Monitoring of Aging of Solid-Rocket-Motor HTPB Propellant Grains Using an Electromechanical Impedance Method

It is of great significance to monitor the aging state and evaluate the useful life of stored solid-rocket-motor (SRM) propellant grains. In this work, the aging state of hydroxyl terminated polybutadiene (HTPB) propellant grains was studied based on the electromechanical impedance (EMI) method. The relationship between the complex modulus and the mechanical impedance of viscoelastic material was derived. The finite element analysis of the structure with different moduli was carried out. The results show that the peak value of electromechanical impedance increases with an increase of propellant modulus. This report focuses on experimental research on monitoring the aging of cylindrical SRMs based on the EMI method. It is found that the peak of electromechanical impedance spectrum increases with aging time, while the peak frequency decreases slightly. As an aging damage variable, the root mean squared error (RMSD) of electromechanical impedance increases with aging time, and its growth rate is large at first, then decreases, and finally increases. Finally, a tensile test of aging propellant specimens was carried out, and the results show that the rate of change (ROC) of the modulus can be fit by a linear relationship to the RMSD of the electromechanical impedance.