Microstructure and mechanical property analysis of HTPB adhesive under thermal aging based on molecular dynamic simulations

Abstract

The solidified network structure formed by the addition reaction of hydroxyl-terminated polybutadiene and toluene diisocyanate, under the action of long-term internal and external factors, changes over time in its system structure. The resulting mechanical properties have a great impact on the reliability and structural integrity of solid propellants. In this study, an all-atom molecular dynamics method was used to study the sensitivity of the adhesive to temperature and loading rate at different aging stages, as well as the differences in the damage and fracture process under large deformation. The simulation results showed that degradation chain scission weakened the system modulus and strengthened the deformation ability, making nonbonded energy the main storage form of strain energy. Oxidative crosslinking produced an opposite modulus and deformation effects, with the storage form of strain energy changed from nonbonded energy to bond and angular energy during the loading process. In addition, increased temperature increased the distance between molecules and intensified molecular motion, causing the system strain to expand globally, reducing the stress peak, and enhancing deformation ability. The increase in loading rate increased local strain, causing some covalent bonds to break, while viscosity replaced elasticity as the main mechanical property, causing the stress-strain curve to shift to the upper left.