Comportement asymptotique des structures soumises à des chargements thermo-mécaniques cycliques

Comportement asymptotique des structures soumises à des chargements thermomécaniques cycliques : application aux collecteurs d'échappementNational audienceLes structures soumises à des chargements cycliques présentent différents types de comportement asymptotique : l'adaptation, l'accommodation ou le rochet. Cette étude vise à caractériser ces différents comportements et à les identifier pour une structure soumise à des chargements thermomécaniques cycliques et dont le matériau possède des caractéristiques mécaniques variant avec la température. Les définitions proposées sont ensuite illustrées sur quelques cas simples

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Differential cellular gene expression in duck trachea infected with a highly or low pathogenic H5N1 avian influenza viru

Simultaneous eradications of Black Rat (Rattus rattus) and Ice plants (Carpobrotus spp.) on Bagaud Island (Port-Cros National Park, Provence, France): preliminary results on their impacts on Athropods communities

Les invasions biologiques sont reconnues comme l’une des principales menaces pour la conservation de la biodiversité, et de nombreux travaux ont été conduits à travers la planète pour restaurer la biodiversité insulaire par des programmes d’éradication d’espèces invasives. Cependant, peu d’études scientifiques post-éradication ont été conduites notamment pour l’évaluation de la biodiversité des communautés d’Arthropodes. L’île de Bagaud, située dans l’archipel des îles d’Hyères (Var, France), est une réserve intégrale du Parc national de Port-Cros (PNPC) qui a notamment été soumise à deux perturbations majeures d’origine anthropique au cours des derniers siècles : l’invasion du Rat noir (Rattus rattus) et celle des Griffes de sorcière (Carpobrotus spp.). Ces espèces allochtones engendrent des effets particulièrement néfastes sur la flore et la faune des écosystèmes insulaires méditerranéens, notamment sur les Arthropodes. Le PNPC a ainsi lancé un programme décennal de restauration écologique qui implique l’éradication de ces deux taxons invasifs. La communauté des Arthropodes de l’île a fait l’objet d’un état initial au printemps 2011, les éradications ont été effectuées entre septembre 2011 et janvier 2013, et la première campagne d’échantillonnage post-éradication a été réalisée au printemps 2013. L’échantillonnage de la faune épigée a été réalisé au moyen de quatre transects fixes de pièges Barber répartis dans différents milieux écologiques de l’île. Cette première étude post-éradication révèle une augmentation de l’abondance des Arthropodes piégés entre 2011 (4868 individus dans 74 pièges) et 2013 (6892, n = 60). Les effectifs moyens par piège augmentent significativement dans les zones où les Carpobrotus spp. ont été arrachés, mais chutent dans la zone de maquis qui abritait une forte densité de R. rattus. La richesse spécifique reste globalement stable (220 morpho-espèces en 2011, 216 en 2013), cependant les communautés de décomposeurs explosent a contrario des populations de prédateurs. Les suivis doivent être poursuivis afin de mieux déterminer les impacts directs et indirects à long terme de ces éradications s’exerçant sur la biodiversité des communautés d’Arthropodes de l’île.Biological invasions are recognized as one of the major threats to island biodiversity conservation, and numerous studies have been conducted around the world to restore the biodiversity of islands submitted to invasive species impacts. However, few scientific post-eradication studies were piloted notably for the biodiversity assessment of Arthropod communities. Bagaud Island is an integral reserve of the Port-Cros National Park (PNPC), located in the îles d’Hyères Archipelago (Var, France). In the last centuries, it has undergone two major anthropogenic disturbances: the invasion of the Black Rat (Rattus rattus) and the Ice plants (Carpobrotus spp.), two alien taxa known for their particularly negative effects on the flora and fauna of the Mediterranean island ecosystems, including Arthropods. PNPC has launched a ten-year program of ecological restoration that involves the eradication of these two invasive taxa. The Arthropod communities of the island have been analysed in their initial state in spring 2011, eradications were conducted between September 2011 and January 2013, and the first post-eradication campaign began in spring 2013. The ground fauna was sampled using four transects of Barber traps distributed in different ecological contexts of the island. This first post-eradication study reveals an increase in the abundance of arthropods trapped between 2011 (4868 individuals in 74 traps) and 2013 (6892, n = 60). The average number of trapped Arthropods was significantly higher in areas where Carpobrotus spp. have been eradicated, but declined in the bush area that housed a high density of R. rattus. The communities of decomposers explode, in contrast to predator populations. However, the global specific richness remains stable (220 morphospecies in 2011, 216 in 2013). Scientific monitoring by the PNC must be continued to better determine the direct and indirect long-term impacts of these eradications upon the structure and the functioning of the Arthropods communities of the Bagaud Island

Asymptotic behaviour of structures subjected to thermomechanical cyclic loadings: application to exhaust manifolds

