Durabilité des composites pour énergie marine renouvelable

International audienceLes matériaux composites joueront un rôle essentiel dans le développement de systèmes de conversion d'énergie marine renouvelable, et pour cette application compte tenu des contraintes liées à la maintenance une excellente durabilité à long terme s'avère indispensable. On dispose d'une bonne expérience de ces matériaux en milieu marin, et pour des applications, telles les éoliennes, où ils sont soumis à un chargement cyclique, mais on ne trouve que très peu d'informations sur leur comportement sous sollicitation cyclique dans l'eau de mer. Cet article adresse cette lacune, et présente les résultats d'une étude du comportement sous chargement quasi-statique et cyclique de composites renforcés de différentes fibres de verre dans l'eau de mer. Pour ces conditions de chargement couplé, le type de fibre, la résine et l'interface fibre/matrice influent tous sur la durée de vie

On modelling the long term thermo-mechanical behaviour of field joint of thermally insulated populine.

International audienc

Multilayer systems for thermal insulation : thermomechanical behaviour of prototypes

October 4-

Systèmes multicouches d'isolation thermique par grande profondeur : méthodologie d'étude du comportement thermomécanique

22-24 mar

Influence of residual stresses and geometric imperfections on the elastoplastic collapse of cylindrical tubes under external pressure

International audienceThe buckling problem of a circular cylindrical shell has long been widely investigated due to its great importance in the design of aerospace and marine structures. Geometric imperfections and residual stresses are inevitable in practice and have been so far frequently considered in analytical and numerical predictions. But little attention has been paid until now on the combined influence of such initial defects on the critical and often unstable response of such elastoplastic structures. In this paper, a shell finite element is designed within the total Lagrangian formulation framework to deal with the elastoplastic buckling and post-buckling of thin cylindrical tubes under external pressure and axial compression. A specific experimental process will be introduced in order to measure residual stresses in the shell very accurately, so as to include them in the numerical calculations. The present formulation will enable us to describe the complete non-linear solutions, namely the critical pressures (bifurcation and limit (collapse) loads), the bifurcation modes and the bifurcated equilibrium branches up to advanced post-critical states. Comparisons will be made between numerical results and the experimental critical value and deformation patterns of a new generation profiler. Furthermore, the combined effects of geometric imperfections, residual stresses and plasticity will be analyzed

Composite cylinders for deep sea applications, an overview

In order to develop the knowledge base necessary to design deep sea pressure vessels it is essential to understand the full chain from design and manufacturing through NDT and characterization to long term behavior under hydrostatic pressure. This paper describes results from European and national research programs focusing on the use of composites for underwater applications over the last 20 years. Initial tests on small glass/epoxy cylinders were followed by large demonstration projects on carbon/epoxy cylinders with implosion pressures of up to 600 bar, corresponding to 6000 meter depth. Numerical modeling has enabled end closures design to be optimized for test performance. Thin and thick wall cylinders have been tested under quasi-static, and long term loading. Both thermosetting and thermoplastic matrix composites have been tested to failure, and the influence of defects and impact damage on implosion pressure has been studied. These deep sea exploitation and exploration studies were performed for oceanographic, military and offshore applications, and extensive data are available. The aim of this paper is to indicate existing results, particularly from European projects, in order to avoid costly repetition

In situ observation of syntactic foams under hydrostatic pressure using X-ray tomography

Syntactic foams (hollow glass microspheres embedded in a polymeric matrix) are being used increasingly for the purpose of thermal insulation in ultradeep water. A better understanding of the damage mechanisms of these materials at the microsphere scale under such a hydrostatic loading condition is of prior importance in determining actual material limits, improving phenomenological modelling and developing novel formulations in the future. To achieve this goal, a study based on X-ray microtomography was performed on two syntactic foam materials (polypropylene and polyurethane matrix) and a standard foamed PP. A special set up has been designed in order to allow the X-ray microtomographic observation of the material during hydrostatic pressure loading using ethanol as the pressure fluid. Spatial resolution of (3.5 mu m)(3) and in situ non-destructive scanning allowed a unique qualitative and quantitative analysis of the composite microstructure during stepwise isotropic compression by hydrostatic pressure up to 50 MPa. The collapse of weaker microspheres were observed during pressure increase and the damage parameters could be estimated. It is shown that the microspheres which are broken or the porosities which are close to the surface in the foamed PP are filled by a fluid (either the ethanol or the polymeric matrix itself). The hydrostatic pressure decreases the volume of the foam only slightly. In the PU matrix, ethanol diffusion is seen to induce swelling of the matrix, which is an unexpected phenomenon but reveals the high potential of X-ray microtomographic observation to improve diffusion analysis in complex media

Evaluation of Long Term Behaviour of Polymers for Offshore Oil and Gas Applications

Polymers and composites are very attractive for underwater applications, but it is essential to evaluate their long term behaviour in sea water if structural integrity of offshore structures is to be guaranteed. Accelerated test procedures are frequently required, and this paper will present three examples showing how the durability of polymers, in the form of fibres, matrix resins in fibre reinforced composites for structural elements, and thermal insulation coatings of flow-lines, have been evaluated for offshore use. The influence of the ageing medium, temperature, and hydrostatic pressure will be discussed first, then an example of the application of ageing test results to predict long term behavior of the thermal insulation coating of a flowline will be presented.Les polymères et composites sont largement utilisés pour les applications en mer et particulièrement dans le domaine de l’industrie pétrolière. La fiabilisation des structures utilisées pour ces applications nécessite la prise en considération du comportement à long terme des matériaux. L’évaluation de la durabilité des polymères et composites en milieu marin exige la mise en place de vieillissements accélérés spécifiques. La nature de ces vieillissements ainsi que les paramètres influant tels que la nature de l’eau, la température ou la pression hydrostatique seront discutés dans cet article à travers trois exemples. Le premier sera dédié au comportement à long terme de fibres polymériques utilisées principalement pour l’amarrage, le second traitera de la durabilité des composites. Enfin le dernier traitera de la prédiction du comportement à long terme de polyuréthane utilisé comme isolant thermique sur des pipes