A simplified polycrystalline model (the so-called RL model) is proposed to simulate the anisotrop... more A simplified polycrystalline model (the so-called RL model) is proposed to simulate the anisotropic viscoplastic behavior of metallic materials. A generic method is presented that makes it possible to build a simplified anisotropic material texture, based on the principal features of the pole figures. The method is applied to a recrystallised zirconium alloy, used as clad material in the fuel rods of nuclear power plants. An important data base consisting in mechanical tests performed on Zircaloy tubes is collected. Only a small number of tests (pure tension, pure shear) are used to identify the material parameters, and the texture parameters. It is shown that 6 crystallographic orientations (6 "grains") are sufficient to describe the large anisotropy of such hcp alloy. The identified crystallographic orientations match the experimental pole figures of the material, not used in the identification procedure. Special attention is paid to the predictive ability of the model, i.e. its ability to simulate correctly experimental tests not belonging to the identification data base. These predictive results are good, thanks to an identification procedure that enables to consider the contribution of each slip system in each crystallographic orientation.
In the fust part of the paper a constitutive model for the pseudoelastic behavior of shape memory... more In the fust part of the paper a constitutive model for the pseudoelastic behavior of shape memory alloys (SMA) is presented in a finite element context. The model frame (state equation and phase transition kinetics) is rapidly described. Then the implemenration of the model into a finite element code based on a fully implicit method consisting in an elastic prediction and phase transition correction is presented. Hence, the stress tensor and the tangent operator are calculated at each displacement increment. For a structural component as a thin plate subjected to bending loads, experimental data and finite element results are in a fair agreement. At last, an industrial application is treated for bronchial protheses used in medicine.
The present work aims at exploring self and latent hardening for FCC polycrystals under complex l... more The present work aims at exploring self and latent hardening for FCC polycrystals under complex loading paths at room temperature. Combinations of simple loading paths sequences, such as tension and simple shear, with different orientations with regard to rolling direction, are considered. Experimental results are compared to finite element computations of polycrystalline aggregates taking into account the material microstructure, and to simulations based on mean field models.
This paper proposes a damaged viscoplastic model to simulate, for different isotherms (320, 350, ... more This paper proposes a damaged viscoplastic model to simulate, for different isotherms (320, 350, 380, 400 and 420°C), the out-of-flux anisotropic mechanical behavior of Zircaloy-4 claddings in a stress relieved state over the fluence range 0-85. 1024 nm2 (E>lMeV). The model, identified from uni and biaxial tests conducted at 350 and 400°C, is validated from tests made at 320, 380 and 420°C. This model is able to simulate strain hardening under an internal pressure followed by a stress relaxation period, since the loading produces an interaction between the pellet and the cladding (thermal creep). Both the integration of a scalar state variable, characterizing the damage caused by a bombardment with neutrons, and the modification of the static recovery law allowed us to simulate the fast neutron flux effect (irradiation creep).
This paper proposes a damaged viscoplastic model to simulate, for different isotherms (320, 350, ... more This paper proposes a damaged viscoplastic model to simulate, for different isotherms (320, 350, 380, 400 and 420°C), the out-of-flux anisotropic mechanical behavior of cold work stress relieved Zircaloy-4 cladding tubes over the fluence range 0-85.10 24 nm -2 (E>1MeV). The model, identified from uni and biaxial tests conducted at 350 and 400°C, is validated from tests performed at 320, 380 and 420°C. This model is able to simulate strain hardening under internal pressure followed by a stress relaxation period (thermal creep), which is representative of a pellet cladding mechanical interaction occurring during a power transient (class 2 incidental condition). Both the integration of a scalar state variable, characterizing the damage caused by a bombardment with neutrons, and the modification of the static recovery law allowed us to simulate the fast neutron flux effect (irradiation creep).
This paper proposes a damaged viscoplastic model to simulate, for different isotherms (320, 350, ... more This paper proposes a damaged viscoplastic model to simulate, for different isotherms (320, 350, 380, 400 and 420°C), the out-of-flux anisotropic mechanical behavior of cold work stress relieved Zircaloy-4 cladding tubes over the fluence range 0-85.10 24 nm -2 (E>1MeV). The model, identified from uni and biaxial tests conducted at 350 and 400°C, is validated from tests performed at 320, 380 and 420°C. This model is able to simulate strain hardening under internal pressure followed by a stress relaxation period (thermal creep), which is representative of a pellet cladding mechanical interaction occurring during a power transient (class 2 incidental condition). Both the integration of a scalar state variable, characterizing the damage caused by a bombardment with neutrons, and the modification of the static recovery law allowed us to simulate the fast neutron flux effect (irradiation creep).
