Quantitative Propellant Diagnostics with Ultrasonic Guided Waves

ABSTRACT: Solid rocket motor propellant degrades over time. Currently, health determinations are either destructive or involve expensive and time-consuming off-site tomographic techniques. In Phase I, Luna proposed a nondestructive, in-situ Ageing and Defect Monitor suitable for use in depot or field. In Phase I, Luna has shown feasibility of an ultrasonic nondestructive depot/field test set for the health of solid rocket motor (SRM) propellant. The link between propellant ageing and ultrasonic properties of the propellant was investigated: formulation differences in samples were distinguished ultrasonically. Using a multilayer aluminum/propellant test artifact, a debond between the aluminum case and propellant was detected. The equations of guided-wave propagation in cylindrical multilayer structures were obtained. In Phase II, these results will be extended to correlation of propellant mechanical properties with propellant acoustic properties in motor geometry. The measurements will be verified on actual propellant. A demonstration prototype will be designed and built. The results of the Phase II effort will be a field prototype test set that will dramatically reduce the cost and time needed to determine the health and readiness of SRM assets. As a result, the probability of a mission failure due to motor malfunction, or catastrophic motor destruction, will be reduced. BENEFIT: For military, scientific and commercial solid rocket motors, the development of Luna"s Ageing and Defect Monitor will decrease the costs associated with assurance of readiness and reliability. Destructive testing and off-site tomographic testing are expensive and time consuming, and cannot be applied to all assets. Nondestructive testing, however, can be used regularly and on all assets at a lower cost than destructive or invasive methods. Other devices exist that use embedded energetic materials: explosive forming presses, explosive bolts. This technology could be applied to problems in those areas. Other systems of multilayer metal/composite/energy absorptive materials exist both on airframes and military ground vehicles. Luna"s guided-wave interrogation techniques can be applied to these structures as well, in order to find defects during manufacture or after suspected damage in the field. Examples include helicopter rotor fabrication, composite multilayer airframe structures, hull and armored vehicle systems to mitigate secondary blast effects, and similar layered structures. Ageing effects may not be of primary importance in many of these systems, but defect detection may be crucial to correct operation. Nondestructive, nonintrusive evaluation from an exterior surface will find great acceptance in the manufacturing process, and for depot maintenance/evaluation.