A turbulent melt-lubrication model of surface wear in railgun armatures

This paper describes a melt-lubrication model of the liquid film interface in solid-armature railguns that includes the effects of turbulence. The liquid film is modeled as a high-speed Couette flow with viscous heating. The model focuses strictly on mechanical wear and does not include magnetohydrodynamic body forces or Joule heating. The effects of turbulence are incorporated by using Prandtl's mixing-length theory and semiempirical methods. Turbulent viscosity is added to the laminar viscosity for the solution of the momentum equations. Thermal resistance is accounted for at the thermal contact between the melt film and rail. Expressions are obtained for the quantities of film thickness and melt wear rate. Results from the model are compared with experimental data that measured high-speed mechanical wear of 7075 aluminum sliding against ETP copper for face pressures ranging from 45 to 150 MPa in railguns. Although the model reproduces general trends in the data, it predicts melt speeds that are significantly greater than measured; in this regard, a previously published laminar model provides a better fit. However, given the shortcomings of both models, it is quite possible that a purely thermal hydraulic formulation is inadequate to the task of modeling high-speed, high-pressure mechanical wear, and that viscoplastic processes in the slider should be considered next.