Effect of Number of Impacts on Erosion of Polycrystalline MgF2 in the Elastic‐Plastic Response Regime

Abstract

Targets of MgF 2 were subjected to impact conditions from single‐particle to 10 10 impacts, simulating a natural dust environment (quartz particles) in the subsonic velocity regime. The functional relation of erosion to particle size and velocity predicted by the elastic‐plastic impact model is followed for this system. Impact damage is characterized by a heavily deformed contact area between particle and target, with radial cracks propagating outward from the contact zone and with subsurface lateral cracks propagating outward on planes nearly parallel to the surface. The laterally cracked regions are responsible for most of the erosion loss. This type of damage is also consistent with the elastic‐plastic model. For a given particle size‐velocity test condition, the volume of material removed for a single impact can vary over three orders of magnitude. This large variation is due primarily to differences in particle orientation during impact which results from the irregular shape of the angular natural quartz particles. For these conditions there is no significant difference between the amount of material removed by the first impact and by subsequent impacts on the damage area of the initial impact. The results imply that there is no incubation period or damage‐enhancement effect for erosion in the elastic‐plastic impact response regime.