SAM
https://sam.ensam.eu:443
The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Fri, 05 Mar 2021 09:32:15 GMT2021-03-05T09:32:15ZModeling of niobium precipitates effect on the Ni 47Ti 44Nb 9 Shape Memory Alloy behavior
http://hdl.handle.net/10985/10098
Modeling of niobium precipitates effect on the Ni 47Ti 44Nb 9 Shape Memory Alloy behavior
PIOTROWSKI, Boris; BEN ZINEB, Tarak; PATOOR, Etienne; EBERHARDT, André
Commercial Ni 47Ti 44Nb9 Shape Memory Alloy (SMA) is generally adopted for tightening applications thanks to its wide transformation hysteresis, compared with classical NiTi. Its sensibility to thermo-mechanical treatments allows it to be either martensitic or austenitic in a wide range of temperature, between -60 °C and 80 °C. A modeling of niobium precipitates effects on Ni 47Ti 44Nb9 SMA behavior is proposed. For this object, a two phase thermo-mechanical model is developed. It describes the global effective behavior of an elastoplastic inclusion (niobium precipitates) embedded within an SMA matrix. The constitutive law developed by Peultier et al. (2006) and improved by Chemisky et al. (2011) is adopted to model the matrix shape memory behavior. The elastoplastic constitutive law for inclusion is the one proposed by Wilkins with Simo and Hughes's radial return algorithm. The Mori-Tanaka scale transition scheme is considered for the determination of the effective constitutive equations. Obtained results highlight the effect of niobium precipitates on the thermomechanical behavior of Ni47Ti 44Nb9, and particularly on the corresponding hysteresis size. It appears that the niobium plasticity increases this hysteresis size. The developed constitutive law has been implemented in the ABAQUS Finite Element code and considered for the numerical prediction of the tightening pressure in a connection application
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10985/100982012-01-01T00:00:00ZPIOTROWSKI, BorisBEN ZINEB, TarakPATOOR, EtienneEBERHARDT, AndréCommercial Ni 47Ti 44Nb9 Shape Memory Alloy (SMA) is generally adopted for tightening applications thanks to its wide transformation hysteresis, compared with classical NiTi. Its sensibility to thermo-mechanical treatments allows it to be either martensitic or austenitic in a wide range of temperature, between -60 °C and 80 °C. A modeling of niobium precipitates effects on Ni 47Ti 44Nb9 SMA behavior is proposed. For this object, a two phase thermo-mechanical model is developed. It describes the global effective behavior of an elastoplastic inclusion (niobium precipitates) embedded within an SMA matrix. The constitutive law developed by Peultier et al. (2006) and improved by Chemisky et al. (2011) is adopted to model the matrix shape memory behavior. The elastoplastic constitutive law for inclusion is the one proposed by Wilkins with Simo and Hughes's radial return algorithm. The Mori-Tanaka scale transition scheme is considered for the determination of the effective constitutive equations. Obtained results highlight the effect of niobium precipitates on the thermomechanical behavior of Ni47Ti 44Nb9, and particularly on the corresponding hysteresis size. It appears that the niobium plasticity increases this hysteresis size. The developed constitutive law has been implemented in the ABAQUS Finite Element code and considered for the numerical prediction of the tightening pressure in a connection applicationDetermination of the characteristic parameters of tension-compression asymmetry of Shape Memory Alloys using full-field measurements
http://hdl.handle.net/10985/11190
Determination of the characteristic parameters of tension-compression asymmetry of Shape Memory Alloys using full-field measurements
CHEMISKY, Yves; ECHCHORFI, Rachid; MERAGHNI, Fodil; BOURGEOIS, Nadine; PIOTROWSKI, Boris
In this work, a method for the identification of the transformation surface of Shape Memory Alloys based on full field measurements is presented. An inverse method coupled with a gradient-based algorithm has been developed to determine the characteristic parameters of the transformation surface. The constitutive equations of the chosen model that capture the macroscopic behavior of Shape Memory Alloys are first presented. The material parameters, to be identified, that are characteristic of the tension-compression asymmetry of the alloy are detailed. The identification algorithm, based on full field measurements obtained by Digital Image Correlation (DIC) and numerical simulation by Finite Element Analysis are introduced. The identification algorithm is validated using a numerically generated strain field on a Meuwissen-type specimen.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/111902013-01-01T00:00:00ZCHEMISKY, YvesECHCHORFI, RachidMERAGHNI, FodilBOURGEOIS, NadinePIOTROWSKI, BorisIn this work, a method for the identification of the transformation surface of Shape Memory Alloys based on full field measurements is presented. An inverse method coupled with a gradient-based algorithm has been developed to determine the characteristic parameters of the transformation surface. The constitutive equations of the chosen model that capture the macroscopic behavior of Shape Memory Alloys are first presented. The material parameters, to be identified, that are characteristic of the tension-compression asymmetry of the alloy are detailed. The identification algorithm, based on full field measurements obtained by Digital Image Correlation (DIC) and numerical simulation by Finite Element Analysis are introduced. The identification algorithm is validated using a numerically generated strain field on a Meuwissen-type specimen.Identification and interpretation of material parameters of a shape memory alloy (SMA) model
