Impedance Characterization and Validation of Solid Propellant Based on Electro-Mechanical Impedance Method

In order to further study the aging of solid propellants by the Electro-mechanical impedance (EMI) method of surface paste, a one-dimensional electromechanical coupling model based on linear viscoelastic rod structure was constructed. Based on the theory of viscoelastic waves and boundary conditions, a relationship between the complex modulus of solid propellant and its mechanical impedance was established. Numerical calculation and experimental verification of the electromechanical impedance model were carried out. High-temperature thermal accelerated aging experiments and piezoelectric active excitation experiments for HTPB solid propellants were carried out, and according to the admittance spectrum obtained from monitoring, the structural mechanical impedance is extracted and analyzed. The results show that when the piezoelectric ceramic plate is coupled with the propellant structure, it has obvious resonance phenomenon when it moves at high frequency(300kHz, 280kHz). The natural frequency of the structure is higher than the electromechanical coupling resonance frequency. Moreover, The peak value of mechanical impedance spectrum in 200kHz ~ 400kHz and 700kHz ~ 900kHz will decrease with the increase of thermal aging time of solid propellant, and there is a linear relationship between the peak value and thermal aging time. It can be seen that the mechanical properties of the solid propellant can be characterized by the EMI method, by obtaining the mechanical impedance of the solid propellant structure, the aging damage can be monitored. © 2019, Editorial Department of Journal of Propulsion Technology. All right reserved.