Global dynamics model for screw extrusion of single-base propellants incorporating granular-to-viscous transition

Single-screw extrusion of single-base propellants constitutes a critical forming process wherein temperature constraints imposed by energetic properties necessitate exclusive reliance on mechanical plasticization. Accurately describing the extrusion dynamics of single-base propellants has long presented a challenge due to the lack of precise mathematical models. Integrating friction drag theory with hydrodynamic principles, this study establishes a multizone coupled dynamics model for screw extrusion. This model characterizes the complex physical processes—including material deformation, shear, compaction, and transport—while elucidating the dynamic transition from a loose granular state to viscous flow. By incorporating the dynamic variations in material viscous and elastic effects under screw mechanical action and employing the finite difference method and the particle swarm optimization algorithm, the model efficiently simulates distributions of key parameters such as velocity, temperature, pressure, shear rate, and viscosity. Simulation results demonstrate excellent agreement with Tadmor's experimental results, validating the model's predictive capability. Further analysis reveals that increasing the screw speed significantly enhances barrel pressure, heating rate, and average material temperature, whereas raising barrel temperature improves material fluidity and reduces barrel pressure.