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Phase-segregated polyureas (PU) have received considerable interest due totheir use as tough, impact-resistant coatings. Polyureas are favored for theseapplications due to their mechanical strain rate sensitivity and energydissipation. Predicting and tailoring the mechanical response of PU remainschallenging due to the complex interaction between its elastomeric and glassyphases. To elucidate the role of PU microstructure on its mechanicalproperties, we developed a finite element modeling framework in which eachphase is represented by a volume fraction within a representative volumeelement (RVE). Critically, we used separate constitutive models to describe theelastomeric and glassy phases. We developed a plasticity-driven breakdownprocess in which we model the glassy phase disaggregating into a new phase. Theoverall contribution of each phase at a material point is determined by theirrespective volume fractions within the RVE. We applied our modeling methods totwo compositions of PU with differing elastomeric segment lengths derived fromoligoether diamines, Versalink P650 and P1000. Our simulations show that acombination of microstructural differences and elastomeric phase propertiesaccounts for the difference in mechanical response between P650 and P1000. Weshow our model's ability to predict PU behavior in various loading conditions,including low-rate cyclic loading and monotonic loading over a wide range ofstrain rates. Our model produces microstructure transformations that mirrorthose indicated by small-angle X-ray scattering (SAXS) experiments. Fouriertransform analysis of our RVEs reveals glassy phase fibrillation due todeformation, a finding consistent with SAXS experiments.

Elucidating the impact of microstructure on mechanical properties of  phase-segregated polyurea: Finite element modeling of molecular dynamics  derived microstructures