Lower extremity characterization and injury mitigation

Lower extremity injuries are among the most common seen in the event of an underbody blast (UBB) to an armored vehicle. Lower extremity accelerations typically exceed 500g with positive phase durations around 5ms while automotive rates typically peak around 250g with 10ms durations. Lack of injury criteria for UBB rates and the inability of injury criteria for automotive rates to predict lower extremity injury pose challenges for soldier safety during UBB. Until such an injury criterion exists and protective vehicle designs can be made, methods to mitigate soldier injury are essential. One potential method is to optimize the boot heel or add a protective layer on the floor of current military vehicles. To investigate effectiveness of these layers, material properties were combined with an existing lumped-mass model capable of calculating accelerations of the lower extremity. Viscoelastic materials were investigated for their ability to dissipate energy and store remaining energy long enough for the foot to disengage the floor. Sorbothane®-50 was used for two PMHS experiments to benchmark the effectiveness of injury prediction of the lumped-mass model and material mitigating properties. Inclusion of the mitigation layer reduced distal tibia accelerations by 75% for the most severe test.