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Papers by Martin Poncelet

HAL (Le Centre pour la Communication Scientifique Directe), 2013

This paper is devoted to the analysis of the load path effect on I+II+III mixed mode fatigue crac... more This paper is devoted to the analysis of the load path effect on I+II+III mixed mode fatigue crack propagation in a 316L stainless steel. Experiments were conducted in mode I+II and in mode I+II+III. The same maximum, minimum and mean values of the stress intensity factors were used for each loading path in the experiments. The main result of this set of experiments is that very different crack growth rates and crack paths are observed for load paths that are however considered as equivalent in most fatigue criteria. The experiments conducted in mode I+II and in mode I+II+III, also allowed to show that the addition of mode III loading steps to a mode I+II loading sequence is increasing the fatigue crack growth rate, even when the crack path is not significantly modified.

HAL (Le Centre pour la Communication Scientifique Directe), 2012

Predicting the growth of fatigue cracks under multi-axial loading conditions remains difficult fo... more Predicting the growth of fatigue cracks under multi-axial loading conditions remains difficult for at least two main reasons. Firstly, the crack path can be very complicated, which makes the determination of stress intensity factors difficult and induces non-linear effects due to contact and friction between the faces of the crack. Secondly, the elastic-plastic behaviour of the crack tip region also introduces non-linear effects on both the growth rate and the crack path. This paper is devoted to the experimental analysis of plastic flow within the crack tip region. A set of specific experiments were conducted so as to validate a novel approach to model the mixed mode elastic-plastic behaviour of a cracked component. The velocity field at the vicinity of the crack tip was determined using digital image correlation in I + II mixed mode loading conditions. The mode I and mode II components of the experimental velocity field were extracted using symmetry considerations with respect to a coordinate system attached to the crack tip. Each mode was then partitioned into elastic and plastic parts and each part was approached by the product of an intensity factor and a spatial reference field, constructed once for all. With this approach, the experimental velocity field is described using only four degrees of freedom, which are respectively the mode I and mode II intensity factors of the elastic and plastic part of the velocity field. The experimental results showed that the error associated with this approximation is small. A criterion was proposed to determine the yield surface, and it was shown that the experimental yield surface agrees well with the theoretical one. In particular it is shown that the LEFM framework can still be used in elastic-plastic conditions provided that the centre of the elastic domain is allowed to evolve with plastic flow. The plastic flow direction was also measured and is consistent the hypothesis of a normality flow rule that is used in the model. And finally, the measured transient evolutions the plastic flow in complex loading conditions are consistent with the hypotheses of the model.

Advanced Modeling and Simulation in Engineering Sciences, Sep 5, 2018

A series of experiments has been performed to build a benchmark for the numerical modeling of mix... more A series of experiments has been performed to build a benchmark for the numerical modeling of mixed mode crack propagation in concrete. Two tests are selected so that the propagation is almost always stable although the material is quasi-fragile. Moreover the variation of mode mixity enables the study of the reorientation of the crack, as well as more complex phenomena such as branching or link-up. To control stability and mode mixity, the loading is imposed with a 6-axis testing machine while the crack propagation is assessed by full-field measurement. In this paper, a description of the experimental setup is provided as well as numerical simulation results illustrating the sensitivity to boundary conditions and geometry. Links to data needed to perform numerical simulations of these benchmark experiments are given, together with references to publications giving full descriptions of the protocol and experiment results.

HAL (Le Centre pour la Communication Scientifique Directe), 2015

4D motion during a scan acquisition in a lab-tomograph is measured using a recently developed Pro... more 4D motion during a scan acquisition in a lab-tomograph is measured using a recently developed Projection-based Digital Volume Correlation (P-DVC) method in no more than 1.3 s acquisition time per state. The 4D procedure exploits an initial full reconstruction of the sample obtained by classical means. Following 100 motion steps, the full space-time displacement field is measured based on one radiograph.

Measurements of kinematic fields are performed with an original combination of two different imag... more Measurements of kinematic fields are performed with an original combination of two different imaging modalities, (i.e. one IR and one visible camera). Stereo Digital Image Correlation (SDIC) procedures are performed with a global approach [1]. The stereovision system is first calibrated by performing lens distortion corrections [2]. Then the projection model parameters are determined thanks to the CAD (NURBS) representation of the 3D sample surface using an integrated approach. This CAD-based SDIC, offers the possibility to determine the specimen deformation. The simple case of3D rigid translational motions is experimentally tested and validated.

