Gerard L. Vignoles
University of Bordeaux
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Publication
Featured researches published by Gerard L. Vignoles.
Journal of Materials Research | 2000
Xavier Bourrat; Beatrice Trouvat; Guillaume Limousin; Gerard L. Vignoles; Francois Doux
This work deals with the measurement of pyrocarbon anisotropy on very thin fiber coatings used to control the interfacial behavior in carbon/carbon composites. Differentiation of the various pyrocarbons was performed through computerized image analysis of the electron diffraction patterns by measuring the azimuth opening of the carbon 002 diffraction arcs. This orientation angle decreases when the texture switches from rough to smooth laminar. The relationship with the polarized light measurement technique at a lower resolution is discussed.
Carbon | 2001
Gerard L. Vignoles
In the aim of producing high-quality discretized 3D images of the porous architecture of C/C composites, computerized microtomographs have been acquired with synchrotron radiation X-rays. Due to the weak X-ray absorption coefficient of carbon, the result of acquisition at 2 or 1 μm resolution are phase contrast images, not usable as such for the evaluation of geometrical or transport properties. We present here an image treatment algorithm designed to overcome this inconvenience.
IEEE Transactions on Image Processing | 2005
Frédéric Flin; Jean-Bruno Brzoska; David Coeurjolly; Romeu Andre Pieritz; Bernard Lesaffre; Cecile Coleou; Pascal Lamboley; Olivier Teytaud; Gerard L. Vignoles; Jean-François Delesse
Estimating the normal vector field on the boundary of discrete three-dimensional objects is essential for rendering and image measurement problems. Most of the existing algorithms do not provide an accurate determination of the normal vector field for shapes that present edges. Here, we propose a new and simple computational method in order to obtain accurate results on all types of shapes, whatever their local convexity degree. The presented method is based on the gradient vector field analysis of the object distance map. This vector field is adaptively filtered around each surface voxel using angle and symmetry criteria so that as many relevant contributions as possible are accounted for. This optimizes the smoothing of digitization effects while preserving relevant details of the processed numerical object. Thanks to the precise normal field obtained, a projection method can be proposed to immediately derive the surface area from a raw discrete object. An empirical justification of the validity of such an algorithm in the continuous limit is also provided. Some results on simulated data and snow images from X-ray tomography are presented, compared to the Marching Cubes and Convex Hull results, and discussed.
Journal of The Electrochemical Society | 2001
Cédric Descamps; Gerard L. Vignoles; Olivier Féron; F. Langlais; Jéro⁁me Lavenac
Pyrocarbon deposition through propane pyrolysis is studied in a 1-D hot-wall CVD furnace. The gas-phase pyrolysis is modeled with a partially reduced kinetic mechanism leading to polycyclic aromatic compounds (PAHs). The C2-C4 and C3 reaction paths are in competition for benzene formation. There is also an independent C3-C5 path leading to naphthalene. The gas-phase concentrations are correlated with experimental data including in situ Fourier transform infrared spectra intensities, pyrocarbon deposition rates, and pyrocarbon nanotextures. Rough laminar pyrocarbon deposition appears to be more related to PAHs than smooth laminar pyrocarbon.
Journal of the Brazilian Chemical Society | 2006
Xavier Bourrat; F. Langlais; G. Chollon; Gerard L. Vignoles
Este artigo e uma sintese das pesquisas recentes na area dos pirocarbonos. Pirocarbono e uma forma de carbono preparada por deposicao quimica em substratos quentes (acima de 900 oC) mediante pirolise de hidrocarbonetos. Aplicacoes se encontram nas areas de materiais compositos termostruturais, de reatores nucleares ou de biomateriais. Muito recentemente, um avanco importante foi obtido na compreensao dos processos de crescimento. Uma classificacao dos pirocarbonos de baixa temperatura e apresentada, que se fundamenta na medicao da quantia de defeitos e do grau de anisotropia, fazendo uso da espectroscopia Raman. Ela traz uma relacao bem estabelecida entre mecanismos de crescimento, estrutura e propriedades dos pirocarbonos.
