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 a nd brittle and during flight, impact with raindrops and sand, or dust parti cles, may cause serious optical degradation. These problems have been exten sively researched individually, but very little work has been carried out i nto to the combined effects of liquid impact followed by solid impact or vi ce versa. The effect of pre-impact by liquid drops followed by sand erosion of FLIR ZnS (Forward Looking InfraRed zinc sulphide) was investigated usin g optical microscopy, transmission loss and residual strength measurements of samples. The results show that pre-impact of ZnS with liquid drops follo wed by impact by sand particles can enhance erosion and the paper quantifie s this for a range of exposure conditions. (C) 2000 Elsevier Science S.A. A ll rights reserved.