As part of a safety program, we studied the fracture of several rocket propellants under plate impacts and Taylor tests, thus examining fracture under both one- dimensional planar and two-dimensional axisymmetric loadings. Here we outline the experimental results for one propellant (termed Propellant B), describe the constitutive model developed, and show how we derived the fracture parameters for the propellant. The deviatoric stress portion of the constitutive relations is viscoelastic because of the marked rate dependence of the shear modulus and is viscoplastic to represent the variation of yield strength with strain rate. Fracture appears to be caused by tensile strains ; shearing strains of 1 or more appeared to cause no damage.