Experimentally-validated predictions of impact response of polyurea foams using viscoelasticity based on bulk properties

Polymeric foams are ubiquitous in body armors for civilian and military applications due to their functional and economic advantage. This class of materials offers good impact mitigation properties without the weight penalty associated with other classes of materials. Generally, foams inherit the mechanical properties of their base material while the performance can be defined by the cellular structure. In this study, new polyurea foams were manufactured and subjected to low energy dynamic impacts to experimentally validate the time-dependent response of polyurea foams based on linear viscoelastic modeling. The time-dependent properties of bulk polyurea were scaled down by accounting for the change in density and microstructure of the polyurea foam. Drop-weight testing of approximately 7 J in a fully-instrumented drop weight testing machine was conducted on newly-fabricated polyurea foams of two nominal densities, namely, 227 kg/m(3) and 355 kg/m(3). Simultaneous to the impact event, high-speed photography was used to capture the deformation and recovery response of the samples. The performance was then compared with a promising off-the-shelf, closed-cell foam material used to protect against biomechanical impacts. The polyurea foams proved to mitigate the impact more effectively than the benchmark foam without the addition of a severe weight penalty. The finite element simulation performed well in predicting the amplitude and the rise time of the dynamic impact testing of the two foams; the numerical results were found to be in close agreement with the experimental data.