SAM
https://sam.ensam.eu:443
The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Fri, 24 May 2024 19:53:12 GMT2024-05-24T19:53:12ZIndividual fibre separation in 3D fibrous materials imaged by X‐ray tomography
http://hdl.handle.net/10985/21616
Individual fibre separation in 3D fibrous materials imaged by X‐ray tomography
ROLLAND DU ROSCOAT, Sabine; ORGÉAS, Laurent; GEINDREAU, Christian; LEVRARD, Benjamin; BRÉMOND, Florian; DEPRIESTER, Dorian
Modelling the physical behaviour of fibrous materials still remains a great challenge because it requires to evaluate the inner structure of the different phases at the phase scale (fibre or matrix) and the at constituent scale (fibre). X-ray Computed Tomography (CT) imaging can help to characterize and to model these structures, since it allows separating the phases, based on the grey level of CT scans. However, once the fibrous phase has been isolated, automatically separating the fibres from each other is still very challenging. This work aims at proposing a method which allows separating the fibres and localizing the fibre-fibre contacts for various fibres geometries, that is: straight or woven fibres, with circular or non circular cross sections, in a way that is independent of the fibres orientations. This method uses the local orientation of the structure formed by the fibrous phase and then introduces the misorientation angle. The threshold of this angle is the only parameter required to separate the fibres. This paper investigates the efficiency of the proposed algorithm in various conditions, for instance by changing the image resolution or the fibre tortuosity on synthetic images. Finally, the proposed algorithm is applied to real images or samples made up of synthetic solid fibres.
Sat, 01 Jan 2022 00:00:00 GMThttp://hdl.handle.net/10985/216162022-01-01T00:00:00ZROLLAND DU ROSCOAT, SabineORGÉAS, LaurentGEINDREAU, ChristianLEVRARD, BenjaminBRÉMOND, FlorianDEPRIESTER, DorianModelling the physical behaviour of fibrous materials still remains a great challenge because it requires to evaluate the inner structure of the different phases at the phase scale (fibre or matrix) and the at constituent scale (fibre). X-ray Computed Tomography (CT) imaging can help to characterize and to model these structures, since it allows separating the phases, based on the grey level of CT scans. However, once the fibrous phase has been isolated, automatically separating the fibres from each other is still very challenging. This work aims at proposing a method which allows separating the fibres and localizing the fibre-fibre contacts for various fibres geometries, that is: straight or woven fibres, with circular or non circular cross sections, in a way that is independent of the fibres orientations. This method uses the local orientation of the structure formed by the fibrous phase and then introduces the misorientation angle. The threshold of this angle is the only parameter required to separate the fibres. This paper investigates the efficiency of the proposed algorithm in various conditions, for instance by changing the image resolution or the fibre tortuosity on synthetic images. Finally, the proposed algorithm is applied to real images or samples made up of synthetic solid fibres.Modélisation polycristalline du comportement d’un Alliage `a M´emoire de Forme (AMF) de type Ni-Ti sous sollicitations multiaxiales
http://hdl.handle.net/10985/11937
Modélisation polycristalline du comportement d’un Alliage `a M´emoire de Forme (AMF) de type Ni-Ti sous sollicitations multiaxiales
MAYNADIER, Anne; LAVERNHE-TAILLARD, Karine; HUBERT, Olivier; DEPRIESTER, Dorian
Les propriétés des AMF sont dues à une transformation de phase solide solide réversible induite par la contrainte ou la température. Pour les AMF de type Ni49,75%at-Ti, c’est une transformation isochore qui, d’une phase cubique (austénite), forme une phase monoclinique (martensite) avec 24 orientations possibles (variantes). A partir des géométries locales et des énergies par variante, nous proposons un modèle polycristallin multiaxial qui rend compte du fort couplage thermomécanique lors de la transformation de phase. Des essais quasi statiques permettent de le valider.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10985/119372011-01-01T00:00:00ZMAYNADIER, AnneLAVERNHE-TAILLARD, KarineHUBERT, OlivierDEPRIESTER, DorianLes propriétés des AMF sont dues à une transformation de phase solide solide réversible induite par la contrainte ou la température. Pour les AMF de type Ni49,75%at-Ti, c’est une transformation isochore qui, d’une phase cubique (austénite), forme une phase monoclinique (martensite) avec 24 orientations possibles (variantes). A partir des géométries locales et des énergies par variante, nous proposons un modèle polycristallin multiaxial qui rend compte du fort couplage thermomécanique lors de la transformation de phase. Des essais quasi statiques permettent de le valider.On the damage criteria and their critical values for flowforming of ELI grade Ti64
http://hdl.handle.net/10985/11940
On the damage criteria and their critical values for flowforming of ELI grade Ti64
MASSONI, Elisabeth; DEPRIESTER, Dorian
Cold flowforming is a chipless forming process that deforms tubular parts by reducing their outer diameter and thickness while increasing their length. It consists of a rotating mandrel and one or more rollers that are translated along the tube axis, thus plastically deforming it. Flowforming of Ti-6Al-4V (also known as Ti64) is of great interest for improving the mechanical properties of the material, such as yield stress and fatigue strength. However this alloy is known to have poor ductility at room temperature. Therefore, flowforming of Ti64 without failure or crack is a great challenge. In this present paper, the authors have attempted to predict the different failure modes occurring during flowforming. An experimental machine has been built at the Center for Material Forming (CEMEF) in order to monitor the force on the single roller, the torque on the mandrel and the actual rotation speed of the roller as well. Numerous flowforming tests have been performed using different processing parameters, such as working depth, roller feed and initial geometry, in order to investigate the critical values which lead to the failure of the flowformed tube. In addition, numerical simulations of the process have been performed using the FORGE FEM solver. The results of the simulations have been used to evaluate the relevance of usual failure criteria (Crockford-Latham, Rice-Tracey and Oyane).
