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.
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.
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 and structural properties of dried colloidal layers
Drying a colloidal suspension results in the formation of a porous solid layer.
The ability to control fracture and self-organization in these materials
is relevant to many applications such as the sol-gel process,
the design of solar cells, and the drying of paints and lacquers.
Using sound velocity measurements, atomic force microscopy and Vickers indentation,
we characterize the structural and mechanical properties of dry colloidal silica layers
and relate them to parameters such as particle size, porosity and drying rate.
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?
Fingering and effective toughness of highly heterogeneous brittle interfaces
Discover a way to obtain numerically nice flower-shape crack fronts at low energy costs by patterning a brittle interface.
Viscous fingering and flow of active fluid
The situation where one fluid is displaced by a second one is a basic situation found in many applications.
Our investigation focusses on the possible flow changes arising when one of the fluid is active. This is achieved here by using suspensions of various strains of motile bacteria injected in Hele Shaw cell.
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.
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.
Dynamics of the peeling of adhesives
We study experimentally the dynamics of the peeling of adhesives: the link between the adhesion level and
the rheology of the glue at small and large strains as well as the "stick-slip" dynamical instability
observed in certain ranges of peeling velocity. We use micro-textured substrates as tools to explore
the mechanisms of energy dissipation as well as possible solutions for the control of adhesion force.
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.