HAL (Le Centre pour la Communication Scientifique Directe), Jul 1, 2019
Mesure et prédiction des déformations et contraintes résiduelles lors du refroidissement d'un str... more Mesure et prédiction des déformations et contraintes résiduelles lors du refroidissement d'un stratifié composite thermoplastique Measurement and prediction of the residual strains and stresses during the cooling of a thermoplastic composite laminate
HAL (Le Centre pour la Communication Scientifique Directe), Jul 1, 2019
Nous présentons une analyse des propriétés hygro-thermo-mécaniques de matériaux composites sandwi... more Nous présentons une analyse des propriétés hygro-thermo-mécaniques de matériaux composites sandwichs à applications navales, en fonction du temps de combustion. Dans cette optique, des échantillons ont été analysés en terme de cinétique de tenue au feu et de résistance mécanique post-combustion.
HAL (Le Centre pour la Communication Scientifique Directe), Jun 28, 2017
Nous présentons une analyse des propriétés thermo-mécaniques de matériaux composites sandwichs à ... more Nous présentons une analyse des propriétés thermo-mécaniques de matériaux composites sandwichs à applications navales, en fonction du temps de combustion et en fonction du vieillissement humide. Dans cette optique, des échantillons sec et humide (saturé en eau) ont été analysés en terme de cinétique de tenue au feu et de résistance mécanique post-combustion. Un travail de modélisation est également en cours.
International Journal of Adhesion and Adhesives, Sep 1, 2017
Moisture diffusion can decrease the mechanical stiffness and strength of organic matrix composite... more Moisture diffusion can decrease the mechanical stiffness and strength of organic matrix composites. Recently, Fibre Bragg Grating (FBG) sensors have been used in order to study the hygroscopic ageing of polyester/glass composites at room temperature. In the present study, the hygroscopic strain measurement of polyester /glass composite has been achieved at room temperature. Furthermore, measurements have been done at higher temperatures in order to better understand the combination of both hygroscopic ageing and varying temperatures on the mechanical properties of these composite samples. The Bragg wavelength () was found to shift linearly over a temperature range from room temperature to 35 °C. Beyond 35 °C, the Bragg wavelength does not linearly vary as a function of the temperature. A strong variation of the Bragg wavelength above a specific temperature threshold was found. This could be explained according to two mechanisms. Firstly, hygroscopic ageing could result in a decrease of the glass transition temperature (T g) of the polymer matrix. Therefore viscoelastic behavior may appear beyond this temperature. Hygroscopic ageing could also degrade the interfacial shear strength between the fibre and the resin. Differential Scanning Calorimetry (DSC) analyses showed that hygroscopic aging does not affect the Tg of the polyester resin. Furthermore, it has been found that the hygroscopic aging degrades the interfacial adhesion of the optical fibre/polyester according to the considerable decreases of the interfacial shear strength observed in practice.
21ème Journées Nationales sur les Composites, Jul 1, 2019
Les recherches se sont multipliées dans le développement des nouvelles familles de matériaux comp... more Les recherches se sont multipliées dans le développement des nouvelles familles de matériaux composites multiaxiaux afin de répondre aux critères de hautes performances, telles que la résistance et la durabilité. Cette dernière décennie a notamment vu l'apparition d'une nouvelle génération de matériaux composites du type Non-Crimp Fabric (NCF). Il s'agit de matériaux composés de renforts multiaxiaux non-tissés, et cousus avec un fil textile. Cette spécificité a été développée sur ces matériaux pour améliorer non seulement leurs propriétés mais aussi pour les adapter à des procédés de fabrication innovants. En revanche, la présence de fil de couture dans ces composites induit la formation d'une morphologie spécifique imposant une nouvelle approche vis-à-vis de l'étude de durabilité. Dans cette étude, les composites sont sollicités avec des cycles hygrothermiques accélérés contenant un conditionnement d'humidité relative préalable et un bloc de chargement thermique provoquant des microfissurations dans des zones spécifiques riches en résine. Une variable de densité de microfissures basée sur une méthode d'observation 2D a été utilisée afin de suivre l'évolution des microfissures au cours des cycles appliqués. La caractérisation des morphologies permettant d'étudier l'initiation et le développement de la fissuration a été réalisée.