http://hdl.handle.net/10985/10575
Identification and interpretation of material parameters of a shape memory alloy (SMA) model
PIOTROWSKI, Boris; CHEMISKY, Yves; MERAGHNI, Fodil; ECHCHORFI, Rachid; BOURGEOIS, Nadine; PATOOR, Etienne
The thermomechanical behavior of Shape Memory Alloys (SMAs) is described by many micromechanical and phenomenological models. The first ones have material parameters whose physical meaning is based on the crystallography of the phase transformation related to the studied alloy. In contrast, phenomenological models often have material parameters whose physical meaning is not obvious and that makes them difficult to identify, some of which are based on mathematical considerations. In this paper, we propose to use the formulation of the phenomenological model of Chemisky et al., and to consider the particular case of a superelastic SMA. In this case, the constitutive equation should be easily expressed analytically through the strain tensor as a function of applied load direction and material parameters. The behavior is then characterized by a complete and proportional loading. This analytical model contains 7 material parameters, 1 related to the elasticity and 6 to the phase transformation. Based on several isothermal tensile tests at various temperatures, material parameters of this model are identified using the Levenberg-Marquardt algorithm and an analytical calculation of the sensitivity matrix. Their physical meaning and their influence on the thermomechanical behavior of the studied alloy are highlighted and discussed.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/105752013-01-01T00:00:00ZPIOTROWSKI, BorisCHEMISKY, YvesMERAGHNI, FodilECHCHORFI, RachidBOURGEOIS, NadinePATOOR, EtienneThe thermomechanical behavior of Shape Memory Alloys (SMAs) is described by many micromechanical and phenomenological models. The first ones have material parameters whose physical meaning is based on the crystallography of the phase transformation related to the studied alloy. In contrast, phenomenological models often have material parameters whose physical meaning is not obvious and that makes them difficult to identify, some of which are based on mathematical considerations. In this paper, we propose to use the formulation of the phenomenological model of Chemisky et al., and to consider the particular case of a superelastic SMA. In this case, the constitutive equation should be easily expressed analytically through the strain tensor as a function of applied load direction and material parameters. The behavior is then characterized by a complete and proportional loading. This analytical model contains 7 material parameters, 1 related to the elasticity and 6 to the phase transformation. Based on several isothermal tensile tests at various temperatures, material parameters of this model are identified using the Levenberg-Marquardt algorithm and an analytical calculation of the sensitivity matrix. Their physical meaning and their influence on the thermomechanical behavior of the studied alloy are highlighted and discussed.Three-dimensional FE2 method for the simulation of non-linear, rate-dependent response of composite structures
http://hdl.handle.net/10985/12935
Three-dimensional FE2 method for the simulation of non-linear, rate-dependent response of composite structures
TIKARROUCHINE, El-Hadi; CHATZIGEORGIOU, George; PRAUD, Francis; PIOTROWSKI, Boris; CHEMISKY, Yves; MERAGHNI, Fodil
In this paper, a two scale Finite Element method (FE2 ), is presented to predict the non-linear macroscopic response of 3D composite structures with periodic microstructure that exhibit a time-dependent response. The sensitivity to the strain rate requires an homogenization scheme to bridge the scales between the macroscopic boundary conditions applied and the local evaluation of the strain rate. In the present work, the effective response of composite materials where the matrix has a local elasto-viscoplastic behavior with ductile damage are analyzed using periodic homogenization, solving simultaneously finite element problems at the microscopic scale (unit cell) and at the macroscopic scale. This approach can integrate any kind of periodic microstructure with any type of non-linear behavior for the constituents (without the consideration of non-linear geometric effects), allowing to treat complex mechanisms that can occur in every phase and at their interface. The numerical implementation of this simulation strategy has been performed with a parallel computational technique in ABAQUS/Standard,with the