Granular Matter

In the present work, the squeeze flow geometry is used to investigate the properties of concentrated suspensions. The suspensions consist on hard glass spherical particles dispersed in a viscoplastic fluid. With such a material, following the solid volume fraction, the material rheological behaviour ranges from purely viscoplastic fluid to granular media. During the squeezing action, the material structure evolves with energy variation due to particle displacement and interaction. The goal of our study is to identify the effect of energy evolution on the flow properties of suspensions and detect granular contact evolution. The proposed study consists on an energy approach based on the analysis of the global squeeze force and sample height with time. The squeeze force is decomposed in a combination of an average force component and a fluctuating one. This local fluctuating component is investigated from Fourier analysis as a function of solid volume fraction and compression velocity. Results show the evolution of the energy distribution during compression and allow the flow regime modification to be evaluated.

This paper describes an experimental study of failure and softening behaviour in dense Toyoura sand. A true triaxial apparatus equipped with three pairs of rigid loading platens is used to test sand sample under three-dimensional stress condition. The testing results demonstrate that the rigid boundary around the sand samples cannot prevent formation of shear localization. Shear localization are observed to emerge in the hardening or the softening regime in the loading depending on the magnitude of intermediate principal stress. Uniform deformation for the whole strain range is obtained only in triaxial compression tests. The peak stress state obtained from tests of sand samples of the same initial density can be described with good approximation by the Matsuoka–Nakai criterion.

With the assumption of a linear–dashpot interaction force, the coefficient of restitution, $$\varepsilon_d^0(k, \gamma)$$ , can be computed as a function of the elastic and dissipative material constants, k and γ by integrating Newton’s equation of motion for an isolated pair of colliding particles. If we require further that the particles interact exclusively repulsive, which is a common assumption in granular systems, we obtain an expression $$\varepsilon_d(k, \gamma)$$ which differs even qualitatively from the known result $$\varepsilon_d^0(k, \gamma)$$ . The expression $$\varepsilon_d(k, \gamma)$$ allows to relate Molecular Dynamics simulations to event-driven Molecular Dynamics for a widely used collision model.

In the frame of a well established lattice gas model for granular compaction, we investigate the high intensity tapping regime where a pile expands significantly during external excitation. We find that this model shows the same general trends as more sophisticated models based on molecular dynamic type simulations. In particular, a minimum in packing fraction as a function of tapping strength is observed in the reversible branch of an annealed tapping protocol.

A novel method, designated as the Rotation of Principal Axes Method (RPAM), capable of examining the double-shearing type kinematic models for granular materials is presented herein. A planar velocity field, which is proposed to represent a continuous rotation of principal strain rate axes, is applied to each model to analyse the rotation of principal stress axes. The proposed approach was proven to show main features of the double-shearing model, the double-sliding free-rotating model, and the revised double-shearing model, in a simple way interesting to geo-researchers. Furthermore, the RPAM was efficient in investigating the choice of a Cosserat rotation rate in kinematic theories and determining a key model parameter in the revised double-shearing model.

The behaviour of titanium white (TiO2) particles with particle size smaller than 45 μm during the modification with nanoparticles (5–50 nm) of hydrophobic silica powder on the vibrating screen and following examination of the newly formed particle clusters is described. Using the vibrating screen aerated in certain places using loudspeaker the subsequent fluidization of the titania particles via simultaneous modification with silica was achieved. The particles of titania are being less cohesively bounded, the van der Walls are weaker and flowability of the system is radically improved. By the targeted fluidization of regions on the screen, was possible to experiment with resulting shapes of particle clusters from the nanoparticles of silica and titanium white in this research. Resulting structure can appear at approximately 2 s of 222.32 Hz excitation using loudspeaker acoustic waves. Methyl groups of hydrophobic nanoparticles of silica can be source for advanced surface applications.

It is shown that the partial pressure, i.e. the contribution of contacts with a given force to the total average pressure, in a granular packing in quasistatic flow increases linearly from zero with the force level both in two and three dimensions. It reaches its maximum for the average force and decays for larger forces. We found that a well-defined sub-texture, composed of the contacts carrying a force below the average force, does not contribute to the shear stress, so that its contribution to the average pressure is mechanically similar to a hydrostatic pressure.