Active Sensing for Monitoring the Properties of Solid Rocket Motor Propellant Grains

摘要

Aging induced changes in the mechanical properties of solid propellant can lead to defects, such as cracks and grain-liner separations, that limit the service lifetime of solid rocket motors. The use of embedded sensors is one approach that is being explored by various researchers to augment legacy inspection and prediction methods. We present herein an active sensing technique that is particularly suited for monitoring the properties of solid propellant, as it does not introduce electrical wires into the motor. Based on the use of magnetic induction for excitation and an optical fiber Bragg grating sensor to measure deformation, the method can be used to characterize the properties of a material with which it is in contact. In this paper, we first present proof-of-principal experiments demonstrating the utility of the method in characterizing the visco-elastic properties of an adhesive, and in following changes in viscosity of an epoxy resin during cure. We next apply the method to solid propellant, and present data demonstrating that the method can be used to measure a deflection-load curve of an aluminized HTPB propellant. In addition, we also show that the observed strain rate sensitivity matches that found in the literature and that the method had more than adequate resolution to observe the expected changes in material properties due to aging.