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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 | Year: 2016

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.

Amari N.,Laboratoire PRISME | Folio D.,Laboratoire PRISME | Ferreira A.,Laboratoire PRISME
IEEE International Conference on Intelligent Robots and Systems | Year: 2014

This paper reports a control strategy of a micro-gripper based on two AFM tips for manipulation at micro/nano scale. It is composed of dual micro/nano manipulators in order to handle and to maintain a microsample through the focus of a X-ray or laser beam for material characterization and analysis. The main idea is to control and to drive in a robust way the micro/nanomanipulators by focusing the beam on the center part of the handled micro-object. To this aim, the maximum intensity of the laser beam is measured in real-time by a four-quadrant photodiode sensor. As the sample under consideration here is a superparamagnetic microsphere of 8.2 μm (focusing laser spot less than few μm2), the laser tracking system is very sensitive to light intensity variations, mechanical vibrations, microhandling force perturbations and thermal relaxation of magnetic microsamples. First, we propose to compensate the laser beam variations by estimating the position of the laser beam using a particle filter (PF) algorithm. Then, a robust control strategy based on H∞controllers ensures a robust microhandling task under the focus of the laser beam whatever the external perturbations involved and parametric model uncertainties. The dual manipulators are controlled cooperatively by combining the different actuator dynamics to track a laser beam with nanometer precision. Finally, experimental results demonstrate the robustness of the microhandling task using the proposed robust control scheme. © 2014 IEEE.

Belayachi N.,Laboratoire PRISME | Do D.P.,Laboratoire PRISME | Hoxha D.,Laboratoire PRISME
Computers and Geotechnics | Year: 2012

This paper deals with a micromechanical analysis of the nonlinear behaviour of a composite-like rock material using a numerical approach based on finite element analysis. The rock material is assumed to be a composite with an argillaceous matrix and quartz or calcite inclusions. A nonlinear Voce model combined with the viscoplastic Perzyna's law is chosen to describe the behaviour of the matrix material, while the quartz and calcite particles were modelled with classical linear elasticity theory. The effect of mineral inclusions' morphology on the macroscopic behaviour was examined with the aim of highlighting the choice of spherical shape in similar studies. © 2011 Elsevier Ltd.

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 | Year: 2012

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.

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 | Year: 2011

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.

Do D.P.,Laboratoire PRISME | Hoxha D.,Laboratoire PRISME
International Journal for Numerical and Analytical Methods in Geomechanics | Year: 2013

The present work aims at introducing an efficient numerical approach based on the immersed interface method to estimate the effective thermal conductivity and permeability of geomaterials as porous media with either perfect or debonded interfaces. The first part deals with the problem of the overall thermal properties of a medium containing perfectly bonded inclusions. The evolution of the homogenized properties with respect to the properties of individual constituents, the volume fraction, the spatial distribution, and the shape of inclusions is highlighted. The second part of the paper is devoted to the case of imperfectly bonded inclusions. An extension of the immersed interface method in this context makes it possible to study other aspects that have an influence on the effective properties such as the interfacial resistance and the size of inclusions. The application of the proposed numerical tool to some porous rocks in partially saturated condition shows good agreement with the available experimental results and demonstrates the performance and the flexibility of the developed procedure. © 2013 John Wiley & Sons, Ltd.

Delvare F.,Laboratoire PRISME | Cimetiere A.,University of Poitiers
European Journal of Computational Mechanics | Year: 2011

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.

Ladjal H.,University Claude Bernard Lyon 1 | Hanus J.-L.,Laboratoire PRISME | Ferreira A.,Laboratoire PRISME
IEEE International Conference on Intelligent Robots and Systems | Year: 2011

This paper presents a complete computer-based biological training system to simulate intracytoplasmic sperm injection (ICSI) procedures in a virtual environment (VE). Using the proposed system, the technician can practice and improve his control by developing a gesture similar to that performed in reality. The human-machine user's interface also provides an efficient haptic-based guidance tool to minimize the risk of damaging membranes during the injection. The key challenge of deformable simulation is to satisfy the conflicting requirements of real-time interactivity and physical realism. The compromise between the realism of bio-mechanical models used, the accuracy and stability of computational algorithms for real-time haptic rendering are fullfilled with the use of a mechanical modeling based on a hyperelastic model (St-Venant-Kirchhoff) and the writing of a specific dynamic finite element code. Simulated responses are compared to experimental data to show the effectiveness of the proposed physically-based model. © 2011 IEEE.

Destrez R.,Laboratoire PRISME | Treuillet S.,Laboratoire PRISME | Lucas Y.,Laboratoire PRISME | Albouy-Kissi B.,University uvergne
Progress in Biomedical Optics and Imaging - Proceedings of SPIE | Year: 2013

In orthodontics, a common practice used to diagnose and plan the treatment is the dental cast. After digitization by a CTscan or a laser scanner, the obtained 3D surface models can feed orthodontics numerical tools for computer-aided diagnosis and treatment planning. One of the pre-processing critical steps is the 3D registration of dental arches to obtain the occlusion of these numerical models. For this task, we propose a vision based method to automatically compute the registration based on photos of patient mouth. From a set of matched singular points between two photos and the dental 3D models, the rigid transformation to apply to the mandible to be in contact with the maxillary may be computed by minimizing the reprojection errors. During a precedent study, we established the feasibility of this visual registration approach with a manual selection of singular points. This paper addresses the issue of automatic point detection. Based on a priori knowledge, histogram thresholding and edge detection are used to extract specific points in 2D images. Concurrently, curvatures information detects 3D corresponding points. To improve the quality of the final registration, we also introduce a combined optimization of the projection matrix with the 2D/3D point positions. These new developments are evaluated on real data by considering the reprojection errors and the deviation angles after registration in respect to the manual reference occlusion realized by a specialist. © 2013 SPIE.

Luengo L.,CDR Hutchinson | Treuillet S.,Laboratoire PRISME | Gomez E.,CDR Hutchinson
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2015

Carbon blacks are widely used as filler in industrial products to modify their mechanical, electrical and optical properties. For rubber products, they are the subject of a standard classification system relative to their surface area, particle size and structure. The electron microscope remains the most accurate means of measuring these characteristics on condition that boundaries of aggregates and particles are correctly detected. In this paper, we propose an image processing chain allowing subsequent characterization for automatic grading of the carbon black aggregates. Based on literature review, 31 features are extracted from TEM images to obtain reliable information on the particle size, the shape and microstructure of the carbon black aggregates. Then, they are used for training several classifiers to compare their results for automatic grading. To obtain better results, we suggest to use a cluster identification of aggregates in place of the individual characterization of aggregates. © 2015 SPIE.

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