High-velocity, small-particle impact erosion of sapphire windows

Recent wind tunnel tests have been used to establish baseline characteristics of the effect of small particle impacts on two sapphire window plates. These two window plates have been exposed to wind tunnel flowfields of approximately Mach 10 at a simulated altitude of 50,000 feet. Test conditions indicate a free stream velocity, of approximately 4800 ft/sec. Within the wind tunnel flowfield, small particles were carried along and have appeared as impact sites on the exposed surface of each window plate. Examination of the impacted sites indicate that the particles were composed of Deirin (a hard acetal homo-polymer) or stainless steel, both of which resulted in small but measurable damage to each window plate. Characterization of the plate surface appearance and impact damage was conducted at two locations: 1) the University of Alabama in Huntsville, (UAH), Optical Measurements Laboratory (OML) and, 2) Oak Ridge National Laboratories (ORNL), Optical Component Characterization Laboratory (OCCL).