Gramat, France
Gramat, France

Time filter

Source Type

Erzar B.,CEA DAM Gramat | Buzaud E.,CEA DAM Gramat
European Physical Journal: Special Topics | Year: 2012

Ceramic materials are commonly used to build multi-layer armour. However reliable test data is needed to identify correctly models and to be able to perform accurate numerical simulation of the dynamic response of armour systems. In this work, isentropic loading waves have been applied to alumina samples to induce spalling damage. The technique employed allows assessing carefully the strain-rate at failure and the dynamic strength. Moreover, specimens have been recovered and analysed using SEM. In a damaged but unbroken specimen, interactions between cracks has been highlighted illustrating the fragmentation process. © 2012 EDP Sciences and Springer.

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.

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.

Genetier M.,CEA DAM Gramat | Osmont A.,CEA DAM Gramat | Baudin G.,CEA DAM Gramat
Journal of Physics: Conference Series | Year: 2014

The objective is to compare the ignition and detonation properties of various liquid high explosives having negative up to positive oxygen balance (OB): nitromethane (OB < 0), saccharose and hydrogen peroxide based mixture (quasi nil OB), hydrogen peroxide with more than 90% purity (OB > 0). The decomposition kinetic rates and the equations of state (EOS) for the liquid mixtures and detonation products (DP) are the input data for a detonation model. EOS are theoretically determined using the Woolfolk et al. universal liquid polar shock law and thermochemical computations for DP. The decomposition kinetic rate laws are determined to reproduce the shock to detonation transition for the mixtures submitted to planar plate impacts. Such a model is not sufficient to compute open field explosions. The aerial overpressure is well reproduced in the first few microseconds, however, after it becomes worse at large expansion of the fireball and the impulse is underestimated. The problem of the DP EOS alone is that it takes only the detonation into account, the secondary combustion DP-air is not considered. To solve this problem a secondary combustion model has been developed to take the OB effect into account. The detonation model has been validated on planar plate impact experiments. The secondary combustion parameters were deduced from thermochemical computations. The whole model has been used to predict the effects of the oxygen balance on open air blast effects of spherical charges. © Published under licence by IOP Publishing Ltd.

Pontiroli C.,CEA DAM Gramat | Rouquand A.,CEA DAM Gramat | Mazars J.,Grenoble Institute of Technology
European Journal of Environmental and Civil Engineering | Year: 2010

This paper presents the main results obtained during a long and intensive research period on the modelling of the main physical mechanisms related to damage and fracture of concrete. The starting point has been the Mazars one scalar damage model (Mazars, 1984, 1986). On this base Pontiroli & Rouquand have proposed in 1995 a two scalar damage model (PRM model) which takes into account the crack closure mechanism, irreversible strains, strain rate effects and internal friction stresses. This model has been recently completed in order to take into account pore collapse phenomena, plastic shear deformations and the water content effect on the behaviour of concrete for confined loading. All these mechanisms allow the simulation of a large range of loadings from static to high velocity impacts. After a presentation of the most important features of the "PRM coupled model"several applications are given related to quasi static loading, blast or impact effects on concrete structures. © 2010 Lavoisier, Paris.

Baudin G.,CEA DAM Gramat | Serradeill R.,CEA DAM Gramat
EPJ Web of Conferences | Year: 2011

The JWL EOS is widely used in different forms (two, three terms) according to the level of accuracy in the pressure-volume domain that applications need. The foundations of the relationship chosen to represent the reference curve, Chapman-Jouguet (CJ) isentrope, can be found assuming that the DP expansion isentrope issued from the CJ point is very nearly coincident with the Crussard curve in the pressure-material velocity plane. Its mathematical expression, using an appropriate relationship between shock velocity and material velocity leads to the exponential terms of the JWL EOS. It well validates the pressure-volume relationship chosen to represent the reference curves for DP. Nevertheless, the assumption of constant Gruneisen coefficient and heat capacity in the EOS thermal part remains the more restrictive assumption. A new derivation of JWL EOS is proposed, using a less restrictive assumption for the Gruneisen coefficient suggested by W.C. Davis to represent both large expansions and near-CJ states. © Owned by the authors, published by EDP Sciences, 2010.

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.

Phillips A.E.,University of Cambridge | Phillips A.E.,Queen Mary, University of London | Cole J.M.,University of Cambridge | Cole J.M.,University of New Brunswick | And 3 more authors.
Inorganic Chemistry | Year: 2012

The photoinduced O-bound coordination mode in RuSO 2 complexes, previously observed only at 13 K, has been generated at 100 K in tetraammineaqua(sulfur dioxide)ruthenium(II) (±)-camphorsulfonate. This coordination state, often denoted MS1, decays to the η 2-bound MS2 state, with an estimated half-life of 3.4(8) h and a long-lived population of 2.9(4)% at 120 K. © 2012 American Chemical Society.

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.

Loading CEA DAM Gramat collaborators
Loading CEA DAM Gramat collaborators