Les énergies marines renouvelables représentent des développements économiques et politiques maje... more Les énergies marines renouvelables représentent des développements économiques et politiques majeurs.. La majorité des développeurs de systèmes récupérateurs d'énergie ont préféré utiliser des organes en carbone/époxy ou d'une combinaison verre/carbone/époxy pour les systèmes EMR. Dans un environnement très sévère comme les océans, la fiabilité des composants est cruciale pour la productivité de ces systèmes récupérateur d'énergie marine. Ces structures sont soumises à de nombreuses forces telles que les courants marins, les vagues, les tempêtes mais aussi de nombreuses agressions, telles que l'eau de mer et la corrosion. En conséquence il y a un besoin de comprendre comment une longue immersion en environnement marin affecte ces structures composites. Basé sur de précédents travaux [1],[2], le projet VICOMTE a pour objectif d'investiguer et de développer de nouvelles méthodologies pour étudier et modéliser l'impact complexe du vieillissement en milieux marin sur des pièces composites. Ces méthodologies sont basées sur l'accélération des phénomènes de vieillissement physique et mécanique.
The study focus on the fatigue characterization of composite sandwich structures. Recent work has... more The study focus on the fatigue characterization of composite sandwich structures. Recent work has shown that improvement of a foam fatigue test provides a ten-fold improvement in durability. On sandwich structures, fatigue behavior is often characterized by the ASTM C393 4-point bending test standard. This standard is discussed here and we propose a new 4-point bending specimen geometry to limit edge effects. Fatigue tests were carried out on five test pieces, the purpose is to estimate the variability of the lifetime. In addition, a modeling under Abaqus ® with the use of a UMAT is developed in order to take into account the self heating of the foam under dynamic loading. The model is improved by taking into account the density gradient of the foam observed in the thickness of the core.
The identification of the mechanical behavior of adhesives is necessary to describe the developme... more The identification of the mechanical behavior of adhesives is necessary to describe the development of residual stresses during their curing, which might impact their mechanical strength and lead to early failure of the bonding. A simple characterization and modeling approach is therefore developed and presented, which permits to monitor and identify the mechanical behavior of a thermosetting adhesive during the whole curing process. The test method is based on a compressive test, which consists in applying a periodic displacement and recording the subsequent load variations during cure. The test set-up relies on a simple apparatus as it consists in steel cylinders mounted on a standard tensile test machine. The analysis of the mechanical behavior is based on an analytical description of a visco-elastic constitutive law following the Maxwell model, leading to the identification of the material apparent viscosity and Young’s modulus. This characterization methodology is applied to an...
Thermoforming allows the manufacture of structural parts for the automotive and aeronautical doma... more Thermoforming allows the manufacture of structural parts for the automotive and aeronautical domains using long fiber thermoplastic prepregs with short cycle times. During this operation, several sheets of molten prepregs are stacked and subjected to large macroscale strains, mainly via in-plane shear, out-of-plane consolidation or dilatation, and bending of the fibrous reinforcement. These deformation modes and the related meso and microstructure evolutions are still poorly understood. However, they can drastically alter the end-use macroscale properties of fabricated parts. To better understand these phenomena, bias extension tests were performed using specimens made of several stacked layers of glass woven fabrics and polyamide matrix. The macroscale shear behavior of these prepregs was investigated at various temperatures. A multiscale analysis of deformed samples was performed using X-ray microtomography images of the deformed specimens acquired at two different spatial resolutions. The low-resolution images were used to analyze the deformation mechanisms and the structural characteristics of prepregs at the macroscale and bundle scales. It was possible to analyze the 3D shapes of deformed samples and, in particular, the spatial variations of their thickness so as to quantify the out-of-plane dilatancy or consolidation phenomena induced by the in-plane shear of prepregs. At a lower scale, the analysis of the high-resolution images showed that these mechanisms were accompanied by the growth of pores and the deformation of fiber bundles. The orientation of the fiber bundles and its through-thickness evolution were measured along the weft and warp directions in the deformed samples, allowing the relevance of geometrical models currently used to analyze bias extension tests to be discussed. Results can be used to enhance the current rheological models for the prediction of thermoforming of thermoplastic prepregs.
