Impact response of thick composite plates under uniaxial tensile preloading

This work focuses on the impact response of composite plates 5 mm thick subjected to uniaxial tension preload. Laminated carbon/epoxy with quasi-isotropic stacking sequence ([0/45/90/-45]2)S samples were used. Doehlert-type design of experiments was proposed to investigate the influence of both preload and impact energy on impact composite responses. Deformation, varying from 300 to 3000 micro-strain, was imposed thanks to a preload device designed for this purpose. Impacts were generated using a home made drop tower. Imposed impact energy was varying from 30 to 214 J. Post-impact damage was characterized by both non-destructive (ultrasound) and destructive (deply) techniques. Influence of the preloading on delamination areas (total and projected) was quantified and found sensitive to the preloading

Évaluer et quantifier les effets des aménagements soutenus ou réalisés par les Fédérations des chasseurs en faveur de la petite faune gibier sédentaire de plaine sur la biodiversité ordinaire et remarquable en zone méditerranéenne française

The high biodiversity seen in the Mediterranean basin underlines the importance of traditional agricultural practices in landscape management and ecosystem functioning. Agricultural abandonment in rural areas has led to the spread of scrubland. This closure of environments is jeopardizing the proper functioning of Mediterranean lowland ecosystems, generating losses of species in open environments and undermining a large number of ecosystem, cultural and heritage services. Nowadays, hunting managers have been keen to restore areas suitable for small game species, which are in decline throughout Europe. However, the effects of these actions on biodiversity remain poorly understood. The aim of this doctoral thesis was to assess the ecological value of habitat management actions for small game in relation to biodiversity conservation. While the benefits of habitat management actions for small game species have been highlighted for passerines, further studies are needed to assess the impact of these actions on the conservation of bats, small terrestrial mammals and macro-arthropods, as current results remain preliminary, if not mixed. Seasonal bat activity is impacted by factors other than the habitat management itself. The diversity of small terrestrial mammal communities is naturally restricted in scrublands, making it difficult to assess the impact of habitat management on them. Moreover, the structure and enrichment of terrestrial macro-arthropod communities in scrublands are affected by various spatial descriptors of the local landscape. This manuscript proposes (1) four comparative studies of scrubland areas managed for small game fauna, compared with unmanaged areas, in order to assess the impact of habitat management on the conservation of non-target species; (2) inventory methods designed and suited to environments with restricted access, featuring dense evergreen and thorny vegetation ; (3) ideas to guide future research into the design of a simplified technical itinerary for hunters wishing to become involved in land-use planning, in support of sustainable, biodiversity-friendly hunting.La riche biodiversité observée dans les régions du bassin méditerranéen souligne l'importance des pratiques agricoles traditionnelles dans la gestion des paysages et le fonctionnement des écosystèmes. La déprise agricole dans les zones rurales ont conduit à l'expansion des garrigues. Cette fermeture des milieux met en péril le bon fonctionnement des écosystèmes méditerranéens de plaine, génère des pertes en espèces de milieux ouverts et fragilise de nombreux services écosystémiques, culturels et patrimoniaux. Ces dernières décennies, les gestionnaires à des fins cynégétiques souhaitent restaurer des zones favorables aux espèces de petit gibier, ces dernières étant en régression partout en Europe. Or, les effets de ces actions sur la biodiversité restent méconnus. Ce travail de thèse a pour objet d'évaluer le potentiel écologique de stratégies de gestion de l'habitat pour le petit gibier sur la conservation de la biodiversité. Si les avantages de la garrigue aménagée pour le petit gibier ont été relevés pour les passereaux, des études supplémentaires sont nécessaires pour préciser l'impact de ces stratégies sur la conservation des chauves-souris, des petits mammifères terrestres et des macro-arthropodes, les résultats actuels demeurent préliminaires voire ambivalents. L'activité saisonnière des chauves-souris est influencée par d'autres facteurs que les aménagements eux-mêmes. Les communautés de petits mammifères terrestres présentent une diversité naturellement limitée dans les garrigues, rendant difficile l'évaluation de l'impact des aménagements sur celles-ci. Enfin, l'organisation et l'enrichissement des communautés de macro-arthropodes terrestres dans les garrigues sont influencés par divers descripteurs spatiaux du paysage à l'échelle locale. Dans ce manuscrit il est proposé (1) quatre études comparatives des zones garrigues aménagées pour la petite faune gibier, par rapport à des zones non aménagées, afin d'évaluer l'impact de la gestion de l'habitat sur la conservation d'espèces non ciblées ; (2) des méthodes d'inventaire développées et adaptées aux environnements contraints d'accès, caractérisés par de denses végétations à feuilles persistantes et épineuses ; (3) des pistes de réflexion pour orienter les futurs travaux de recherche dans l'élaboration d'un itinéraire technique simplifié pour les chasseurs désireux de s'investir dans l'aménagement des territoires, en faveur d'une chasse durable et soucieuse de la biodiversité

Réponse à l'impact de plaques composites épaisses préchargées en tension uniaxiale.

