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Mesolithic settlements (9th to 6th millennia cal.BCE) at Roquemissou (Aveyron, France)
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Analytical study of the elastoplastic buckling of conical shells under external pressure
No full textInternational audienceAbstractPressure vessels are traditionally made up of cylindrical shells and hemispherical or ellipsoidal ends, but in some cases, conical sections are also present so as to ensure the transition between cylindrical sections of different radii. The buckling phenomenon is one of the main failure mode of such pressure equipments, due to the thinness of the components and the compressive stresses commonly undergone throughout standard loads like external pressure, and thus an essential dimensioning factor. If the buckling behavior of cylindrical and spherical shells has been widely investigated in the literature, the specific case of conical shells has received much less attention, all the more so in plasticity. Therefore, the present paper aims to address the problem of elastoplastic buckling of a conical shell under external pressure in an analytical way. This study is based on the plastic bifurcation theory and relies on the simplest possible hypotheses in terms of kinematics, constitutive law and boundary conditions. However, in absence of closed-form expressions, approximate solutions for the critical pressure are sought, based on the choice of appropriate shape functions in the framework of the Rayleigh–Ritz method. Unlike the case of cylindrical or spherical shells under external pressure which display uniform pre-critical stress states, the stress field appears to be heterogeneous in the length direction of a conical shell, so that three scenarios may occur. A conical shell may buckle elastically, entirely in the plastic range, or in an intermediate situation where the shell is partially elastic and plastic at the critical time. The present analytical solution is validated against reference numerical results obtained through finite element computations, considering a wide range of geometric and material parameters so as to cover all three scenarios
Elastic analytical model of riveted double web angle connections in tension
No full textInternational audienceT-stubs and L-stubs loaded in tension are generally assumed to be in contact with a rigid foundation due to symmetry that influences the prying force and stiffness of these components. However, for double web angle riveted connections the angle rests on deformable beam/column web. The objective of the present paper is to take into account the effects of this deformability on the development of the contact area, the rivet forces and the tensile stiffness. For this purpose, an enhanced theory of beam in contact with a tensionless Winkler foundation is adopted in the contact and lift-off areas and the axial/bending flexibility of the rivet are also considered. The two legs of the angle are fully modelled in interaction with rivets. A numerical analysis is also developed with ANSYS in order to conduct a sensitivity study to assess the influence of the horizontal leg thickness. The analytical model determines with a good accuracy the rivet force, initial stiffness, position of the prying forces but also the shape of the contact pressure distribution
Les fabriques du terrain naturaliste. L’archive du père Plumier en mouvement (années 1680-1700-1830)
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Modélisation multi-échelle du comportement dissipatif de composites tissés 3D
No full textInternational audienceModélisation multi-échelle du comportement dissipatif de composites tissés 3
Influence de l'orientation des plis sur les mécanismes de fissuration d'un stratifié : Réamorçage de fissures ou décohésion inter-pli?
No full textInternational audienceInfluence de l'orientation des plis sur les mécanismes de fissuration d'un stratifié : Réamorçage de fissures ou décohésion inter-pli
Effects of drying processes, pulsed electric fields and pressing on functional properties, color and biochemical composition of Sargassum muticum (Yendo) Fensholt 1955 (Ochrophytina, Fucales)
No full textInternational audienceThis study examines the effects of pretreatments (pulsed electric fields and mechanical pressing with a rubber membrane) and drying methods (freeze-drying, oven drying, and air jets impingement drying) on the physical properties and biochemical composition seaweed Sargassum muticum (Yendo) Fensholt 1955 (Ochrophytina, Fucales). The research analyzes changes in functional properties, color, biochemical composition, and microstructure. Results show that pretreatments and drying methods can significantly impact the biochemical composition and color of dried seaweeds. Freeze-drying preserves neutral sugars, uronic acids and mineral matter better with value of 1.75 ± 0.12 % Fresh Seaweed(FS) , 2.06 ± 0.20 % FS and 3.37 ± 0.22 % FS respectively. Oven drying however, has the most significant impact, as is also the case for mineral compounds after the succession of pulsed electric fields and freeze-drying. A reduction of 5.7 % to 9.0 % in mineral content was observed. Concerning the pressing pretreatment, it increases compounds retention in dried seaweeds. The effects on uronic acids content vary depending on the combination of pretreatment and drying method, passing for example, from 2.75 %FS after a 5-min pressing and air jets drying at 21 m s -1 to 3.08 %FS for a 10-min pressing and 7 m s -1 air jets drying. Moreover, microstructure analysis reveals that drying processes, including freeze-drying, alter the seaweed's internal structure. The study highlights the importance of selecting appropriate pretreatment and drying methods based on the desired properties of the final dried seaweed product.</div
Putting the human back in the system : a cybersecurity activity system modeling
No full textInternational audienceThis study aims to model Cybersecurity by using Engeström’s activity system model to challenge the notion of human error as the primary cause of cyber-security breaches. By emphasizing the influence of organizational constraints, it highlights the need for a cybersecurity approach that integrates human actors
