ECOLE DOCTORALE SI-MMEA (http://simmea.ed.univ-poitiers.fr/)
2016 Doctoral research projects for PhD recruitment
I-
General information :
VILLE, LABORATOIRE
Town, Laboratory
Etablissement
Institution
TITRE en français
French title
TITRE en anglais
English title
Directeur(s) de thèse (HDR)
Supervisor(s)
Taux d’encadrement prévu (%)
Supervising rates (%)
Co-encadrant(s)
Co-supervisor(s)
Taux d’encadrement prévu (%)
Supervising rates (%)
Contact pour informations
Contact for information
Compétences requises
Pre requisite
Poitiers (FR) :
P’D1*
P’D2*
P’D3*
Limoges (FR) :
SPCTS*
GEMH*
La Rochelle (FR) :
LaSIE*
UP*
ENSMA*
UL*
ENSCI*
ULR*
COMPREHENSION DE MECANISMES ELEMENTAIRES DE LA
PLASTICITE AUX ECHELLES NANO, DANS DES STRUCTURES
COMPLEXES
UNDERSTANDING OF THE ELEMENTARY MECHANISMS OF
PLASTICITY AT NANOSCALE, IN COMPLEXE STRUCTURES
Nom 1 : Pizzagalli
Prénom 1 : Laurent
Nom 2 : Prénom 2 :
%:
Nom 1 :
Nom 2 :
Godet
% :50
Prénom 1 :
HDR ?
oui
non
Prénom 2 :
HDR ?
oui
non
Julien
% : 50
%:
Nom : Godet
Prénom : Julien
Tel : +33 5 49 49 65 58
Email : julien.godet@univ-poitiers.fr
Formation in material science, mechanical properties (plasticity,
elasticity), classical molecular dynamics simulations, DFT methods,
basic programmation skill.
*Sigle : P’D1, P’D2 et P’D3 : Départements D1, D2 et D3 de l’institut P’ :
http://www.pprime.fr/;
SPCTS :
http://www.unilim.fr/spcts/;
GEMH :
http://www.avrul.fr/spip.php?rubrique39; LaSIE : http://www.univ-larochelle.fr/LaSIE,
UP http://www.univ-poitiers.fr/, ENSMA http://www.ensma.fr/, UL : http://www.unilim.fr/,
ENSCI : http://www.ensci.fr/, ULR : http://www.univ-larochelle.fr/.
II- Description of the 3 year doctoral research project
(please make a complete description of the doctoral research project. Do not forget to
mention when the contrat will start and to give an estimation of the net salary per
month)
One of the goal of materials science is to understand the relation between microstructures
at the atomic scale and physical properties. The narrow link between the strength and the
density of materials observed in the Ashby diagram shows a nearly linear proportionality
between both properties. The question raised by this observation is about the possibility
to fill empty areas in this diagram in order to build hard materials with low density. The
architectured materials, as for exemple the metal nano-foams, have been proposed as a
possible answer [Fleck et al. 2010 PRSA], in particular with architectures based on
several length scale to mimic nature [Schaedler et al. 2011 Science, Dunlop et al. 2013
Scripta Materialia].
The high strength of the architectured materials partly comes from the nanoscale
dimension. Indeed, the mechanical study performed on nanomaterials revealed an
important size effect when the dimensions reach few hundred of nanometers; for the
smallest dimension, the yield stress can attaign the theoretical yield stress for a perfect
crystal. In addition, at small size, the brittle behavior of different materials
(semiconductor, ceramic, oxide...) disappears to the profit of a ductile behavior. The
challenge of is to understand the elementary mechanisms crack and plasticity at the
atomic scale in nano-composite materials, such as core-shell nanowires, in order to
propose new elementary bricks to build high strength-to-weight ratio architecture.
The study already performed in our group about the brittle-ductile transition at low
dimension have revealed different mechanisms of the opening of cavity in silicon
nanowires (see figures below). However, the driving force governing the growth of the
cavity in the large pillars is not yet identified. This will be the first part of the thesis. In a
second part, the student will investigate the role of the interface in the modification of the
onset of plasticity and crack in core-shell nanowires ( Si/SiO2, Si/metals or
Si/amorphous-Si), in order to explore different ways to build new materials with
remarkable mechanical properties.
The student will use the molecular dynamics (MD) code LAMMPS to simulate the
mechanical tests. Some DFT calculations could be performed on small systems to check
the validity of the empirical potential used in MD simulations.
The Ph.D. thesis will start in October 1, 2016 and will stop in September 30, 2019, the
net salary is about 1360 euros a month.
Cavity
Opening of cavity in silicon nanowire under a tensile
stress at 10K (5 millions of atoms) due to the
dislocation interactions.
Cross section of the nanowire showing the cavity.