Quality Testing of Gaseous Helium Pressure Vessels by Acoustic Emission

The resistance of pressure equipment is currently tested, before commissioning or at periodic maintenance, by means of normal pressure tests. Defects occurring inside materials during the execution of these tests or not seen by usual non-destructive techniques can remain as undetected potential sources of failure . The acoustic emission (AE) technique can detect and monitor the evolution of such failures. Industrial-size helium cryogenic systems employ cryogens often stored in gaseous form under pressure at ambient temperature. Standard initial and periodic pressure testing imposes operational constraints which other complementary testing methods, such as AE, could significantly alleviate. Recent reception testing of 250 m3 GHe storage vessels with a design pressure of 2.2 MPa for the LEP and LHC cryogenic systems has implemented AE with the above-mentioned aims

Reproductive performance of male rabbits of algerian local population

[EN] A total of 267 rabbit does and 46 bucks from a local Algerian population were controlled during 6 generations (from G0 to G5) at the experimental farm of the University of Tizi-Ouzou. Natural mating was used and 1412 presentations were analysed. Reproductive and growing performance were analysedtaking into account the effect of the buck, its age, the generation, the season of mating (or kindling) and the physiological status of does at the moment of the mating. The buck influenced the acceptance rate(P<0.001), kindling rate (P=0.032), litter size at birth and at weaning (P<0.001), litter weight at birth (P<0.001)and at weaning (P=0.034), the mean weaning weight (P=0.018) and consequently the ponderal productivity at weaning (weight of rabbits produced at weaning/mating, P<0.001). Nevertheless, the ponderal productivity was also influenced by the age of bucks, the generation, the season and the physiological status of does at the moment of mating. The highest acceptation rate was recorded in autumn in non lactating does (primiparous and multiparous). Productivity was higher for bucks 5-10 mo old but decreased thereafter.Productivity was higher in spring, particularly for multiparous and lactating does and highly varied with the generation, evidencing the importance of environmental conditions.Dj, C.; M, T.; N, Z.; M, B. (2013). Reproductive performance of male rabbits of algerian local population. World Rabbit Science. 21(2):91-99. doi:10.4995/wrs.2013.1173.SWORD919921

Oxydation du zircaloy-4 dans l'air à haute température

The oxidation of zircaloy-4 in air was studied in the temperature range 350-750 °C. The oxidation kinetics cannot be described by a single rate law. At the beginning of the reaction, the rate decreases regularly. Then, after a few hours, an acceleration is observed and finally a linear law is obeyed. The morphological observations show that the acceleration is related to the formation of cracks in the oxide scale. Moreover, two different zirconia phases (monoclinic and tetragonal) are identified. When the kinetic transition occurs, the tetragonal phase partially disappears. All these observations show that a mechanism, similar to that proposed to describe the oxidation of zircaloy-4 in steam, may be used to describe the reaction. In parallel, the oxidation reaction was studied by using acoustic emission. The frequency, the amplitude and the energy were used to characterize the signal. Typical groups were identified and their appearance was strongly correlated to the different parts of the reaction

ÉMISSION ACOUSTIQUE APPLIQUÉE À L'ÉTUDE DES MATÉRIAUX DE CHAUSSÉES

Ce travail original donne une description du comportement des matériaux de chaussées sollicités en traction à l'aide des techniques de mesures des déformations et de l'émission acoustique. La déformation d'éprouvettes est accompagnée de sources d’événements microseismiques qui peuvent être interprétées comme une conséquence de l'initiation et du développement des fissures. Les mesures d'émission acoustique et de déformation semblent indiquer trois mécanismes de fissuration.This original work describes measurements of the deformation behaviour and acoustic emission (AE) in materials of the pavements loading by tensile. The test specimen deformation is accompanied by location of microseismic sources as are sult of the formation and growth of cracks. The results of acoustion and deformation measurements indicate three mechanisms of failure