Characterization of a glycidyl azide polymer composite propellant: Strain rate effects and relaxation response

Abstract

AbstractUniaxial tension tests were completed on a developmental GAP/PSAN solid rocket propellant at constant strain rates ranging over three decades and at five different temperatures. An analysis of the maximum stress (strength) and the strain at maximum stress showed that there is a relatively narrow range of temperatures and strain rates that give rise to strains at maximum stress that exceed 18%. The long‐term equilibrium strain capability (strain endurance) appears to be between 10% and 12%. The trend of the strength and initial deformation moduli were log‐linear with the reciprocal of the strain rate across three decades. However, the shifted master curves were log‐curvilinear in form. The relationship between the strength and the initial modulus can be approximated by a power law. A series of stress relaxation tests was completed at a level of 4% strain and at five different temperatures. The initial portion of the shifted master relaxation curve is concave‐up with correspondingly high stresses and moduli. It decays with time approaching a log‐constant slope. Tensile moduli derived from constant strain rate tests were found to be consistently higher in value than the moduli as a function of time determined from relaxation tests, for an equivalent shifted time. Preliminary evidence suggests that the tensile modulus as a function of the reciprocal of shifted strain rate can be equated to the relaxation modulus as a function of shifted time through an adjustment factor. This relationship extends the relaxation modulus results back a further three and one‐half decades of shifted time. © 1995 John Wiley & Sons, Inc.