The week starts with 2 theoretical sessions dealing with multiscale approaches in mechanics and numerical and experimental tools and methods, followed by two practical sessions during which the attendants will be dispatched in the laboratories to manipulate some of the most up-to-date equipment used in research. The last day is dedicated to the specific problem of nanoscale mechanics.
(click on the programme to go to the corresponding lecture / lab-course description)
8:30 Welcome coffee
8:50 Introduction to the winter school
9:00 A brief introduction to fluid turbulence
In spite of centuries of active research Turbulence remains one of the deepest mysteries of fluid mechanics. The complexity relies on the random and multi-scale nature of the phenomenon. This lecture will review the origin and the characteristics of fluid Turbulence, as well as the phenomenological framework and statistical tools commonly used to describe the phenomenon. These rely on the concept of energy cascade, introduced by L. Richardson in the 1920’s, later refined by A. Kolmogorov, who’s ideas still dominate the Turbulence research community.
10:30 Coffee break
10:50 Multiscale approaches for the modelling and simulations of gas-particle reactive flows under dense
Dense gas-particle reactors are encountered in many industrial systems involving chemical reactions such as the polymerisation of PE and PP for plastic making, the chlorination of zircon in the metallurgical industry, uranium oxide fluorination in the nuclear power industry, as well as biomass gasification, fossil fuels conversion (chemical looping combustion of coal and gas), or crude oil processing in petroleum refineries by fluid catalytic cracking, amongst many others. The modelling of dense gas-particle reactive flows is a very challenging problem as many physical mechanisms need to be taken into account, in particular the numerous interactions between particles (collisions, agglomeration, attrition), between the particles and the fluid (with mass, momentum and energy transfer), and also between the particles and the walls (frictional bouncing, rough wall surface, deposition and resuspension), all of these being coupled with chemical reactions (gaseous and solid combustion, polymerisation…) This presentation will show how different numerical methods capable of describing the phenomena at the micro, meso and the macro scales, are coupled to provide relevant simulations of processes involving dense gas-particle reactive flows.
12:20 Lunch break
13:45 Rheology of suspensions - Structure and flow properties of colloidal suspensions
Courses objectives are the characterization of the link between the flow mechanical properties (flow field, shear or extensional stresses, viscoelasticity moduli) and the structural organizations (aggregation, orientation, phase changes). The goal is to bring an understanding of the mechanisms controlling the flows properties of colloidal dispersions used in several processes (membrane separation, extrusion, film casting) involved in several industrial applications (chemical, bio- and agro-industries, pharmaceutical, water treatment...)
14:30 Hydrodynamics of suspensions - When particles come to life
Suspensions are encountered in nature as well as in various industrial processes. Suspensions refer to particles immersed in a liquid like mud, fresh concrete, blood, paints or ink to site but a few examples. A very recent interest with an exponential growing number of publications concerns active suspensions where particles can actively swim in the liquid phase like planktonic suspensions. Usually, the small size of the particles often means that the surrounding flow is dominated by viscous effects, and therefore that inertial forces can be neglected relative to viscous forces. This means that the Reynolds number associated with the particles is small and the flow can be considered as a Stokes flow. The present course aims at providing a physically based introduction to the dynamics of particulate suspensions and focuses on hydrodynamical aspects. We will also briefly summarize recent researches concerning active suspensions.
15:15 Coffee break
15:40 Homogenisation of coupled phenomena in heterogeneous materials
The macroscopic mechanical behaviour of heterogeneous material strongly depends on the arrangement of the constituents according to various microstructures (granular or porous media, fibrous network) and the physical phenomena involved at the microscale (heterogeneity scale). A fine scale description of such material is often impossible due to the large number of heterogeneities.
In practice, a macroscopic equivalent modelling is more efficient. An overview of the different methods that can be used to derived such equivalent macroscopic behaviour will be given.
17:10 Cocktail and poster session
All participants are kindly asked to prepare a poster about their work that will be exposed over the whole school.
Please don't forget to bring your poster with you on Monday morning.
9:00 A brief review of turbulence metrology
Because of its intrinsic multi-scale nature, the experimental characterization of turbulence requires dedicated metrological tools, capable to resolve (simultaneously if possible) the whole range of relevant involved scales (both in time and space). The present lecture will review the main contemporary instruments used by the scientific community for such high resolution and multi-scale disgnosis. These include Eulerian methods (such as hot-wire anemometry, laser-Doppler velocimetry and Particle Image Velocimetry) as well as new Lagrangian methods, based on acoustical and optical 3D particle tracking.
10:30 Coffee break
10:50 Numerical predictions of turbulent flows
Turbulent flows are characterised by a large range of motion scales. When turbulent flows are studied by numerical simulations, the explicit discretization of the overall range of scales is still an issue, even with the exponential rise in computational capability over the last few decades. In this presentation, some methods to overcome this limitation will be presented. The methods can consist to model a part of the turbulent fields (RANS and LES approaches), but the methods can also consist to develop numerical algorithm to allow direct numerical simulation with a lower computational cost (hybrid method for turbulent mixing).
