Effect of Incorporating Foam Based FlexibleBlunt Trauma Pads on the Shock WaveProtective Performance of FlexibleBody Armour

This paper presents results from shock tube experiments on the transmitted overpressure through multiple layers of ballistic fabrics backed by various foam based flexible blunt trauma pads. The results corroborate previous reports that multiple layers of ballistic protection fabrics alone are not effective in reducing the occurrence of shock/blast wave injury. On the contrary, multiple layers of fabric and flexible laminates (Twaron T717, Twaron UD41 and Spectra Shield SA-1211) amplified the transmitted shock wave pressure. Moreover, this amplification in the transmitted peak pressure increased further when more plies were added. Incorporating foam based flexible blunt trauma pads behind the Twaron fabric resulted in mixed outcomes on the transmitted shock wave depending on the makeup of the blunt trauma pads. Adding pads comprising open cell polyurethane foams resulted in further and significant amplification of the recorded peak pressure. Attempts were made to reduce the pressure amplification by infusing the foams with shear thickening fluid. Although successful in reducing the peak pressure compared to a system of fabric backed by neat foam padding, the transmitted peak pressure was still slightly higher or at best equal to a system of fabrics without any padding. It was also found that padding made of auxetic foams fared better than conventional foams as they did not give rise to the large amplification in peak pressures.