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Identification expérimentale de l’ouverture, de la croissance et de la coalescence de pores dans un assemblage collé, en utilisant la µ-tomographie aux rayons X
No full textInternational audienceStructural bonding is increasingly used in various industrial sectors such as i) naval, ii) automotiveand iii) aeronautics [1]. The adhesives traditionally used in the context of structural assemblies aretwo-component epoxy adhesive type (resin and hardener). Thus, during the resin-hardener mixingphase, but also during the polymerization step, it can be observed the appearance of the pores in thejoint. The size and distribution of the pores are greatly influenced by the nature of adhesive components, their viscosity, their temperature, mixing time, etc. It can be observed experimentally [2] that this population of porosity considerably influences the mechanical strength of the seal and consequently leads to the degradation of the adhesive. Naturally, the changes in the morphology of the joint could be due to mechanisms (opening, growth, coalescence of the pores), occurring during the mechanical loading of the joint. So, the objective of this study concerns the establishment of a robust strategy for the experimental identification of these damage mechanisms, using X-ray μ-tomography. The proposed strategy is built first from synthetic tomographic data for which the appearance of the different mechanisms (opening, growth, coalescence) is mastered. The effect of voxelization of porosities on the identification of these mechanisms is studied and a coalescence criterion is proposed. The second step aims to validate the proposed strategy, using semi-synthetic data obtained from the results of a finite element model. Finally, the strategy is applied to two concrete cases: a monotonic tensile test on a bulk sample and a tensile test on a bonded joint based on a mini-scarf type sample stressed in the out-of-plane direction
Influence des effets d’histoire de vitesse de déformation lors du développement d’instabilités de striction
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Element differentiation with a Hartmann- based X-ray phase imaging system
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On the key role of crack surface area on the lifetime of arbitrarily shaped flat cracks
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Short and long term creep behaviour of polyamide ropes for mooring applications
No full textInternational audiencePolyamide 6 fibres are of interest for mooring lines of floating wind turbines and these are continuously loaded throughout their service life. Such applications require the long term response of polyamide 6 ropes in water to be characterized. This paper presents results describing the long term creep behaviour of polyamide 6 sub-ropes with tests that lasted 2 years. A specially designed experimental set-up for long term creep test in water is presented first. Then, a kinetic study comparing creep and recovery is performed using a logarithmic identification of the strain rate. The need for performing long term creep tests is evaluated by comparing the long term creep results to those from short term creep tests lasting 3 h. The results show that a 3 h long creep test provides a reasonable prediction of long term creep strain using a single logarithmic linear law. Finally, a latch-based Weibull model is compared to a single linear logarithmic law to describe and predict creep and recovery response. It is shown that the Weibull model allows a better description of the recovery behaviour of polyamide 6 but is less well adapted for the description of creep
Réseau d'antennes Vivaldi en impression 3D métallisée Ultra-Large-Bande pour applications In-Band Full-duplex
No full textNational audienceUn prototype de réseau d'antennes fonctionnant en In-Band Full Duplex (IBFD) ultra-large bande est présentée. Le réseau est formé de quatre antennes Vivaldi réalisées en impression 3D métallisée et alimenté par deux baluns basés sur des transitions microruban-fente. Une attention particulière est portée sur l'effet de l'épaisseur de la fente sur le niveau d'adaptation de la transition. Le réseau mesuré atteint en moyenne 60 dB d'annulation de l'auto-interférence dans la bande de 4,4 GHz à 28,6 GHz et un gain moyen de 9,8 dBi
Pratiques et formation aux défis environnementaux: une enquête auprès des élèves-ingénieurs en Algérie, au Maroc et en Tunisie.
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Mixed integer (non)linear approaches for the satellite constellation design problem
No full textInternational audienceIn this paper, we propose mathematical optimization models to solve the satellite constellation design problem for discontinuous coverage. In such a design problem, the aim is to determine the minimal number of satellites (and, incidentally, their 3D placements) in order to observe a fixed Earth region within a given revisiting time. Two Mixed Integer Nonlinear formulations are introduced. The first one is a feasibility problem based on the direct mathematical definition of pixel observability. The second one consists in introducing a set of indicator variables which specify if a satellite observes a pixel at a given time-stamp. In order to obtain a linear problem, the possible positions of the satellites are discretized. Finally, computational results show the potential and limitations of the proposed approaches