Computational investigation of impact energy absorption capability of polyurea coatings via deformation-induced glass transition

A number of experimental investigations reported in the open literature have indicated that the application of polyurea coatings can substantially improve blast and ballistic impact resistance/survivability of buildings, vehicles and laboratory test plates. While several potential mechanisms (e.g., shock-impedance mismatch, shock-wave dispersion, fracture-mode conversion and strain delocalization) have been proposed for the observed enhancement in the blast-wave/projectile-energy absorption, direct experimental or analytical evidence for the operation of these mechanisms has been lacking. Recently, it has been proposed that transition of polyurea between its rubbery-state and its glassy-state under high deformation-rate loading conditions is another possible mechanism for the improved ballistic impact resistance of polyurea-coated structures/test plates. In the present work, an attempt is made to provide computational support for this deformation-induced glass transition based energy-dissipation/absorption mechanism. Towards that end, a series of finite-element analyses of the projectile/coated-plate interactions are carried out using a transient non-linear dynamics finite-element approach. The results obtained are used to assess the extent of energy absorption and to identify the mode of failure of the test plate as a function of the imposed impact conditions. The results obtained show that the mechanical response of polyurea under impact conditions is a fairly sensitive function of the difference between the test temperature and the glass transition temperature. Specifically, when this difference is large, polyurea tends to display high-ductility behavior of a stereotypical elastomer in its rubbery-state. On the other hand, when the test temperature is closer to the glass transition temperature, polyurea tends to transform into its glassy-state during deformation and this process is associated with viscous type energy-dissipation. It is also argued that additional energy absorbing/dissipating mechanisms may contribute to the superior ballistic/blast protection capability of polyurea.