implementation of a set of dedicated scripts. The homogenization process is performed using a user-defined constitutive law that solve a set full-field non-linear simulations of a Unit Cell and perform the necessary homogenization of the mechanical quantities. The effectiveness of the method is demonstrated with three examples of 3D composite structures with plastic or viscoplastic and ductile damage matrix. In the first example, the numerical results obtained by this full field approach are compared with a semi-analytical solution on elastoplastic multilayer composite structure. The second example investigates the macroscopic response of a complex viscoplastic composite structure with ductile damage and is compared with the mean field Mori-Tanaka method. Finally, 3D corner structure consisting of periodically aligned short fibres composite is analysed under complex loading path. These numerical simulations illustrate the capabilities of the FE2 strategy under non-linear regime, when time dependent constitutive models describe the response of the constituents
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/10985/129352018-01-01T00:00:00ZTIKARROUCHINE, El-HadiCHATZIGEORGIOU, GeorgePRAUD, FrancisPIOTROWSKI, BorisCHEMISKY, YvesMERAGHNI, FodilIn this paper, a two scale Finite Element method (FE2 ), is presented to predict the non-linear macroscopic response of 3D composite structures with periodic microstructure that exhibit a time-dependent response. The sensitivity to the strain rate requires an homogenization scheme to bridge the scales between the macroscopic boundary conditions applied and the local evaluation of the strain rate. In the present work, the effective response of composite materials where the matrix has a local elasto-viscoplastic behavior with ductile damage are analyzed using periodic homogenization, solving simultaneously finite element problems at the microscopic scale (unit cell) and at the macroscopic scale. This approach can integrate any kind of periodic microstructure with any type of non-linear behavior for the constituents (without the consideration of non-linear geometric effects), allowing to treat complex mechanisms that can occur in every phase and at their interface. The numerical implementation of this simulation strategy has been performed with a parallel computational technique in ABAQUS/Standard,with the implementation of a set of dedicated scripts. The homogenization process is performed using a user-defined constitutive law that solve a set full-field non-linear simulations of a Unit Cell and perform the necessary homogenization of the mechanical quantities. The effectiveness of the method is demonstrated with three examples of 3D composite structures with plastic or viscoplastic and ductile damage matrix. In the first example, the numerical results obtained by this full field approach are compared with a semi-analytical solution on elastoplastic multilayer composite structure. The second example investigates the macroscopic response of a complex viscoplastic composite structure with ductile damage and is compared with the mean field Mori-Tanaka method. Finally, 3D corner structure consisting of periodically aligned short fibres composite is analysed under complex loading path. These numerical simulations illustrate the capabilities of the FE2 strategy under non-linear regime, when time dependent constitutive models describe the response of the constituentsA continuous crystallographic approach to generate cubic lattices and its effect on relative stiffness of architectured materials
http://hdl.handle.net/10985/12914
A continuous crystallographic approach to generate cubic lattices and its effect on relative stiffness of architectured materials
FAVRE, Julien; LOHMULLER, Paul; PIOTROWSKI, Boris; KENZARI, Samuel; LAHEURTE, Pascal; MERAGHNI, Fodil
This original work proposes to investigate the transposition of crystallography rules to cubic lattice architectured materials to generate new 3D porous structures. The application of symmetry operations provides a complete and convenient way to configure the lattice architecture with only two parameters. New lattice structures were created by slipping from the conventional Bravais lattice toward non-compact complex structures. The resulting stiffness of the porous materials was thoroughly evaluated for all the combinations of architecture parameters. This exhaustive study revealed attractive structures having high specific stiffness, up to twice as large as the usual octet-truss for a given relative density. It results in a relationship between effective Young modulus and relative density for any lattice structure. It also revealed the opportunity to generate auxetic structures at will, with a controlled Poisson ratio. The collection of the elastic properties for all the cubic structures into 3D maps provides a convenient tool for lattice materials design, for research, and for mechanical engineering. The resulting mechanical properties are highly variable according to architecture, and can be easily tailored for specific applications using the simple yet powerful formalism developed in this work.
