A cylindrical rod (bottom center) floats in an upward flow between two parallel glass rectangular plates parallel to the plane of the figure. It displays here a swinging motion with a periodic oscillation of its angle with respect to the horizontal: this motion has been visualized by injecting two parallel streaks of dye reaching the cylinder near its ends (the false colors correspond to the concentration of dye). The trajectory of the dye demonstrates a possible mixing mechanism associated to this instability.
Yield stress fluid flow in porous media
The non-Newtonian fluids intervene in numerous industrial processes.
The flow of yield stress fluids, viz. that require a minimal shear stress for flowing, is investigated in different heterogenous media (porous media, factures...).
The presence of heterogeneities induces many different flowing regimes that we aim to characterize.
Mixing in X-junctions
The behavior of fluids in junctions is particularly critical for applications such as mixing, chemical reactions or heat exchange. While most previous studies dealt only with orthogonal or parallel channels, we analyze numerically and experimentally the influence of geometrical parameters such as the angle of intersection and the aspect ratio (Width / Height) of the channels. The figure shows typical streamlines obtained numerically for different intersection angles. For angles lower than 33.8 degrees, the flow is blocked by recirculation cells.
Fracture toughness increase by crack front pinning
One way to increase the fracture toughness is the introduction of tougher heterogeneities: when a crack front is pinned by those places, it deforms and changes the fracture resistance of the material.
How to quantify this effect?
We have shown, by close comparison with cleavage tests, that perturbation approaches, which are computational
time-efficient enough to be further used in some optimisations scheme, can be used for this purpose.
Crack Front Segmentation and Facet Coarsening in Mixed-ModeI+III Fracture
When a fracture is loaded by some plane shear or tearing (mode III in fracture mechanics theory), the initial fracture splits into facets that further coalesce to form a complex fully three-dimensional fracture facies. This situation is common at different scales, in engineering (e.g. tearing of aircraft fuselage), in buildings (e.g. tear due to land subsidence), but also in nature (e.g. earthquakes). Some recent phase-field simulations and experiments have evidenced that the bifurcation from propagating a planar to segmented crack
front is strongly subcritical and that facet coarsening is a self-similar process driven by a
spatial period-doubling instability of facet arrays.
Front propagation of an autocatalytic reaction
Collaboration : Y.C. Yortsos
We investigate the propagation of an autocatalytic front in porous media. We are particulary interested in the coupling of the flow field and the front propagation (velocity, shape, interface thickness..).
Imbibition of a model painting
M. Leang, L. Pauchard, F. Giorgiutti
Collaboration :L.-T. Lee (LLB)
What are the impacts of the conservation techniques based on the deposition of solvent on a pictorial layer?
Chemical wave fronts in disordered flow
Interface motion are relevant to a wide variety of dynamical processes including population dynamics in biology, chemical reaction, solidification, flame propagation in combustion and marine ecology systems. We investigate the coupling between reaction fronts and disordered flow through a model porous medium. The front is generated by a reaction between two chemical species which produces Fisher waves. These reaction fronts propagate as solitary waves with a constant velocity and a stationary concentration profile. We study the dynamics and morphology of these fronts resulting from the interaction between the flow and the sustained reaction.
Dynamics of adhesive peeling
We study experimentally the physics of the adhesive peeling, focusing
on the relationship between adhesion and the rheology of the glue
at small and large strains as well as on the dynamical
instability, called "stick-slip", which develops in certain
ranges of peeling velocity.
Crack patterns in paintings
The large variety of craquelures reveal some characteristics of the pictorial layer. Moreover studying the stability of a crack network is essential in the domain of heritage conservation. The formation of a crack network is investigated using model systems in a multi-layered geometry.
Stability of a coating submitted to cycling mechanical stresses
How does a crack network evolve under the effect of a cycling mechanical stress? We consider the case of a nanospring coating.
Movement of bacteria in a porous medium
We study the transport of E-coli bacteria in a microfluidic cell (height 100 mu / width 500 mu)
containing obstacles (white circles).
The colored lines show the trajectories of the bacteria transported by a fluid flowing
at 70 microns / second.
The insert illustrates the fluid-bacteria coupling:
we see a bacteria (yellow line) that flows along the surface of grains and moves upstream.
Mechanical stresses induced by drying
How to determine the mechanical stress field leading to fracture during drying of a suspension?
We show using beam deflection experiments, that (i) poroelasticity theory predicts them accurately and that (ii) the setup allows for the identification of some poroelastic constants.