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/119402014-01-01T00:00:00ZMASSONI, ElisabethDEPRIESTER, DorianCold flowforming is a chipless forming process that deforms tubular parts by reducing their outer diameter and thickness while increasing their length. It consists of a rotating mandrel and one or more rollers that are translated along the tube axis, thus plastically deforming it. Flowforming of Ti-6Al-4V (also known as Ti64) is of great interest for improving the mechanical properties of the material, such as yield stress and fatigue strength. However this alloy is known to have poor ductility at room temperature. Therefore, flowforming of Ti64 without failure or crack is a great challenge. In this present paper, the authors have attempted to predict the different failure modes occurring during flowforming. An experimental machine has been built at the Center for Material Forming (CEMEF) in order to monitor the force on the single roller, the torque on the mandrel and the actual rotation speed of the roller as well. Numerous flowforming tests have been performed using different processing parameters, such as working depth, roller feed and initial geometry, in order to investigate the critical values which lead to the failure of the flowformed tube. In addition, numerical simulations of the process have been performed using the FORGE FEM solver. The results of the simulations have been used to evaluate the relevance of usual failure criteria (Crockford-Latham, Rice-Tracey and Oyane).Thermo-mechanical description of phase transformation in Ni-Ti Shape Memory Alloy
http://hdl.handle.net/10985/11939
Thermo-mechanical description of phase transformation in Ni-Ti Shape Memory Alloy
MAYNADIER, Anne; LAVERNHE-TAILLARD, Karine; HUBERT, Olivier; DEPRIESTER, Dorian
The pseudo-elasticity of Shape Memory Alloys is due to a change in volumetric fraction between the high temperature phase (Austenite) and the low temperature phase (Martensite) under a mechanical loading. When a tensile loading is considered, transformation bands occur leading to strong localization of the deformation and a strong local heating. The modeling of this strongly coupled phenomenon is discussed for a polycrystalline specimen in a multiaxial mechanical framework. Three different scales are considered: the variant scale (or phase scale), the single-crystal scale and the polycrystalline scale. The free energy of each variant is first computed from the loading and the geometrical lattice transformations associated to each variant. The volumetric fraction of each phase is then defined at the grain scale as function of their free energy. A simple averaging operation allows to estimate the deformation at the grain scale. The polycrystalline scale is not considered at present.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10985/119392011-01-01T00:00:00ZMAYNADIER, AnneLAVERNHE-TAILLARD, KarineHUBERT, OlivierDEPRIESTER, DorianThe pseudo-elasticity of Shape Memory Alloys is due to a change in volumetric fraction between the high temperature phase (Austenite) and the low temperature phase (Martensite) under a mechanical loading. When a tensile loading is considered, transformation bands occur leading to strong localization of the deformation and a strong local heating. The modeling of this strongly coupled phenomenon is discussed for a polycrystalline specimen in a multiaxial mechanical framework. Three different scales are considered: the variant scale (or phase scale), the single-crystal scale and the polycrystalline scale. The free energy of each variant is first computed from the loading and the geometrical lattice transformations associated to each variant. The volumetric fraction of each phase is then defined at the grain scale as function of their free energy. A simple averaging operation allows to estimate the deformation at the grain scale. The polycrystalline scale is not considered at present.Submicrocristalline structure and dynamic recovery of cold flowformed ELI grade Ti-6Al-4V
http://hdl.handle.net/10985/11941
Submicrocristalline structure and dynamic recovery of cold flowformed ELI grade Ti-6Al-4V
MASSONI, Elisabeth; DEPRIESTER, Dorian
