Skull Flexure from Blast Waves: A Mechanism for Brain Injury with Implications for Helmet Design

Traumatic brain injury (TBI) has become a signature injury of current military conflicts, with debilitating, costly, and long-lasting effects. Although mechanisms by which head impacts cause TBI have been well researched, the mechanisms by which blasts cause TBI are not understood. From numerical hydrodynamic simulations, we have discovered that nonlethal blasts can induce sufficient skull flexure to generate potentially damaging loads in the brain, even without a head impact. The possibility that this mechanism may contribute to TBI has implications for injury diagnosis and armor design.

Figure 1

Simulation geometry: A 2.3 kg spherical charge of C4 high explosive is located 4.6 m from a head consisting of three components—the skull, CSF layer, and brain tissue—that are supported by a low detail body structure.

Figure 2

Pressure and skull motion for impact and blast simulations: (a) Angled impact at maximum deceleration. (b) Blast wave propagating past the simulated victim 5.6 ms after detonation. (c) Expanded view of the head as the blast wave passes over it. Inward and outward rippling of the skull cause pressure extrema in the brain. The skull deflections are $\sim 50\mu \mathrm{m}$.

Figure 3

Selected results of sensitivity studies: (a) Time history of maximum and minimum pressures occurring anywhere in the brain for the base case, case (iii), and case (iv). (b) Pressure and skull motion for case (iv), 5.6 ms after detonation. Skull deflections are $\sim 50\mu \mathrm{m}$.

Figure 4

Amplification of the blast pressure and loads on the head due to underwash for a helmet without foam pads.