https://sam.ensam.eu:443 The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material. Mon, 13 Jul 2026 07:24:47 GMT 2026-07-13T07:24:47Z http://hdl.handle.net/10985/10100 A finite-element based numerical tool for Ni47Ti44Nb9 SMA structures design application to tightening rings PIOTROWSKI, Boris; BEN ZINEB, Tarak; EBERHARDT, André; PATOOR, Etienne This paper deals with the design of Ni47Ti44Nb9 Shape Memory Alloy (SMA) tightening components. The tightening of an SMA ring on an elastic pipe is analyzed using the finite element code ABAQUS® and a UMAT subroutine developed in our group to model the specific behavior of Ni47Ti44Nb9 SMA. Main features of the thermomechanical model implemented in this UMAT routine are briefly recalled. Numerical predictions are validated using experimental tightening pressures obtained on a test bed developed in this work. The validation strategy is documented and the results for different ring thicknesses are presented. This finite element tool is then applied to a parametric study of the influence of ridges on the tightening pressure. Eventually, geometrical defects like out of roundness are considered. Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/10985/10100 2012-01-01T00:00:00Z PIOTROWSKI, Boris BEN ZINEB, Tarak EBERHARDT, André PATOOR, Etienne This paper deals with the design of Ni47Ti44Nb9 Shape Memory Alloy (SMA) tightening components. The tightening of an SMA ring on an elastic pipe is analyzed using the finite element code ABAQUS® and a UMAT subroutine developed in our group to model the specific behavior of Ni47Ti44Nb9 SMA. Main features of the thermomechanical model implemented in this UMAT routine are briefly recalled. Numerical predictions are validated using experimental tightening pressures obtained on a test bed developed in this work. The validation strategy is documented and the results for different ring thicknesses are presented. This finite element tool is then applied to a parametric study of the influence of ridges on the tightening pressure. Eventually, geometrical defects like out of roundness are considered. 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 GMT http://hdl.handle.net/10985/10575 2013-01-01T00:00:00Z 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. 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 I Wed, 01 Jan 2014 00:00:00 GMT http://hdl.handle.net/10985/9966 2014-01-01T00:00:00Z 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 http://hdl.handle.net/10985/14096 Stress Concentration and Mechanical Strength of Cubic Lattice Architectures LOHMULLER, Paul; FAVRE, Julien; PIOTROWSKI, Boris; KENZARI, Samuel; LAHEURTE, Pascal The continuous design of cubic lattice architecture materials provides a wide range of mechanical properties. It makes possible to control the stress magnitude and the local maxima in the structure. This study reveals some architectures specifically designed to reach a good compromise between mass reduction and mechanical strength. Decreased local stress concentration prevents the early occurrence of localized plasticity or damage, and promotes the fatigue resistance. The high performance of cubic architectures is reported extensively, and structures with the best damage resistance are identified. The fatigue resistance and S–N curves (stress magnitude versus lifetime curves) can be estimated successfully, based on the investigation of the stress concentration. The output data are represented in two-dimensional (2D) color maps to help mechanical engineers in selecting the suitable architecture with the desired stress concentration factor, and eventually with the correct fatigue lifetime. Mon, 01 Jan 2018 00:00:00 GMT http://hdl.handle.net/10985/14096 2018-01-01T00:00:00Z LOHMULLER, Paul FAVRE, Julien PIOTROWSKI, Boris KENZARI, Samuel LAHEURTE, Pascal The continuous design of cubic lattice architecture materials provides a wide range of mechanical properties. It makes possible to control the stress magnitude and the local maxima in the structure. This study reveals some architectures specifically designed to reach a good compromise between mass reduction and mechanical strength. Decreased local stress concentration prevents the early occurrence of localized plasticity or damage, and promotes the fatigue resistance. The high performance of cubic architectures is reported extensively, and structures with the best damage resistance are identified. The fatigue resistance and S–N curves (stress magnitude versus lifetime curves) can be estimated successfully, based on the investigation of the stress concentration. The output data are represented in two-dimensional (2D) color maps to help mechanical engineers in selecting the suitable architecture with the desired stress concentration factor, and eventually with the correct fatigue lifetime. http://hdl.handle.net/10985/16043 Architectural effect on 3D elastic properties and anisotropy of cubic