A constitutive model for nonlinear viscoelastic particulate composite materials

This paper describes a constitutive model for viscoelastic materials with damage, and its numerical implementation in a finite element code. The model is based on a phenomenological approach and accounts for large deformations, dilatation, softening due to damage and nonlinearities during cyclic loading. An efficient numerical algorithm with symmetric tangent stiffness is developed and Newton-Raphson iterations are used to solve the resulting algebraic equations. A step by step discussion of model calibration is provided and calculations are carried out for a solid rocket propellant test data. The performance of the viscoelastic analysis is illustrated for the pressurization/depressurization of a subscale flexible rocket motor. The effect of the material model stability on convergence properties is also discussed.