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/10985/129142018-01-01T00:00:00ZFAVRE, JulienLOHMULLER, PaulPIOTROWSKI, BorisKENZARI, SamuelLAHEURTE, PascalMERAGHNI, FodilThis original work proposes to investigate the transposition of crystallography rules to cubic lattice architectured materials to generate new 3D porous structures. The application of symmetry operations provides a complete and convenient way to configure the lattice architecture with only two parameters. New lattice structures were created by slipping from the conventional Bravais lattice toward non-compact complex structures. The resulting stiffness of the porous materials was thoroughly evaluated for all the combinations of architecture parameters. This exhaustive study revealed attractive structures having high specific stiffness, up to twice as large as the usual octet-truss for a given relative density. It results in a relationship between effective Young modulus and relative density for any lattice structure. It also revealed the opportunity to generate auxetic structures at will, with a controlled Poisson ratio. The collection of the elastic properties for all the cubic structures into 3D maps provides a convenient tool for lattice materials design, for research, and for mechanical engineering. The resulting mechanical properties are highly variable according to architecture, and can be easily tailored for specific applications using the simple yet powerful formalism developed in this work.Parameter identification of a thermodynamic model for superelastic shape memory alloys using analytical calculation of the sensitivity matrix
http://hdl.handle.net/10985/9966
Parameter identification of a thermodynamic model for superelastic shape memory alloys using analytical calculation of the sensitivity matrix
MERAGHNI, Fodil; CHEMISKY, Yves; PIOTROWSKI, Boris; ECHCHORFI, Rachid; BOURGEOIS, Nadine; PATOOR, Etienne
This paper presents an identification procedure for the parameters of a thermodynamically based constitutive model for Shape memory Alloys (SMAs). The proposed approach is a gradient-based method and utilizes an analytical computation of the sensitivity matrix. For several loading cases, including superelasticity, that are commonly utilized for the model parameters identification of such a constitutive model, a closed-form of the total infinitesimal strain is derived. The partial derivatives of this state variable are developed to find the components of the sensitivity matrix. A LevenbergeMarquardt algorithm is utilized to solve the inverse problem and find the best set of model parameters for specific SMA materials. Moreover, a pre-identification method, based on the second derivative of the total strain components is proposed. This provides a suitable initial set of model parameters, which increases the efficiency of the inverse method. The proposed approach is applied for the simultaneous identification of the non-linear constitutive parameters for two superelastic SMAs. The comparison between experimental and numerical curves obtained for different temperatures shows the capabilities of the developed identification approach. The robustness and the efficiency of the developed approach are then experimentally validated
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Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/99662014-01-01T00:00:00ZMERAGHNI, FodilCHEMISKY, YvesPIOTROWSKI, BorisECHCHORFI, RachidBOURGEOIS, NadinePATOOR, EtienneThis paper presents an identification procedure for the parameters of a thermodynamically based constitutive model for Shape memory Alloys (SMAs). The proposed approach is a gradient-based method and utilizes an analytical computation of the sensitivity matrix. For several loading cases, including superelasticity, that are commonly utilized for the model parameters identification of such a constitutive model, a closed-form of the total infinitesimal strain is derived. The partial derivatives of this state variable are developed to find the components of the sensitivity matrix. A LevenbergeMarquardt algorithm is utilized to solve the inverse problem and find the best set of model parameters for specific SMA materials. Moreover, a pre-identification method, based on the second derivative of the total strain components is proposed. This provides a suitable initial set of model parameters, which increases the efficiency of the inverse method. The proposed approach is applied for the simultaneous identification of the non-linear constitutive parameters for two superelastic SMAs. The comparison between experimental and numerical curves obtained for different temperatures shows the capabilities of the developed identification approach. The robustness and the efficiency of the developed approach are then experimentally validatedMechanical properties of a nanoporous membrane used in implantable medical devices. Correlation between experimental characterization and 2D numerical simulation