ABSTRACT This paper proposes a damaged viscoplastic model to simulate, for different isotherms (3... more ABSTRACT This paper proposes a damaged viscoplastic model to simulate, for different isotherms (320, 350, 380, 400 and 420°C), the out-of-flux anisotropic mechanical behavior of Zircaloy-4 claddings in a stress relieved state over the fluence range 0-85.10$^{24}$ nm$^{-2}$ ($\rm E>l$MeV). The model, identified from uni and biaxial tests conducted at 350 and 4000°C, is validated from tests made at 320, 380 and 420°C. This model is able to simulate strain hardening under an internal pressure followed by a stress relaxation period, since the loading produces an interaction between the pellet and the cladding (thermal creep). Both the integration of a scalar state variable, characterizing the damage caused by a bombardment with neutrons, and the modification of the static recovery law allowed us to simulate the fast neutron flux effect (irradiation creep).
... The chemical composition of the ASTM Grade 91 steel used in this study is shown in ... is rep... more ... The chemical composition of the ASTM Grade 91 steel used in this study is shown in ... is replaced by an equiaxed structure [20] in the ICHAZ after the post weld heat treatment ... weakest part of the HAZ (ie the ICHAZ) prohibits the study of its mechanical behavior using specimens ...
ABSTRACT This paper presents two case studies in which the use of full field measurements could p... more ABSTRACT This paper presents two case studies in which the use of full field measurements could provide valuable information to allow the development of R&D methods having the potential of assessing industrial issues.The first example is related to the study of the fracture properties of the nuclear fuel rods after a postulated Loss of Coolant Accident (LOCA) event. It will be shown that 3-D Digital Image Correlation strain measurements performed on a non-conventional mechanical test (expansion due to compression) can help to assess failure properties and derive fracture criteria of highly oxydized and hydrided Zircaloy cladding. These fracture criteria are therefore used in the Safety Demonstrations due conducted by EDF in reply to the French Safety Authority.The second example is related to the investigation of potentially brittle failure of an irradiation aged nuclear reactor pressure vessel (RPV) during a Loss of Coolant Accident event. As a matter of fact, the reactor pressure vessel is one of the non replaceable components of a nuclear power plant. Consequently, the study of the RPV ageing is of major importance for assessing plants lifetime. One consequence of the RPV ageing is the increasing risk of brittle fracture during postulated LOCA events. As a first step to better characterize experimentally the embrittlement of RPV steel, the second example presents in-situ strain heterogeneities in the plastic response of bainitic-ferritic 16MND5 steel, with respect to crystalline phases and orientations. These local observations are then used by a specific identification procedure, in order to obtain experimentally the crystal plasticity hardening flow behaviour of RPV steel.
A simplified polycrystalline model (the so-called RL model) is proposed to simulate the anisotrop... more A simplified polycrystalline model (the so-called RL model) is proposed to simulate the anisotropic viscoplastic behavior of metallic materials. A generic method is presented that makes it possible to build a simplified anisotropic material texture, based on the principal features of the pole figures. The method is applied to a recrystallised zirconium alloy, used as clad material in the fuel rods of nuclear power plants. An important data base consisting in mechanical tests performed on Zircaloy tubes is collected. Only a small number of tests (pure tension, pure shear) are used to identify the material parameters, and the texture parameters. It is shown that 6 crystallographic orientations (6 "grains") are sufficient to describe the large anisotropy of such hcp alloy. The identified crystallographic orientations match the experimental pole figures of the material, not used in the identification procedure. Special attention is paid to the predictive ability of the model, i.e. its ability to simulate correctly experimental tests not belonging to the identification data base. These predictive results are good, thanks to an identification procedure that enables to consider the contribution of each slip system in each crystallographic orientation.
In the fust part of the paper a constitutive model for the pseudoelastic behavior of shape memory... more In the fust part of the paper a constitutive model for the pseudoelastic behavior of shape memory alloys (SMA) is presented in a finite element context. The model frame (state equation and phase transition kinetics) is rapidly described. Then the implemenration of the model into a finite element code based on a fully implicit method consisting in an elastic prediction and phase transition correction is presented. Hence, the stress tensor and the tangent operator are calculated at each displacement increment. For a structural component as a thin plate subjected to bending loads, experimental data and finite element results are in a fair agreement. At last, an industrial application is treated for bronchial protheses used in medicine.
The present work aims at exploring self and latent hardening for FCC polycrystals under complex l... more The present work aims at exploring self and latent hardening for FCC polycrystals under complex loading paths at room temperature. Combinations of simple loading paths sequences, such as tension and simple shear, with different orientations with regard to rolling direction, are considered. Experimental results are compared to finite element computations of polycrystalline aggregates taking into account the material microstructure, and to simulations based on mean field models.
