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The effect of CO2 laser drilling on glass microballoon/epoxy syntactic foams are investigated in this study to optimize machining parameters to achieve a clean hole for various industrial applications. The epoxy matrix is reinforced with glass microballoons in concentrations of 0, 20 and 40 vol%. Cutting speed, laser power and additive percentage are input parameters for optimization. Kerf taper angle, surface roughness and ovality percentage are used as output responses to evaluate hole quality. For the optimization study, hybrid multi-criteria decision-making methods such as grey relational analysis and multi-objective optimization with ratio assessment methods are used, with equal weightage given to each output response. According to the study, low power and high speed produce better machining results such as a smaller kerf taper angle, lower surface roughness and a lower ovality percentage. Furthermore, a higher additive percentage is not appropriate for laser in epoxy/glass microballoon composite because it burns the area near the laser and increases surface roughness. © 2023 The Author(s)

The current work focuses on predicting the buckling and free vibration frequencies (fn) of cenosphere reinforced epoxy based syntactic foam beam under varying loads. Critical buckling loads (Ncr) and fn are predicted using the differential quadrature method (DQM). Ncr and fn have been calculated for beams of varying cenosphere volume fractions subjected to axial load under clamped-clamped (CC), clamped-simply (CS), simply-simply (SS), and clamped-free (CF) boundary conditions (BC′s). Upon increasing the cenosphere volume fraction, Ncr and fn of syntactic foam composites increases. These numerical outcomes are compared with the theoretical values evaluated through the Euler-Bernoulli hypothesis and further compared with experimental outcomes. Results are observed to be in precise agreement. The results of the DQM numerical analysis are given out for the different BC′s, aspect ratios, cenosphere volume fractions, and varying loads. It is perceived that depending on the BC′s, the type of axial varying loads and aspect ratios has a substantial effect on the Ncr and fn behaviour of the syntactic foam beams. A comparative study of the obtained results showed that the beam subjected to parabolic load under CC boundary conditions exhibited a higher buckling load. © 2023 The Authors

The effect of CO2 laser drilling on glass microballoon/epoxy syntactic foams are investigated in this study to optimize machining parameters to achieve a clean hole for various industrial applications. The epoxy matrix is reinforced with glass microballoons in concentrations of 0, 20 and 40 vol%. Cutting speed, laser power and additive percentage are input parameters for optimization. Kerf taper angle, surface roughness and ovality percentage are used as output responses to evaluate hole quality. For the optimization study, hybrid multi-criteria decision-making methods such as grey relational analysis and multi-objective optimization with ratio assessment methods are used, with equal weightage given to each output response. According to the study, low power and high speed produce better machining results such as a smaller kerf taper angle, lower surface roughness and a lower ovality percentage. Furthermore, a higher additive percentage is not appropriate for laser in epoxy/glass microballoon composite because it burns the area near the laser and increases surface roughness. © 2023 The Author(s)

The current work focuses on predicting the buckling and free vibration frequencies (fn) of cenosphere reinforced epoxy based syntactic foam beam under varying loads. Critical buckling loads (Ncr) and fn are predicted using the differential quadrature method (DQM). Ncr and fn have been calculated for beams of varying cenosphere volume fractions subjected to axial load under clamped-clamped (CC), clamped-simply (CS), simply-simply (SS), and clamped-free (CF) boundary conditions (BC′s). Upon increasing the cenosphere volume fraction, Ncr and fn of syntactic foam composites increases. These numerical outcomes are compared with the theoretical values evaluated through the Euler-Bernoulli hypothesis and further compared with experimental outcomes. Results are observed to be in precise agreement. The results of the DQM numerical analysis are given out for the different BC′s, aspect ratios, cenosphere volume fractions, and varying loads. It is perceived that depending on the BC′s, the type of axial varying loads and aspect ratios has a substantial effect on the Ncr and fn behaviour of the syntactic foam beams. A comparative study of the obtained results showed that the beam subjected to parabolic load under CC boundary conditions exhibited a higher buckling load. © 2023 The Authors