lattice structures LOHMULLER, Paul; FAVRE, Julien; KENZARI, Samuel; PIOTROWSKI, Boris; PELTIER, Laurent; LAHEURTE, Pascal This article investigates the elastic properties of a large panel of lattice architectures using a continuous description of geometry. The elastic constants of the orthotropic material are determined, and discussed in terms of specific stiffness and of its density dependence. Different kind of topology families are emerging depending on their specific deformation behavior. For some of them, interesting properties in term of traction-compression were measured, while some other families are predominantly adapted to shear loading. Homogenization technique also allows to quantify the anisotropy of the structures and to compare them. Specific structures having quasi-isotropic properties even at low relative densities were detected. Experimental works demonstrated the validity of the numerical models, and highlighted the necessity to consider carefully the effect of defects on the specific strength, which are of the second-order however not negligible. Finally, this article provides user-friendly maps for selection of optimal architectures for a large variety of specific needs, like a target stiffness or anisotropy. Tue, 01 Jan 2019 00:00:00 GMT http://hdl.handle.net/10985/16043 2019-01-01T00:00:00Z LOHMULLER, Paul FAVRE, Julien KENZARI, Samuel PIOTROWSKI, Boris PELTIER, Laurent LAHEURTE, Pascal This article investigates the elastic properties of a large panel of lattice architectures using a continuous description of geometry. The elastic constants of the orthotropic material are determined, and discussed in terms of specific stiffness and of its density dependence. Different kind of topology families are emerging depending on their specific deformation behavior. For some of them, interesting properties in term of traction-compression were measured, while some other families are predominantly adapted to shear loading. Homogenization technique also allows to quantify the anisotropy of the structures and to compare them. Specific structures having quasi-isotropic properties even at low relative densities were detected. Experimental works demonstrated the validity of the numerical models, and highlighted the necessity to consider carefully the effect of defects on the specific strength, which are of the second-order however not negligible. Finally, this article provides user-friendly maps for selection of optimal architectures for a large variety of specific needs, like a target stiffness or anisotropy. http://hdl.handle.net/10985/16041 Numerical tool for SMA material simulation: application to composite structure design CHEMISKY, Yves; DUVAL, Arnaud; PIOTROWSKI, Boris; BEN ZINEB, Tarak; TAHIRI, Vanessa; PATOOR, Etienne Composite materials based on shape memory alloys (SMA) have received growing attention over these last few years. In this paper, two particular morphologies of composites are studied. The first one is an SMA/elastomer composite in which a snake-like wire NiTi SMA is embedded into an elastomer ribbon. The second one is a commercial Ni47Ti44Nb9 which presents elastic–plastic inclusions in an NiTi SMA matrix. In both cases, the design of such composites required the development of an SMA design tool, based on a macroscopic 3D constitutive law for NiTi alloys. Two different strategies are then applied to compute these composite behaviors. For the SMA/elastomer composite, the macroscopic behavior law is implemented in commercial FEM software, and for the Ni47Ti44Nb9 a scale transition approach based on the Mori–Tanaka scheme is developed. In both cases, simulations are compared to experimental data. Thu, 01 Jan 2009 00:00:00 GMT http://hdl.handle.net/10985/16041 2009-01-01T00:00:00Z CHEMISKY, Yves DUVAL, Arnaud PIOTROWSKI, Boris BEN ZINEB, Tarak TAHIRI, Vanessa PATOOR, Etienne Composite materials based on shape memory alloys (SMA) have received growing attention over these last few years. In this paper, two particular morphologies of composites are studied. The first one is an SMA/elastomer composite in which a snake-like wire NiTi SMA is embedded into an elastomer ribbon. The second one is a commercial Ni47Ti44Nb9 which presents elastic–plastic inclusions in an NiTi SMA matrix. In both cases, the design of such composites required the development of an SMA design tool, based on a macroscopic 3D constitutive law for NiTi alloys. Two different strategies are then applied to compute these composite behaviors. For the SMA/elastomer composite, the macroscopic behavior law is implemented in commercial FEM software, and for the Ni47Ti44Nb9 a scale transition approach based on the Mori–Tanaka scheme is developed. In both cases, simulations are compared to experimental data. 