http://hdl.handle.net/10985/11801
Mechanical properties of a nanoporous membrane used in implantable medical devices. Correlation between experimental characterization and 2D numerical simulation
CRISTOFARI, François; PIOTROWSKI, Boris; PESCI, Raphaël
Nanoporous membranes are used for the elaboration of implantable medical devices. In order to guaranty their integrity after implantation in a patient body, it is necessary to characterize the microstructure and the mechanical behavior of such membranes. They present randomly distributed pores around 1 µm in diameter at the surface. X-ray nanotomography permits to get the geometry of the pores through the thickness with a reduction of the diameter in the core. A multiscale study is done to characterize the membranes: macroscopic tensile tests permit to get the behavior law of the non porous material and in situ tensile tests are carried on in a Scanning Electron Microscope in order to observe the evolution of pores and cracks during loading. A 2D Finite Element Model is also developed in parallel. The confrontation between experiments and numerical simulations permit to validate the accuracy of the model. The latter is then used to simulate several types of loadings considering various pore distributions and sizes.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/10985/118012017-01-01T00:00:00ZCRISTOFARI, FrançoisPIOTROWSKI, BorisPESCI, RaphaëlNanoporous membranes are used for the elaboration of implantable medical devices. In order to guaranty their integrity after implantation in a patient body, it is necessary to characterize the microstructure and the mechanical behavior of such membranes. They present randomly distributed pores around 1 µm in diameter at the surface. X-ray nanotomography permits to get the geometry of the pores through the thickness with a reduction of the diameter in the core. A multiscale study is done to characterize the membranes: macroscopic tensile tests permit to get the behavior law of the non porous material and in situ tensile tests are carried on in a Scanning Electron Microscope in order to observe the evolution of pores and cracks during loading. A 2D Finite Element Model is also developed in parallel. The confrontation between experiments and numerical simulations permit to validate the accuracy of the model. The latter is then used to simulate several types of loadings considering various pore distributions and sizes.Modéliation multi-échelle non-linéaire par homogénéisation périodique et analyses par EF2 : application aux composites à matrice elastoviscoplastique endommageable
http://hdl.handle.net/10985/11999
Modéliation multi-échelle non-linéaire par homogénéisation périodique et analyses par EF2 : application aux composites à matrice elastoviscoplastique endommageable; Non-linear multi-scale modelling through periodic homogenization and FE2 analyses: application for composites with elastoviscoplastic damageable matrix
TIKARROUCHINE, El-Hadi; PRAUD, Francis; CHATZIGEORGIOU, George; PIOTROWSKI, Boris; CHEMISKY, Yves; MERAGHNI, Fodil
Dans ce papier, une technique de modélisation multi-échelle (EF2) basée sur le principe d’homogénéisation périodique a été développée pour décrire le comportement des structures composites 3D avec un comportement élastoviscoplastique des endommageable. L’approche proposée permet de simuler le comportement macroscopique non linéaire d’un composite à microstructure périodique à partir d’un calcul EF sur sa cellule unitaire, elle-même alimentée par les lois de comportement de chacun de ses constituants. La méthode introduit ainsi le concept de méta modèle. Le principal avantage de cette méthode est de s’affranchir totalement des limitations sur les lois de comportement locales, ainsi que les lois constitutives à l’échelle macroscopique ne sont pas nécessaire La mise en œuvre numérique de cette stratégie a été réalisée dans ABAQUS Implicit. Enfin l’approche a été validée sur macro-structure 3D sur laquelle, une cellule unitaire est affectée à chaque point d’intégration.; In this paper, a two-level Finite Element method (FE2), based on periodic homogenization, has been introduced to describe the behavior of 3D composite structures with elastoviscoplastic behavior and ductile damage. In the present approach, the unknown constitutive relationship at the macroscale is obtained by solving a local finite element problem at the microscale (unit cell). The main advantage of the proposed strategy is that the FE 2 method does not require an analytical form for the constitutive law at the macroscale. It can integrate any kind of microstructure with any type of non-linear behavior of the reinforcement (fibers and/or particles) embedded in the matrix. The numerical implementation of this model has been achieved with parallel computation technique in ABAQUS Implicit, where a python script and user subroutines UMAT have been developed for this goal. Finally numerical results are presented for a 3D composite structure.