Study of porous structure and gas permeation properties of micro-spalled metal driven by shock loading

Shock-induced micro-jets and micro-spalls on metal surfaces and the subsequent mixing with surrounding gas are of interest for a wide range of applications, such as inertial-confinement fusion and armor design. This study interprets the mixing of micro-spalled metal with gas as the permeation of gas into the evolving porous structure created by micro-spalled liquid debris. A technical route is established based on the combination of fluid mechanics in porous media and shock dynamics. The topology of the porous metal is studied through molecular dynamic simulation, which captures the major characters of a micro-spalling process driven by shock loading. Pore-network modeling is applied to convert the porous structure of the micro-spalled metal into an assembly of pores and throats. Accordingly, the main porous characteristics of the micro-spalled metal are described by five nondimensional parameters, including porosity, specific area, coordination number, ratio of pore to throat radius, and tortuosity. In addition, the permeability of the micro-spalled metal, characterizing its gas-transport capacity, is also determined by directly simulating a single-phase flow throughout the pore network. The evolution of both porous structure and permeability of the micro-spalled metal subjected to various shock conditions is systematically analyzed. Moreover, the dependence of permeability on porous structure is clarified via a sensitivity analysis, which builds a cross-scale connection between the microvoid morphology and gas permeation at continuum level. The results and conclusions of this study could serve as useful references for both the characterization and design of porous samples in future experimental studies on micro-spalled metal-gas mixing.