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; PIOTROWSKI, Boris; PESCI, Raphaël 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 GMT http://hdl.handle.net/10985/18176 2020-01-01T00:00:00Z LEBAUDY, Anne-Laure PIOTROWSKI, Boris PESCI, Raphaël 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. http://hdl.handle.net/10985/16042 Mechanical stability of custom-made implants: Numerical study of anatomical device and low elastic Young's modulus alloy DIDIER, Paul; PIOTROWSKI, Boris; FISCHER, Marie; LAHEURTE, Pascal The advent of new manufacturing technologies such as additive manufacturing deeply impacts the approach for the design of medical devices. It is now possible to design custom-made implants based on medical imaging, with complex anatomic shape, and to manufacture them. In this study, two geometrical configurations of implant devices are studied, standard and anatomical. The comparison highlights the drawbacks of the standard configuration, which requires a specific forming by plastic strain in order to be adapted to the patient’s morphology and induces stress field in bones without mechanical load in the implant. The influence of low elastic modulus of the materials on stress distribution is investigated. Two biocompatible alloys having the ability to be used with SLM additive manufacturing are considered, commercial Ti-6Al-4V and Ti-26Nb. It is shown that beyond the geometrical aspect, mechanical compatibility between implants and bones can be significantly improved with the modulus of Ti-26Nb implants compared with the Ti-6Al-4V. Sun, 01 Jan 2017 00:00:00 GMT http://hdl.handle.net/10985/16042 2017-01-01T00:00:00Z DIDIER, Paul PIOTROWSKI, Boris FISCHER, Marie LAHEURTE, Pascal The advent of new manufacturing technologies such as additive manufacturing deeply impacts the approach for the design of medical devices. It is now possible to design custom-made implants based on medical imaging, with complex anatomic shape, and to manufacture them. In this study, two geometrical configurations of implant devices are studied, standard and anatomical. The comparison highlights the drawbacks of the standard configuration, which requires a specific forming by plastic strain in order to be adapted to the patient’s morphology and induces stress field in bones without mechanical load in the implant. The influence of low elastic modulus of the materials on stress distribution is investigated. Two biocompatible alloys having the ability to be used with SLM additive manufacturing are considered, commercial Ti-6Al-4V and Ti-26Nb. It is shown that beyond the geometrical aspect, mechanical compatibility between implants and bones can be significantly improved with the modulus of Ti-26Nb implants compared with the Ti-6Al-4V. http://hdl.handle.net/10985/16055 Contribution of computational model for assessment of heart tissue local stress caused by suture in LVAD implantation CHALON, Antoine; FAVRE, Julien; PIOTROWSKI, Boris; LANDMANN, V.; GRANDMOUGIN, David; MAUREIRA, Juan Pablo; LAHEURTE, Pascal; TRAN, Nguyen Study: Implantation of a Left Ventricular Assist Device (LVAD) may produce both excessive local tissue stress and resulting strain-induced tissue rupture that are potential iatrogenic factors influencing the success of the surgical attachment of the LVAD into the myocardium. By using a computational simulation compared to mechanical tests, we sought to investigate the characteristics of stress-induced suture material on porcine myocardium. Methods: Tensile strength experiments (n = 8) were performed on bulk left myocardium to establish a hyperelastic reduced polynomial constitutive law. Simultaneously, suture strength tests on left myocardium (n = 6) were performed with a standard tensile test setup. Experiments were made on bulk ventricular wall with a single U-suture (polypropylene 3–0) and a PTFE pledget. Then, a Finite Element simulation of a LVAD suture case was performed. Strength versus displacement behavior was compared between mechanical and numerical experiments. Local stress fields in the model were thus analyzed. Results: A strong correlation between the experimental and the numerical responses was observed, validating the relevance of the numerical model. A secure damage limit of 100 kPa on heart tissue was defined from mechanical suture testing and used to describe numerical results. The impact of suture on heart tissue could be accurately determined through new parameters of numerical data (stress diffusion, triaxiality stress). Finally, an ideal spacing between sutures of 2 mm was proposed. Conclusion: Our computational model showed a reliable ability to provide and predict various local tissue stresses created by suture penetration into the myocardium. In addition, this model contributed to providing valuable information useful to design less traumatic sutures for LVAD implantation. Therefore, our computational model is a promising tool to predict and optimize LVAD myocardial suture. Mon, 01 Jan 2018 00:00:00 GMT http://hdl.handle.net/10985/16055 2018-01-01T00:00:00Z CHALON, Antoine FAVRE, Julien