This study concerns Carbon / epoxy composite plates. Three di erent thickness were investigated ([0°=45°=90°=45°]i)S for i = 2, 3 or 4 (5, 10 and 15mm thick). An instrumented falling-weight-impact test machine was used for test in this work. Impact energies were 30 J to 214 J. Tensile preloadings were de ned according to the ultimate tensile strength of the plates (300 to 3000 micro strain). Tests were de ned using Doelhert design of experiments for which parameters were thickness, tensile preloading and impact energy and were performed on a drop tower. Impact behavior were characterized from impact force and displacement measurements. The strain state of back sheet was determined using digital correlation. Damage was characterized using non destructive control technique and deply technique.Post impact tension are carried to characterize the residual strength and to see the dammage evolution

Statistical assessment of multiaxial HCF criteria at the grain scale

Multiaxial high cycle fatigue modeling of materials is an issue that concerns many industrial domains (automotive, aerospace, nuclear, etc.) and in which many progress still remains to be achieved. Several approaches exist in the literature: invariants, energy, integral and critical plane approaches all of them having their advantages and drawbacks. These different formulations are usually based on mechanical quantities at the micro or mesoscales using localization schemes and strong assumptions to propose simple analytical forms. This study aims to revisit these formulations using a numerical approach based on crystal plasticity modeling coupled with explicit description of microstructure (morphology and texture) and proposes a statistical procedure for the analyses of numerical results in the HCF context. This work has three steps: First, 2.5D periodic digital microstructures based on a random grain sizes distribution are generated. Second, multiaxial cyclic loading conditions corresponding to the fatigue strength at 106 cycles are applied to these microstructures. Third, the mesoscopic Fatigue Indicator Parameters (FIPs), formulated from the different criteria existing in the literature, are identified using the finite element calculations of the mechanical fields. These mesoscopic FIP show the limits of the original criteria when it comes to applying them at the grain scale. A statistical method based on extreme value probability is used to redefine the thresholds of these criteria. These new thresholds contain the sensitivity of the HCF behavior to microstructure attributes. Finally, the biaxiality and phase shift effects are discussed at the grain scale and the loading paths of some critical grains are analyzed

Experimental and Theoretical Study of Multiscale Damage-Failure Transition in Very High Cycle Fatigue

Multiscale mechanisms of failure of metals (Armco iron, titanium, aluminum) are studied for high cycle and very high cycle fatigue. By correlating with the results of structural studies, a theoretical approach is developed to describe fatigue crack kinetics in damaged material under high cycle and very high cycle fatigue loading conditions. Stages of crack nucleation and propagation are analyzed using the profilometry data from the fracture surface. The scale invariance of fracture surface roughness is established, which allows an explanation of the self-similar nature of fatigue crack kinetics under high cycle and very high cycle fatigue. Variation of elastic-plastic properties of Armco iron under very high cycle fatigue is studied using an acoustic resonance method. It is found that the material density decreases during fatigue damage accumulation, with the minimum of the material density in the bulk of the specimen

The DeepFaune initiative: a collaborative effort towards the automatic identification of Europeanfauna in camera trap images

Camera traps have revolutionized how ecologists monitor wildlife, but their full potential is realized only when the hundreds of thousands of collected images can be readily classified with minimal human intervention. Deep-learning classification models have allowed extraordinary progress towards this end, but trained models remain rare and are only now emerging for European fauna. We report on the first milestone of the DeepFaune initiative (https://www.deepfaune.cnrs.fr), a large-scale collaboration between more than 50 partners involved in wildlife research, conservation and management in France. We developed aclassification model trained to recognize 26 species or higher-level taxa that are common in Europe, with an emphasis on mammals. The classification model achieved 0.97 validation accuracy and often >0.95 precision and recall for many classes. These performances were generally higher than 0.90 when tested on independent out-of-sample datasets for which we used image redundancy contained in sequences of images. We implemented our model in a software to classify images stored locally on a personal computer, so as to provide a free, user-friendly and high-performance tool for wildlife practitioners to automatically classify camera trap images. The DeepFaune initiative is an ongoing project, with new partners joining regularly,which allows us to continuously add new species to the classification model