Investigation into helmet–head shock wave interactions at low overpressures through free-field blasts and schlieren imagery

Brain injuries in warfighters due to low-level blasts, even while wearing a helmet, are common. Understanding how the form of a shock wave changes when impacting a head donning a helmet may present solutions to reducing shock loading on the head, thereby reducing the prevalence of blast-induced traumatic brain injury. A manikin with PCB piezoelectric transducers throughout the head was exposed to low-pressure free-field blasts using an RDX-based explosive charge designed to output a side-on overpressure of 4 pounds per square inch (psi) [27.5 kilopascals (kPa)] with and without a helmet. Orientations of 0, 45, 90, 135, and 180 degrees were evaluated to observe changes in overpressure versus time (p(t)) waveforms. The waveforms were compared to schlieren imagery in which a shock wave impacted 3D-printed silhouettes of a warfighter donning a helmet, showing shock wave flow under the helmet at 0-, 90-, and 180-degree orientations. It was found that trapped shock waves under the helmet create regions of high overpressure and increase the duration of exposure, resulting in higher impulses imparted onto the head. While wearing a helmet, the 90-degree orientation resulted in the greatest reduction in overall peak overpressure, with an 8% decrease compared to the 0-degree orientation. In contrast, the 180-degree orientation led to an increase by 30%. For impulse, the 90-degree orientation showed the greatest reduction, with a decrease of 21%. The 0-degree orientation had the highest overall impulse among all orientations when wearing a helmet.