PIOTROWSKI, Boris LANDMANN, V. GRANDMOUGIN, David MAUREIRA, Juan Pablo LAHEURTE, Pascal TRAN, Nguyen Study: Implantation of a Left Ventricular Assist Device (LVAD) may produce both excessive local tissue stress and resulting strain-induced tissue rupture that are potential iatrogenic factors influencing the success of the surgical attachment of the LVAD into the myocardium. By using a computational simulation compared to mechanical tests, we sought to investigate the characteristics of stress-induced suture material on porcine myocardium. Methods: Tensile strength experiments (n = 8) were performed on bulk left myocardium to establish a hyperelastic reduced polynomial constitutive law. Simultaneously, suture strength tests on left myocardium (n = 6) were performed with a standard tensile test setup. Experiments were made on bulk ventricular wall with a single U-suture (polypropylene 3–0) and a PTFE pledget. Then, a Finite Element simulation of a LVAD suture case was performed. Strength versus displacement behavior was compared between mechanical and numerical experiments. Local stress fields in the model were thus analyzed. Results: A strong correlation between the experimental and the numerical responses was observed, validating the relevance of the numerical model. A secure damage limit of 100 kPa on heart tissue was defined from mechanical suture testing and used to describe numerical results. The impact of suture on heart tissue could be accurately determined through new parameters of numerical data (stress diffusion, triaxiality stress). Finally, an ideal spacing between sutures of 2 mm was proposed. Conclusion: Our computational model showed a reliable ability to provide and predict various local tissue stresses created by suture penetration into the myocardium. In addition, this model contributed to providing valuable information useful to design less traumatic sutures for LVAD implantation. Therefore, our computational model is a promising tool to predict and optimize LVAD myocardial suture. http://hdl.handle.net/10985/25421 Flip-chip technology at room temperature: A new design of microtube-based interconnect for improved mechanical and electrical properties DESBORDES, Cloé; PESCI, Raphaël; PIOTROWSKI, Boris; MAILLIART, Olivier; RAPHOZ, Natacha Flip-chip assembly of photonic components can be achieved at room temperature by using 10 μm pitch interconnects made of metallised oxide microtubes inserted into ductile reception pads. In order to reduce the electrical resistance of interconnects and the assembly force required, interconnect design in regard to geometry and materials used are optimised through electrical and mechanical finite elements (FEM) simulations. To reduce electrical resistance, one may increase the metallisation thickness or microtube inner diameter. To minimise the assembly force, reducing the reception pad diameter is recommended. Experiments on silicon (Si) test vehicles are conducted to validate these predictions; they indicate that there is no short circuit, with an effectiveness of 100 %. This is achieved first through the assembly of Al-0.5 %wCu metallised oxide microtubes into Al-0.5 %wCu reception pads, using a force less than 10 mN/interconnect and proved to have a resistance of 230 mΩ. Second, with gold (Au) metallised oxide microtubes in indium (In) pads assembled with a force less than 0.7 mN/ interconnect. Last interconnects have a resistance of 670 mΩ/interconnect and can still be reduced to 500 mΩ by 2 h annealing at 100 ◦C. Tue, 01 Oct 2024 00:00:00 GMT http://hdl.handle.net/10985/25421 2024-10-01T00:00:00Z DESBORDES, Cloé PESCI, Raphaël PIOTROWSKI, Boris MAILLIART, Olivier RAPHOZ, Natacha Flip-chip assembly of photonic components can be achieved at room temperature by using 10 μm pitch interconnects made of metallised oxide microtubes inserted into ductile reception pads. In order to reduce the electrical resistance of interconnects and the assembly force required, interconnect design in regard to geometry and materials used are optimised through electrical and mechanical finite elements (FEM) simulations. To reduce electrical resistance, one may increase the metallisation thickness or microtube inner diameter. To minimise the assembly force, reducing the reception pad diameter is recommended. Experiments on silicon (Si) test vehicles are conducted to validate these predictions; they indicate that there is no short circuit, with an effectiveness of 100 %. This is achieved first through the assembly of Al-0.5 %wCu metallised oxide microtubes into Al-0.5 %wCu reception pads, using a force less than 10 mN/interconnect and proved to have a resistance of 230 mΩ. Second, with gold (Au) metallised oxide microtubes in indium (In) pads assembled with a force less than 0.7 mN/ interconnect. Last interconnects have a resistance of 670 mΩ/interconnect and can still be reduced to 500 mΩ by 2 h annealing at 100 ◦C.