Studies of Rain Erosion Mechanisms in a Range of IR Transmitting Ceramics - Including Coated Samples.

This report starts by reviewing what is known about the rainfield an aircraft or missile flies through. It then looks at some of the methods available to simulate it. Although not a perfect reproduction of a high velocity raindrop impact, the waterjet techniques, developed in the Cavendish Laboratory, Cambridge, are found to be close enough simulations of the real environment to be useful research tools. A standard method of operation for both SIJA Single Impact Jet Apparatus and MIJA Multiple Impact Jet Apparatus, however is urgently needed. The report therefore reanalyses the theory behind the damage threshold velocity DTV and the possible ways of evaluating it. A standard method of data presentation is defined from this analysis and reapplied to the results from MIJA. The last half of the report is therefore a catalogue of the infrared material rain erosion resistance properties evaluated by us over the last two years and presented according to this standard. Data are given on Zns, Ge, sapphire, spinel, CaLa2S4, BP, CVD diamond, natural diamond, silicon magnesium fluoride and various coated systems.