Flowforming is a means to produce seamless tubes by plastic deformation at room temperature. It consists in reducing the thickness of a tubular part mounted on a mandrel by deforming it using several rollers translating along the tube axis, while the tube is rotating along its axis. Thanks to the high compressive stresses, and to the incremental nature of the deformation process, flowforming can lead to a high thickness reduction and thus to high elongation of the deformed tubes. Ti-6Al-4V (Extra Low Interstitial grade) tubes have been deformed by cold flowforming, with a thickness reduction ratio higher than 60%, and their microstructures have been investigated using light optical microscopy (LOM), scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). Based on EBSD data, a post-processing analysis has been performed in order to study the texture of the flowformed parts. Optical Microscopy showed that the material could be deformed without displaying flow instability such as adiabatic shear banding, despite the fact that it has been processed out of the stable processing maps (high strain rate and low temperature). It also evidenced a major deformation along the tube axis accompanied with a slight twist due to torsion stress. EBSD analysis indicated the occurrence of continuous dynamic recrystallization, which is rarely reported in the α-β domain of such alloys. The recovery/ recrystallization effects resulted in a submicrocrystalline equiaxed structure, which is consistent with that previously reported for Ti-6Al-4V subjected to severe plastic deformation (SPD). The texture of the hexagonal α-phase appeared to be similar to that obtained on extruded Ti-6Al-4V, with a basal component perpendicular to the tube axis
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/119412013-01-01T00:00:00ZMASSONI, ElisabethDEPRIESTER, DorianFlowforming is a means to produce seamless tubes by plastic deformation at room temperature. It consists in reducing the thickness of a tubular part mounted on a mandrel by deforming it using several rollers translating along the tube axis, while the tube is rotating along its axis. Thanks to the high compressive stresses, and to the incremental nature of the deformation process, flowforming can lead to a high thickness reduction and thus to high elongation of the deformed tubes. Ti-6Al-4V (Extra Low Interstitial grade) tubes have been deformed by cold flowforming, with a thickness reduction ratio higher than 60%, and their microstructures have been investigated using light optical microscopy (LOM), scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). Based on EBSD data, a post-processing analysis has been performed in order to study the texture of the flowformed parts. Optical Microscopy showed that the material could be deformed without displaying flow instability such as adiabatic shear banding, despite the fact that it has been processed out of the stable processing maps (high strain rate and low temperature). It also evidenced a major deformation along the tube axis accompanied with a slight twist due to torsion stress. EBSD analysis indicated the occurrence of continuous dynamic recrystallization, which is rarely reported in the α-β domain of such alloys. The recovery/ recrystallization effects resulted in a submicrocrystalline equiaxed structure, which is consistent with that previously reported for Ti-6Al-4V subjected to severe plastic deformation (SPD). The texture of the hexagonal α-phase appeared to be similar to that obtained on extruded Ti-6Al-4V, with a basal component perpendicular to the tube axisThermomechanical modelling of a NiTi SMA sample submitted to displacement-controlled tensile test
http://hdl.handle.net/10985/11938
Thermomechanical modelling of a NiTi SMA sample submitted to displacement-controlled tensile test
MAYNADIER, Anne; LAVERNHE-TAILLARD, Karine; HUBERT, Olivier; DEPRIESTER, Dorian
Shape Memory Alloys (SMAs) undergo an austenite–martensite solid–solid phase transformation which confers its pseudo-elastic and shape memory behaviours. Phase transformation can be induced either by stress or temperature changes. That indicates a strong thermo-mechanical coupling. Tensile test is one of the most popular mechanical test, allowing an easy observation of this coupling: transformation bands appear and enlarge giving rise to a large amount of heat and strain localisation. We demonstrate that the number of transformation bands is strongly associated with the strain rate. Recent progress in full field measurement techniques have provided accurate observations and consequently a better understanding of strain and heat generation and diffusion in SMAs. These experiments bring us to suggest the creation of a new one-dimensional thermomechanical modelling of the pseudo-elastic behaviour. It is used to simulate the heat rise, strain localisation and thermal evolution of the NiTi SMA sample submitted to tensile loading.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/119382014-01-01T00:00:00ZMAYNADIER, AnneLAVERNHE-TAILLARD, KarineHUBERT, OlivierDEPRIESTER, DorianShape Memory Alloys (SMAs) undergo an austenite–martensite solid–solid phase transformation which confers its pseudo-elastic and shape memory behaviours. Phase transformation can be induced either by stress or temperature changes. That indicates a strong thermo-mechanical coupling. Tensile test is one of the most popular mechanical test, allowing an easy observation of this coupling: transformation bands appear and enlarge giving rise to a large amount of heat and strain localisation. We demonstrate that the number of transformation bands is strongly associated with the strain rate. Recent progress in full field measurement techniques have provided accurate observations and consequently a better understanding of strain and heat generation and diffusion in SMAs. These experiments bring us to suggest the creation of a new one-dimensional thermomechanical modelling of the pseudo-elastic behaviour. It is used to simulate the heat rise, strain localisation and thermal evolution of the NiTi SMA sample submitted to tensile loading.Mechanical behavior of polycrystals: Coupled in situ DIC-EBSD analysis of pure copper under tensile test