The current work focuses on predicting the buckling and free vibration frequencies (fn) of cenosphere reinforced epoxy based syntactic foam beam under varying loads. Critical buckling loads (Ncr) and fn are predicted using the differential quadrature method (DQM). Ncr and fn have been calculated for beams of varying cenosphere volume fractions subjected to axial load under clamped-clamped (CC), clamped-simply (CS), simply-simply (SS), and clamped-free (CF) boundary conditions (BC′s). Upon increasing the cenosphere volume fraction, Ncr and fn of syntactic foam composites increases. These numerical outcomes are compared with the theoretical values evaluated through the Euler-Bernoulli hypothesis and further compared with experimental outcomes. Results are observed to be in precise agreement. The results of the DQM numerical analysis are given out for the different BC′s, aspect ratios, cenosphere volume fractions, and varying loads. It is perceived that depending on the BC′s, the type of axial varying loads and aspect ratios has a substantial effect on the Ncr and fn behaviour of the syntactic foam beams. A comparative study of the obtained results showed that the beam subjected to parabolic load under CC boundary conditions exhibited a higher buckling load. © 2023 The Authors

The effect of CO2 laser drilling on glass microballoon/epoxy syntactic foams are investigated in this study to optimize machining parameters to achieve a clean hole for various industrial applications. The epoxy matrix is reinforced with glass microballoons in concentrations of 0, 20 and 40 vol%. Cutting speed, laser power and additive percentage are input parameters for optimization. Kerf taper angle, surface roughness and ovality percentage are used as output responses to evaluate hole quality. For the optimization study, hybrid multi-criteria decision-making methods such as grey relational analysis and multi-objective optimization with ratio assessment methods are used, with equal weightage given to each output response. According to the study, low power and high speed produce better machining results such as a smaller kerf taper angle, lower surface roughness and a lower ovality percentage. Furthermore, a higher additive percentage is not appropriate for laser in epoxy/glass microballoon composite because it burns the area near the laser and increases surface roughness. © 2023 The Author(s)

This study deals with the hydrostatic strength of hollow glass microspheres composites, commonly known as syntactic foams, using model materials made of 0.15 g/cm3 microspheres with 3 types of matrix, two epoxies and one paraffin. More than 100 model material samples are characterized for that work. The hydrostatic strength of these composite materials is determined in a pressure vessel, which can go up to 100 MPa. Two major parameters are studied: stiffness of the matrix and microsphere volume content within the composite material. The results clearly show that the hydrostatic strength of the syntactic foam can be improved by an increase in matrix stiffness or a reduction in microspheres content. Based on experimental data an empirical model with two parameters is proposed to describe the hydrostatic strength of syntactic foam. The relevance of the model is discussed.

This study deals with the hydrostatic strength of hollow glass microspheres composites, commonly known as syntactic foams, using model materials made of 0.15 g/cm3 microspheres with 3 types of matrix, two epoxies and one paraffin. More than 100 model material samples are characterized for that work. The hydrostatic strength of these composite materials is determined in a pressure vessel, which can go up to 100 MPa. Two major parameters are studied: stiffness of the matrix and microsphere volume content within the composite material. The results clearly show that the hydrostatic strength of the syntactic foam can be improved by an increase in matrix stiffness or a reduction in microspheres content. Based on experimental data an empirical model with two parameters is proposed to describe the hydrostatic strength of syntactic foam. The relevance of the model is discussed.

