The shear resistance of glass beads with wetting liquid incorporated (polyethylene glycol of molecular weight of 400 g/mol) is experimentally and theoretically investigated in a large range of both liquid content (from 0.007 % to 20 % in volume) and normal loading, in a steady state flowing situation. It is observed that the behaviour is not purely frictional (shear stress proportional to the normal stress) except for the lowest liquid content (up to 0.1 %) for which it is observed that the friction coefficient of wet granular material is slightly higher than the dry mate rial. At high normal loading, an apparent cohesion is observed and the behaviour may be interpreted as frictional, with the same friction coefficient plus an additional normal stress due to the capillary forces between the beads. At low normal loading, the apparent cohesion is less and may be qualitatively explained by the diminution of bro ken capillary contacts during shearing when the porosity of the granular bed increases. This result is corroborated by a theoretical approach estimating the capillary forces in play.

The size of particle is a relevant parameter in the study of the granular material behaviour. For wet granular materials, it affects the capillary force and the number of liquid bridges. We present quantitative and qualitative investigations of the effect of the particle size on the steady-state shear behaviour of partially wet granular material. Two sizes of glass beads have been used: 12-40 μm and 70-110 μm in diameter and the shear behaviour was studied using an annular shear cell. The results show different regimes of the shear-normal stresses relationship depending on the particle size, with a general increase of the magnitude of the shear stress for a decrease in the particle size. Most studies of wet granular material behaviour have focused on the pendular state of saturation with liquid bridge formed between particles. In this study, the states of saturation are explored going up to completely filling the space between beads of 70-110 μm. Different regimes are identified depending on the liquid fraction and the applied normal stress. A theoretical approach was used to estimate the tensile strength for the different states of saturation. An agreement between both experimental and theoretical data was observed and discussed.

The current concerns of sustainable development make the biobased polymers the object of many studies. Chitosan is a biobased, biocompatible and biodegradable polysaccharide with antibacterial and cytocompatible properties. In this study, we aimed to generate chitosan particles with two processes using CO 2 under pressure, in order to decrease the use of organic solvent and to obtain nanoparticles.The first is a supercritical anti-solvent process: CO 2 acts as an anti-solvent toward an acetic acid aqueous solution of dissolved chitosan in which ethanol was added to enhance the anti-solvent effect. The reciprocal miscibility of CO 2 with the solvents induces the reduction of their solvating power, leading to supersaturation at the capillary outlet and causing the crystallization of the particles.This process led to the generation of more or less agglomerated chitosan nanoparticles with an individual average size of 378 nm.In the second process, the pressurized CO 2 is dissolved in water to lower the pH. This in turn allows the chitosan to be dissolved and the resulting solution is sprayed, thanks to the pressurized CO 2 , into a hot air stream. This new process allowed the generation of dried chitosan nanoparticles with a median size of 390 nm.

The macroscopic behaviour of cohesive granular material in the FT4 shear tester is studied using the discrete element method (DEM). The shear test is simulated faithfully to the experimental procedure (filling, compaction, pre-shearing and shearing). The angle of internal friction and the apparent bulk cohesion are the macroscopic properties analysed as a result of the variation of the microscopic parameters: the sliding friction coefficient and the adhesive surface energy. The simplified JKR model was used to account for the cohesive contact between spheres. The results of the shear test show that the adhesive forces influence the dilatancy of the granular bed and the incipient failure point. In general, the shear stress increases with the adhesive energy. The sliding friction coefficient and the adhesive energy affect the Yield locus and therefore the angle of internal friction and the apparent cohesion. Two correlations were established between the angle of internal friction and sliding friction coefficient and between cohesion and adhesive energy. The effect of the initial consolidation on the shear test results is also discussed.

From 3D X‐ray computed images and using iMorph software, two graphs are derived from the solid and fluid networks of open‐cell foams. The graphs are constructed based on the foam structure, which satisfies Plateau's laws. We have defined two types of graphs: 1) the representative graphs of solid and fluid phase networks: The graph of the solid phase is, intuitively, constructed by associating vertices to nodes and edges to struts. For the graph of the fluid phase, vertices are associated with porous cells and edges to throats at the interface of two cells. 2) the coupling graph is related to transfer phenomena between the fluid and solid phases: It is constructed by associating effective edges, which connect a vertex of the solid graph with an adjacent vertex of the fluid graph. The graphs lead to discrete element representation (topology preserving) with geometrical information of the foam structure. Physical variables can be attributed to the discrete objects called cell complex: internal energy to finite volume, heat flux to surface/interface, driving force to edge, and temperature to node. This alternative modeling approach based on graphs is promising for heterogeneous systems with large sizes as it reduces the computational complexity of conventional finite element meshing.

In this paper we show the discrete modeling of the heat equation on an open cell metallic foam, exploiting its geometric structure. The topology of the material is described using the incidence matrices of a so called k-complex. Together with the discrete constitutive equations, a finite-dimensional model in port-Hamiltonian form is found.

No abstract

The flow behaviour of a granular media is due to their weight, frictional contact forces between them, and external forces exerted by the walls. If their size is lower than 50 microns, the Van-der-Waals forces between them may also influence their flowability. When adding some wetting liquid, we introduce attractive forces between the particles, whose order of magnitude may overcome the particle weight and Vd-W interactions. This leads to a cohesive behaviour. The shear stress to start the flow is greater than in the dry case but the steady-state flow is also perturbed by the presence of liquid bridges. This later phenomenon has been recently quantitatively studied for 70-110 μm glass beads with a non-volatile liquid, with experimental results for different normal stresses (up to 12 kPa) and liquid content (up to 20 % in volume). These results have been compared to a heuristic model, based on the model for capillary bridges and the simplest hypothesis for the granular bed texture depending on the stresses applied. We extend this study with new results concerning smaller glass beads 12-40 μm in diameter and larger liquid fraction for 70-110 μm glass beads using experimental and theoretical approaches.