Etude de la résistance a la fissuration des plaques en l’aluminium réparées par des patchs en composites

La caractérisation mécanique des matériaux repose sur l’étude de son comportement vis-à-vis des sollicitations extérieures qui engendrent des contraintes et des déformations est l’étape indispensable dans les applications industrielles données qui exigent la connaissance et la maîtrise de caractéristiques mécaniques des matériaux choisis. A ce stade on recourt à un certain nombre d’essais normalisés pour accéder aux grandeurs caractéristiques des matériaux, du module d'Young à la limite d'élasticité, en passant par la ténacité ou la résistance à la fatigue.Le premier objectif de cette étude portera donc sur la caractérisation mécanique usuelle indispensable pour l’estimation le module d’Young ainsi que la limite élastique et plastique  des plaques en aluminiums minces et épais en vue de prédire leur aptitude de résistances aux sollicitations mécaniques impose. Des plaques en résine ont été aussi caractérisées dans cette étude par la présentation une technique expérimentale la  plus couramment utilisée dans les industries, et pour atteindre le deuxième objectif de ce travail, on a  fait une modélisation numérique  par le code de calcul Ansys des plaques  en aluminium minces présentant des défauts centraux à des différentes tailles avec et sans collage des patchs en fibres de carbone.  En utilisant la loi Paris, le nombre de cycle est estimé pour différentes tailles de fissures

About the influence of temperature and environmental relative humidity on the longitudinal and transverse mechanical properties of elementary alfa fibers

International audienceComposites reinforced with plant-based fibers present a high potential for valorization in new industrial applications due to their good specific mechanical characteristics, renewability, and recyclability. In order to accelerate their wide industry adoption, it is critical to assess their behavior and durability in heat and humid environments. This article aims at investigating the effects of temperature and relative humidity (RH) on the longitudinal and transverse mechanical properties of the lignocellulosic fibers extracted from alfa plant (Stipa tenacissima L). For this purpose, tensile and nanoindentation tests were performed on elementary alfa fibers subjected to a thermal cycle of 200°C. The fibers were held at various periods of 15, 30, 60 and 120 min. The test results showed that the longitudinal and transverse Young's moduli are moderately affected by short thermal cycles having duration of 15–30 min. However, for longer thermal cycle (i.e., 2 hr), a degradation of 21% for the transverse modulus was recorded. This degradation doubled for the longitudinal modulus (43 vs. 21%). A similar trend was observed for the breaking strength. This study also showed that the RH strongly affects the mechanical performances of alfa fibers

Effect of Saccharomyces cerevisiae Supplementation on Reproductive Performance and Ruminal Digestibility of Queue Fine de l’Ouest Adult Rams Fed a Wheat Straw-Based Diet

This study aimed to investigate the effect of supplementing a wheat straw-based diet with Saccharomyces cerevisiae (S.C.) on feed intake, nutrient digestibility, nitrogen balance, body weight and reproduction performance. The experiment was conducted on 14 Queue Fine de l’Ouest rams between 3 and 4 years of age (body weight (B.W.): 54.7 ± 2.03 kg; body condition score (B.C.S.): 3.5 ± 0.5), for 80 days during the breeding season. The rams were divided into two homogenous groups (n = 7), housed individually in floor pens, and allocated to two dietary treatments. The control group was offered a basal diet of 1 kg/d of wheat straw and 700 g of concentrate. The experimental group (yeast) received the same basal diet supplemented with 10 g of S.C./head/day. The results indicated that the S.C. supplementation had no significant effect on the animal’s body weight, volume and concentration of semen, dry matter intake, crude protein digestibility and nitrogen balance. Compared to the control group, the S.C. addition improved (p < 0.05) the digestibility of dry matter by 7.3%, organic matter by 11.9% and crude fiber by 24%. In addition, the mass motility score increased for the yeast group compared to the control (3.7 ± 0.24 vs. 1.9 ± 0.27, p < 0.05). The total number of dead and abnormal spermatozoa decreased for the yeast group in contrast to the control group (9.28 ± 0.95 vs. 26.8 ± 3.85% and 25.5 ± 3.33 vs. 59.2 ± 2.78%, respectively; p < 0.05). These results showed that adding S.C. to Queue Fine de l’Ouest ram’s diet during breeding season could improve nutrient digestibility and reproductive performance