Prediction and Comparison of Shelf Life of Solid Rocket Propellants Using Arrhenius and Berthelot Equations

Abstract

AbstractThe Arrhenius equation and the Berthelot equation for the prediction of shelf life of composite propellant formulations are compared. The elongation has a measurable variation with time and is taken as the fastest degrading parameter for HTPB/AP/Al based composite solid rocket propellants. An HTPB based aluminized composite propellant with 85 % solid loading and an initial elongation of 63.24 % is prepared. It is kept at an elevated temperature of 60 °C to achieve a higher rate of degradation for a prolonged time period (1 year). The elongation is monitored at regular intervals using JANNAF class C dog bone specimen in uni‐axial tensile mode. A reduction of the elongation to less than 50 % is taken as the end‐of‐shelf life of the propellant. The shelf life of the propellant is calculated to be 1.2 years at 60 °C. For the extrapolation of the shelf life at 60 °C to the shelf life at 27 °C, the results of both the Arrhenius equation and the Berthelot equation are compared. The activation energy (E) in the Arrhenius equation is obtained as 72.8 kJ mol−1 and the 10 °C reaction rate rise factor (γ10) is found to be 2.4. This comparison is independent of the propellant formulation and other researchers have reported a similar range of values for these parameters. The shelf life of this propellant formulation at 27 °C is conservatively predicted to be 20 years using both equations. In addition to estimation of shelf life by both equations using elongation as control parameter, this paper gives scaling curves, which are valid universally for predicting shelf life at 27 °C from data of shelf life at 60 °C. The use of scaling curves is independent of properties, propellant formulation and degradation mechanism considered for analysis.