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Gramat, France

Labarbe L.,CEA DAM Gramat
Proceedings of the 2013 International Conference on Electromagnetics in Advanced Applications, ICEAA 2013 | Year: 2013

This study deals with a new evaluation method of NEMP (Nuclear ElectroMagnetic Pulse) vulnerability on cots electronic equipments. The method consists in comparing EMC (ElectroMagnetic Compatibility) test severities to NEMP conducted stresses. The comparison uses five characteristic criteria of the induced stresses, calculated with an analytic method. The process is based on a software named 'SUSIE' (in French: SUSceptibilité à l'IEMN « Impulsion électroMagnétique d'origine Nucléaire Haute Altitude »). Today, only conducted stresses are analyzed. An evolution is planned in 2013 to determine the equivalent vulnerability of radiated stresses and to validate the software. © 2013 IEEE.

Guiffaut C.,French National Center for Scientific Research | Reineix A.,French National Center for Scientific Research | Pecqueux B.,CEA DAM Gramat
IEEE Transactions on Antennas and Propagation | Year: 2012

A new oblique thin wire formalism based on Holland's approach is proposed in the FDTD method. The principal achievement of this new formalism is to enable us to model a junction correctly between several oblique wires. To this end, an important criterion is proposed: the continuity of the current traces in the grid must be maintained at each node of the Yee cell that contains a part of one or several wires. This condition prevents undamped parasite oscillations on the wire current responses. In addition, our approach offers versatility in its usage. First the extremities of the wire can be placed freely in a Yee cell. Second it operates in lossy medium and finally, the sensitivity of the wire is minimized when inclined or shifted. With regards to this last point, the in-cell inductance of a wire segment is formulated to take account of the segment position and its obliquity in the Yee cell. © 2006 IEEE.

Jouvaud C.,ESPCI ParisTech | Jouvaud C.,CEA DAM Gramat | Ourir A.,ESPCI ParisTech | De Rosny J.,ESPCI ParisTech
Applied Physics Letters | Year: 2014

A metalens, i.e., a dense array of identical resonators, allows to image an object pattern at subwavelength scale from far field radiation field. Here, we show that the efficiency can be improved when the resonant frequencies of the cell are distributed over a given frequency range. Because in such systems each eigen mode is localized, the subwavelength image is built from a spectral analysis of the radiated field. A simple model based on coupled resonant dipoles is used to find the best frequency distribution. This multifrequency metalens approach is validated using a flat array of split ring resonators. We experimentally demonstrate the subwavelength resolution of such a device at microwave range. © 2014 AIP Publishing LLC.

Erzar B.,CEA DAM Gramat | Forquin P.,CNRS Grenoble Laboratory for Soils, Solids, Structures, and Risks
International Journal of Solids and Structures | Year: 2014

With the exponential increase of computational power, numerical simulations are more and more used to model the response of concrete structures subjected to dynamic loadings such as detonation near a concrete structural element or projectile-impact. Such loadings lead to intense damage modes resulting from high strain-rate tensile loadings in the concrete structure. However, the modelling of the post-peak tensile response of concrete still remains difficult due to the lack of experimental data at high strain-rates. This work aims at improving the modelling of the softening behaviour of concrete based on the following statement: despite the propagation of unstable cracks in the tested specimen cohesion strength exists in the vicinity of triggered cracks and is driving the whole softening behaviour of concrete. This statement is justified in the present work by means of experiments and Monte-Carlo calculations: firstly, concrete samples have been subjected to a dynamic tensile loading by means of spalling experiments. Several specimens have been recovered in a damaged but unbroken state and have been subsequently loaded in quasi-static tensile experiments to characterise the residual strength and damage level in the sample. In addition, Monte-Carlo simulations have been conducted to clarify the possible influence of cohesion strength in the vicinity of cracks. Finally, the DFH (Denoual-Forquin-Hild) anisotropic damage model has been adapted to take into account the cohesion strength in the damaged zone and to describe the softening behaviour of concrete. Numerical simulations of experiments conducted on dry and saturated samples at different levels of loading-rate illustrate the new capability of the model. © 2014 Elsevier Ltd. All rights reserved.

Forquin P.,Grenoble Alpes University | Sallier L.,University of Lorraine | Pontiroli C.,CEA DAM Gramat
Mechanics of Materials | Year: 2015

During the impact of a kinetic penetrator against a plain-concrete target severe damage modes are observed such as spalling on the front face, radial cracking in the whole target and, in the case of perforation, scabbing on the rear face. These damage mechanisms are substantially decreasing the penetration resistance of the concrete structure. Moreover, high confining pressures are observed in front of the projectile that involve mechanisms such as micro-cracking and collapse due to porosity. Both confined compressive and tensile behaviors are influenced by the concrete's moisture content. Therefore, the constitutive model used for numerical calculation for describing the confined behavior and tensile resistance of the concrete has to take into account the amount of free water in the concrete. In the present work, a series of numerical simulations of impact tests have been conducted considering two saturation ratios (dry and water-saturated) plus two target thicknesses. The confined behavior of the concrete material is modeled using the KST (Krieg-Swenson-Taylor) plasticity model and the so-called DFH (Denoual-Forquin-Hild) anisotropic damage model which allows the description of the tensile strength and softening behavior of concrete in tension. These calculations are used to investigate the influence of the concrete's free water content through its confined behavior and tensile strength and the influence of friction at the projectile-target interface on the ballistic performance of concrete slabs. © 2015 Published by Elsevier Ltd.

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