http://hdl.handle.net/10985/23782
Mechanical behavior of polycrystals: Coupled in situ DIC-EBSD analysis of pure copper under tensile test
GOULMY, Jean-Patrick; DEPRIESTER, Dorian; GUITTONNEAU, F.; JÉGOU, Sébastien; BARRALLIER, Laurent
Understanding the mechanisms at the microstructure scale is of great importance for modeling the behavior of materials at different scales. To this end, digital image correlation (DIC) is an effective measurement method for evaluating the strains generated by various loading conditions. The objective of this paper is to describe the experimental setup and the use of high resolution digital image correlation (HRDIC) during in situ Scanning Electron Microscope (SEM) tests in order to provide a coupling between polycrystalline modeling and experiment in the near future. The HRDIC technique is used to evaluate the tensile behavior of a pure copper polycrystal at room temperature. Several magnitudes are investigated in order to discuss the representativeness of the results with respect to the macroscopic scale. The selected image correlation parameters are discussed regarding the ability of the technique to define inter- and intra- granular strain heterogeneities. Finally, based on EBSD analyzes, the impact of grain orientation on the mechanical behavior is discussed. The Schmid factor, calculated from a macroscopic stress, appears to be the determining factor concerning the orientation of the location bands. On the other hand, it is not sufficient to define the mean strains in the grains.
Thu, 01 Dec 2022 00:00:00 GMThttp://hdl.handle.net/10985/237822022-12-01T00:00:00ZGOULMY, Jean-PatrickDEPRIESTER, DorianGUITTONNEAU, F.JÉGOU, SébastienBARRALLIER, LaurentUnderstanding the mechanisms at the microstructure scale is of great importance for modeling the behavior of materials at different scales. To this end, digital image correlation (DIC) is an effective measurement method for evaluating the strains generated by various loading conditions. The objective of this paper is to describe the experimental setup and the use of high resolution digital image correlation (HRDIC) during in situ Scanning Electron Microscope (SEM) tests in order to provide a coupling between polycrystalline modeling and experiment in the near future. The HRDIC technique is used to evaluate the tensile behavior of a pure copper polycrystal at room temperature. Several magnitudes are investigated in order to discuss the representativeness of the results with respect to the macroscopic scale. The selected image correlation parameters are discussed regarding the ability of the technique to define inter- and intra- granular strain heterogeneities. Finally, based on EBSD analyzes, the impact of grain orientation on the mechanical behavior is discussed. The Schmid factor, calculated from a macroscopic stress, appears to be the determining factor concerning the orientation of the location bands. On the other hand, it is not sufficient to define the mean strains in the grains.Grain size estimation in polycrystals: Solving the corpuscle problem using Maximum Likelihood Estimation
http://hdl.handle.net/10985/20635
Grain size estimation in polycrystals: Solving the corpuscle problem using Maximum Likelihood Estimation
DEPRIESTER, Dorian; KUBLER, Regis
In materials science, the microstructures of materials are generally characterized by 2D observation (e.g. electron microscopy). For polycrystalline materials, such as crystalline rocks or ceramics, those observations can be used to measure the grain size distribution. However, the fact that grain sizes are measured in planar cuts introduces a statistical bias, since the real (3D) grain sizes cannot be directly measured. For almost spherical grains, this bias can be computed thanks to the so-called Wicksell's equation. This paper proposes a method, based on Maximum Likelihood Estimation (MLE) for unfolding the apparent 2D distribution. The efficiency of this method is extensively investigated in the special case of lognormal distribution. In this case, 10% uncertainty on the distribution parameters can be reached with only 580 empirical values.
