Effect of pre-strain during ageing on the maximum elongation of composite solid propellants and its modelling

In this study, the effects of accelerated ageing under pre-strain on the maximum elongation of composite solid propellants were investigated. The maximum elongation of aged composite solid propellants at different ageing times, temperatures and pre-strains were determined. An ageing model was developed to analyse the effects of pre-strain and temperature on model parameters. Results show that pre-strain can increase the maximum elongation significantly during accelerated ageing, and the increasing amplitude exhibits a linear relationship with ageing temperature and pre-strain. The physical tension effect caused by pre-strain is a cumulative effect of the stress on samples and shows obvious characteristics of stress relaxation. The relaxation time is independent of pre-strain and exhibits an exponential relationship with ageing temperature. The effect of pre-strain on chemical ageing is related to a critical temperature TC. For the HTPB propellant investigated in this study, the TC is between 65 °C and 70 °C. When the ageing temperature is below TC, pre-strains have almost no effect on the ageing rate constant for maximum elongation kε; however, at temperatures above TC, they may promote chain scission reactions and decrease kε.