The effect of surface indentations on gouging in railguns

• Aluminum railgun armatures were launched against copper rails up to 2.1 km/s.
• All investigated gouges started at microscopic or macroscopic defects.
• Macroscopic indentations do not affect the observed gouging threshold velocity.
• Gouging of copper rails can evolve gradually from galling damage.

Hypervelocity gouging occurs in high speed sliding systems such as rocket sled test tracks, light gas guns, and electromagnetic railguns. Gouging takes the form of teardrop-shaped craters on the rail surface, and occurs above a threshold speed which is dependent on the slider and rail materials. In this study, gouging of aluminum railgun armatures on flat and indented copper rails was performed to examine the effect of macroscopic surface defects on gouge onset velocity and morphology. Both galling and gouge craters were shown to initiate at existing macroscopic and microscopic defects. Macroscopically flat rail surfaces provide no practical advantage over indented surfaces insofar as gouge onset velocity is concerned. However, the shape of the resulting gouge craters can be significantly affected.