Polyamide based composites are increasingly used in automobile industry. During their lifetime, t... more Polyamide based composites are increasingly used in automobile industry. During their lifetime, they are subjected to aggressive environments including moisture which acts as a plasticizer of the polymer network, affecting its mechanical behaviour. Besides, the heterogeneous in-depth moisture content induces a differential hygroscopic swelling that may eventually cause damage. In practice, hygroscopic expansion depends on both the moisture content and coefficient of moisture expansion. Often, the polymer database do not provide detailed information on the dependence of the coefficient of moisture expansion on the moisture content. This work describes a multiscale and multiphysics approach enabling to identify the local evolution of the materials parameter of the hygro-mechanical behaviour law of a neat PA6 polymer, occurring during the transient stage of humid aging tests, from the numerical simulation of the dimensional change experienced by macroscopic samples. This study highlights the nonlinear evolution of the measured hygroscopic strain at the beginning of the moisture diffusion, as well as the need to account for the water induced plasticization effects (i.e. the fall down of the Young's modulus of the polymer material), for building an appropriate, effective modelling of the material behaviour.
The main objective of the present study was to develop a fire thermal model able to predict the e... more The main objective of the present study was to develop a fire thermal model able to predict the evolution of the temperature gradient across a sandwich composite structure when exposed to fire. Thermal response of sandwich panels, with glass/polyester skins and balsa core, was investigated under severe temperature conditions as samples were exposed to high temperatures up to 570°C. Based on experimental measurements, an accurate three-dimensional thermal model was developed using finite element analysis. The obtained predictions of the temperature field are in excellent agreement with the experimental data, showing the importance of combined numerical-experimental analyses. This allowed us to propose a new approach that can be used for the prediction of thermo-mechanical post-combustion properties in a very large number of fire and material scenarios according to its simplicity and robustness.
The design and qualification of composite repairs for pipelines usually requires hydrostatic test... more The design and qualification of composite repairs for pipelines usually requires hydrostatic tests for the determination of the failure pressure. In this work, the use of a shaft blister test to assess the failure pressure of composite repairs is proposed. Blister tests were conducted to investigate the interfacial debonding of a composite plate bonded to steel substrate. The blister test specimen represents a composite repair applied to a pipeline with a defect. The onset debonding load is used to predict the failure pressure. A 3D digital image correlation (DIC) has been used to follow up the debonding propagation and evaluate the blister shape. 3D finite element model with a cohesive zone model has been used to simulate loaded shaft blister test. A good correlation between blister tests results and finite element simulation results was obtained. The validated finite element model was used to predict failure pressure in bonded composite repaired pipes with different values of defect diameter and repair thickness. The results show that the blister test could replace hydrostatic tests for the analysis of the composite repairs performance.
Moisture diffusion can induce a decrease of the mechanical stiffness of organic matrix composites... more Moisture diffusion can induce a decrease of the mechanical stiffness of organic matrix composites. Recently, optical sensors have been used in order to measure the hygroscopic strains of organic matrix composites. In this study, the Bragg wavelength shift (λb) has been recorded at room temperature. The measurement have been achieved at higher temperatures also, in order to verify the possible coupling effect of a hygroscopic aging simultaneously with the temperature on the mechanical properties. Authors find a brutal variation of λb above a specific temperature threshold. This could be explaine doing to two mechanisms. First, composite hygroscopic ageing could result in a decrease of the glassy temperature (Tg).Therefore a viscoelastic behavior may appear beyond this temperature. Secondly, the hygroscopic ageing could decrease the fibre/resin interfacial shear strength. The present study is dedicated to the characterization of the influence of hygroscopic aging on the strength of th...
HAL (Le Centre pour la Communication Scientifique Directe), Jul 1, 2019
Mesure et prédiction des déformations et contraintes résiduelles lors du refroidissement d'un str... more Mesure et prédiction des déformations et contraintes résiduelles lors du refroidissement d'un stratifié composite thermoplastique Measurement and prediction of the residual strains and stresses during the cooling of a thermoplastic composite laminate
HAL (Le Centre pour la Communication Scientifique Directe), Jul 1, 2019
Nous présentons une analyse des propriétés hygro-thermo-mécaniques de matériaux composites sandwi... more Nous présentons une analyse des propriétés hygro-thermo-mécaniques de matériaux composites sandwichs à applications navales, en fonction du temps de combustion. Dans cette optique, des échantillons ont été analysés en terme de cinétique de tenue au feu et de résistance mécanique post-combustion.