Machined surface quality and integrity affect the corrosion performance of AZ31 magnesium composites. These novel materials are preferred for temporary orthopedic and vascular implants. In this paper, the drilling performance of AZ31-magnesium reinforced with hollow alumina microsphere syntactic foam under LN2 cryogenic, dry, and Almag® Oil is presented. Cutting tests were conducted using TiAlN physical vapor deposition (PVD) coated multilayer carbide and K10 uncoated carbide twist drills. AZ31 magnesium matrices were reinforced with hollow alumina ceramic microspheres with varying volume fractions (5%, 10%, 15%) and average bubble sizes. Experimental results showed that the drilling thrust forces increased by 250% with increasing feed rate (0.05 to 0.6 mm/tooth) and 46% with the increasing volume fraction of alumina microspheres (5% to 15%). Cryogenic machining generated 45% higher thrust forces compared to dry and wet machining. The higher the volume fraction and the finer the average size of hollow microspheres, the higher were the thrust forces. Cryogenic machining (0.42 μm) produced a 75% improvement in surface roughness (Ra) values compared to wet machining (1.84 μm) with minimal subsurface machining-induced defects. Surface quality deteriorated by 129% with an increasing volume fraction of alumina microspheres (0.61 μm to 1.4 μm). Burr height reduction of 53% was achieved with cryogenic machining (60 μm) compared to dry machining (130 μm). Overall, compared to dry and wet machining methods, cryogenic drilling can be employed for the machining of AZ31 magnesium syntactic foams to achieve good surface quality and integrity., American University of Sharjah

This article reports the mechanical and biocorrosion behaviour of hollow silica nanosphere (SiO₂) reinforced (0.5–2 vol.%) magnesium (Mg) syntactic foams. Room temperature tensile properties’ characterization suggests that the increased addition of hollow silica nanospheres resulted in a progressive increase in tensile yield strength (TYS) and ultimate tensile strength (UTS) with Mg-2 vol.% SiO₂ exhibiting a maximum TYS of 167 MPa and a UTS of 217 MPa. The degradation behaviour of the developed Mg-SiO₂ syntactic foams in four different simulated body fluids (SBFs): artificial blood plasma solution (ABPS), phosphate-buffered saline solution (PBS), artificial saliva solution (ASS) and Hanks’ balanced saline solution (HBSS) was investigated by using potentiodynamic polarization studies. Results indicate that corrosion resistance of the Mg-SiO₂ syntactic foam decreases with increasing chloride ion concentration of the SBF. Mg-1.0 vol.% SiO₂ displayed the best corrosion response and its corrosion susceptibility pertaining to corrosion rate and polarisation curves in different SBF solutions can be ranked in the following order: ABPS > PBS > HBSS > ASS. The surface microstructure demonstrated the presence of a better passivated layer on the syntactic foams compared to pure Mg. The observed increase in corrosion resistance is correlated with intrinsic changes in microstructure due to the presence of hollow silica nanospheres. Further, the effect of corrosive environment on the degradation behaviour of Mg has been elucidated., Singapore Ministry of Education, American University of Sharjah

EX-CORE, a novel foam core material developed by Donkervoort Automobielen B.V., allows the creation of complexly shaped sandwich structures in a one-shot out-of-autoclave manufacturing process. Products with small tolerances and high surface quality on all surfaces can be obtained. The EX-CORE technology has achieved its intended goal at Donkervoort of saving cost and time for the production of sandwich structures for their cars. Now Donkervoort has the ambition to further develop EX-CORE for larger scale automotive manufacturing. To make the EX-CORE technology competitive with other composite production processes, the cycle time of several hours should be reduced to several minutes. The present work contributes to this development by re-engineering the EX-CORE foam composition such that cure cycle time reductions can be achieved., Aerospace Engineering

This paper presented the stress concentration factor (SCF) around the half circular edge of tensile specimens made of syntactic foam using finite element software Strand7 software. The study is a preliminary effort, which investigates the effect of variations of crack geometry on the stress concentration factor on a tensile specimen subjected to a constant, uniform, uniaxial tensile load. The material property is graded for varying Young’s Modulus and Poisson’s Ratio with different composition of glass microballoons. Finally, a uniform pressure is applied at the top and the model is constrained with symmetric boundary conditions at the left and bottom. As the result, these numerical results for both SCF experimental and simulation model are compared to those obtained from analytic fracture mechanics procedures and are found to be varied. In addition, the SCF is sensitive to the modulus of elasticity, particularly for lower composition weight percentage (wt.%), while it is also varied with the different weight percentage (wt.%) of glass microballoons, which is led by 2 wt.% specimen.