HAL (Le Centre pour la Communication Scientifique Directe), 2013

HAL (Le Centre pour la Communication Scientifique Directe), Jan 17, 2022

HAL (Le Centre pour la Communication Scientifique Directe), Jan 17, 2022

HAL (Le Centre pour la Communication Scientifique Directe), Apr 8, 2021

Several test results on standard 40x40x280 mm specimens.<br>Material is a mortar (w/c=0.42)... more Several test results on standard 40x40x280 mm specimens.<br>Material is a mortar (w/c=0.42).Bending test following 50-FMC Draft Recommendation.

To improve the characterization and dimensioning of plane engine turbine disks the propulsion sys... more To improve the characterization and dimensioning of plane engine turbine disks the propulsion systems manufacturer Snecma develops constitutive laws, damage laws and fatigue criteria that are better adapted to the solicitations that occur in practice. As part of this effort, a study has been launched in order to obtain a plasticity model adapted to Inco718DA, an alloy used extensively in the manufacturing of turbine disks, and validate it under multiaxial conditions close to normal engine functioning.This work focuses on the development of cyclic behaviour tests on cross-shaped samples using Digital Image Correlation to control the testing machine. Mots clefs : multiaxial, comportement, CIN, Inco718DA

The current work is an attempt of experimental study of high-order behaviors. It comes from the n... more The current work is an attempt of experimental study of high-order behaviors. It comes from the noticing that such behaviors are up to now nearly exclusively studied from a theoretical and numerical point of view. Materials with coarse inner architecture can easily be design with modern production process (3D printing, 2D and 3D corrugation). The question of the actual behavior of those architectured media rises. Do they behave like classical elastic continua, or do they exhibit extraneous high-order effects? Further, if present are those effects stable with respect to imperfections (geometry, constitutive material ...). In the present study a non-centro symmetric sample has been process. The geometrical anisotropy of the elementary cell has been chosen in order to detect straingradient effect. Samples are obtained by 3D printing and are representative of industrial honeycombs used for aeronautic/aerospace composite material. To that aim, simple experiments based on load controlled ...

L'amélioration des simulations numériques de tenue à la fatigue nécessite des modèles multiaxiaux... more L'amélioration des simulations numériques de tenue à la fatigue nécessite des modèles multiaxiaux et leurs essais d'identification. Nombre d'entre eux se font sur des éprouvettes « en croix » depuis la démocratisation des machines de traction biaxiale [1]. La majorité des mors utilisés actuellement pour ce type d'essai a plusieurs avantages : robustesse vis-à-vis des charges radiales, montage simple et rapide des éprouvettes. Généralement, ils ont comme défauts communs une précision d'alignement insuffisante (induisant une flexion statique au montage) et potentiellement une flexion sous charge. Ces défauts sont évidemment de première importance lorsque des essais de fatigue sont réalisés. D'autres mors suppriment une partie de ces inconvénients, mais habituellement au prix d'un encombrement significatif. En outre, les techniques de mesure mises en place au sein des machines biaxiales ont beaucoup évolué depuis leur apparition [2-7]: Corrélation d'Images Numériques, Stéréo-corrélation, Thermographie, DRX. Il est donc nécessaire de prendre en compte ces nouvelles contraintes en plus des défauts des mors actuels. La solution proposée offre une plus grande raideur en flexion tout en conservant un encombrement très réduit, permettant de nombreuses instrumentations. En outre, elle permet l'alignement du mors par rapport à son palier pour diminuer au maximum les mouvements hors plan (ce qui est vérifié avec une éprouvette étalon instrumentée). Plusieurs capteurs peuvent être embarqués sur le mors pour répondre à différentes fonctions, en particulier des capteurs de déplacement LASER offrent une mesure directe de l'écart entre mors et de leur inclinaison relative.

Most of the planar biaxial machine grips currently used for cross-shaped specimens have several a... more Most of the planar biaxial machine grips currently used for cross-shaped specimens have several advantages: stiffness to radial loads, fast and easy sample mounting. Generally, they lack a sufficient alignment precision (inducing a static bending during clamping) and might exhibit flexion during load. These shortcomings are obviously of major importance when it comes to fatigue tests. Other types of grips avoid some of these problems, but usually at the cost of a significantly larger size. Moreover, measurement techniques used with biaxial testing machines have evolved considerably: Digital Image Correlation, Stereo Correlation, Thermography, X-Ray Diffraction. It is thus necessary to take into account these new requirements along with the defects of the existing grips. The considered solution offers a higher bending stiffness without considerable increase in size, permitting significant additional instrumentation. Also, it allows the measurement and the adjustment of the alignment ...