This paper proposes a damaged viscoplastic model to simulate, for different isotherms (320, 350, ... more This paper proposes a damaged viscoplastic model to simulate, for different isotherms (320, 350, 380, 400 and 420°C), the out-of-flux anisotropic mechanical behavior of Zircaloy-4 claddings in a stress relieved state over the fluence range 0-85. 1024 nm2 (E>lMeV). The model, identified from uni and biaxial tests conducted at 350 and 400°C, is validated from tests made at 320, 380 and 420°C. This model is able to simulate strain hardening under an internal pressure followed by a stress relaxation period, since the loading produces an interaction between the pellet and the cladding (thermal creep). Both the integration of a scalar state variable, characterizing the damage caused by a bombardment with neutrons, and the modification of the static recovery law allowed us to simulate the fast neutron flux effect (irradiation creep).
This paper proposes a damaged viscoplastic model to simulate, for different isotherms (320, 350, ... more This paper proposes a damaged viscoplastic model to simulate, for different isotherms (320, 350, 380, 400 and 420°C), the out-of-flux anisotropic mechanical behavior of cold work stress relieved Zircaloy-4 cladding tubes over the fluence range 0-85.10 24 nm -2 (E>1MeV). The model, identified from uni and biaxial tests conducted at 350 and 400°C, is validated from tests performed at 320, 380 and 420°C. This model is able to simulate strain hardening under internal pressure followed by a stress relaxation period (thermal creep), which is representative of a pellet cladding mechanical interaction occurring during a power transient (class 2 incidental condition). Both the integration of a scalar state variable, characterizing the damage caused by a bombardment with neutrons, and the modification of the static recovery law allowed us to simulate the fast neutron flux effect (irradiation creep).
This paper proposes a damaged viscoplastic model to simulate, for different isotherms (320, 350, ... more This paper proposes a damaged viscoplastic model to simulate, for different isotherms (320, 350, 380, 400 and 420°C), the out-of-flux anisotropic mechanical behavior of cold work stress relieved Zircaloy-4 cladding tubes over the fluence range 0-85.10 24 nm -2 (E>1MeV). The model, identified from uni and biaxial tests conducted at 350 and 400°C, is validated from tests performed at 320, 380 and 420°C. This model is able to simulate strain hardening under internal pressure followed by a stress relaxation period (thermal creep), which is representative of a pellet cladding mechanical interaction occurring during a power transient (class 2 incidental condition). Both the integration of a scalar state variable, characterizing the damage caused by a bombardment with neutrons, and the modification of the static recovery law allowed us to simulate the fast neutron flux effect (irradiation creep).
ABSTRACT This paper proposes a damaged viscoplastic model to simulate, for different isotherms (3... more ABSTRACT This paper proposes a damaged viscoplastic model to simulate, for different isotherms (320, 350, 380, 400 and 420°C), the out-of-flux anisotropic mechanical behavior of Zircaloy-4 claddings in a stress relieved state over the fluence range 0-85.10$^{24}$ nm$^{-2}$ ($\rm E>l$MeV). The model, identified from uni and biaxial tests conducted at 350 and 4000°C, is validated from tests made at 320, 380 and 420°C. This model is able to simulate strain hardening under an internal pressure followed by a stress relaxation period, since the loading produces an interaction between the pellet and the cladding (thermal creep). Both the integration of a scalar state variable, characterizing the damage caused by a bombardment with neutrons, and the modification of the static recovery law allowed us to simulate the fast neutron flux effect (irradiation creep).
... The chemical composition of the ASTM Grade 91 steel used in this study is shown in ... is rep... more ... The chemical composition of the ASTM Grade 91 steel used in this study is shown in ... is replaced by an equiaxed structure [20] in the ICHAZ after the post weld heat treatment ... weakest part of the HAZ (ie the ICHAZ) prohibits the study of its mechanical behavior using specimens ...
ABSTRACT This paper presents two case studies in which the use of full field measurements could p... more ABSTRACT This paper presents two case studies in which the use of full field measurements could provide valuable information to allow the development of R&D methods having the potential of assessing industrial issues.The first example is related to the study of the fracture properties of the nuclear fuel rods after a postulated Loss of Coolant Accident (LOCA) event. It will be shown that 3-D Digital Image Correlation strain measurements performed on a non-conventional mechanical test (expansion due to compression) can help to assess failure properties and derive fracture criteria of highly oxydized and hydrided Zircaloy cladding. These fracture criteria are therefore used in the Safety Demonstrations due conducted by EDF in reply to the French Safety Authority.The second example is related to the investigation of potentially brittle failure of an irradiation aged nuclear reactor pressure vessel (RPV) during a Loss of Coolant Accident event. As a matter of fact, the reactor pressure vessel is one of the non replaceable components of a nuclear power plant. Consequently, the study of the RPV ageing is of major importance for assessing plants lifetime. One consequence of the RPV ageing is the increasing risk of brittle fracture during postulated LOCA events. As a first step to better characterize experimentally the embrittlement of RPV steel, the second example presents in-situ strain heterogeneities in the plastic response of bainitic-ferritic 16MND5 steel, with respect to crystalline phases and orientations. These local observations are then used by a specific identification procedure, in order to obtain experimentally the crystal plasticity hardening flow behaviour of RPV steel.
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