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/10985/119992017-01-01T00:00:00ZTIKARROUCHINE, El-HadiPRAUD, FrancisCHATZIGEORGIOU, GeorgePIOTROWSKI, BorisCHEMISKY, YvesMERAGHNI, FodilDans ce papier, une technique de modélisation multi-échelle (EF2) basée sur le principe d’homogénéisation périodique a été développée pour décrire le comportement des structures composites 3D avec un comportement élastoviscoplastique des endommageable. L’approche proposée permet de simuler le comportement macroscopique non linéaire d’un composite à microstructure périodique à partir d’un calcul EF sur sa cellule unitaire, elle-même alimentée par les lois de comportement de chacun de ses constituants. La méthode introduit ainsi le concept de méta modèle. Le principal avantage de cette méthode est de s’affranchir totalement des limitations sur les lois de comportement locales, ainsi que les lois constitutives à l’échelle macroscopique ne sont pas nécessaire La mise en œuvre numérique de cette stratégie a été réalisée dans ABAQUS Implicit. Enfin l’approche a été validée sur macro-structure 3D sur laquelle, une cellule unitaire est affectée à chaque point d’intégration.
In this paper, a two-level Finite Element method (FE2), based on periodic homogenization, has been introduced to describe the behavior of 3D composite structures with elastoviscoplastic behavior and ductile damage. In the present approach, the unknown constitutive relationship at the macroscale is obtained by solving a local finite element problem at the microscale (unit cell). The main advantage of the proposed strategy is that the FE 2 method does not require an analytical form for the constitutive law at the macroscale. It can integrate any kind of microstructure with any type of non-linear behavior of the reinforcement (fibers and/or particles) embedded in the matrix. The numerical implementation of this model has been achieved with parallel computation technique in ABAQUS Implicit, where a python script and user subroutines UMAT have been developed for this goal. Finally numerical results are presented for a 3D composite structure.Interaction of bone-dental implant with new ultra low modulus alloy using a numerical approach
http://hdl.handle.net/10985/10097
Interaction of bone-dental implant with new ultra low modulus alloy using a numerical approach
PIOTROWSKI, Boris; BAPTISTA, André; PATOOR, Etienne; BRAVETTI, Pierre; EBERHARDT, André; LAHEURTE, Pascal
Although mechanical stress is known as being a significant factor in bone remodeling, most implants are still made using materials that have a higher elastic stiffness than that of bones. Load transfer between the implant and the surrounding bones is much detrimental, and osteoporosis is often a consequence of such mechanical mismatch. The concept of mechanical biocompatibility has now been considered for more than a decade. However, it is limited by the choice of materials, mainly Ti-based alloys whose elastic properties are still too far from cortical bone. We have suggested using a bulk material in relation with the development of a new beta titanium-based alloy. Titanium is a much suitable biocompatible metal, and beta-titanium alloys such as metastable TiNb exhibit a very low apparent elastic modulus related to the presence of an orthorhombic martensite. The purpose of the present work has been to investigate the interaction that occurs between the dental implants and the cortical bone. 3D finite element models have been adopted to analyze the behaviour of the bone-implant system depending on the elastic properties of the implant, different types of implant geometry, friction force, and loading condition. The geometry of the bone has been adopted from a mandibular incisor and the surrounding bone. Occlusal static forces have been applied to the implants, and their effects on the bone-metal implant interface region have been assessed and compared with a cortical bone/ bone implant configuration. This work has shown that the low modulus implant induces a stress distribution closer to the actual physiological phenomenon, together with a better stress jump along the bone implant interface, regardless of the implant design.