A device for studying elementary plasticity fluctuations in granular media

In this manuscript, we describe a scientific device specifically designed for the study of the plasticity fluctuations preceding the fracture of granular media. Biaxial tests on model granular media are performed using a commercial uniaxial loading system. Strain field fluctuations are measured using a method based on the interference of coherent light scattered by the sample. We show that such a device enables discrete plasticity events to be unambiguously evidenced. Moreover, those discrete plasticity fluctuations depend only on the imposed strain, and not on the strain rate

A relationship between non-exponential stress relaxation and delayed elasticity in the viscoelastic process in amorphous solids: Illustration on a chalcogenide glass

International audienceInorganic glasses are viscoelastic materials since they exhibit, below as well as above their glass transition temperature, a viscoelas-tic deformation under stress, which can be decomposed into a sum of an elastic part, an inelastic (or viscous) part and a delayed elastic part. The delayed elastic part is responsible for the non-linear primary creep stage observed during creep tests. During a stress relaxation test, the strain, imposed, is initially fully elastic, but is transformed, as the stress relaxes, into an inelastic and a delayed elastic strains. For linear viscoelastic materials, if the stress relaxation function can be fitted by a stretched exponential function, the evolution of each part of the strain can be predicted using the Boltzmann superposition principle. We develop here the equations of these evolutions, and we illustrate their accuracy by comparing them with experimental evolutions measured on GeSe 9 glass fibers. We illustrate also, by simple equations, the relationship between any kind of relaxation function based on additive contribution of different relaxation processes and the delayed elastic contribution to stress relaxation: the delayed elasticity is directly correlated to the dispersion of relaxations times of the processes involved during relaxation

Dynamical Coupling between Connected Foam Films: Interface Transfer across the Menisci

International audienceThe highly confined flow of the liquid phase, trapped between the gas bubbles, is at the origin of the large effective viscosity of the liquid foams. Despite the industrial relevance of this complex fluid, the foam viscosity remains difficult to predict because of the lack of flow characterization at the bubble scale. Using an original deformable frame, we provide the first experimental evidence of the interface transfer between a compressed film (or a stretched film) and its first neighbor, across their common meniscus. We measure this transfer velocity, which is a key boundary condition for local flows in foams. We also show the dramatic film thickness variation induced by this interface transfer, which may play an important role in the film thickness distribution of a 3D foam sample