Studies on mechanical behaviour of nitrile butadiene rubber (NBR) based high-energy composite solid propellants

A comparative thermomechanical study of nitrile butadiene rubber (NBR)-based high-energy composite propellants was conducted to clarify formulation-dependent deformation and damage mechanisms. Two compositions, Type I (78 wt.% solids) and Type II (79 wt.% solids), were examined through uniaxial tensile testing (5–1000 mm·min-¹) at −20, 27, and 55 °C, supported by dynamic mechanical analysis (−80 to 80 °C). Stress–strain behavior exhibited three regimes linear elasticity, de-wetting, and strain hardening governed by binder continuity and filler packing. Type I, with higher binder content, demonstrated superior ductility, sustained strain hardening, broader failure boundary envelope, and matrix-dominated damage across loading conditions. Type II showed increased modulus, greater strain-rate sensitivity, and interface-controlled failure marked by accelerated de-bonding. Time–temperature superposition and cumulative damage modeling quantified rheo-kinetic sensitivity and durability limits. The results define formulation-specific thermomechanical operating envelopes, highlighting the trade-off between stiffness and damage tolerance critical for propellant structural reliability.