Sandwich composites or sandwich panels have been widely used as potential materials or building structures and are regarded as a lightweight material for marine applications. In particular, the mechanical properties, such as the compressive, tensile and flexural behaviour, of sandwich composites formed from glass fibre sheets used as the skin and glass microballoon/vinyl ester as the syntactic foam core were investigated in this report. This syntactic foam core is sandwiched between unidirectional glass fibre reinforced plastic (GFRP) using vinyl ester resins to build high performance sandwich panels. The results show that the compressive and tensile strengths decrease when the glass microballoon content is increased in syntactic foam core of sandwich panels. Moreover, compressive modulus is also found to be decreased, and there is no trend for tensile modulus. Meanwhile, the flexural stiffness and effective flexural stiffness for edgewise position have a higher bending as 50% and 60%, respectively. Furthermore, the results indicated that the glass microballoon mixed in a vinyl ester should be controlled to obtain a good combination of the tensile, compressive and flexural strength properties. © 2016 Md Mainul Islam, et al.

Sandwich composites or sandwich panels have been widely used as potential materials or building structures and are regarded as a lightweight material for marine applications. In particular, the mechanical properties, such as the compressive, tensile and flexural behaviour, of sandwich composites formed from glass fibre sheets used as the skin and glass microballoon/vinyl ester as the syntactic foam core were investigated in this report. This syntactic foam core is sandwiched between unidirectional glass fibre reinforced plastic (GFRP) using vinyl ester resins to build high performance sandwich panels. The results show that the compressive and tensile strengths decrease when the glass microballoon content is increased in syntactic foam core of sandwich panels. Moreover, compressive modulus is also found to be decreased, and there is no trend for tensile modulus. Meanwhile, the flexural stiffness and effective flexural stiffness for edgewise position have a higher bending as 50% and 60%, respectively. Furthermore, the results indicated that the glass microballoon mixed in a vinyl ester should be controlled to obtain a good combination of the tensile, compressive and flexural strength properties. © 2016 Md Mainul Islam, et al.

Sandwich composites or sandwich panels have been widely used as potential materials or building structures and are regarded as a lightweight material for marine applications. In particular, the mechanical properties, such as the compressive, tensile and flexural behaviour, of sandwich composites formed from glass fibre sheets used as the skin and glass microballoon/vinyl ester as the syntactic foam core were investigated in this report. This syntactic foam core is sandwiched between unidirectional glass fibre reinforced plastic (GFRP) using vinyl ester resins to build high performance sandwich panels. The results show that the compressive and tensile strengths decrease when the glass microballoon content is increased in syntactic foam core of sandwich panels. Moreover, compressive modulus is also found to be decreased, and there is no trend for tensile modulus. Meanwhile, the flexural stiffness and effective flexural stiffness for edgewise position have a higher bending as 50% and 60%, respectively. Furthermore, the results indicated that the glass microballoon mixed in a vinyl ester should be controlled to obtain a good combination of the tensile, compressive and flexural strength properties. © 2016 Md Mainul Islam, et al.

Syntactic foams, used in submersibles and in pipelines for deep sea oil wells, must be resistant to the severe conditions of the deep sea environment. As these foams will be in service for at least 20 years, their qualification testing is crucial. However, their mechanical characterization under real conditions of use is a challenge. In deep sea, the main loading is hydrostatic compression, however there is no standard procedure for testing material under pure hydrostatic pressure. The aim of this paper is to present a new characterization technique based on buoyancy loss measurement under hydrostatic pressure. To validate the method, two different syntactic foams (one brittle and one ductile) have been tested. Their behaviours under hydrostatic pressure have been followed by the proposed technique. The results from this innovative characterization technique have been compared to those of traditional uniaxial compression tests performed on the same materials.

Syntactic foams, used in submersibles and in pipelines for deep sea oil wells, must be resistant to the severe conditions of the deep sea environment. As these foams will be in service for at least 20 years, their qualification testing is crucial. However, their mechanical characterization under real conditions of use is a challenge. In deep sea, the main loading is hydrostatic compression, however there is no standard procedure for testing material under pure hydrostatic pressure. The aim of this paper is to present a new characterization technique based on buoyancy loss measurement under hydrostatic pressure. To validate the method, two different syntactic foams (one brittle and one ductile) have been tested. Their behaviours under hydrostatic pressure have been followed by the proposed technique. The results from this innovative characterization technique have been compared to those of traditional uniaxial compression tests performed on the same materials.