12:20 Lunch break
13:45 3D experimental micromechanics at the grain scale - What for?
With x-ray micro tomography it is now possible to acquire 3D full-field measurements of granular materials at suitable resolutions. In the first applications of x-ray tomography to soil mechanics, the distribution of porosity was investigated with the aim of analyzing the development of localization phenomena in the soil specimen. More recently, Digital Image Correlation (DIC) has been used to determine the distribution of strain in a specimen – in a continuum framework – and/or individual grain kinematics, i.e., displacements and rotations of individual grains. These works have provided a deep insight into the micro-mechanics of the processes governing the overall behavior of granular materials.
This lecture will present recent advances in experimental micro (geo)mechanics achieved thanks to x-ray tomography and digital image analysis. In particular, we will focus on some recent experimental measurements of a 3D fabric tensor and its evolution during shearing of granular materials. Triaxial compression experiments on natural sands are chosen to investigate the evolution of fabric. Two different subsets of the specimen are chosen for the contact fabric analysis: one inside and another one outside a shear band. Individual contact orientations are measured using advanced image analysis approaches within these subsets. Fabric is then statistically captured using a second order tensor and the evolution of its anisotropy is related to the macroscopic behaviour. Finally, some very recent results obtained on fabric evolution from triaxial compression of lentils (i.e., very anisotropic grains!) are also presented.
More generally, the lecture will try to convey the following two messages: 1) to convince the audience that x-ray imaging is a measurement tool, not only a way to provide fancy images, and 2) to discuss what sort of modeling applications these rather exotic data can help to inform or inspire.
15:15 Coffee break
15:40 Numerical investigations of macroscopic behaviour of heterogeneous materials
The macroscopic effective properties or behaviour of heterogeneous materials are commonly invstigated by solving specific boundary value problem on Representative Elementary Volume (i.e. at the microscale) arising from the homogenization process. Nowadays, these boundary value problems (BVP) are commonly solved on 3D images of the material obtained by microtomography or idealized microstructure. Different numerical methods (Finite volume differences, Finite Element method, Discret Element method…) can used to solved the BVP. An overview of these methods is presented and illustrated.
09:00 Practical session I
The participants will attend 2 out of the 9 proposed lab-courses (1 on Wednesday, the other one on Thursday). Groups of 4-5 participants will be made and each group will be given its planning and location depending on the chosen topic. The lab-courses will be held in parallel sessions at different places on the campus.
A full description of the labcourses is available online to help you chose your topic
12:30 Lunch break
14:00 Practical session II
09:00 Practical session I
12:30 Lunch break
14:00 Practical session II
19:30 Gala dinner in town
The Gala dinner will take place at the Restaurant "l'épicurien" intown.
The Restaurant is easily accessible by tram, line B, "Sainte Claire - Les halles" stop.
FRIDAY 3: MECHANICS AT THE NANOSCALE
9:00 One atom thin angstrom capillaries: confined flows
2D-materials are well known for their extraordinary properties and graphene is an archetypal example with most superlatives to its credit for the description of its properties, thinnest, strongest, most conducting, lightest etc. On the contrary, angstrom-scale capillary can be dubbed as “2D-nothing”; it is an antipode of graphene, created by focusing on what is left behind after extracting one-atomic layer out of a crystal . Angstrom-size capillaries are thus constructed out of 2D-materials, and we investigate properties of gas, liquids and ions confined in molecular scale. A core strand of the work that I will present is the development of Angstrom-capillaries as a platform to probe intriguing molecular-scale phenomena experimentally, including: water flow under extreme atomic-scale confinement  complete steric exclusion of ions [3,5], specular reflection and quantum effects in gas reflections off a surface [2,7], voltage gating of ion flows  translocation of DNA . Previously such phenomena were only modelled by theoretical simulations and this is the first robust experimental platform with controlled angstrom-scale dimensions made from atomically smooth building blocks, alleviating the surface roughness which usually predominates at this scale. Moreover these Å-capillaries represent two-dimensional analogues of artificial sub-nanometer fluidic conduits.
Fig. 1. a, General schematic of Graphene capillary device. b, Cross-sectional bright field image of a bilayer capillary (h about 7 Å) in a scanning transmission electron microscope.
