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Rhéologie de suspensions concentrées de matériaux énergétiques recyclables – Modélisation du temps de coulée

Abstract : In order to limit the handling of pyrotechnical products presenting a risk with respect to the mechanical and thermal shocks, new energetic formulations have emerged. Among these Extremely Insensitive Detonating Substances, the industrial partner Nexter Munitions implements a formulation labeled XF13333 which has the property of being recyclable.

Before being in solid state, XF13333 explosives are in the form of suspensions whose solid volume fraction is about 55%. The flow ability of these pastes is governed by the rheology of concentrated suspensions. The method of preparation used by the industrial partner being the melt-cat process, the aim of the work presented in this manuscript is to propose a model that can predict the time required for an energetic concentrated suspension to flow by gravity from an agitated mixing reactor to an initially empty shell body.

The study of the influence of the solid volume fraction on the rheological behaviour of model inert suspensions has been performed. Two grains sizes scales have been considered: micrometric and nanometric. Depending on the particles size, pastes adopt different rheological behaviours: the suspension containing micrometric particles adopts a Newtonian behaviour, while the suspension containing nanoscaled particles evolves from a Newtonian to a yield stress fluid (Bingham or Herschel-Bulkley) behaviour.

Then, we investigated the influence of the state of organization of the solid phase, which can be described by the maximum volume fraction of solid. We have studied the influence of this parameter on the rheological behaviour of suspensions. Given the strong behavioural analogy between a paste of explosives and cement, we took benefit from researches conducted over past years in civil engineering. In particular, we used the De Larrard model to calculate the maximum volume fraction of solid from the size distribution of the grains of the mixture.

To characterize the rheology of XF13333suspensions, the use of a Couette rheometer is not appropriate because the particle sedimentation and the destabilization of the emulsion – which constitutes the suspending fluid – make the suspension inhomogenous. To maintain its usage function (i.e. homogeneous), we developed an unconventional rheometer and applied the Couette analogy. It emerged from this experimental study that the suspensions are Ostwal fluids.

The modelling of the flow time for XF13333 suspensions in industrial configuration is based on the Quemada viscosity relationship. The theoretical values have been compared with the experimental values of emptying time of a certain amount of XF13333 suspensions. It appears that the proposed flow time model matches the reality correctly.
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Submitted on : Tuesday, April 29, 2008 - 3:00:08 PM
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  • HAL Id : tel-00276364, version 1

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Jean-Philippe Guillemin. Rhéologie de suspensions concentrées de matériaux énergétiques recyclables – Modélisation du temps de coulée. Sciences de l'ingénieur [physics]. Ecole Nationale Supérieure des Mines de Saint-Etienne, 2008. Français. ⟨tel-00276364⟩

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