■ Mesoscale modelling of memory effects in glasses

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Description of the PhD project

Glasses are disordered solids that are usually obtained after the abrupt cooling of a liquid. Unlike that of crystals, the atomic structure of glass is disordered. Glass actually resembles a frozen liquid. The arrangement of atoms and molecules in glass is hardly distinguishable from that of a liquid. But how can a liquid be as strikingly hard as glass? [1]

The study of the glass transition (how it forms) and the mechanical properties of glass (how it deforms) is a very active field of research. Due to their out-of-equilibrium nature, glassy materials exhibit puzzling properties. In particular they keep a memory of their thermal and mechanical past. Thermal and mechanical effects are usually discussed independently : the glass structure depends on the rate of the thermal quench from the liquid phase to the glass phase ; the plastic behavior of an amorphous material depends on the past mechanical loading (strain hardening). However more and more recent results suggest a strong coupling between thermal and mechanical effects.

Here we propose to develop a minimal model at mesoscopic scale allowing us to account for mechanical and thermal effects in the glassy dynamics. In the spirit of depinning models generally used to describe the motion of a triple contact line in wetting or a crack front in fracture, we plan to study the yielding behavior of an amorphous material in a simple elastoplastic lattice model [2]. Such models are based on the coupling between a stochastic dynamics at local scale and long-range elastic interactions. They exhibit critical features (avalanches, finite size effects) but also reproduce other features more specific of amorphous plasticity (hardening, shear-banding).

Using recent results on the characterization of local plastic properties in model glasses [3] we will try to reproduce memory effects in the framework of these simplified models. A particular focus will be given to the localization behavior of the plastic strain (shear-banding).

References :
[1] K. Chang, The nature of glass remains anything but clear, The New-York Times, July 29, 2008
[2] M. Talamali et al., Avalanches, precursors and finite-size effects in a mososcopic model of amorphous plasticity, Phys. Rev .E , 84, 016115 (2011).
[3] S. Patinet et al., Connecting, Local Yield Stresses with Plastic Activity in Amorphous Solids, Phys. Rev. Lett. 117, 045501 (2016)

Keywords

Glass, Plasticity, Memory effects, Lattice Models, Design, Architectured Materials, Yielding transition, statistical physics

Research unit

UMR7636 Physics & Mechanics of Heterogeneous Media

Description of the research Unit/subunit

Research at PMMH covers the fields of Physics and Mechanics of Inhomogeneous Media. Experimental, numerical and theoretical studies are performed about various subjects ranging from turbulence in fluids, wetting, surface waves, rheology of complex fluids (bacterial suspensions, granular media) to the non-linear behavior of elongated structures or the mechanics of active or disordered matter. Lots of the research subjects lie at the interface between different fields : geophysics (emergence of dunes or river landscapes) or living matter (growth or vegetal roots in granular soil, fluid structures interactions in the flight of insects, etc.).

Name of the supervisor
Damien Vandembroucq (damien.vandembroucq (arobase) espci.fr)

Name of the co-supervisor
Sylvain Patinet (sylvain.patinet (arobase) espci.fr)

3i Aspects of the proposal

The present study lies at the interface between statistical physics and mechanics of materials. Organic as well as metallic glasses are brittle, which limits their technological use and increases the energetic imprint of glass products. A key phenomenon for the nucleation of cracks is the localization of plastic strain along very thin shear-bands. In the framework of a long-standing collaboration with Saint-Gobain Recherche (the main research center of the glass making company Saint-Gobain), these subjects will be discussed on a regular basis with members of the joint research unit CNRS/Saint-Gobain « Surface du Verre et Interfaces ». In the framework of a collaboration with prof. Craig E. Maloney, visits will be scheduled in Boston, USA at the department of mecanical engineering of North-Eastern University.

Expected Profile of the candidate

Applicants are expected to hold or prepare a Master’s degree in physics, mechanics, soft matter, material science or a related subject. The ideal candidate would have a strong interest in non-equilibrium statistical physics and/or mechanics of materials, excellent computing skills, experience in performing numerical simulations on either particle based models, finite elements or lattice models.

Important dates

Call for applications : from July 16th to September 17th 2018
Eligibility check results : Late September
3i Committee evaluation results : Late October
Interviews from the shortlisted candidates with the Selection Committee : Mid-December (week of December 10th)
Final results : Late December





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