Fri, 01 Jan 2021 00:00:00 GMThttp://hdl.handle.net/10985/206352021-01-01T00:00:00ZDEPRIESTER, DorianKUBLER, RegisIn materials science, the microstructures of materials are generally characterized by 2D observation (e.g. electron microscopy). For polycrystalline materials, such as crystalline rocks or ceramics, those observations can be used to measure the grain size distribution. However, the fact that grain sizes are measured in planar cuts introduces a statistical bias, since the real (3D) grain sizes cannot be directly measured. For almost spherical grains, this bias can be computed thanks to the so-called Wicksell's equation. This paper proposes a method, based on Maximum Likelihood Estimation (MLE) for unfolding the apparent 2D distribution. The efficiency of this method is extensively investigated in the special case of lognormal distribution. In this case, 10% uncertainty on the distribution parameters can be reached with only 580 empirical values.Resolution of the Wicksell's equation by Minimum Distance Estimation
http://hdl.handle.net/10985/17597
Resolution of the Wicksell's equation by Minimum Distance Estimation
DEPRIESTER, Dorian; KUBLER, Regis
The estimation of the grain size in granular materials is usually performed by 2Dobservations. Unfolding the grain size distribution from apparent 2D sizes is commonly referred as the corpuscle problem. For spherical particles, the distribution of the apparent size can be related to that of the actual size thanks to the Wicksell’s equation. The Saltikov method, which is based on Wicksell’s equation, is the most widely used method for resolving corpuscle problems. This method is recursive and works on the finite histogram of the grain size. In this paper, we propose an algorithm based on a minimizing procedure to numerically solve the Wicksell’s equation, assuming a parametric model for the distribution (e.g. lognormal distribution). This algorithm is applied on real material and the results are compared to those found using Saltikov or Saltikov-basedstereology techniques. A criterion is proposed for choosing the number of bins in the Saltikov method. The accuracy of the proposed algorithm, depending on the sample size, is studied.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/10985/175972019-01-01T00:00:00ZDEPRIESTER, DorianKUBLER, RegisThe estimation of the grain size in granular materials is usually performed by 2Dobservations. Unfolding the grain size distribution from apparent 2D sizes is commonly referred as the corpuscle problem. For spherical particles, the distribution of the apparent size can be related to that of the actual size thanks to the Wicksell’s equation. The Saltikov method, which is based on Wicksell’s equation, is the most widely used method for resolving corpuscle problems. This method is recursive and works on the finite histogram of the grain size. In this paper, we propose an algorithm based on a minimizing procedure to numerically solve the Wicksell’s equation, assuming a parametric model for the distribution (e.g. lognormal distribution). This algorithm is applied on real material and the results are compared to those found using Saltikov or Saltikov-basedstereology techniques. A criterion is proposed for choosing the number of bins in the Saltikov method. The accuracy of the proposed algorithm, depending on the sample size, is studied.Calculs Éléments Finis à l’échelle des grains depuis des données EBSD
http://hdl.handle.net/10985/18497
Calculs Éléments Finis à l’échelle des grains depuis des données EBSD
DEPRIESTER, Dorian; KUBLER, Regis
For the sake of understanding the behaviour of a polycrystal at its grain scale, Finite Element (FE) numerical simulations can be performed, taking into account the physical properties of each grain. Those simulations must take into account the phase heterogeneities, the local anisotropies and the crystalline orientations as well. In addition, the actual grain morphologies must be well described in order to model localization phenomena. An algorithm, named MTEX2Gmsh, is proposed to automatically generate an EF mesh from EBSD data. The resulting mesh gives smooth and accurate descriptions of the grain boundaries together with reduced Degrees of Freedom (DoF), hence limited computational times. Using this algorithm, the fragile-elastic behaviour of a ceramic and micro-plasticity phenomena in a nitrided steel are studied as application cases. The latter is based on a crystal-plasticity model for the ferrite phase.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/10985/184972019-01-01T00:00:00ZDEPRIESTER, DorianKUBLER, RegisFor the sake of understanding the behaviour of a polycrystal at its grain scale, Finite Element (FE) numerical simulations can be performed, taking into account the physical properties of each grain. Those simulations must take into account the phase heterogeneities, the local anisotropies and the crystalline orientations as well. In addition, the actual grain morphologies must be well described in order to model localization phenomena. An algorithm, named MTEX2Gmsh, is proposed to automatically generate an EF mesh from EBSD data. The resulting mesh gives smooth and accurate descriptions of the grain boundaries together with reduced Degrees of Freedom (DoF), hence limited computational times. Using this algorithm, the fragile-elastic behaviour of a ceramic and micro-plasticity phenomena in a nitrided steel are studied as application cases. The latter is based on a crystal-plasticity model for the ferrite phase.