Effects of Long-term Exposure on E-glass Composite Material Subjected to Stress Corrosion in a Saline Medium

[EN] This work provides an insight on very long-term degradation of polyester-fiber glass composites immersed more than 30,000 h in saline medium under service stresses. Samples were loaded under bending conditions with stresses both in the elastic and plastic fields, with the result that characteristics in a flexural mode were able to be determined and the ensuing decrease in characteristics was fitted to an exponential model. The degree of losses ranged from 25 to 31% for the bending modulus, from 28 to 35% for the flexural strength, and from 40 to 51% for the specific fracture energy. The most notable losses were for specimens immersed in artificial sea water under a continuous stress of 140 MPa, corresponding to the plastic behavior of the material. Although the existence of matrix plasticization is doubtful, the osmotic effects of the diffusion on the matrix and the junction to the fibers, the presence of microcracks, and the effects of chemical ions in the medium on the surface fiber composition became evident in the strength degradation of the material.Segovia López, EF.; Salvador Moya, MD.; Sahuquillo Navarro, O.; Vicente Escuder, Á. (2007). Effects of Long-term Exposure on E-glass Composite Material Subjected to Stress Corrosion in a Saline Medium. Journal of Composite Materials. 41(17):2119-2128. doi:10.1177/0021998307074134S21192128411

Detection potential of the KM3NeT detector for high-energy neutrinos from the Fermi bubbles

A recent analysis of the Fermi Large Area Telescope data provided evidence for a high-intensity emission of high-energy gamma rays with a E 2 spectrum from two large areas, spanning 50 above and below the Galactic centre (the ‘‘Fermi bubbles’’). A hadronic mechanism was proposed for this gamma-ray emission making the Fermi bubbles promising source candidates of high-energy neutrino emission. In this work Monte Carlo simulations regarding the detectability of high-energy neutrinos from the Fermi bubbles with the future multi-km3 neutrino telescope KM3NeT in the Mediterranean Sea are presented. Under the hypothesis that the gamma-ray emission is completely due to hadronic processes, the results indicate that neutrinos from the bubbles could be discovered in about one year of operation, for a neutrino spectrum with a cutoff at 100 TeV and a detector with about 6 km3 of instrumented volume. The effect of a possible lower cutoff is also considered.Published7–141.8. Osservazioni di geofisica ambientaleJCR Journalrestricte

Expansion cone for the 3-inch PMTs of the KM3NeT optical modules

[EN] Detection of high-energy neutrinos from distant astrophysical sources will open a new window on the Universe. The detection principle exploits the measurement of Cherenkov light emitted by charged particles resulting from neutrino interactions in the matter containing the telescope. A novel multi-PMT digital optical module (DOM) was developed to contain 31 3-inch photomultiplier tubes (PMTs). In order to maximize the detector sensitivity, each PMT will be surrounded by an expansion cone which collects photons that would otherwise miss the photocathode. Results for various angles of incidence with respect to the PMT surface indicate an increase in collection efficiency by 30% on average for angles up to 45 degrees with respect to the perpendicular. Ray-tracing calculations could reproduce the measurements, allowing to estimate an increase in the overall photocathode sensitivity, integrated over all angles of incidence, by 27% (for a single PMT). Prototype DOMs, being built by the KM3NeT consortium, will be equipped with these expansion cones.This work is supported through the EU, FP6 Contract no. 011937, FP7 grant agreement no. 212252, and the Dutch Ministry of Education, Culture and Science.Adrián Martínez, S.; Ageron, M.; Aguilar, JA.; Aharonian, F.; Aiello, S.; Albert, A.; Alexandri, M.... (2013). Expansion cone for the 3-inch PMTs of the KM3NeT optical modules. Journal of Instrumentation. 8(3):1-19. https://doi.org/10.1088/1748-0221/8/03/T03006S1198

Analyse expérimentale et modélisation du comportement thermomécanique d'un assemblage composite-polymère

International audienceL'exploitation offshore pétrolière en eau extra profonde (désormais jusqu'à 3000 mètres de profondeur) conduit à de nouvelles exigences pour les compagnies d'opérations d'offshore, en particulier dans le domaine du choix des matériaux. Le fait de devoir, dans des conditions d'environnement extrêmes (forte pression hydrostatique, fort gradient thermique 4°C à l'extérieur et jusqu'à 150°C à la surface du pipe), maintenir un débit d'effluent pétrolier à l'intérieur des conduites amène à une sélection sévère des matériaux utilisés pour assurer une isolation thermique passive des conduites. Dans ce domaine une attention particulière a été récemment portée sur le comportement à long terme de la zone dite de " Field joint ". Après l'assemblage des pipes par soudage, la zone non revêtus des extrémités doit être isolée thermiquement pour garantir un bon comportement thermique de l'ensemble. Ceci est réalisé par moulage ou injection d'un polymère, généralement de nature différente du matériau d'isolation utilisé sur la partie courante du pipe, sur la partie libre de revêtement, conduisant à un assemblage composite - polymère (partie appelée : Field joint). L'objectif du travail est de développer un modèle permettant la description du comportement thermomécanique de l'assemblage. Le comportement mécanique du matériau de revêtement des pipes (généralement une mousse syntactique de polypropylène) et des matériaux utilisés dans la réalisation des Field joints sont préalablement analysés en utilisant des essais de compression hydrostatique (statique et fluage) à différentes températures et par analyse mécanique dynamique (DMA). Un modèle thermomécanique du matériau prenant en compte une déformation hydrostatique de fluage est ensuite élaboré et implémenté dans le logiciel COMSOL Multiphysics Ô. Un modèle global de l'assemblage dans les conditions de service est alors proposé pour prédire la distribution des déformations dans la structure. Cette distribution révèle la criticité de la zone l'assemblage entre le matériau d'isolation du pipe et le Field joint. La dernière étape de cette étude se concentre sur la caractérisation mécanique de l'interface entre le revêtement et les matériaux du Field joint à l'aide d'un montage ARCAN modifié permettant la détermination de l'enveloppe de rupture d'un joint composite-polymère

Description and modeling of polyurethane hydrolysis used as thermal insulation in oil offshore conditions

Polymers are widely used for passive thermal insulation coatings on steel pipe in offshore oil and gas production. In this industry, structures used in deep sea have to be reliable, as they are in service for more than 20 years in a very severe environment: sea water, hydrostatic pressure and temperature gradient. One of the main questions is how to test and predict the lifetime of such structures in the laboratory? This study presents one approach that has been developed to characterize and predict the degradation of polymers used as thermal insulation materials. This paper is dedicated to polyurethane (polyether based) degradation in sea water at high temperature. Ageing has been performed in natural sea water under hydrostatic pressure at temperatures ranging from 70 to 120 °C on 2 mm thick samples. Water diffusion in the material and hydrolysis have been characterized using mass evolution and tensile tests. Based on these results, a model for the urethane hydrolysis reaction is proposed