R. Guillén - Academia.edu (original) (raw)

Papers by R. Guillén

Materials Science Forum, 2011

The scope of this work is the determination of single-crystals elastic constants (SEC) from X-ray... more The scope of this work is the determination of single-crystals elastic constants (SEC) from X-ray diffraction lattice strains measurements performed on multi-phase polycrystals submitted to mechanical load through a bending device. An explicit three scales inverse self-consistent model is developed in order to express the SEC of a cubic phase, embedded in a multi-phase polycrystal, as a function of its X-ray Elasticity Constants. Finally, it is applied to a two-phases (α+β) titanium based alloy (Ti-17), in order to estimate Ti-17 β-phase unknown SEC. The purpose of the present work is to account the proper microstructure of the material. In particular, the morphologic texture of Ti-17 a-phase, i.e. the relative disorientation of the needle-shaped grains constituting this phase, is considered owing to the so-called Generalized Self-Consistent model.

Acta Mechanica, 2015

A self-consistent scheme taking into account the intragranular microstructure is applied for the ... more A self-consistent scheme taking into account the intragranular microstructure is applied for the micromechanical modelling of the elastoplastic material behaviour during monotonic and sequential loading paths. The intragranular description used in the model is initially based on experimental observations of the dislocations evolution in body-centred cubic polycrystals. We have extended this description to face-centred cubic materials. For each crystallite, three internal variables are introduced to describe the microstructural features allowing to determine the mechanical characteristics of the grain. Next, a meso-macro transition using an elastoplastic self-consistent model is used to deduce the polycrystal behaviour from the grain one. A correct agreement is observed between simulations and experimental results at the mesoscopic and the macroscopic levels.

Optics and Lasers in Engineering, 2012

Direct Laser Fabrication is a promising new manufacturing technology coming from laser cladding p... more Direct Laser Fabrication is a promising new manufacturing technology coming from laser cladding process. From a coaxially nozzle, powder is fed through a laser beam on a substrate. The powder melting and solidification processes lead to the fabrication of a part layer by layer. In this work 316L stainless steel powder is used to form laser tracks on a low carbon steel substrate. The layer geometry is an important process characteristic to control the final part fabrication. This paper presents analytical relationships between the laser tracks geometrical characteristics (width, height, area, penetration depth) and the processing parameters (laser power P, scanning speed V and powder mass flow Qm). Three values of each processing parameters are fixed and so 27 different experiments have been made and analyzed. The validity of these results is discussed studying the correlation coefficient R, the graphical analysis of the residuals and the uncertainty evaluations. Two kinds of models are studied to predict the form and the geometrical characteristics of the single laser tracks cross sections. The first one is an analytical model in which the distribution of the powder in the feed jet is supposed to govern the laser clad geometry. Three distributions are proposed: Gaussian, Uniform and polynomial. In the second Model the general form of the clad cross section is supposed to be a disk due to the surface tension forces. Analytical relationships are established between the radius and the center of the disk in one hand and the process parameters in the other hand. This way we show that we can reproduce the laser track geometry in all the area experimentally explored.

Optics and Lasers in Engineering, 2012

ABSTRACT Direct Laser Fabrication is a promising manufacturing technology. A moving laser beam he... more ABSTRACT Direct Laser Fabrication is a promising manufacturing technology. A moving laser beam heats a coaxially delivered powder in a gas jet through nozzle in order to fabricate an end-use part directly. The clad geometry is an important process characteristic. In this work, different velocities and different laser shift-distances between two successive layers are used to build walls. For each condition, 1, 3, 5 and 10 layers walls are analyzed, showing the domain of a success and optimal construction. A relationship between the process parameters and the wall height is obtained with a good correlation. In addition a linear relationship relates the wall height to the number of layers. Columnar dendrites are observed on the bottom laser clad and equiaxed grains on the top one. Microhardness measurements show a homogeneous microhardness in each layer but a higher microhardness in the first one.

Materials Science Forum, 2006

A two-level homogenisation approach is applied to the micro-mechanical modelling of the elasto-pl... more A two-level homogenisation approach is applied to the micro-mechanical modelling of the elasto-plasticity of polycrystalline materials during various strain-path changes. The model is tested by simulating the development of intragranular strains during different complex loads. Mechanical tests measurements are used as a reference in order to validate the model. The anisotropy of plastic deformation in relation to the evolution of the dislocation structure is analysed. The results demonstrate the relevance of this approach for FCC polycrystals.

