Elucidating Damage Evolution in HTPB-Based Composite Propellants under Varying Displacement Rates and Temperatures using Dual-Surface 2D-DIC

This study investigates the mechanical behaviour and damage mechanisms of HTPB-based composite solid propellants (CSPs) across varying temperatures − 40 , − 10 , and 55 ∘ C ) and displacement rates (1, 50, and 1000 mm/min) under uniaxial tensile loading. Full-field deformation and strain fields are measured using a dual-surface 2D-DIC setup, enabling enhanced measurement of Poisson’s ratio and dilatation. Results show that both temperature and displacement rate significantly influence the mechanical responses of HTPB-based CSPs. The failure stress, failure strain, and tensile modulus increased with increasing displacement rate. A reduction in temperature from atmospheric conditions led to higher failure stress and tensile modulus but a decrease in failure strain. Observations indicate that Poisson’s ratio is initially close to 0.5 but decreases nonlinearly with increasing longitudinal strain, attributed to the formation and growth of vacuoles around particles resulting in the reduction of lateral deformation. The dilatation response of HTPB-based CSPs is characterized by three distinct regions associated with void initiation, growth, and coalescence, and low-temperature conditions lead to an earlier onset of mean dewetting strain and a higher slope of the dilatation curve. Fractography and elemental mapping were conducted on the fractured surfaces to examine patterns and features on the broken surfaces and to understand the causes and mechanisms of failure. With decreasing temperature, solid-particle fracture becomes visible, along with interfacial debonding, while no qualitative change in the fracture mechanism is observed with variation in displacement rate.