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Leroux H.,CNRS Materials and Transformations Unit of UMET
Meteoritics and Planetary Science | Year: 2012

The deceleration tracks in the Stardust aerogel display a wide range of morphologies, which reveal a large diversity of incoming particles from comet 81P/Wild 2. If the large and dense mineral grains survived the extreme conditions of hypervelocity capture, this was not the case for the fine-grained material that is found strongly damaged within the aerogel. Due to their low mechanical strength, these assemblages were disaggregated, dispersed, and flash melted in the aerogel in walls of bulbous deceleration tracks. Their petrologic and mineralogical properties are found significantly modified by the flash heating of the capture. Originating from a quenched melt mixture of comet material and aerogel, the representative microstructure consists of silica-rich glassy clumps containing Fe-Ni-S inclusions, vesicles and "dust-rich" patches, the latter being remnants of individual silicate components of the impacting aggregate. The average composition of these melted particle fragments is close to the chondritic CI composition. They might originate from ultrafine-grained primitive components comparable to those found in chondritic porous IDPs. Capture effects in aerogel and associated sample biases are discussed in terms of size, chemical and mineralogical properties of the grains. These properties are essential for the grain survival in the extremely hot environment of hypervelocity impact capture in aerogel, and thus for inferring the correct properties of Wild 2 material. © 2012 The Meteoritical Society.

Lu G.-H.,Beihang University | Zhou H.-B.,Beihang University | Becquart C.S.,CNRS Materials and Transformations Unit of UMET
Nuclear Fusion | Year: 2014

Tungsten (W) is considered to be one of the most promising plasma-facing materials (PFMs) for next-step fusion energy systems. However, as a PFM, W will be subjected to extremely high fluxes of low-energy hydrogen (H) isotopes, leading to retention of H isotopes and blistering in W, which will degrade the thermal and mechanical properties of W. Modelling and simulation are indispensable to understand the behaviour of H isotopes including dissolution, diffusion, accumulation and bubble formation, which can contribute directly to the design, preparation and application of W as a PFM under a fusion environment. This paper reviews the recent findings regarding the behaviour of H in W obtained via modelling and simulation at different scales. © 2014 IAEA, Vienna.

Ji G.,CNRS Materials and Transformations Unit of UMET | Morniroli J.-P.,Ecole Nationale Superieure de Chimie de Lille
Journal of Applied Crystallography | Year: 2013

The space group of a new metastable orthorhombic Al2Cu phase, located in the Al-rich interfacial region of an Al-Cu friction stir weld, was unambiguously identified as Ic2m by a recently developed systematic method combining precession electron diffraction and convergent-beam electron diffraction. This metastable phase has the same tetragonal lattice as its stable θ-Al2Cu counterpart (tetragonal, I4/mcm, No. 140). The tetragonal-to-orthorhombic symmetry lowering is due to slight modifications of the atomic positions in the unit cell. This metastable phase can be transformed into the stable θ-Al2Cu phase by in situ irradiation within the transmission electron microscope. Copyright © International Union of Crystallography 2013.

Ayoub G.,Texas A&M University at Qatar | Zairi F.,Lille Laboratory of Mechanics | Nait-Abdelaziz M.,Lille Laboratory of Mechanics | Gloaguen J.M.,CNRS Materials and Transformations Unit of UMET | Kridli G.,University of Michigan
International Journal of Plasticity | Year: 2014

The large deformation time-dependent mechanical response of rubber-like materials under cyclic loading is characterized by stress-softening, hysteresis and permanent set. To describe this set of first-order phenomena a constitutive model integrating the physics of polymer chains and their alteration under cyclic loading is proposed. The time-dependency is considered using a Zener-type framework in which the chain extensibility limit is described with both physical and phenomenological approaches. The efficiency of the proposed constitutive model is illustrated by comparisons with experimental data obtained on a styrene-butadiene rubber submitted to cyclic tension loading up to failure both in constant and variable amplitudes. © 2014 Published by Elsevier Ltd.

Affouard F.,CNRS Materials and Transformations Unit of UMET | Correia N.T.,New University of Lisbon
Journal of Physical Chemistry B | Year: 2010

By means of molecular dynamics simulations, dynamical properties of racemic ibuprofen glass-forming liquid are investigated at different temperatures from 360 to 500 K. The origin of the peculiar low amplitude Debye-type relaxation observed experimentally by dielectric relaxation spectroscopy is addressed (Bras, A. R.; Noronha, J. P.; Antunes, A. M. M.; Cardoso, M. M.; Schönhals, A.; Affouard, F.; Dionisio, M.; Correia, N. T. J. Phys. Chem. B 2008, 112, 11087). Single and total dipolar autocorrelation functions are calculated. It is found that the behavior of the total dipole correlation is dominated at short and long times by the single function. It mainly originates from the antiparallel dipoles correlations in agreement with a value of the Kirkwood correlation factor slightly smaller than unity. The simulation suggests that the long time Debye-type decay of the dipole-dipole correlation is dominated by the internal cis-trans conversion of the O - C - O - H group coupled to the change of the intermolecular linear/cyclic HB structures. The overall rotation of the molecules is about 1-2 decades faster than the cis to trans transformation, so all the O - C - O - H group environments are equal on average. The effective rotational potential energy barriers of the O - C - O - H groups due to the surroundings are thus averaged and dipolar relaxation follows a simple Debye law. It is found that cyclic dimers inhibit the cis to trans conversion unlike the linear dimers and trimers which favor this conversion and stabilize the trans isomer. It is well in line with the very low amplitude of the dielectric strength associated with the Debye relaxation observed experimentally and its increase when the liquid is maintained isothermally above the melting temperature since this amplitude mainly relates to the low fraction of ibuprofen molecules in the trans conformation. A comparison is made with the Debye-type relaxation found in microstructured monohydroxy alcohols. © 2010 American Chemical Society.

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