Modelling dynamic and irreversible powder compaction

Abstract

International audienceA multiphase hyperbolic model for dynamic and irreversible powder compactionis built. Four important points have to be addressed in this case. The first one isrelated to the irreversible character of powder compaction. When a granular media issubjected to a loading–unloading cycle, the final volume is lower than the initial one.To deal with this hysteresis phenomenon, a multiphase model with relaxation is built.During loading, mechanical equilibrium is assumed corresponding to stiff mechanicalrelaxation, while during unloading non-equilibrium mechanical transformation isassumed. Consequently, the sound speed of the limit models are very different duringloading and unloading. These differences in acoustic properties are responsible forirreversibility in the compaction process. The second point is related to dynamiceffects, where pressure and shock waves play an important role. Wave dynamics isguaranteed by the hyperbolic character of the equations. Phase compressibility aswell as configuration energy are taken into account. The third point is related tomulti-dimensional situations that involve material interfaces. Indeed, most processeswith powder compaction entailfree surfaces.Consequently, the model should be ableto solve interfaces separating pure fluids and granular mixtures. Finally, the fourthpoint is related to gas permeation that may play an important role in some specificpowder compaction situations. This poses the difficult question of multiple-velocitydescription. These four points are considered in a unique model fitting the frameof multiphase theory of diffuse interfaces . The ability of the model to deal with thesevarious effects is validated on basic situations, where each phenomenon is consideredseparately. Except for the material EOS (hydrodynamic and granular pressures andenergies), which are determined on the basis of separate experiments found in theliterature, the model is free of adjustable parameter

Modelling compressible dense and dilute two-phase flows

“…Moreover, it can be expected that the dispersive nature of a compression wave from the BN and the new models is different. Intergranular stress (Bdzil et al, 1999, Saurel et al, 2010) has been considered as a possible effect to improve the computations of Figure 12. These effects have been added to the present formulation and coded, but no noticeable improvement appeared.…”

A Cell-Centered Multiphase ALE Scheme With Structural Coupling

“…This added stress results in non-equilibrium between the gas and particle pressures. Many researchers have discussed the importance of compaction on multiphase dynamics [18,[69][70][71].…”

Modelling cavitating flow around underwater missiles

“…The same equations are solved everywhere with a unique numerical scheme. Extension to extra physics is possible: capillary effects (Perigaud and Saurel, 2005), mass transfer , combustion and detonations (Petitpas et al, 2009b), elastic solid -fluid interfaces (Favrie et al, 2009), granular materials (Saurel et al, 2010). Dynamic interface creation.…”