Study of equation of state and deviatoric response in polyurea elastomers via hydrodynamic instability experiments.*

Polyurea has shown potential as a protective coating in body and vehicle armor, due to reductions in damage and fragmentation when coated plates are exposed to blasts and ballistic impacts. Hence, the behavior of polyurea at high pressures and strain rates needs to be better understood to design protective coatings. Laser-driven shock experiments were performed to monitor perturbed shock fronts in polyurea at pressures ~ 60 GPa. Changes on the wavelength of the surface perturbations that generated the rippled shocks were used to probe effects of equation of state (EOS) and strength on the propagation of these perturbed shocks, the amplitude of which was measured via spatially resolved laser velocity at the breakout surface. Experimental results were compared to hydrocodes simulations, and they indicate that a decrease of wavelength reduced the amplitude of the shock perturbation. This is consistent with EOS and strength effects, as opposed to viscosity effects. In addition, the EOS at high pressures was consistent with an extrapolation of lower pressures results, which allowed obtaining synamic strength estimates for the material.