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/100972014-01-01T00:00:00ZPIOTROWSKI, BorisBAPTISTA, AndréPATOOR, EtienneBRAVETTI, PierreEBERHARDT, AndréLAHEURTE, PascalAlthough mechanical stress is known as being a significant factor in bone remodeling, most implants are still made using materials that have a higher elastic stiffness than that of bones. Load transfer between the implant and the surrounding bones is much detrimental, and osteoporosis is often a consequence of such mechanical mismatch. The concept of mechanical biocompatibility has now been considered for more than a decade. However, it is limited by the choice of materials, mainly Ti-based alloys whose elastic properties are still too far from cortical bone. We have suggested using a bulk material in relation with the development of a new beta titanium-based alloy. Titanium is a much suitable biocompatible metal, and beta-titanium alloys such as metastable TiNb exhibit a very low apparent elastic modulus related to the presence of an orthorhombic martensite. The purpose of the present work has been to investigate the interaction that occurs between the dental implants and the cortical bone. 3D finite element models have been adopted to analyze the behaviour of the bone-implant system depending on the elastic properties of the implant, different types of implant geometry, friction force, and loading condition. The geometry of the bone has been adopted from a mandibular incisor and the surrounding bone. Occlusal static forces have been applied to the implants, and their effects on the bone-metal implant interface region have been assessed and compared with a cortical bone/ bone implant configuration. This work has shown that the low modulus implant induces a stress distribution closer to the actual physiological phenomenon, together with a better stress jump along the bone implant interface, regardless of the implant design.Multilayer CdHgTe-based infrared detector: 2D/3D microtomography, synchrotron emission and finite element modelling with stress distribution at room temperature and 100 K
http://hdl.handle.net/10985/18176
Multilayer CdHgTe-based infrared detector: 2D/3D microtomography, synchrotron emission and finite element modelling with stress distribution at room temperature and 100 K
LEBAUDY, Anne-Laure; PESCI, Raphaël; PIOTROWSKI, Boris
The mechanical behaviour of a CdHgTe-based infrared detector was evaluated after processing at several temperatures to determine the impact of thermomechanical loading on residual stress and reliability. The architecture of the detector was first entirely characterized, relying on SEM, X-ray microtomography and diffraction analysis, in order to get the nature, the morphology and the crystallographic orientation of all the constitutive layers, and in particular the indium solder bumps. The results notably showed the unexpected single crystal aspect of the indium bumps with a repeatable truncated cone geometry. To obtain the thermomechanical response of the structure after processing and in the range of operating temperatures (from 430 K to 100 K), a 3D Finite Element model was then developed. As expected, the numerical results showed a stress gradient evolution in the structure from high to low temperatures, with high loca njvvl stress around 30 MPa in the CdHgTe at 100 K, mainly due to the thermal expansion coefficient mismatch between the different layers. They highlighted the significant influence of the geometry and the single crystal nature of the bumps as well as the behaviour law of the different materials.
Wed, 01 Jan 2020 00:00:00 GMThttp://hdl.handle.net/10985/181762020-01-01T00:00:00ZLEBAUDY, Anne-LaurePESCI, RaphaëlPIOTROWSKI, BorisThe mechanical behaviour of a CdHgTe-based infrared detector was evaluated after processing at several temperatures to determine the impact of thermomechanical loading on residual stress and reliability. The architecture of the detector was first entirely characterized, relying on SEM, X-ray microtomography and diffraction analysis, in order to get the nature, the morphology and the crystallographic orientation of all the constitutive layers, and in particular the indium solder bumps. The results notably showed the unexpected single crystal aspect of the indium bumps with a repeatable truncated cone geometry. To obtain the thermomechanical response of the structure after processing and in the range of operating temperatures (from 430 K to 100 K), a 3D Finite Element model was then developed. As expected, the numerical results showed a stress gradient evolution in the structure from high to low temperatures, with high loca njvvl stress around 30 MPa in the CdHgTe at 100 K, mainly due to the thermal expansion coefficient mismatch between the different layers. They highlighted the significant influence of the geometry and the single crystal nature of the bumps as well as the behaviour law of the different materials.