The structural integrity of composite rocket propellants is critical for the reliability of rocket motors, as insufficient integrity can lead to failure or even motor explosion. However, the material properties of such propellants degrade over time. Ageing is typically monitored using tensile testing, a time-consuming and destructive method that requires substantial sample volumes. Consequently, alternative characterisation techniques are sought. One promising approach is dynamic mechanical analysis (DMA), which requires samples that are orders of magnitude smaller than those used for tensile testing. The aim of this study was to establish relationships between strain and elastic modulus (from tensile testing), storage modulus (from DMA), and hardness. Composite propellants based on hydroxyl-terminated polybutadiene, ammonium perchlorate, and aluminium were manufactured, subjected to accelerated ageing at 75–105 °C in an inert atmosphere for up to 190 days, and characterised by tensile testing, DMA, and hardness measurements. For each ageing temperature, the relative change of each property was plotted as a function of time. Empirical expressions linking strain, elastic modulus, storage modulus, and hardness were derived from the Arrhenius equation. These empirical models enable reliable conversion between, for example, storage modulus and strain for lifetime prediction, thereby demonstrating that DMA can serve as a viable alternative or complement to tensile testing.