Development and parameterization of a time-invariant (equilibrium) material model for segmented elastomeric polyureas

A time-invariant (equilibrium) material mechanical model for segmented polyureas, a class of thermoplastically linked co-polymeric elastomers, is developed and parameterized using experimental data available in open literature. The key components of the model are developed by first constructing a simple molecular-level microstructure model and by relating the microstructural elements and intrinsic material processes to the material mechanical response. The new feature of the present material model relative to the ones currently used is that the physical origin and the evolution equation for the deformation-induced softening and inelasticity observed in polyureas are directly linked to the associated evolution of the soft-matrix/hardsegment molecular-level microstructure of this material. The model is first developed for the case of uniaxial loading, parameterized using one set of experimental results, and finally validated using another set of experimental results. The validation procedure suggested that the model can reasonably well account for the equilibrium mechanical response of polyureas under the simple uniaxial-loading conditions. In the last portion of this study, a general finite-strain three-dimensional material model for polyureas was developed and cast as a subroutine suitable for linking with commercial finite-element programs.