Nous avons développé des modèles à double transition d’échelles qui ont permis de rendre compte d... more Nous avons développé des modèles à double transition d’échelles qui ont permis de rendre compte du comportement réel des matériaux lors de chargements complexes (effet Bauschinger). L'hétérogénéisation intragranulaire est mise en évidence par un écrouissage non local, qui est représenté dans le cas d'une description biphasée de la structure cellulaire de dislocations. Ces approches ont été validées par des essais expérimentaux (traction-compression, diffraction des rayons X).

Revue de Métallurgie, 2003

Acta Materialia, 2002

Internal stresses due to anisotropic thermal and plastic properties were investigated in a rolled... more Internal stresses due to anisotropic thermal and plastic properties were investigated in a rolled Zirconium-α. The thermal stresses induced by a cooling process were predicted using a self-consistent model and compared with experimental results obtained by X-ray diffraction. The study of the elastoplastic response during uniaxial loading was performed along the rolling and the transverse direction of the sheet, considering the influence of the texture and the thermal stresses on the mechanical behaviour. We used an elastoplastic self-consistent formulation and the predicted results are compared with mechanical tests. The role of twinning and slip on the development of internal stresses is also discussed.

physica status solidi (b), 2003

Fréour, S., Gloaguen, D., François, M., Guillén, R. (2003). Modelling and simulation of multi-pha... more Fréour, S., Gloaguen, D., François, M., Guillén, R. (2003). Modelling and simulation of multi-phase effects on X-Ray Elasticity Constants, Physica Status Solidi b, 239, 297-309.

Revue de Métallurgie, 2003

ABSTRACT A self-consistent elastic-plastic model has been developed for the analysis of the behav... more ABSTRACT A self-consistent elastic-plastic model has been developed for the analysis of the behaviour of rolled samples of zirconium 702 during mechanical loading. The thermal residual stresses produced by cooling from the annealing temperature to room temperature have been determined and compared to X-ray diffraction results. The elastoplastic behaviour of zirconium in tensile tests along the rolling and transverse directions has been simulated and compared to the experimental results. The influence of texture and of existing thermal stresses on the response of the material could be studied and explained by this approach.

Journal of Applied Crystallography, 2005

A new approach is developed in order to determine single-crystal elasticity constants of a cubic ... more A new approach is developed in order to determine single-crystal elasticity constants of a cubic phase from the analyse of a multiphase polycrystal. This inverse method is based on the coupling of a three scale self-consistent micro-mechanical model with diffraction lattice strains measurements involving in-situ pure elastic loading. Fréour, S., . Determination of Single-Crystal Elasticity Constants in a cubic phase within a multiphase alloy -X-Ray Diffraction measurements and inverse scale transition modelling, Journal of Applied Crystallography, 38, 30-37.

Mechanics of Composite Materials

Moisture absorption in polymer matrix composites generates hygroscopic internal stresses. Multi-s... more Moisture absorption in polymer matrix composites generates hygroscopic internal stresses. Multi-scale approaches have been recently developed in order to estimate the internal stresses due to hygroscopic loads at the macroscopic ply and constituent local scales. Otherwise, experimental studies on polymers have shown that polymer deformation is de-pendent on both history and time. Therefore, it is important to understand the time dependent response of composite materials exposed to elevated hygroscopic environments: a viscoelastic constitutive model is required. In this work, a self-consistent (SC) approach is used to esti-mate the internal stresses induced by moisture absorption for composite materials with visco-elastic matrix and linear elastic fibers. This work shows the strong interaction between viscoelastic matrix behaviour and humidity on the internal stresses in the structure at the macroscopic and local scales.

Materials Science Forum, 2006

Materials Science Forum, 2003

L'utilisation des matériaux composites à matrice organique est aujourd'hui en forte croissance. L... more L'utilisation des matériaux composites à matrice organique est aujourd'hui en forte croissance. Le développement et l'utilisation des matériaux composites restent conditionnés par leur durabilité. La prédiction des contraintes internes d'origine hygrothermique, est nécessaire à l'identification d'un risque d'endommagement multi-échelle dans un matériau composite soumis à des cycles de température et d'humidité. La conception de cycles de laboratoire accélérés, représentatifs des conditions réelles, est proposée afin d'appréhender, en un temps raisonnable, la durabilité des matériaux composites. Dans notre travail, un modèle auto-cohérent est utilisé pour calculer les contraintes internes à l'échelle microscopique (fibre et matrice) induites par les cycles réels et accélérés. Le but est de comparer les contraintes locales générées par les cycles réels et accélérés en particulier aux voisinages des surfaces où règnent de forts gradients de concentration en eau.