HAL (Le Centre pour la Communication Scientifique Directe), Jun 28, 2017
Nous présentons une analyse des propriétés thermo-mécaniques de matériaux composites sandwichs à ... more Nous présentons une analyse des propriétés thermo-mécaniques de matériaux composites sandwichs à applications navales, en fonction du temps de combustion et en fonction du vieillissement humide. Dans cette optique, des échantillons sec et humide (saturé en eau) ont été analysés en terme de cinétique de tenue au feu et de résistance mécanique post-combustion. Un travail de modélisation est également en cours.
International Journal of Adhesion and Adhesives, Sep 1, 2017
Moisture diffusion can decrease the mechanical stiffness and strength of organic matrix composite... more Moisture diffusion can decrease the mechanical stiffness and strength of organic matrix composites. Recently, Fibre Bragg Grating (FBG) sensors have been used in order to study the hygroscopic ageing of polyester/glass composites at room temperature. In the present study, the hygroscopic strain measurement of polyester /glass composite has been achieved at room temperature. Furthermore, measurements have been done at higher temperatures in order to better understand the combination of both hygroscopic ageing and varying temperatures on the mechanical properties of these composite samples. The Bragg wavelength () was found to shift linearly over a temperature range from room temperature to 35 °C. Beyond 35 °C, the Bragg wavelength does not linearly vary as a function of the temperature. A strong variation of the Bragg wavelength above a specific temperature threshold was found. This could be explained according to two mechanisms. Firstly, hygroscopic ageing could result in a decrease of the glass transition temperature (T g) of the polymer matrix. Therefore viscoelastic behavior may appear beyond this temperature. Hygroscopic ageing could also degrade the interfacial shear strength between the fibre and the resin. Differential Scanning Calorimetry (DSC) analyses showed that hygroscopic aging does not affect the Tg of the polyester resin. Furthermore, it has been found that the hygroscopic aging degrades the interfacial adhesion of the optical fibre/polyester according to the considerable decreases of the interfacial shear strength observed in practice.
21ème Journées Nationales sur les Composites, Jul 1, 2019
Les recherches se sont multipliées dans le développement des nouvelles familles de matériaux comp... more Les recherches se sont multipliées dans le développement des nouvelles familles de matériaux composites multiaxiaux afin de répondre aux critères de hautes performances, telles que la résistance et la durabilité. Cette dernière décennie a notamment vu l'apparition d'une nouvelle génération de matériaux composites du type Non-Crimp Fabric (NCF). Il s'agit de matériaux composés de renforts multiaxiaux non-tissés, et cousus avec un fil textile. Cette spécificité a été développée sur ces matériaux pour améliorer non seulement leurs propriétés mais aussi pour les adapter à des procédés de fabrication innovants. En revanche, la présence de fil de couture dans ces composites induit la formation d'une morphologie spécifique imposant une nouvelle approche vis-à-vis de l'étude de durabilité. Dans cette étude, les composites sont sollicités avec des cycles hygrothermiques accélérés contenant un conditionnement d'humidité relative préalable et un bloc de chargement thermique provoquant des microfissurations dans des zones spécifiques riches en résine. Une variable de densité de microfissures basée sur une méthode d'observation 2D a été utilisée afin de suivre l'évolution des microfissures au cours des cycles appliqués. La caractérisation des morphologies permettant d'étudier l'initiation et le développement de la fissuration a été réalisée.