Syntactic foams, used in submersibles and in pipelines for deep sea oil wells, must be resistant to the severe conditions of the deep sea environment. As these foams will be in service for at least 20 years, their qualification testing is crucial. However, their mechanical characterization under real conditions of use is a challenge. In deep sea, the main loading is hydrostatic compression, however there is no standard procedure for testing material under pure hydrostatic pressure. The aim of this paper is to present a new characterization technique based on buoyancy loss measurement under hydrostatic pressure. To validate the method, two different syntactic foams (one brittle and one ductile) have been tested. Their behaviours under hydrostatic pressure have been followed by the proposed technique. The results from this innovative characterization technique have been compared to those of traditional uniaxial compression tests performed on the same materials.

Ultra-deep water (up to 3000 in) is one of the next frontiers for oil offshore exploitation. It requires the use of conduits having to resist in the long run (durability about 25 years) the mechanical and environmental requests. One of the key points is the thermal insulation of the structure to avoid the formation of hydrates and paraffin plugs inside of the steel pipe. Over the past 10 years, many studies were performed to better understand the behaviour of the syntactic foams used as thermal insulation of pipes for deepwater production, but few tests were run on industrial prototypes to reach the actual thermal properties of the systems. This paper presents the numerical and experimental characterizations of an industrial multilayered insulated pipeline tested in service conditions. Two thermomechanical finite element modellings of the coated pipeline have been developed to predict its behaviour during service condition tests. The first model considers pure conduction through the inner air inside of the structure and the second model considers convection phenomenon between the inner air and the metallic surfaces inside of the structure. In parallel, industrial pipe tests on an immersed instrumented pipeline, internally heated to temperatures up to 95 degrees C and subjected externally to hydrostatic pressure up to 300 bar are presented. Experimental data obtained during industrial pipe tests and related model predictions are compared and discussed. Thermal properties of the syntactic foam are determined with steady and transient states analysis. In complement, a study of the model results sensitivity to the input Poisson coefficient is presented. (C) 2010 Elsevier B.V. All rights reserved.

Ultra-deep water (up to 3000 in) is one of the next frontiers for oil offshore exploitation. It requires the use of conduits having to resist in the long run (durability about 25 years) the mechanical and environmental requests. One of the key points is the thermal insulation of the structure to avoid the formation of hydrates and paraffin plugs inside of the steel pipe. Over the past 10 years, many studies were performed to better understand the behaviour of the syntactic foams used as thermal insulation of pipes for deepwater production, but few tests were run on industrial prototypes to reach the actual thermal properties of the systems. This paper presents the numerical and experimental characterizations of an industrial multilayered insulated pipeline tested in service conditions. Two thermomechanical finite element modellings of the coated pipeline have been developed to predict its behaviour during service condition tests. The first model considers pure conduction through the inner air inside of the structure and the second model considers convection phenomenon between the inner air and the metallic surfaces inside of the structure. In parallel, industrial pipe tests on an immersed instrumented pipeline, internally heated to temperatures up to 95 degrees C and subjected externally to hydrostatic pressure up to 300 bar are presented. Experimental data obtained during industrial pipe tests and related model predictions are compared and discussed. Thermal properties of the syntactic foam are determined with steady and transient states analysis. In complement, a study of the model results sensitivity to the input Poisson coefficient is presented. (C) 2010 Elsevier B.V. All rights reserved.