Materials Science Forum, 2011

The scope of this work is the determination of single-crystals elastic constants (SEC) from X-ray... more The scope of this work is the determination of single-crystals elastic constants (SEC) from X-ray diffraction lattice strains measurements performed on multi-phase polycrystals submitted to mechanical load through a bending device. An explicit three scales inverse self-consistent model is developed in order to express the SEC of a cubic phase, embedded in a multi-phase polycrystal, as a function of its X-ray Elasticity Constants. Finally, it is applied to a two-phases (α+β) titanium based alloy (Ti-17), in order to estimate Ti-17 β-phase unknown SEC. The purpose of the present work is to account the proper microstructure of the material. In particular, the morphologic texture of Ti-17 a-phase, i.e. the relative disorientation of the needle-shaped grains constituting this phase, is considered owing to the so-called Generalized Self-Consistent model.

Acta Mechanica, 2015

A self-consistent scheme taking into account the intragranular microstructure is applied for the ... more A self-consistent scheme taking into account the intragranular microstructure is applied for the micromechanical modelling of the elastoplastic material behaviour during monotonic and sequential loading paths. The intragranular description used in the model is initially based on experimental observations of the dislocations evolution in body-centred cubic polycrystals. We have extended this description to face-centred cubic materials. For each crystallite, three internal variables are introduced to describe the microstructural features allowing to determine the mechanical characteristics of the grain. Next, a meso-macro transition using an elastoplastic self-consistent model is used to deduce the polycrystal behaviour from the grain one. A correct agreement is observed between simulations and experimental results at the mesoscopic and the macroscopic levels.

Optics and Lasers in Engineering, 2012

Direct Laser Fabrication is a promising new manufacturing technology coming from laser cladding p... more Direct Laser Fabrication is a promising new manufacturing technology coming from laser cladding process. From a coaxially nozzle, powder is fed through a laser beam on a substrate. The powder melting and solidification processes lead to the fabrication of a part layer by layer. In this work 316L stainless steel powder is used to form laser tracks on a low carbon steel substrate. The layer geometry is an important process characteristic to control the final part fabrication. This paper presents analytical relationships between the laser tracks geometrical characteristics (width, height, area, penetration depth) and the processing parameters (laser power P, scanning speed V and powder mass flow Qm). Three values of each processing parameters are fixed and so 27 different experiments have been made and analyzed. The validity of these results is discussed studying the correlation coefficient R, the graphical analysis of the residuals and the uncertainty evaluations. Two kinds of models are studied to predict the form and the geometrical characteristics of the single laser tracks cross sections. The first one is an analytical model in which the distribution of the powder in the feed jet is supposed to govern the laser clad geometry. Three distributions are proposed: Gaussian, Uniform and polynomial. In the second Model the general form of the clad cross section is supposed to be a disk due to the surface tension forces. Analytical relationships are established between the radius and the center of the disk in one hand and the process parameters in the other hand. This way we show that we can reproduce the laser track geometry in all the area experimentally explored.

Optics and Lasers in Engineering, 2012

ABSTRACT Direct Laser Fabrication is a promising manufacturing technology. A moving laser beam he... more ABSTRACT Direct Laser Fabrication is a promising manufacturing technology. A moving laser beam heats a coaxially delivered powder in a gas jet through nozzle in order to fabricate an end-use part directly. The clad geometry is an important process characteristic. In this work, different velocities and different laser shift-distances between two successive layers are used to build walls. For each condition, 1, 3, 5 and 10 layers walls are analyzed, showing the domain of a success and optimal construction. A relationship between the process parameters and the wall height is obtained with a good correlation. In addition a linear relationship relates the wall height to the number of layers. Columnar dendrites are observed on the bottom laser clad and equiaxed grains on the top one. Microhardness measurements show a homogeneous microhardness in each layer but a higher microhardness in the first one.

Materials Science Forum, 2006

A two-level homogenisation approach is applied to the micro-mechanical modelling of the elasto-pl... more A two-level homogenisation approach is applied to the micro-mechanical modelling of the elasto-plasticity of polycrystalline materials during various strain-path changes. The model is tested by simulating the development of intragranular strains during different complex loads. Mechanical tests measurements are used as a reference in order to validate the model. The anisotropy of plastic deformation in relation to the evolution of the dislocation structure is analysed. The results demonstrate the relevance of this approach for FCC polycrystals.

