NONLINEAR VISCOELASTIC CONSTITUTIVE MODEL FOR SOLID-PROPELLANT

A nonlinear viscoelastic constitutive model for solid propellant is described. It is based upon a modified form of the classical Coleman-Noll nonlinear viscoelastic constitutive model for material with "fading memory." This constitutive model, referred to as the Burke model, was discretized in time, expressed in matrix form suitable for nonlinear incremental analysis, and incorporated into the MARC finite element code via user subroutines. An ancillary code was developed to calculate required material constants from test data. The model was subsequently applied to different test conditions and the results were compared to propellant test data in a fundamental assessment of the appropriates of this model as a constitutive model for solid propellant. This paper presents the theoretical background for the consecutive model, its discretization, and results of analyses. Additionally, the ancillary code is described. It is shown that the present implementation of the constitutive model provides a sound basis upon which to develop an accurate analysis tool for the prediction of the mechanical response of solid propellant.