Ultra-deep water (up to 3000 in) is one of the next frontiers for oil offshore exploitation. It requires the use of conduits having to resist in the long run (durability about 25 years) the mechanical and environmental requests. One of the key points is the thermal insulation of the structure to avoid the formation of hydrates and paraffin plugs inside of the steel pipe. Over the past 10 years, many studies were performed to better understand the behaviour of the syntactic foams used as thermal insulation of pipes for deepwater production, but few tests were run on industrial prototypes to reach the actual thermal properties of the systems. This paper presents the numerical and experimental characterizations of an industrial multilayered insulated pipeline tested in service conditions. Two thermomechanical finite element modellings of the coated pipeline have been developed to predict its behaviour during service condition tests. The first model considers pure conduction through the inner air inside of the structure and the second model considers convection phenomenon between the inner air and the metallic surfaces inside of the structure. In parallel, industrial pipe tests on an immersed instrumented pipeline, internally heated to temperatures up to 95 degrees C and subjected externally to hydrostatic pressure up to 300 bar are presented. Experimental data obtained during industrial pipe tests and related model predictions are compared and discussed. Thermal properties of the syntactic foam are determined with steady and transient states analysis. In complement, a study of the model results sensitivity to the input Poisson coefficient is presented. (C) 2010 Elsevier B.V. All rights reserved.

This work deals with the study of the thermomechanical behaviour of multilayered thermal insulation systems protecting subsea pipelines, used in the context of deep sea offshore exploitation (down to 3000 m water depth). The first step of this work consisted in obtaining experimental data on the thermal, mechanical and water diffusion behaviour of insulation materials, particularly of syntactic foams (polymer matrix reinforced with hollow glass microspheres), which are widely used in the thermal insulation of pipelines. The development of experimental tests on industrial multilayered coated structures under representative deep sea conditions (until 300 bar external hydrostatic pressure) represented one of the major aims of this work. The global heat transfer coefficient of the structure which is representative of the thermal performances of the multilayered structure has been determined for several thermal gradients, without and under hydrostatic pressure. Moreover, the study of the stationary and transient thermal states allowed the apparent thermal properties of the syntactic foam to be determined, first without additional pressure then under hydrostatic pressure. In parallel, numerical modelling of the thermomechanical behaviour of the industrial multilayered structure, based on the experimental data obtained at a "laboratory scale" on small samples, has been developed with the software Comsol Multiphysics®. This work underlined the importance of the mechanical stress on the damage evolution of the insulation material. The correlation between model prediction and experimental data obtained on structures has contributed to establishing the validity of the models., Ce travail s'inscrit dans le contexte de l'exploitation offshore par grande profondeur (jusqu'à 3000 mètres) et porte sur l'étude du comportement thermomécanique des systèmes multicouches d'isolation thermique protégeant les pipelines immergés. La première phase de ce travail a consisté à acquérir des données expérimentales sur le comportement thermique, mécanique et de diffusion d'eau des matériaux d'isolation, en particulier des mousses syntactiques (matrice polymère renforcée par des microsphères de verre creuses) largement utilisées dans l'isolation thermique de pipelines. La mise en place et la réalisation d'essais sur des structures industrielles isolées dans les conditions d'exploitation en grande profondeur (jusqu'à 300 bar de pression externe), ont constitué un des enjeux majeurs de ce travail. Le coefficient de transfert thermique global de la structure traduisant les performances d'isolation du système multicouches a été déterminé pour différents gradients thermiques, avec et sans pression hydrostatique. Par ailleurs, l'étude des régimes thermiques stationnaires et transitoires a permis de déterminer les propriétés thermiques apparentes de la mousse syntactique sans pression additionnelle puis sous pression hydrostatique. En parallèle, un modèle numérique du comportement thermomécanique de la structure industrielle multicouches, alimenté par la base de données «coupons» a été développé sous Comsol Multiphysics®. Ce travail a souligné l'importance des contraintes mécaniques sur l'évolution de l'endommagement du matériau d'isolation. Les résultats expérimentaux obtenus sur les structures industrielles ont permis de discuter la validité du modèle numérique.

