles Rotors of electric machines are built from stacks of thin steel sheets. The fabrication process of these components usually involves punching operations that generate defects on the steel sheet edges. In this study, high cycle fatigue tests are performed on punched and polished edges specimens to investigate the effect of the punching process on the fatigue behaviour of these thin sheets. Results show a significant decrease of the fatigue strength for punched specimens. SEM observations of fracture surfaces reveal that crack initiation always occurs on a punching defect. Residual stresses on punched edges are analysed using X-Ray diffraction techniques. High tensile residual stresses along the loading direction are found. Some specimens edges were scanned using 3D topography prior to the fatigue tests. This allows for identifying the real geometry of the most critical defect. Murakami criterion was then evaluated in order to take into account the effect of defects. The best trend of the experimental results is given when residual stresses are taken into account. Local elastic stresses for 3 defects geometries have been calculated using FEA. Crossland fatigue criterion has been evaluated to try accounting for the local stress state around defects. Results show that the assessed fatigue strength is overestimated using this criterion.