Determination of the Young's modulus of a TiN Thin Film by nanoindentation: analytical models and numerical FEM simulation.

International audienc

Determination of the Young's modulus of a TiN Thin Film by nanoindentation: analytical models and numerical FEM simulation.

International audienc

Modelling of environmentally assisted crack growth in ceramics

International audienceno abstrac

Multiscale structure of super insulation nano-fumed silicas studied by SAXS, tomography and porosimetry

cited By 2We focus on describing the multi-scale structure of a fumed silica characterized by remarkably low thermal conductivity (ca. 2–5 mW m −1 K −1 ) when used as a core material in vacuum insulating panels. While such powders are known to be highly polydisperse at different lengthscales (hardly quantifiable), we propose to adapt a recent methodology based on small-angle X-ray scattering experiments with the aim of providing simple criteria for characterizing the morphology of these nanostructured silicas. Combining this technique with transmission electron microscopy, electron-tomography and mercury intrusion porosimetry then allows assigning the origin of the super-insulation to the low dimensionality of the silica aggregates at lengthscales smaller than 500 nm. Remarkably, by using independently these three techniques, we always find the compacity of the aggregates (radius of ca. 40 nm) to be equal to 0.29 ± 0.01. This study proposes therefore a robust methodology, potentially of a great interest for industrial applications. © 2019 Acta Materialia Inc

Modelling of environmentally assisted crack growth in ceramics

cited By 3International audienc

Freak Wave Formation from Phase Coherence

This paper describes freak waves by a (pseudo-)maximal wave proposed in [1]. The freak wave is a consequence of a group event that is present in a time signal at some position and contains successive high amplitudes with different frequencies. The linear theory predicts the position and time of the maximal amplitude wave quite well by minimizing the variance of the total wave phase of the given initial signal. The formation of the freak wave is shown to be mainly triggered by the local interaction of waves evolving from the group event that already contained large local energy. In the evolution, the phases become more coherent and the local energy is focussed to develop a larger amplitude. We investigate two laboratory experimental signals, a dispersive focussing wave with harmonic background and a scaled New Year wave. Both signals generate a freak wave at the predicted position and time and the freak wave can be described by a pseudo-maximal wave with specific parameters

Suitability of mullite for high temperature applications

High temperature mechanical behaviour of mullite has been studied. Our study include tensile, flexural and compressive creep behaviour and fracture up to 1400 °C. The results obtained in creep are analysed and compared with previous work in the literature. Two regions with different behaviour can be distinguished. The creep rates in bending, tension and compression are very similar in the first region at low stresses and temperatures. It is shown that in this region creep takes place by accommodated grain boundary sliding assisted by diffusion. At higher stresses slow crack growth from defects present in the sample occurs. The stress at which this transition in the deformation mechanism happens is dependent on several factors, the loading system during testing, the grain size, the amount and distribution of glassy phase and the environment. It is claimed the existence of a network of mullite-mullite grain boundaries free of glassy phase associated to the low surface energy of [001] planes. The diffusion rate through these boundaries controls the creep rate, and explains the high creep resistance of mullite. The results presented in this work lead to the conclusion that the mechanism controlling high temperature deformation resistance of mullite materials in a wide range of stress-temperature working conditions is independent of the glassy phase content. Slow crack growth limit the use of mullite at high stresses and temperatures.This work was supported by the Brite EuRam III Project BRE2CT94 0613

Cell mediated immune response to L5P in longitudinal study of heifers from naturally<em> Mycobacterium avium</em> subsp <em>paratuberculosis</em> infected herd

National audiencePeptidyl moiety of cell wall lipopentapeptide (L5P) specific of Mycobacterium avium subsp paratuberculosis (Map) is immunogenic and a target for specific humoral response in Map infected animals. A chemically synthesized L5P is able to induce specific cell mediated immune response (CMIR) in IFN-γ release assay (IGRA) in selected cows from Map infected herds comparatively to non-infected or M. bovis infected. Following these observations, the aim of this study was to evaluate if L5P was an antigen of early specific immune response and potentially a predictive tool of Map infection. 113 heifers of 6 herds were included in a two years’ longitudinal study: 71 animals from three Map culture-confirmed herds, 11 animals from a Map infected herd Silirum® vaccinated during the study and 31 animals from two certified Map free herds. The analysis of the CMIR was investigated by IGRA following whole blood stimulation with synthetic L5P or mycobacterium purified protein derivative (PPD) from M. avium (PPDa), M. bovis (PPDb), Map (PPDj) and M. phlei (PPDp). Humoral immune response was quantified by L5P-based ELISA using an internal procedure and two commercial Map kits. Moreover, bacilli excretion was estimated by isolation and culture from faecal sample. PPDs’ CMIR was more or less high depending of infected herds context, became high over 2 S/P ratio for 10/11 animals just after Silirum® vaccination and was low, less than 0.1 S/P ratio, in certified Map free herds. L5P CMIR was observed in 9 of 71 animals from Map culture-confirmed herds. These 9 animals with a L5P CMIR positive between 0.05 and 0.6 S/P ratio were from the same herd, knowing that L5P CMIR was previously detected in all included Map culture-confirmed herds. L5P CMIR was fluctuant as already described for PPD but was significantly correlated with PPDj CMIR. For 2 of the 9 animals, the L5P CMIR was predictive of the Map positive serology, whereas it was concomitant with seropositivity for 2 others and that for 5 animals was several times observed without seroconversion. And no seroconversion was observed in other herds. The continuation of this study would assess the predictive potential of L5P CMIR for paratuberculosis diagnosis