Computational Investigation of Impact Energy Absorption Capability of Polyurea Coatings via Deformation-Induced Glass Transition
ARMY RESEARCH LAB ABERDEEN PROVING GROUND MD WEAPONS AND MATERIALS RESEARCH DIRECTORATE
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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 resistancesurvivability 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-waveprojectile-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 structurestest plates. In the present work, an attempt is made to provide computational support for this deformation-induced glass transition based energy-dissipationabsorption mechanism. Towards that end, a series of finite-element analyses of the projectilecoated-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.
- Physical Chemistry
- Coatings, Colorants and Finishes
- Ammunition and Explosives