The use of the change of elongation for comparison of the shelf life of composite solid propellants in the air and nitrogen atmospheres

This work uses the change of elongation with temperature in a composite solid propellant to assess its shelf life for the air and nitrogen atmospheres applying two methods for the temperature parameterization of the measured quantity, the Arrhenius and Berthelot equation. The samples of the composite propellant contain aluminum (Al), ammonium perchlorate (AP), and hydroxyl‐terminated polybutadiene (HTPB) as well as curing agent toluene diisocyanate (TDI), which were aged at three temperatures 323.15, 333.15, and 343.15 K during 15, 30, 60, 90, and 120 days. Stress‐strain curves for the samples are investigated to study the effects of the atmospheres of air and nitrogen on the samples. The ratio of the changes in percentage elongation (ϵ) to the initial value of percentage elongation (ϵr) is the degradation criterion, which is defined as a reduction of the elongation to less than 50 %. The calculated activation energy by the Arrhenius method is 80.48 kJ mol−1 for the air atmosphere. The shelf life of the samples were found to be 7.912 and 7.906 years (air atmosphere) to 23.38 and 23.36 years (nitrogen atmosphere) as well as Arrhenius and Berthelot methods, respectively.