Comparison of the uniaxial tensile modulus and dynamic shear storage modulus of a filled hydroxy-terminated polybutadiene and GAP propellant

Abstract

The uniaxial tensile moduli for two filled composite solid propellants, one based on a hydroxy-terminated polybutadiene with an ammonium perchlorate oxidizer and the other on a glycidyl azide polymer with a phase-stabilized ammonium nitrate oxidizer, were measured at various temperatures and over a three decade range of strain rates. Dynamic shear moduli were measured at various strains and temperatures over a three decade range of frequencies. Values of the tensile modulus, ET/3 (assuming Poisson's ratio equals 0.5), were compared with the dynamic storage modulus, G′, for each of the dynamic strain levels investigated. The results demonstrate that it is possible to compare 3G′ measured at different dynamic strains and frequencies with the incremental tangent moduli obtained at corresponding uniaxial strains from constant strain rate tests on specimens with a JANNAF geometry. The comparisons are most favourable when the concave-up region of the stress-strain curve extends only up to approximately 2.0% strain. It was observed that G′ obtained at a dynamic shear strain of 2.0% provided the best overall correlation with ET/3 measured over a range of temperatures and strain rates.