An experimental and numerical study of blast induced shock wave mitigation in sandwich structures

The liners of US military helmets are typically made using common soft foams. In order to better protect troops from Traumatic Brain Injury resulting from Improvised Explosive Devices, it is necessary to better understand the material properties involved in air blast mitigation. In this work, mitigation properties are studied using sandwich samples made from a vinyl-nitrile foam shell filled with materials which were selected to span a range of material properties. These materials—water, glycerin, glass beads, Aerogel®, CAB-O-SIL®, tuff volcanic rock, and expanding foam—were compared to both uniform vinyl-nitrile foam and a US Army helmet pad. Possible modes of shock attenuation include inertial effects based on density and acoustic impedance, dispersion based on porosity, and thermal effects. Since no standard test exists, we developed two experimental configurations to evaluate performance. The results were additionally used to verify a numerical model made using ABAQUS® software. Both the numerical model and the experimental results were consistent in showing that most materials attenuate the peak blast pressure while Aerogel® actually enhances the blast. Density and acoustic impedance mismatch are shown to be of primary importance while porosity is shown to have an effect as well. Furthermore, a differentiation is made between reflective and absorptive shock mitigation.