International audienceno abstrac

HAL (Le Centre pour la Communication Scientifique Directe), 2013

This paper is devoted to the analysis of the load path effect on I+II+III mixed mode fatigue crac... more This paper is devoted to the analysis of the load path effect on I+II+III mixed mode fatigue crack propagation in a 316L stainless steel. Experiments were conducted in mode I+II and in mode I+II+III. The same maximum, minimum and mean values of the stress intensity factors were used for each loading path in the experiments. The main result of this set of experiments is that very different crack growth rates and crack paths are observed for load paths that are however considered as equivalent in most fatigue criteria. The experiments conducted in mode I+II and in mode I+II+III, also allowed to show that the addition of mode III loading steps to a mode I+II loading sequence is increasing the fatigue crack growth rate, even when the crack path is not significantly modified.

HAL (Le Centre pour la Communication Scientifique Directe), 2012

Predicting the growth of fatigue cracks under multi-axial loading conditions remains difficult fo... more Predicting the growth of fatigue cracks under multi-axial loading conditions remains difficult for at least two main reasons. Firstly, the crack path can be very complicated, which makes the determination of stress intensity factors difficult and induces non-linear effects due to contact and friction between the faces of the crack. Secondly, the elastic-plastic behaviour of the crack tip region also introduces non-linear effects on both the growth rate and the crack path. This paper is devoted to the experimental analysis of plastic flow within the crack tip region. A set of specific experiments were conducted so as to validate a novel approach to model the mixed mode elastic-plastic behaviour of a cracked component. The velocity field at the vicinity of the crack tip was determined using digital image correlation in I + II mixed mode loading conditions. The mode I and mode II components of the experimental velocity field were extracted using symmetry considerations with respect to a coordinate system attached to the crack tip. Each mode was then partitioned into elastic and plastic parts and each part was approached by the product of an intensity factor and a spatial reference field, constructed once for all. With this approach, the experimental velocity field is described using only four degrees of freedom, which are respectively the mode I and mode II intensity factors of the elastic and plastic part of the velocity field. The experimental results showed that the error associated with this approximation is small. A criterion was proposed to determine the yield surface, and it was shown that the experimental yield surface agrees well with the theoretical one. In particular it is shown that the LEFM framework can still be used in elastic-plastic conditions provided that the centre of the elastic domain is allowed to evolve with plastic flow. The plastic flow direction was also measured and is consistent the hypothesis of a normality flow rule that is used in the model. And finally, the measured transient evolutions the plastic flow in complex loading conditions are consistent with the hypotheses of the model.

Advanced Modeling and Simulation in Engineering Sciences, Sep 5, 2018

A series of experiments has been performed to build a benchmark for the numerical modeling of mix... more A series of experiments has been performed to build a benchmark for the numerical modeling of mixed mode crack propagation in concrete. Two tests are selected so that the propagation is almost always stable although the material is quasi-fragile. Moreover the variation of mode mixity enables the study of the reorientation of the crack, as well as more complex phenomena such as branching or link-up. To control stability and mode mixity, the loading is imposed with a 6-axis testing machine while the crack propagation is assessed by full-field measurement. In this paper, a description of the experimental setup is provided as well as numerical simulation results illustrating the sensitivity to boundary conditions and geometry. Links to data needed to perform numerical simulations of these benchmark experiments are given, together with references to publications giving full descriptions of the protocol and experiment results.

HAL (Le Centre pour la Communication Scientifique Directe), 2015

4D motion during a scan acquisition in a lab-tomograph is measured using a recently developed Pro... more 4D motion during a scan acquisition in a lab-tomograph is measured using a recently developed Projection-based Digital Volume Correlation (P-DVC) method in no more than 1.3 s acquisition time per state. The 4D procedure exploits an initial full reconstruction of the sample obtained by classical means. Following 100 motion steps, the full space-time displacement field is measured based on one radiograph.

Measurements of kinematic fields are performed with an original combination of two different imag... more Measurements of kinematic fields are performed with an original combination of two different imaging modalities, (i.e. one IR and one visible camera). Stereo Digital Image Correlation (SDIC) procedures are performed with a global approach [1]. The stereovision system is first calibrated by performing lens distortion corrections [2]. Then the projection model parameters are determined thanks to the CAD (NURBS) representation of the 3D sample surface using an integrated approach. This CAD-based SDIC, offers the possibility to determine the specimen deformation. The simple case of3D rigid translational motions is experimentally tested and validated.

