Synergistic effects of rain and sand erosion

Infrared transmitting materials are often used by the aerospace industry to make “windows” over guidance systems. These materials are typically weak and brittle and during flight, impact with raindrops and sand, or dust particles, may cause serious optical degradation. These problems have been extensively researched individually, but very little work has been carried out into to the combined effects of liquid impact followed by solid impact or vice versa. The effect of pre-impact by liquid drops followed by sand erosion of FLIR ZnS (Forward Looking InfraRed zinc sulphide) was investigated using optical microscopy, transmission loss and residual strength measurements of samples. The results show that pre-impact of ZnS with liquid drops followed by impact by sand particles can enhance erosion and the paper quantifies this for a range of exposure conditions.