Liquid jet impact damage on zinc sulphide

Zinc sulphide is an important infra-red transparent window material. When used in forward-facing aircraft components, these windows can be damaged by the impact of rain drops. The drop impact is simulated using a high-velocity jet technique and the resulting damage is described quantitatively and qualitatively for impact velocities up to 600 m sec^–1. For the 0.8 mm jets used, which simulate 4 mm diameter drop impacts, no loss of strength was observed for impacts at or below 125 m sec^–1. The calculated threshold velocity for a 2 mm drop impact of 175±5 m sec^–1 agrees well with results obtained on whirling-arm installations. Visual examination of the impact damage emphasized the importance of careful specimen preparation.