Surface erosion rates of graphite from high-speed solid particle impacts

Aerospace vehicles are highly susceptible to damage from particle-laden flows; such encounters can lead to high-speed impacts from airborne particles such as dust, sand, and other particulate matter. We have characterized the rate of graphite surface erosion from the impact of monodisperse ferrous sulfate particles ranging in diameter (1.8 $\mu$m, 3.7 $\mu$m, and 6.1 $\mu$m) at different impact angles (90°, 75° and 45°) and variable impact velocities ($340-520m{s}^{-1}$). Measurements were carried out by generating particles at known number densities, and accelerating them via a converging–diverging nozzle to impact on graphite substrates, positioned at variable angles relative to the flow direction. Laser Doppler velocimetry was used to characterize particle velocities prior to impact. Measurements reveal that impact angle had a minimal effect on erosion rate. The eroded volume increased with total kinetic energy of the impacting particles, integrating over the entire experimental time. We develop empirical expressions linking eroded volume, erosion rate, and erosion propagation velocity to the velocity and size of the particles. The increase in surface roughness as erosion progressed is also quantified. In total, measurements yield an erosion rate model for graphite which may be used to predict rates of surface removal for graphite surfaces exposed to solid particles impacting at transonic to supersonic speeds.