Jean-Dominique Bartout

Mechanical properties and non-homogeneous deformation of open-cell nickel foams: application of the mechanics of cellular solids and of porous materials

Abstract The mechanical properties of open-cell nickel foams are investigated for the range of densities used in industrial applications for energy storage. The obtained Young’s modulus, compression yield stress and tensile fracture stress are compared to the predictions of models based on periodic, Penrose and Voronoi beam networks. It is found that Gibson and Ashby’s model [L.J. Gibson, M.F. Ashby, Cellular Solids, Cambridge University Press, Cambridge, 1998] provides the proper scaling laws with respect to relative density for almost all investigated properties. The strong anisotropy of the observed overall responses can also be accounted for. The two-dimensional strain field during the tension of a nickel foam strip has been measured using a photomechanical technique. Non-homogeneous deformation patterns are shown to arise. The same technique is used to obtain the strain field around a circular hole in a nickel foam strip. The observed deformation fields are compared to the results of a finite element analysis using anisotropic compressible continuum plasticity.

Microstructural and analytical characterization of Al2O3(AlMg) composite interfaces

Abstract Mechanical properties of composite materials depend on the reactions taking place at the ceramic-matrix interface. This study was devoted to the identification of the mechanisms of interaction for a Saffil-(AlMg) composite during squeeze casting and heat treatment. Transmission electron microscopy characterization and microanalysis clearly show migration of magnesium to the interface and reactions during processing of the composite and appropriate heat treatments allowed MgO and MgAl 2 O 4 clusters to be identified along the interface. Additionally, structural hardening of matrix through Mg 2 Si precipitation was made clear. Some evidence of macroheterogeneity in composition is also given.

Influence of thermal treatments on Ag Sn Cu powders in order to reduce mercury contents in dental amalgam.

The mercury content of dental amalgams is a controversial subject with regard to the biological properties of these materials. The object of this study is to optimize the thermal treatments performed on an experimental powder in order to obtain a low mercury ratio (41% by weight) while preserving the desirable clinical qualities of the material. Using atomized powder, two types of thermal treatments are performed: A1, to obtain a partially annealed structure and A2, to obtain a complete homogenization. The kinetics of the amalgamation reaction is mainly evaluated by X-ray diffraction to identify the newly formed phases as a function of setting time. Mechanical properties are evaluated according to the ISO norms at 37 °C. Metallographical examination of the amalgams shows a «Ag-Hg» phase which acts as a matrix incorporating the «Cu-Sn» and «Ag-Sn» compounds. The setting kinetics of the A1 amalgams is linear and slightly more rapid than that of the A2 amalgam. The mechanical properties of the amalgams are significantly improved regarding the higher mercury content commercial amalgams. A specific thermal treatment permits us to slow down the diffusion of mercury between the different intermetallic compounds into the powder. The final amalgam composition, thus, most approaches the stoechiometric ratio calculated from a quaternary diagram.

Mechanical Behavior of Nickel Base Foams for Diesel Particle Filter Applications

An original processing route by powder metallurgy was developped to alloy pure Ni foams so, that the foam becomes refractory for high temperature applications. The modelling of such a foam at high temperature starts from the behavior of the basic constitutive material, then we use micromechanical models to predict the mechanical properties under tension and in compression creep. A 3D finite element analysis of a volume analysed by X-ray tomography is performed to study the foam deformation mechanisms in both conditions.