Implementation and validation of a three dimensional damaging finite strain viscoelastic model

In this paper a complete pathway to construct a constitutive model well suited for finite element analysis of viscoelastic media undergoing large deformation and damage is described. In particular, a systematic calibration, verification and validation procedure of the implementation of a solid propellant constitutive model was developed. As a first step a three dimensional model valid for all deformation ranges was selected and implemented as a user material into commercial finite element software. The second step consisted of calibrating the model without damage and verifying the algorithm against the built-in material model available in the software. In the third step the damage parameters were determined using a set of solid propellant test data. Finally, the full constitutive model was validated by comparing the results with the test data not used in the calibration. For both verification and validation, homogeneous and inhomogeneous deformation states were considered, and various element types were investigated. The comprehensive approach outlined in the paper aims to emphasize the need of a methodology to be followed for a successful use of a constitutive model in a computational stress analysis.