The widespread use of explosive weapons in recent military conflicts has
contributed to an increased incidence of traumatic brain injuries. Although
current infantry helmets provide effective protection against fragmentation,
ballistic impact, and blunt trauma, they are not designed to mitigate primary
blast loading. Previous studies suggest that blast waves may infiltrate the
space between the head and helmet, leading to localized increases in pressure on
the head surface, a phenomenon referred to as the underwash effect. However,
experimental validation of the underwash effect remains limited, particularly
for blast scenarios representative of buried-charge detonations, despite their
potential to increase underwash-related loading across large regions of the
cranial surface. This study experimentally evaluated the effects of combat
helmet use, blast orientation, and blast intensity on head surface loading to
assess helmet protective performance across various blast scenarios. A human
surrogate headform instrumented with four flush-mounted pressure sensors was
exposed to blast overpressures of approximately 16 and 24 psi using a large
advanced blast simulator. Tests were conducted at 0° and 45° head orientations
(rotation about the transverse axis), both with and without a combat helmet,
with three repetitions per combination of experimental conditions. In the 0°
orientation, helmet use reduced loading at the forehead and anterior head but
increased loading at the posterior region. In the 45° orientation, helmet use
led to increased peak pressure and total impulse at all measured locations.
Increasing the blast intensity resulted in similar trends for both orientations
and helmet conditions but with greater peak pressures and total impulses at each
measured location. These findings suggest that certain blast orientations
exacerbate the underwash effect and amplify cranial loading beneath the helmet.
This work advances understanding of orientation-dependent blast loading,
highlights limitations in current helmet performance, and offers guidance to
support the development of future protective technologies.
