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Rekik A.,Laboratoire PRISME | Rekik A.,Ecole Polytechnique - Palaiseau | Bornert M.,Ecole Polytechnique - Palaiseau | Bornert M.,ParisTech National School of Bridges and Roads | And 2 more authors.
Mechanics of Materials

This paper is devoted to the evaluation of various classical and more recent linearization schemes for nonlinear homogenization in terms of their efficiency to characterize local field fluctuations in nonlinear heterogeneous composites. It relies on an unbiased comparison between field statistics predicted by homogenization theories and those obtained from a reference solution solved using finite element techniques, based on the same microgeometry and boundary conditions and in which local nonlinear constitutive relations are exactly verified at each point. Two categories of linearization methods have been investigated: classical approaches based on a "stress-strain" approach (classical secant, classical and simplified affine) and methods based on "variational principles" (variational and Lahellec-Suquet procedures). For each approach, the maps and the statistical distribution functions of the local fields (strain, stress and incremental work) illustrating the intra- and inter-phase heterogeneities are provided for reinforced and porous power-law composites. This study supplements an earlier study focused on comparisons at the global level (Rekik, 2006; Rekik et al., 2007) and provides additional information on the accuracy of some available classical and recent linearization procedures. The proposed methodology gives access to a deeper insight on nonlinear homogenization schemes and may eventually lead to improvements of these formulations. © 2012 Elsevier Ltd. All rights reserved. Source

Recoquillon Y.,Renault S.A. | Kourta A.,Laboratoire PRISME | Andres E.,Renault S.A.
Mecanique et Industries

The air supply of car passenger compartment is realized through the water box, receptacle collecting also rainwater streaming from the windshield. A better knowledge of air and water flows and instabilities produced inside the water box is necessary to ensure both good water draining outside the car and a feeding in fresh air, devoid of droplets inside. Results coming from this experimental view should allow to improve numerical models used by the firm. © AFM, EDP Sciences 2011. Source

Delvare F.,Laboratoire PRISME | Cimetiere A.,University of Poitiers
European Journal of Computational Mechanics

Our aim is to propose an improved regularization method for data completion problems. This method is presented on the Cauchy problem for the Laplace equation in 2D situations. This method is an iterative one, uses a regularization with fading effect and penalization terms which take into account the fact that, under some regularity assumptions, the partial derivatives of a harmonic function is also harmonic. Many numerical simulations using the finite element method highlight the efficiency, accuracy, stability when data are noisy and the ability of the method to take into account and deblur noisy data. © 2011 Lavoisier, Paris. Source

Durand B.,Ecole Normale Superieure de Cachan | Delvare F.,University of Caen Lower Normandy | Bailly P.,Laboratoire PRISME | Picart D.,CEA Le Ripault
International Journal of Impact Engineering

Numerical simulations of mechanical loadings on pyrotechnic structures require the determination of the friction coefficient between steel and explosives. Our study focuses on contact pressures of around 100MPa and sliding velocities of around 10m/s. Explosives are brittle materials which fracture when submitted to such pressures in uniaxial compression. They have therefore to be confined to avoid any fracture during the tests. A new Hopkinson bar device which simultaneously enables to confine a sample and rub it on steel has therefore been designed. This device is composed of two coaxial transmission bars. It consists in a cylindrical sample confined in a steel tube, the cylindrical sample being inserted between the incident bar and the internal transmission bar, and the confinement tube being leant against the external transmission bar. The high impedance of the external transmission bar keeps the confinement tube quasi-motionless whereas the impedance of the internal transmission bar is calculated to reach the desired pressure and the desired velocity at the tube-sample interface. Tests have been carried out with an inert material mechanically representative of explosives. The friction coefficient and the stresses at the tube-sample interface are deduced from strain measurements on the Hopkinson bars and on the external face of the confinement tube, and from an analytical model. © 2015 Elsevier Ltd. All rights reserved. Source

Collumeau J.-F.,INSA Val de Loire | Leconge R.,Laboratoire PRISME | Emile B.,Laboratoire PRISME | Laurent H.,INSA Val de Loire
ISPA 2011 - 7th International Symposium on Image and Signal Processing and Analysis

Asepsis preservation in operating rooms is essential for limiting patient infection by hospital-acquired diseases. For health reasons, surgeons may not be directly in contact with sterile equipment surrounding them, and must instead rely on assistants to interact with these in their place. Gesture-based Human-Computer Interfaces constitute an interesting option for allowing surgeons to control such equipment without breaking asepsis-preservation rules. © 2011 University of Zagreb. Source

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