HAL (Le Centre pour la Communication Scientifique Directe), 2013

HAL (Le Centre pour la Communication Scientifique Directe), Jan 17, 2022

HAL (Le Centre pour la Communication Scientifique Directe), Jan 17, 2022

HAL (Le Centre pour la Communication Scientifique Directe), Apr 8, 2021

Several test results on standard 40x40x280 mm specimens.<br>Material is a mortar (w/c=0.42)... more Several test results on standard 40x40x280 mm specimens.<br>Material is a mortar (w/c=0.42).Bending test following 50-FMC Draft Recommendation.

To improve the characterization and dimensioning of plane engine turbine disks the propulsion sys... more To improve the characterization and dimensioning of plane engine turbine disks the propulsion systems manufacturer Snecma develops constitutive laws, damage laws and fatigue criteria that are better adapted to the solicitations that occur in practice. As part of this effort, a study has been launched in order to obtain a plasticity model adapted to Inco718DA, an alloy used extensively in the manufacturing of turbine disks, and validate it under multiaxial conditions close to normal engine functioning.This work focuses on the development of cyclic behaviour tests on cross-shaped samples using Digital Image Correlation to control the testing machine. Mots clefs : multiaxial, comportement, CIN, Inco718DA

The current work is an attempt of experimental study of high-order behaviors. It comes from the n... more The current work is an attempt of experimental study of high-order behaviors. It comes from the noticing that such behaviors are up to now nearly exclusively studied from a theoretical and numerical point of view. Materials with coarse inner architecture can easily be design with modern production process (3D printing, 2D and 3D corrugation). The question of the actual behavior of those architectured media rises. Do they behave like classical elastic continua, or do they exhibit extraneous high-order effects? Further, if present are those effects stable with respect to imperfections (geometry, constitutive material ...). In the present study a non-centro symmetric sample has been process. The geometrical anisotropy of the elementary cell has been chosen in order to detect straingradient effect. Samples are obtained by 3D printing and are representative of industrial honeycombs used for aeronautic/aerospace composite material. To that aim, simple experiments based on load controlled ...

L'amélioration des simulations numériques de tenue à la fatigue nécessite des modèles multiaxiaux... more L'amélioration des simulations numériques de tenue à la fatigue nécessite des modèles multiaxiaux et leurs essais d'identification. Nombre d'entre eux se font sur des éprouvettes « en croix » depuis la démocratisation des machines de traction biaxiale [1]. La majorité des mors utilisés actuellement pour ce type d'essai a plusieurs avantages : robustesse vis-à-vis des charges radiales, montage simple et rapide des éprouvettes. Généralement, ils ont comme défauts communs une précision d'alignement insuffisante (induisant une flexion statique au montage) et potentiellement une flexion sous charge. Ces défauts sont évidemment de première importance lorsque des essais de fatigue sont réalisés. D'autres mors suppriment une partie de ces inconvénients, mais habituellement au prix d'un encombrement significatif. En outre, les techniques de mesure mises en place au sein des machines biaxiales ont beaucoup évolué depuis leur apparition [2-7]: Corrélation d'Images Numériques, Stéréo-corrélation, Thermographie, DRX. Il est donc nécessaire de prendre en compte ces nouvelles contraintes en plus des défauts des mors actuels. La solution proposée offre une plus grande raideur en flexion tout en conservant un encombrement très réduit, permettant de nombreuses instrumentations. En outre, elle permet l'alignement du mors par rapport à son palier pour diminuer au maximum les mouvements hors plan (ce qui est vérifié avec une éprouvette étalon instrumentée). Plusieurs capteurs peuvent être embarqués sur le mors pour répondre à différentes fonctions, en particulier des capteurs de déplacement LASER offrent une mesure directe de l'écart entre mors et de leur inclinaison relative.

Most of the planar biaxial machine grips currently used for cross-shaped specimens have several a... more Most of the planar biaxial machine grips currently used for cross-shaped specimens have several advantages: stiffness to radial loads, fast and easy sample mounting. Generally, they lack a sufficient alignment precision (inducing a static bending during clamping) and might exhibit flexion during load. These shortcomings are obviously of major importance when it comes to fatigue tests. Other types of grips avoid some of these problems, but usually at the cost of a significantly larger size. Moreover, measurement techniques used with biaxial testing machines have evolved considerably: Digital Image Correlation, Stereo Correlation, Thermography, X-Ray Diffraction. It is thus necessary to take into account these new requirements along with the defects of the existing grips. The considered solution offers a higher bending stiffness without considerable increase in size, permitting significant additional instrumentation. Also, it allows the measurement and the adjustment of the alignment ...

International audienceno abstrac