Nous avons développé des modèles à double transition d’échelles qui ont permis de rendre compte d... more Nous avons développé des modèles à double transition d’échelles qui ont permis de rendre compte du comportement réel des matériaux lors de chargements complexes (effet Bauschinger). L'hétérogénéisation intragranulaire est mise en évidence par un écrouissage non local, qui est représenté dans le cas d'une description biphasée de la structure cellulaire de dislocations. Ces approches ont été validées par des essais expérimentaux (traction-compression, diffraction des rayons X).

Revue de Métallurgie, 2003

Acta Materialia, 2002

Internal stresses due to anisotropic thermal and plastic properties were investigated in a rolled... more Internal stresses due to anisotropic thermal and plastic properties were investigated in a rolled Zirconium-α. The thermal stresses induced by a cooling process were predicted using a self-consistent model and compared with experimental results obtained by X-ray diffraction. The study of the elastoplastic response during uniaxial loading was performed along the rolling and the transverse direction of the sheet, considering the influence of the texture and the thermal stresses on the mechanical behaviour. We used an elastoplastic self-consistent formulation and the predicted results are compared with mechanical tests. The role of twinning and slip on the development of internal stresses is also discussed.

physica status solidi (b), 2003

Fréour, S., Gloaguen, D., François, M., Guillén, R. (2003). Modelling and simulation of multi-pha... more Fréour, S., Gloaguen, D., François, M., Guillén, R. (2003). Modelling and simulation of multi-phase effects on X-Ray Elasticity Constants, Physica Status Solidi b, 239, 297-309.

Revue de Métallurgie, 2003

ABSTRACT A self-consistent elastic-plastic model has been developed for the analysis of the behav... more ABSTRACT A self-consistent elastic-plastic model has been developed for the analysis of the behaviour of rolled samples of zirconium 702 during mechanical loading. The thermal residual stresses produced by cooling from the annealing temperature to room temperature have been determined and compared to X-ray diffraction results. The elastoplastic behaviour of zirconium in tensile tests along the rolling and transverse directions has been simulated and compared to the experimental results. The influence of texture and of existing thermal stresses on the response of the material could be studied and explained by this approach.

Journal of Applied Crystallography, 2005

A new approach is developed in order to determine single-crystal elasticity constants of a cubic ... more A new approach is developed in order to determine single-crystal elasticity constants of a cubic phase from the analyse of a multiphase polycrystal. This inverse method is based on the coupling of a three scale self-consistent micro-mechanical model with diffraction lattice strains measurements involving in-situ pure elastic loading. Fréour, S., . Determination of Single-Crystal Elasticity Constants in a cubic phase within a multiphase alloy -X-Ray Diffraction measurements and inverse scale transition modelling, Journal of Applied Crystallography, 38, 30-37.

Mechanics of Composite Materials

Moisture absorption in polymer matrix composites generates hygroscopic internal stresses. Multi-s... more Moisture absorption in polymer matrix composites generates hygroscopic internal stresses. Multi-scale approaches have been recently developed in order to estimate the internal stresses due to hygroscopic loads at the macroscopic ply and constituent local scales. Otherwise, experimental studies on polymers have shown that polymer deformation is de-pendent on both history and time. Therefore, it is important to understand the time dependent response of composite materials exposed to elevated hygroscopic environments: a viscoelastic constitutive model is required. In this work, a self-consistent (SC) approach is used to esti-mate the internal stresses induced by moisture absorption for composite materials with visco-elastic matrix and linear elastic fibers. This work shows the strong interaction between viscoelastic matrix behaviour and humidity on the internal stresses in the structure at the macroscopic and local scales.

Materials Science Forum, 2006

Materials Science Forum, 2003

L'utilisation des matériaux composites à matrice organique est aujourd'hui en forte croissance. L... more L'utilisation des matériaux composites à matrice organique est aujourd'hui en forte croissance. Le développement et l'utilisation des matériaux composites restent conditionnés par leur durabilité. La prédiction des contraintes internes d'origine hygrothermique, est nécessaire à l'identification d'un risque d'endommagement multi-échelle dans un matériau composite soumis à des cycles de température et d'humidité. La conception de cycles de laboratoire accélérés, représentatifs des conditions réelles, est proposée afin d'appréhender, en un temps raisonnable, la durabilité des matériaux composites. Dans notre travail, un modèle auto-cohérent est utilisé pour calculer les contraintes internes à l'échelle microscopique (fibre et matrice) induites par les cycles réels et accélérés. Le but est de comparer les contraintes locales générées par les cycles réels et accélérés en particulier aux voisinages des surfaces où règnent de forts gradients de concentration en eau.