Les énergies marines renouvelables représentent des développements économiques et politiques maje... more Les énergies marines renouvelables représentent des développements économiques et politiques majeurs.. La majorité des développeurs de systèmes récupérateurs d'énergie ont préféré utiliser des organes en carbone/époxy ou d'une combinaison verre/carbone/époxy pour les systèmes EMR. Dans un environnement très sévère comme les océans, la fiabilité des composants est cruciale pour la productivité de ces systèmes récupérateur d'énergie marine. Ces structures sont soumises à de nombreuses forces telles que les courants marins, les vagues, les tempêtes mais aussi de nombreuses agressions, telles que l'eau de mer et la corrosion. En conséquence il y a un besoin de comprendre comment une longue immersion en environnement marin affecte ces structures composites. Basé sur de précédents travaux [1],[2], le projet VICOMTE a pour objectif d'investiguer et de développer de nouvelles méthodologies pour étudier et modéliser l'impact complexe du vieillissement en milieux marin sur des pièces composites. Ces méthodologies sont basées sur l'accélération des phénomènes de vieillissement physique et mécanique.
The study focus on the fatigue characterization of composite sandwich structures. Recent work has... more The study focus on the fatigue characterization of composite sandwich structures. Recent work has shown that improvement of a foam fatigue test provides a ten-fold improvement in durability. On sandwich structures, fatigue behavior is often characterized by the ASTM C393 4-point bending test standard. This standard is discussed here and we propose a new 4-point bending specimen geometry to limit edge effects. Fatigue tests were carried out on five test pieces, the purpose is to estimate the variability of the lifetime. In addition, a modeling under Abaqus ® with the use of a UMAT is developed in order to take into account the self heating of the foam under dynamic loading. The model is improved by taking into account the density gradient of the foam observed in the thickness of the core.
The identification of the mechanical behavior of adhesives is necessary to describe the developme... more The identification of the mechanical behavior of adhesives is necessary to describe the development of residual stresses during their curing, which might impact their mechanical strength and lead to early failure of the bonding. A simple characterization and modeling approach is therefore developed and presented, which permits to monitor and identify the mechanical behavior of a thermosetting adhesive during the whole curing process. The test method is based on a compressive test, which consists in applying a periodic displacement and recording the subsequent load variations during cure. The test set-up relies on a simple apparatus as it consists in steel cylinders mounted on a standard tensile test machine. The analysis of the mechanical behavior is based on an analytical description of a visco-elastic constitutive law following the Maxwell model, leading to the identification of the material apparent viscosity and Young’s modulus. This characterization methodology is applied to an...
Thermoforming allows the manufacture of structural parts for the automotive and aeronautical doma... more Thermoforming allows the manufacture of structural parts for the automotive and aeronautical domains using long fiber thermoplastic prepregs with short cycle times. During this operation, several sheets of molten prepregs are stacked and subjected to large macroscale strains, mainly via in-plane shear, out-of-plane consolidation or dilatation, and bending of the fibrous reinforcement. These deformation modes and the related meso and microstructure evolutions are still poorly understood. However, they can drastically alter the end-use macroscale properties of fabricated parts. To better understand these phenomena, bias extension tests were performed using specimens made of several stacked layers of glass woven fabrics and polyamide matrix. The macroscale shear behavior of these prepregs was investigated at various temperatures. A multiscale analysis of deformed samples was performed using X-ray microtomography images of the deformed specimens acquired at two different spatial resolutions. The low-resolution images were used to analyze the deformation mechanisms and the structural characteristics of prepregs at the macroscale and bundle scales. It was possible to analyze the 3D shapes of deformed samples and, in particular, the spatial variations of their thickness so as to quantify the out-of-plane dilatancy or consolidation phenomena induced by the in-plane shear of prepregs. At a lower scale, the analysis of the high-resolution images showed that these mechanisms were accompanied by the growth of pores and the deformation of fiber bundles. The orientation of the fiber bundles and its through-thickness evolution were measured along the weft and warp directions in the deformed samples, allowing the relevance of geometrical models currently used to analyze bias extension tests to be discussed. Results can be used to enhance the current rheological models for the prediction of thermoforming of thermoplastic prepregs.
