  Phase-segregated polyureas (PU) have received considerable interest due to
their use as tough, impact-resistant coatings. Polyureas are favored for these
applications due to their mechanical strain rate sensitivity and energy
dissipation. Predicting and tailoring the mechanical response of PU remains
challenging due to the complex interaction between its elastomeric and glassy
phases. To elucidate the role of PU microstructure on its mechanical
properties, we developed a finite element modeling framework in which each
phase is represented by a volume fraction within a representative volume
element (RVE). Critically, we used separate constitutive models to describe the
elastomeric and glassy phases. We developed a plasticity-driven breakdown
process in which we model the glassy phase disaggregating into a new phase. The
overall contribution of each phase at a material point is determined by their
respective volume fractions within the RVE. We applied our modeling methods to
two compositions of PU with differing elastomeric segment lengths derived from
oligoether diamines, Versalink P650 and P1000. Our simulations show that a
combination of microstructural differences and elastomeric phase properties
accounts for the difference in mechanical response between P650 and P1000. We
show our model's ability to predict PU behavior in various loading conditions,
including low-rate cyclic loading and monotonic loading over a wide range of
strain rates. Our model produces microstructure transformations that mirror
those indicated by small-angle X-ray scattering (SAXS) experiments. Fourier
transform analysis of our RVEs reveals glassy phase fibrillation due to
deformation, a finding consistent with SAXS experiments.