Under cyclic loadings, structures can show different types of asymptotic behaviour: elastic shakedown when the asymptotic answer is purely elastic, cyclic plasticity when plastic deformations become periodic and ratchetting, plastic deformations will then accumulate and lead to the ruin of the structure. For industrial components, elastic shakedown is related to high cycle fatigue, while cyclic plasticity and ratchetting mean low cycle fatigue, but ratchetting must be prevented since it could drastically limits the lifetime of the structure. In the automotive industry, cold parts like suspension systems often present elastic shakedown whereas hot parts like exhaust systems and cylinder heads are subjected to thermomechanical loadings and often exhibit cyclic plasticity. To evaluate the lifetime of components, one can follow the evolution of a damage variable or use a fatigue criterion that assesses the lifetime of a structure from macroscopic thermomechanical quantities evaluated on the stabilized cycle. Ambrico and Begley suggested a method to identify the different types of asymptotic behaviour in the case of fretting. In this study, we propose slightly different definitions of the cyclic part and of the ratchetting part of the deformation. The ratchetting part of the deformation er(t) is built for all instants t, taking account of the whole evolution of the plastic deformation during the cycle. Then a new definition of the amplitude of the cyclic plastic deformation during cycle k, Dec(k) is given. This definition takes into account multiaxial loadings and corresponds to the difference between two deformation states really reached during the cycle. This method is adapted to thermo-mechanical loadings with a material which mechanical characteristics depend on temperature. Finally, an application example is given on an exhaust manifold subjected to a classical thermomechanical fatigue tes

Genetic Diversity among Pseudorabies Viruses Isolated from Dogs in France from 2006 to 2018

Pseudorabies (PR), also known as Aujeszky’s disease, is an economically important disease for the pig industry. It has been eradicated in domestic pigs in many European countries, including France, but its causative agent—Suid Herpesvirus 1—is still circulating in wild boars. The risk of endemic PR in wild fauna lies in reintroducing the virus among domestic pigs and transmitting it to other mammals, especially hunting dogs for which the disease is rapidly fatal. As such infections are regularly reported in France, this study genetically characterized canine PR virus strains in the country to obtain information on their diversity and evolution. Partial sequencing of the glycoprotein C-encoding gene from 55 virus strains isolated from dogs between 2006 and 2018 showed that 14 strains belonged to genotype I-clade A and another 38 to genotype I-clade B, two clades usually reported in Western Europe. More surprisingly, three strains were found to belong to genotype II, suggesting an Asian origin. Genotype I-clade A strains exhibited the highest diversity as five geographically segregated genogroups were identified

Cyclic behaviour of structures under thermomechanical loadings: Application to exhaust manifolds

International audienceA structure subjected to thermomechanical cyclic loadings may exhibit various cyclic behaviours: perfect elasticity, elastic shakedown, plastic shakedown and ratchetting. The quantitative characterization of these different asymptotic states is addressed in this paper, in the context of the Generalized Standard Materials (GSM). Criteria are established to identify them and capture the trend line of their evolution, in the context of numerical simulation. The definitions are extended to the case of temperature dependent mechanical properties. Simple strain paths are first considered to illustrate the relevancy of the proposition. Finally, as an application, the example of an exhaust manifold subjected to a classical thermomechanical fatigue test is analyzed

A review of the issues, methods and perspectives for yield estimation, prediction and forecasting in viticulture

International audienceHighlights:• Operational grapevine yield development includes vineyard/winery specific operations.• Operational needs drive the challenges that yield reporting methods have to meet.• Yield reporting methods are related to measurement, sampling and modelling issues.• Yield estimation, prediction and forecast address different levels of uncertainty.• Yield reporting methods should ensure a temporal, local, operational yield monitoring.Abstract: Grapevine yield is defined as the quantity of harvest, expressed as either grape mass or wine volumeunits, which has been collected per surface unit are and per crop cycle. The information about current and future yield, termed a yield assessment in this paper, is an essential decision-making element for the grape and wine industry. Crop management, wine-making, commercial, accounting and strategic operations are all adapted to and all impact on the expected yield of the current vintage. Numerous yield assessment approaches have been proposed in the scientific literature. However, only a few of them have considered their adaptation to the operational context under the constraints, needs and strategies of commercial vineyards and wineries. The few studies that have worked on the operational implementation of yield assessment methods have only partially addressed this issue, concentrating their improvement efforts on a single step in the yield assessment process. This paper first proposes to review the characteristics of yield development in an operational context that must be taken into account by yield assessment methodsThese characteristics are consolidated into three main challenges for yield assessment methods: (i) addressing the complex temporality of yield development, (ii) ensuring a local monitoring of yield development and (iii) fitting to the operational needs and constraints to allow for relevant decision support systems in the field. The approaches of yield estimation, prediction and forecast are discussed in the context of these challenges. In a second step, the paper proposes a generic framework for the yield assessment process, including a review of the variables that are used to explain grapevine yield. Issues and proposals from the literature associated respectively with measurement, sampling and yield modelling are reviewed and the need for improved modelling of relationships between explanatory variables and the desired, reported yield variable is discussed. The yield assessment methods found in the literature are categorised and compared according to measurement, estimation and modelling approaches, and then according to the three challenges identified for yield assessment in operational conditions, such that the yield assessment method is adapted to commercial needs and not to research objectives. In conclusion, concrete proposals for new grape yield assessment methods are discussed in order to investigate the as yet unexplored opportunities for the improvement in yield assessment in operational contexts that have been identified in the paper. These considerations could easily be transposed to other perennial crops

Experimental investigation of the behavior and the low cycle fatigue life of a welded structure

International audienceStrain controlled low cycle fatigue tests are performed at 300 °C under tension compression on an 18%Cr ferritic stainless steel using base metal and welded specimens. Changes in the microstructure and geometry of the weld bead have a negative impact on the specimens' lifetime. Digital image correlation is used to get information on strain gradient in specimens. Potential drop measurements as metallographic observations are used to monitor micro-cracking. The significance of the results is discussed using finite element computations of welded specimens and observations of fracture surfaces. A tentative rationale is proposed using an energy based micro-crack growth model