Polyamide based composites are increasingly used in automobile industry. During their lifetime, t... more Polyamide based composites are increasingly used in automobile industry. During their lifetime, they are subjected to aggressive environments including moisture which acts as a plasticizer of the polymer network, affecting its mechanical behaviour. Besides, the heterogeneous in-depth moisture content induces a differential hygroscopic swelling that may eventually cause damage. In practice, hygroscopic expansion depends on both the moisture content and coefficient of moisture expansion. Often, the polymer database do not provide detailed information on the dependence of the coefficient of moisture expansion on the moisture content. This work describes a multiscale and multiphysics approach enabling to identify the local evolution of the materials parameter of the hygro-mechanical behaviour law of a neat PA6 polymer, occurring during the transient stage of humid aging tests, from the numerical simulation of the dimensional change experienced by macroscopic samples. This study highlights the nonlinear evolution of the measured hygroscopic strain at the beginning of the moisture diffusion, as well as the need to account for the water induced plasticization effects (i.e. the fall down of the Young's modulus of the polymer material), for building an appropriate, effective modelling of the material behaviour.
The main objective of the present study was to develop a fire thermal model able to predict the e... more The main objective of the present study was to develop a fire thermal model able to predict the evolution of the temperature gradient across a sandwich composite structure when exposed to fire. Thermal response of sandwich panels, with glass/polyester skins and balsa core, was investigated under severe temperature conditions as samples were exposed to high temperatures up to 570°C. Based on experimental measurements, an accurate three-dimensional thermal model was developed using finite element analysis. The obtained predictions of the temperature field are in excellent agreement with the experimental data, showing the importance of combined numerical-experimental analyses. This allowed us to propose a new approach that can be used for the prediction of thermo-mechanical post-combustion properties in a very large number of fire and material scenarios according to its simplicity and robustness.
The design and qualification of composite repairs for pipelines usually requires hydrostatic test... more The design and qualification of composite repairs for pipelines usually requires hydrostatic tests for the determination of the failure pressure. In this work, the use of a shaft blister test to assess the failure pressure of composite repairs is proposed. Blister tests were conducted to investigate the interfacial debonding of a composite plate bonded to steel substrate. The blister test specimen represents a composite repair applied to a pipeline with a defect. The onset debonding load is used to predict the failure pressure. A 3D digital image correlation (DIC) has been used to follow up the debonding propagation and evaluate the blister shape. 3D finite element model with a cohesive zone model has been used to simulate loaded shaft blister test. A good correlation between blister tests results and finite element simulation results was obtained. The validated finite element model was used to predict failure pressure in bonded composite repaired pipes with different values of defect diameter and repair thickness. The results show that the blister test could replace hydrostatic tests for the analysis of the composite repairs performance.
Moisture diffusion can induce a decrease of the mechanical stiffness of organic matrix composites... more Moisture diffusion can induce a decrease of the mechanical stiffness of organic matrix composites. Recently, optical sensors have been used in order to measure the hygroscopic strains of organic matrix composites. In this study, the Bragg wavelength shift (λb) has been recorded at room temperature. The measurement have been achieved at higher temperatures also, in order to verify the possible coupling effect of a hygroscopic aging simultaneously with the temperature on the mechanical properties. Authors find a brutal variation of λb above a specific temperature threshold. This could be explaine doing to two mechanisms. First, composite hygroscopic ageing could result in a decrease of the glassy temperature (Tg).Therefore a viscoelastic behavior may appear beyond this temperature. Secondly, the hygroscopic ageing could decrease the fibre/resin interfacial shear strength. The present study is dedicated to the characterization of the influence of hygroscopic aging on the strength of th...
Nous présentons une analyse des propriétés thermo-mécaniques de matériaux composites sandwichs à ... more Nous présentons une analyse des propriétés thermo-mécaniques de matériaux composites sandwichs à applications navales, en fonction du temps de combustion et en fonction de l'état d'hydratation. Dans cette optique, des échantillons sec et humide (saturé en eau) ont été analysés en terme de cinétique de tenue au feu et de résistance mécanique post-combustion. Un travail de modélisation est également en cours.
We analyzed the thermo-mechanical properties of sandwich composite materials used in marine applications, as a function of the combustion time and as a function of the hydration state. In this light, dry and wet samples (saturated with water) were analyzed in terms of fire resistance kinetic and of post-combustion mechanical strength.
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Papers by Pascal Casari
We analyzed the thermo-mechanical properties of sandwich composite materials used in marine applications, as a function of the combustion time and as a function of the hydration state. In this light, dry and wet samples (saturated with water) were analyzed in terms of fire resistance kinetic and of post-combustion mechanical strength.