Technique for Evaluating the Erosive Properties of Ablative Internal Insulation Materials

A technique for determining the average erosion rate versus Mach number of candidate internal insulation materials was developed for flight motor applications in 12 inch I.D. test firing hardware. The method involved the precision mounting of a mechanical measuring tool within a conical test cartridge fabricated from either a single insulation material or two non-identical materials each of which constituted one half of the test cartridge cone. Comparison of the internal radii measured at nine longitudinal locations and between eight to thirty two azimuths, depending on the regularity of the erosion pattern before and after test firing, permitted calculation of the average erosion rate and Mach number. Systematic criteria were established for identifying erosion anomalies such as the formation of localized ridges and for excluding such anomalies from the calculations. The method is discussed and results presented for several asbestos-free materials developed in-house for the internal motor case insulation in solid propellant rocket motors.