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2 International Journal of Applied Mechanics and Engineering

2 2003

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Squeeze flow of concentrated suspensions of spheres in Newtonian or shear-thinning fluids

Collomb J., Chaari F., Chaouche M.

International Journal of Applied Mechanics and Engineering

2003

Vol. 8, no spec.

219-224

The squeeze flow behaviour of concentrated suspensions of spheres in both Newtonian and shear thinning fluids is investigated experimentally. Analysing the evolution of the squeeze force as a function of time for different controlled velocities, the suspension is found to present two main flow regimes. The first regime is characterized by the situation in which the force decreases when the velocity decreases, which is expected and corresponds to a power-law fluid flow of the suspension. In the second regime the force increases when the velocity decreases which is an indication of solvent filtration through the particle skeleton that behaves then as a quasi-rigid porous media. It is found that the transition between the two regimes is a result of a competition between the viscous shear forces due the flow of the suspension and the damping force caused by the filtration of the fluid through the porous media made up by the particles. It is shown that the addition of a small amount (1000ppm) of a polymer (Xanthan) to the solvent significantly decreases the squeeze velocity for which we have fluid filtration.

Rheo-optical characterisation of linear low density polyethylene crystallization under shear

Chaari F., Chaouche M., Benyahia l., Tassin J. F.

International Journal of Applied Mechanics and Engineering

2003

Vol. 8, no spec.

213-218

Metallocene linear low density polyethylene (mLLDPE) crystallization under shear flow at controlled shear rates and above its crystallization temperature was investigated experimentally. The evolution of the material optical properties (turbidity, birefringence and dichroism) was monitored following a temperature jump from the melting point to a final crystallization temperature . These properties are discussed in terms of the evolution of the polymer semi-crystalline microstructure. In light of the optical properties evolution, the crystallization process can be split into three regimes (i) incubation phase in which small (compared to the light wavelength) crystalline nuclei spread over the medium, (ii) isotropic crystallite growth phase and (iii) anisotropic crystallite growth phase.