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms | 2003
Olivia Coindreau; Gerard L. Vignoles; Peter Cloetens
Abstract As part of the modelling of chemical vapor infiltration, one of the processing techniques of carbon–carbon composites, a better understanding of the relation between fiber architecture and transport properties is required. An excellent starting point for the pore-scale modeling of heat and gas transport is the acquisition of 3D images of the porous media through computed microtomography at various densification stages. Due to the low X-ray absorption rate of light materials such as carbon, a poor image contrast is obtained with absorption tomography. On the other hand, phase contrast imaging is readily feasible using the coherence properties of modern synchrotron beams. Holotomography has been performed on these materials and it provides quantitative density images where fibers and pyrocarbon matrix deposit are easily distinguishable. Such images are appropriate for the pore-scale computation of many effective transport properties.
Applied Physics Letters | 2009
Jean-Marc Leyssale; Jean-Pierre Da Costa; Christian Germain; Patrick Weisbecker; Gerard L. Vignoles
A method for the generation of atomistic models of dense nanotextured carbons is presented. This method is based on the statistical analysis of high resolution transmission electron microscopy images and their three-dimensional (3D) extension through image synthesis under constraint. The resulting 3D images then serve as an external potential bringing the atoms to settle preferentially on the black areas during a conventional simulated annealing simulation. Application of this method to the case of two laminar pyrocarbons, differing in their degree of disorder, highlights the promising nature of this approach.
Journal of Materials Research | 2007
Gerard L. Vignoles; Olivia Coindreau; Azita Ahmadi; Dominique Bernard
The authors wish to thank Snecma Propulsion Solide and Centre National de la Recherche Scientifique (CNRS) for a joint Ph.D. grant to O.C. They are indebted to the European Synchratron Radiation Facility (ESRF) ID 19 team (Jose Baruchel, Peter Cloetens, Elodie Boller) for the acquisition of CMT scans and to Marie- Anne Dourges and Mickael Vignes for experimental determination of gas transport coefficients at Laboratoire
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms | 2003
Alexandre Velhinho; P.D Sequeira; Rui F. Martins; Gerard L. Vignoles; F.M. Braz Fernandes; José D. Botas; L.A. Rocha
Abstract The present work refers to an X-ray microtomography experiment aiming at the elucidation of some aspects regarding particle distribution in SiC-particle-reinforced functionally graded aluminium composites. Precursor composites were produced by rheocasting. These were then molten and centrifugally cast to obtain the functionally graded composites. From these, cylindrical samples, around 1 mm in diameter, were extracted, which were then irradiated with a X-ray beam produced at the European Synchrotron Radiation Facility. The 3-D images were obtained in edge-detection mode. A segmentation procedure has been adapted in order to separate the pores and SiC particles from the Al matrix. Preliminary results on the particle and pore distributions are presented.
Journal of The European Ceramic Society | 1998
S. Bertrand; J.F. Lavaud; R. El Hadi; Gerard L. Vignoles; René Pailler
Three-dimensional carbon fibre preforms were infiltrated with pyrocarbon or silicon carbide using a new process which combines a thermal gradient variation with a pressure pulsed chemical vapor infiltration. In this work, the principle of this TP-CVI process is presented. Thermal evaluations are carried out as guidelines to set up a model. Experimental infiltrations were performed, to validate the model. A comparison with experiments performed by P-CVI (i.e. without thermal gradient) shows that the TP-CVI process yields a better in-depth densification of the preform and a better deposit homogeneity. The thickness gradient depends chiefly on the thermal quenching ΔT. Process and equipment improvements led to samples more densified in the core than near the surface, that is, to samples still densifiable after considerable densification. This new technique also allows the use of preforms with higher fibre volume fractions. Three-dimensional carbon fibre preforms were infiltrated with pyrocarbon or silicon carbide using a new process which combines a thermal gradient variation with a pressure pulsed chemical vapor infiltration. In this work, the principle of this TP-CVI process is presented. Thermal evaluations are carried out as guidelines to set up a model. Experimental infiltrations were performed, to validate the model. A comparison with experiments performed by P-CVI (i.e. without thermal gradient) shows that the TP-CVI process yields a better in-depth densification of the preform and a better deposit homogeneity. The thickness gradient depends chiefly on the thermal quenching ΔT. Process and equipment improvements led to samples more densified in the core than near the surface, that is, to samples still densifiable after considerable densification. This new technique also allows the use of preforms with higher fibre volume fractions.