Homogénéisation du comportement élastoplastique anisotrope d'un polycristal poreux avec interfaces imparfaites

On s'intéresse à une modélisation polycristalline pour un matériau argileux. On étudie sa réponse élastoplastique en considérant simultanément deux mécanismes de plasticité: déformation des cristaux et glissement dans les interfaces intercristallines. On présente une solution originale du problème d'Eshelby pour une inclusion isotrope transverse avec interface imparfaite. Puis on met en uvre un schéma auto-cohérent prenant en compte des grains plastiques de type Schmid entourés d'interfaces de type Tresca et des pores. La réponse non linéaire prédite par cette modélisation est discutée

Refining of metallurgical silicon for crystalline solar cells

International audienceA plasma-retining technique is applied to upgraded metallurgical grade silicon (UMG) to produce solar grade silicon for multi-c silicon ingots at direct costs lower than 15€/kg. Using oxygen and hydrogen as reactive gases injected in the plasma, boron is removed from the material mainly in form of BOH and BO. The boron volatili- Zation time has been reduced to 50 min compared to previous processes, by increasing the temperature of the silicon bath. At the same time, the Al, Ca, C, O concentrations are strongly reduced. From a Íirst batch of puritied UMG Silicon, multi-crystalline ingots (l2kg), wafers (125X125mm2) and solar cells have been produced for an evaluation of this intermediate material. The obtained solar cells gave efticiencies of up to ll.7%. Process development towards an up-scaled pilot equipment is on the Way to further increase the puritication efticiency

Holocene marine transgression marker on the Karnataka coast (India)

149-151In the coastal plain of Baindur Hole (Karnataka). a thin layer (30 cm) of clayey silt, rich in organic matter and shells, has been recorded in a well at an altitude close to the present sea - level. This layer has been dated (C-14) to about 6400 years BP by two different methods. At the time of its deposition the paleontological clues (palynology, conchology) point to a very shallow environment. Hence, from this reliable marker of the Holocene transgression, it can be assessed that at about 6400 years BP the sea-level was close (just a few metres below) to the present sea-level on coastal Karnataka

Homogenization of anisotropic elastoplastic behaviors of a porous polycrystal with interface effects

International audienceThis paper is devoted to develop a theoretical framework to predict the macroscopic transversely isotropic elastoplastic behavior of clay-like material, which is viewed as a porous polycrystal. We consider evolutions of two local plastic mechanisms of grains and interface simultaneously, for which a Schmid criterion is used for the strength of sheet-like grains and a Tresca criterion for the strength of interfaces between particles. By adapting the standard incremental method, we propose firstly a classic self-consistent model, which does not consider the effect of interface, then a generalized self-consistent model in which the solid phase is represented by laminated (or isotropic) spherical grains surrounded by interfaces. Comparisons of numerical predictions between these two methods are performed and have demonstrated the validity of the generalized self-consistent model taking account of interface effects. Numerical simulations of uniaxial compression tests have shown that the macroscopic elastoplastic behavior of polycrystalline (clay-like) material can be successfully predicted by the way of considering the two local plastic mechanisms at microscopic scale. © 2013 John Wiley and Sons, Ltd

Refining of metallurgical silicon for crystalline solar cells

International audienceA plasma-retining technique is applied to upgraded metallurgical grade silicon (UMG) to produce solar grade silicon for multi-c silicon ingots at direct costs lower than 15€/kg. Using oxygen and hydrogen as reactive gases injected in the plasma, boron is removed from the material mainly in form of BOH and BO. The boron volatili- Zation time has been reduced to 50 min compared to previous processes, by increasing the temperature of the silicon bath. At the same time, the Al, Ca, C, O concentrations are strongly reduced. From a Íirst batch of puritied UMG Silicon, multi-crystalline ingots (l2kg), wafers (125X125mm2) and solar cells have been produced for an evaluation of this intermediate material. The obtained solar cells gave efticiencies of up to ll.7%. Process development towards an up-scaled pilot equipment is on the Way to further increase the puritication efticiency