This work deals with the study of the thermomechanical behaviour of multilayered thermal insulation systems protecting subsea pipelines, used in the context of deep sea offshore exploitation (down to 3000 m water depth). The first step of this work consisted in obtaining experimental data on the thermal, mechanical and water diffusion behaviour of insulation materials, particularly of syntactic foams (polymer matrix reinforced with hollow glass microspheres), which are widely used in the thermal insulation of pipelines. The development of experimental tests on industrial multilayered coated structures under representative deep sea conditions (until 300 bar external hydrostatic pressure) represented one of the major aims of this work. The global heat transfer coefficient of the structure which is representative of the thermal performances of the multilayered structure has been determined for several thermal gradients, without and under hydrostatic pressure. Moreover, the study of the stationary and transient thermal states allowed the apparent thermal properties of the syntactic foam to be determined, first without additional pressure then under hydrostatic pressure. In parallel, numerical modelling of the thermomechanical behaviour of the industrial multilayered structure, based on the experimental data obtained at a "laboratory scale" on small samples, has been developed with the software Comsol Multiphysics®. This work underlined the importance of the mechanical stress on the damage evolution of the insulation material. The correlation between model prediction and experimental data obtained on structures has contributed to establishing the validity of the models., Ce travail s'inscrit dans le contexte de l'exploitation offshore par grande profondeur (jusqu'à 3000 mètres) et porte sur l'étude du comportement thermomécanique des systèmes multicouches d'isolation thermique protégeant les pipelines immergés. La première phase de ce travail a consisté à acquérir des données expérimentales sur le comportement thermique, mécanique et de diffusion d'eau des matériaux d'isolation, en particulier des mousses syntactiques (matrice polymère renforcée par des microsphères de verre creuses) largement utilisées dans l'isolation thermique de pipelines. La mise en place et la réalisation d'essais sur des structures industrielles isolées dans les conditions d'exploitation en grande profondeur (jusqu'à 300 bar de pression externe), ont constitué un des enjeux majeurs de ce travail. Le coefficient de transfert thermique global de la structure traduisant les performances d'isolation du système multicouches a été déterminé pour différents gradients thermiques, avec et sans pression hydrostatique. Par ailleurs, l'étude des régimes thermiques stationnaires et transitoires a permis de déterminer les propriétés thermiques apparentes de la mousse syntactique sans pression additionnelle puis sous pression hydrostatique. En parallèle, un modèle numérique du comportement thermomécanique de la structure industrielle multicouches, alimenté par la base de données «coupons» a été développé sous Comsol Multiphysics®. Ce travail a souligné l'importance des contraintes mécaniques sur l'évolution de l'endommagement du matériau d'isolation. Les résultats expérimentaux obtenus sur les structures industrielles ont permis de discuter la validité du modèle numérique.

This work deals with the study of the thermomechanical behaviour of multilayered thermal insulation systems protecting subsea pipelines, used in the context of deep sea offshore exploitation (down to 3000 m water depth). The first step of this work consisted in obtaining experimental data on the thermal, mechanical and water diffusion behaviour of insulation materials, particularly of syntactic foams (polymer matrix reinforced with hollow glass microspheres), which are widely used in the thermal insulation of pipelines. The development of experimental tests on industrial multilayered coated structures under representative deep sea conditions (until 300 bar external hydrostatic pressure) represented one of the major aims of this work. The global heat transfer coefficient of the structure which is representative of the thermal performances of the multilayered structure has been determined for several thermal gradients, without and under hydrostatic pressure. Moreover, the study of the stationary and transient thermal states allowed the apparent thermal properties of the syntactic foam to be determined, first without additional pressure then under hydrostatic pressure. In parallel, numerical modelling of the thermomechanical behaviour of the industrial multilayered structure, based on the experimental data obtained at a "laboratory scale" on small samples, has been developed with the software Comsol Multiphysics®. This work underlined the importance of the mechanical stress on the damage evolution of the insulation material. The correlation between model prediction and experimental data obtained on structures has contributed to establishing the validity of the models., Ce travail s'inscrit dans le contexte de l'exploitation offshore par grande profondeur (jusqu'à 3000 mètres) et porte sur l'étude du comportement thermomécanique des systèmes multicouches d'isolation thermique protégeant les pipelines immergés. La première phase de ce travail a consisté à acquérir des données expérimentales sur le comportement thermique, mécanique et de diffusion d'eau des matériaux d'isolation, en particulier des mousses syntactiques (matrice polymère renforcée par des microsphères de verre creuses) largement utilisées dans l'isolation thermique de pipelines. La mise en place et la réalisation d'essais sur des structures industrielles isolées dans les conditions d'exploitation en grande profondeur (jusqu'à 300 bar de pression externe), ont constitué un des enjeux majeurs de ce travail. Le coefficient de transfert thermique global de la structure traduisant les performances d'isolation du système multicouches a été déterminé pour différents gradients thermiques, avec et sans pression hydrostatique. Par ailleurs, l'étude des régimes thermiques stationnaires et transitoires a permis de déterminer les propriétés thermiques apparentes de la mousse syntactique sans pression additionnelle puis sous pression hydrostatique. En parallèle, un modèle numérique du comportement thermomécanique de la structure industrielle multicouches, alimenté par la base de données «coupons» a été développé sous Comsol Multiphysics®. Ce travail a souligné l'importance des contraintes mécaniques sur l'évolution de l'endommagement du matériau d'isolation. Les résultats expérimentaux obtenus sur les structures industrielles ont permis de discuter la validité du modèle numérique.

