Moderate-Velocity Response of Polyurea Elastomeric Foams

The suitability of cellular solids for a specific energy absorption application, whether packaging or sports gear padding, depends on their dynamic mechanical behaviors under impact loadings. The latter is imperative not only to simulate real-life loading conditions but also to interrogate the realistic response of the material, contributions of the geometry, and determination of prominent deformation mechanisms. This research aims to extend the application domain of polyurea elastomeric foams through a mechanistic understanding of their response to loading scenarios at moderate impact velocities. Recent research focused on either leveraging quasi-static stress-strain response to forecast the impact efficacy of these foams or submitting the foam pads to low-velocity impacts. Hence, the approach here is to develop a small-scale shock tube to release a projectile into polyurea foam plugs ~31 cm apart. The shock tube was mounted vertically to (1) reduce the logistical impact of the setup and (2) leverage gravity-assisted increase in impact velocity. The impact velocity was controlled by adjusting the pressure in the driver (high pressure) section of the tube. The impact-induced deformation was captured using a high-speed camera. The velocity-time profiles were used to calculate the stress, while the high-speed images were analyzed using digital image correlation (DIC) to report the evolution of strains and inertia stresses. Samples were also examined post-deformation using optical microscopy to assess the induced structural damage. The outcomes of this research extend the property map of polyurea elastomeric foams, gearing them closer to transition into realistic sports protective gear applications.