Multifunctional hybrids for electromagnetic absorption

in Acta Materialia (2011), 59(8), 3255-3266

Electromagnetic (EM) interferences are ubiquitous in modern technologies and impact on the reliability of electronic devices and on living cells. Shielding by EM absorption, which is preferable over ... [more ▼]

Electromagnetic (EM) interferences are ubiquitous in modern technologies and impact on the reliability of electronic devices and on living cells. Shielding by EM absorption, which is preferable over reflection in certain instances, requires combining a low dielectric constant with high electrical conductivity, which are antagonist properties in the world of materials. A novel class of hybrid materials for EM absorption in the gigahertz range has been developed based on a hierarchical architecture involving a metallic honeycomb filled with a carbon nanotube-reinforced polymer foam. The waveguide characteristics of the honeycomb combined with the performance of the foam lead to unexpectedly large EM power absorption over a wide frequency range, superior to any known material. The peak absorption frequency can be tuned by varying the shape of the honeycomb unit cell. A closed form model of the EM reflection and absorption provides a tool for the optimization of the hybrid. This designed material sets the stage for a new class of sandwich panels combining high EM absorption with mass efficiency, stiffness and thermal management. [less ▲]

Twinning in pure titanium subjected to monotonic simple shear deformation

in Acta Materialia (2010)

Two different textures of pure Ti were subjected to monotonic simple shear and this for three different orientations of the texture versus the shear direction. EBSD and TEM observations reveal the ... [more ▼]

Two different textures of pure Ti were subjected to monotonic simple shear and this for three different orientations of the texture versus the shear direction. EBSD and TEM observations reveal the presence of {10-12} and {11-22} twins. A statistical relevant analysis of the morphology of these twins combined with a resolved shear stress (RSS) analysis was performed. This analysis reveals that {10-12} and {11-22} twins have a similar average thickness, but the {10-12} twins show a far larger spread on their thickness compared to {11- 22} twins and can grow to almost the size of the original parent grain. Correlation of the twin fractions with the RSS analysis shows that this RSS technique is an acceptable method explaining the difference in twin fractions for different textures and orientations. A detailed analysis shows that {11-22} twins occur in average with a smaller volume fraction but with a higher RSS, indicating they are more difficult to nucleate or grow compared to {10-12} twinning. In general a higher RSS value on the twin plane is not connected with a higher twin thickness; only in case of {10-12} twins the highest RSS values show clearly thicker twins. [less ▲]

Interests and limitations of nanoindentation for bulk multiphase material identification: Application to the β phase of Ti-5553

in Acta Materialia (2009), (57), 5186-5195

This paper focuses on the numerical modeling of nanoindentation tests. The first goal of this study is to collect essential material parameters and boundary conditions from the literature and to complete ... [more ▼]

This paper focuses on the numerical modeling of nanoindentation tests. The first goal of this study is to collect essential material parameters and boundary conditions from the literature and to complete the data required to accurately model nanoindentation tests. The second goal of this study consists in validating the material parameters identified from macroscopic tensile tests of the body-centered cubic b phase of Ti-5553, a new generation of titanium alloy. This validation is performed looking at experimental and numerical nanoindentation curves obtained for different grain orientations. [less ▲]