This work deals with the study of the thermomechanical behaviour of multilayered thermal insulation systems protecting subsea pipelines, used in the context of deep sea offshore exploitation (down to 3000 m water depth). The first step of this work consisted in obtaining experimental data on the thermal, mechanical and water diffusion behaviour of insulation materials, particularly of syntactic foams (polymer matrix reinforced with hollow glass microspheres), which are widely used in the thermal insulation of pipelines. The development of experimental tests on industrial multilayered coated structures under representative deep sea conditions (until 300 bar external hydrostatic pressure) represented one of the major aims of this work. The global heat transfer coefficient of the structure which is representative of the thermal performances of the multilayered structure has been determined for several thermal gradients, without and under hydrostatic pressure. Moreover, the study of the stationary and transient thermal states allowed the apparent thermal properties of the syntactic foam to be determined, first without additional pressure then under hydrostatic pressure. In parallel, numerical modelling of the thermomechanical behaviour of the industrial multilayered structure, based on the experimental data obtained at a "laboratory scale" on small samples, has been developed with the software Comsol Multiphysics®. This work underlined the importance of the mechanical stress on the damage evolution of the insulation material. The correlation between model prediction and experimental data obtained on structures has contributed to establishing the validity of the models., Ce travail s'inscrit dans le contexte de l'exploitation offshore par grande profondeur (jusqu'à 3000 mètres) et porte sur l'étude du comportement thermomécanique des systèmes multicouches d'isolation thermique protégeant les pipelines immergés. La première phase de ce travail a consisté à acquérir des données expérimentales sur le comportement thermique, mécanique et de diffusion d'eau des matériaux d'isolation, en particulier des mousses syntactiques (matrice polymère renforcée par des microsphères de verre creuses) largement utilisées dans l'isolation thermique de pipelines. La mise en place et la réalisation d'essais sur des structures industrielles isolées dans les conditions d'exploitation en grande profondeur (jusqu'à 300 bar de pression externe), ont constitué un des enjeux majeurs de ce travail. Le coefficient de transfert thermique global de la structure traduisant les performances d'isolation du système multicouches a été déterminé pour différents gradients thermiques, avec et sans pression hydrostatique. Par ailleurs, l'étude des régimes thermiques stationnaires et transitoires a permis de déterminer les propriétés thermiques apparentes de la mousse syntactique sans pression additionnelle puis sous pression hydrostatique. En parallèle, un modèle numérique du comportement thermomécanique de la structure industrielle multicouches, alimenté par la base de données «coupons» a été développé sous Comsol Multiphysics®. Ce travail a souligné l'importance des contraintes mécaniques sur l'évolution de l'endommagement du matériau d'isolation. Les résultats expérimentaux obtenus sur les structures industrielles ont permis de discuter la validité du modèle numérique.