Blast Overpressure Measured On A Bare Vs. Helmeted Rigid Headform

There is significant concern that blast overpressure can cause mild traumatic brain injury (mTBI). An accurate understanding of the blast flow and overpressure event as well as it's interaction with the head and helmet system is a necessary first step in establishing loading conditions to the head. It also provides a means for model validation and other predictive capabilities. A custom-designed Blast Overpressure Bust (BOB) containing 22 surface pressure sensors was rigidly mounted in a live-fire blast event. The blast field tests were conducted in an open field using 4 lbs. of cylindrical C4 charges suspended 48 '' above the pad. The BOB was mounted to a torso surrogate and positioned 92 '' from the hanging charge. The BOB was oriented at blast impact angles of 0 (front-facing), 45, 90, and 180 degrees. The BOB was tested in both bare and helmeted configurations. Data recorded across a bare headform at each angle established a baseline for the pressure trace at each sensor location. Two helmeted cases were investigated: Advanced Combat Helmet (ACH) with the sling suspension system and ACH with Team Wendy pads. Results showed peak pressures on exposed surfaces normal to the blast were similar to 200kPa with side-on pressures of similar to 400kPa. The addition of a helmet did not alter the peak normal pressures, but showed slight to moderate increases in pressure beneath the helmet based on the amount of cushioning present. The sling suspension, which leaves an open gap between the head and helmet, resulted in several recorded amplification points beneath the helmet with the peaks reaching similar to 800kPa. The Team Wendy pads trials, which effectively fill the gap between the head and helmet, showed amplifications with peaks of similar to 500kPa. An additional set of tests was conducted using an ingress barrier positioned between the head and helmet at the brim. Results showed pressures under the helmet that were lower than the bare headform trials. While it was shown that adding a helmet did in fact increase pressures relative to the bare headform case, these amplifications were still far less than the peak pressure exerted on the exposed surfaces of the headform. The data presented herein is the most robust data set to date for pressures exerted on a helmeted headform and is considered applicable to the first 3-5ms of an unconstrained system, during which time motion is minimal.