 B. Radha et al., Molecular transport through capillaries made with atomic-scale precision. Nature 538, 222 (2016).
 A. Keerthi et al., Ballistic molecular transport through two-dimensional channels, Nature (2018), 558, 420.
 A. Esfandiar et al., Size effect in ion transport through angstrom-scale slits. Science 358, 511 (2017).
 T. Mouterde et al., Molecular streaming and voltage gated response in Angstrom scale channels. Nature 567, 87 (2019).
 K. Gopinadhan et al., Complete ion exclusion and proton transport through monolayer water. Science 363, 145 (2019).
 W. Yang et al., Translocation of dna through ultrathin nanoslits. Advanced Materials 2007682, (2021).  J. Thiruraman et al., Gas flows through atomic-scale apertures, Science Advances 6, eabc7927, (2020)
10:00 Bottom-Up Model of Adsorption and Transport in Nanoporous Materials
Nanoporous materials are at the heart of important applications: adsorption (gas sensing, drug delivery, chromatography), energy (hydrogen storage, fuel cells and batteries), environment (phase separation, water treatment, nuclear waste storage), Earth science (exchange between the soil and the atmosphere), etc. In this talk, I will present the state-of-the-art on adsorption/condensation and transport in nanoporous materials which possess pore sizes spanning several orders of magnitude (from the sub-nm scale to a few tens of nm).1,2
I will show how adsorption and transport in such media can be described without having to rely on macroscopic concepts such as hydrodynamics.3,4,5
Then, using parameters and coefficients available to experiments, we will see that transport coefficients can be upscaled in a bottom-up fashion using statistical physics models such as free volume theory and intermittent brownian motion6
1 Coasne, B., Galarneau, A.; Pellenq, R.; Di Renzo, F., Chem. Soc. Rev. 2013, 42, 4141.
2 Coasne, B. New J. Chem. 2016, 40, 4078.
3 Falk, K.; Coasne, B.; Pellenq, R.; Ulm, F. J.; Bocquet, L., Nature Comm. 2015, 6, 6949.
4 Botan, A.; Ulm, F. J.; Pellenq, R.; Coasne, B., Phys. Rev. E. 2015, 91, 032133.
5 Lee, T.; Bocquet, L.; Coasne, B., Nature Comm. 2016, 7, 11890.
6 Bousige, C.; Levitz, P. E.; Coasne, B., Nature Comm. 2021, in press.
10:30 Coffee break
11:00 Polymer nanocomposites for ballistic protection: synthesis, characterization and molecular
Nanocomposites and nanostructures often behave in ways that are counterintuitive to our expectations from macroscopic analogues, and we are interested in exploring these behaviours and exploiting them for improved material performance. In particular we have been interested in polymer-based systems, either with a nanoscale filler material or combined with other nanostructured materials, for applications at high strain rate. We have synthesized polyurethane composites with Halloysite nanotubes (HNTs) at less than 1 wt%, and demonstrated that these materials show a 21% increase in fracture toughness and 35% increase in spall strength. More importantly, our characterization work elucidates the underlying mechanisms of this improvement, and shows that the HNTs are not behaving as a traditional toughening phase in a composite. Rather, they act to favourably modify the microstructure in the surrounding polymer matrix. We also make use of molecular dynamics simulation to understand the ballistic and spall behaviour of polymer and multilayer systems (polymer with metal or ceramic). Our simulations allow us to test some of the common assumptions made in spall experiments and show that at the nanoscale, extremely high ballistic penetration resistance can be observed. We also find that some nanoscale multilayers behave completely counter to our expectations. In this presentation, I will try to summarize the promise and limitations of these nanostructured materials, and convey an appreciation for how molecular dynamics can genuinely help us to design better ballistic materials.
12:00 X-ray nanotomography from 3D to 4D
Nano-characterization is a key point in the study of microstructures for the understanding of material properties, evolution and degradation. Synchrotron X-ray nano-tomography is one of the key tools for 3D analysis. This presentation will give the characteristics of the technique as well as its limitations. Examples illustrating the use of 3D volumes to feed mechanical and electrochemical simulations will be given. The challenges for in situ experiments will be illustrated with examples of real studies.
12:30 Lunch break
13:45 Dynamics at interfaces: from nanoscale interactions to mechanical response
Transport in nano confined systems is a ubiquitous phenomenon in biological systems, and at the core of various classical fields among which membrane science. Yet a combination of improved technological and theoretical tools lead to the rapid emergence of nanofluidics as a field of its own showing specific properties with high potential applications. In this presentation, I will try to go through some basic elements ruling the transport in liquids at the nanoscale. A first key contribution is associated with the enhanced role of interfaces due to high surface-volume ratio. This includes frictional properties together with cross-coupling capabilities whereby a forcing in one field -say electrical field- generates responses in terms of various currents: electrical but also mass or solute. A second key to nanofluidic response are entrance effects associated with transitions between the nano confined regions towards the macro scale environment. There, conservation constraints are responsible for specific effects such as concentration polarization of large impact over the overall transport properties. Finally, if time allows I will briefly mention recent advances towards ultimate -molecular- confinements bringing in new regime away from continuum approaches.
14:45 Experimental mechanics: a multiscale approach
The transition from the macroscopic to microscopic scales is a central question in mechanics. To address this question, we have developed an original approach based on a surface force apparatus to bridge macroscopic and molecular scales. During the presentation, I will discuss recent results obtained in fluid mechanics, rheology and solid mechanics.