| Summary: | In this dissertation, blast-induced traumatic brain injury (bTBI) is studied with respect to
the blast wave directionality, mitigation capability of helmet/faceshield, and blast flow
mechanics using finite element (FE) and computational fluid dynamics (CFD) schemes. For the
FE study, simulations are performed on a detailed FE head model using LS-DYNA, and CFD
simulations are carried out using the ANSYS-CFX to examine the underwash development by
analyzing the behavior of blast flow from different directions. The following tasks are
conducted.
First, the effects of the loading direction on the mechanical response of the head and
brain is investigated through impact and blast induced loading on the head. Due to the
differences in the shape, function, and tolerance of brain components, the response of the
head/brain varies with the direction of the impact and blast waves. In identical situations, the
head shows to have lower tolerance to side loading.
Second, the inclusion of the faceshield as a potential head protective tool against blast
threats is evaluated with respect to blast direction. The helmet-faceshield and helmeted
assemblies are shown to be most efficient when the head is exposed to blast from the front and
top sides, respectively. Faceshield is observed to be effective only in front blast as it might
impose either adverse or no effects in other directions. The shockwaves are seen to form a high
pressure region in head-helmet-faceshield gap (underwash effect) which induces elevated
pressures on the skull.
Third, the underwash effect’s mechanism is investigated through CFD simulations of
supersonic shockwave flow around the helmeted head assemblies. CFD results reveals that the
backpressure is produced due to the creation of a backflow in the exterior flow on the outgoing interior flow. The bottom and side shockwave directions predict the highest underwash
overpressures, respectively. Finally, the ICP and shear stress of the brain is evaluated in case of underwash incidence.
FEA results show that underwash overpressure greatly changes with the blast direction. It is
concluded that underwash clearly altered the tissue response of the brain as it increases ICP
levels at the countercoup site and imparts elevated skull flexure.
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