THE MECHANICS OF INTRACRANIAL LOADING DURING BLAST AND BLUNT IMPACTS – EXPERIMENTAL AND NUMERICAL STUDIES

Head injuries in an explosion occur as a result of a sudden pressure changes (e.g. shock-blast) in the atmosphere (primary injury), high velocity impacts of debris (secondary injury) and people being thrown against the solid objects (tertiary injury) in the field. In this thesis, experimental and numerical approaches are used to delineate the intracranial loading mechanics of both primary (blast) and tertiary injuries (blunt). The blast induced head injuries are simulated using a fluid-filled cylinder. This simplified model represents the head-brain complex and the model is subjected to a blast with the Friedlander waveform type of loading. We measured the temporal variations in surface pressure and strain in the cylinder and corresponding fluid pressure. Based on these data, the loading pathways from the external blast to the pressure field in the fluid are identified. The results indicate that the net loading at a given point in the fluid comprises direct transmissive loads and deflection-induced indirect loads. The study also shows that the fluid pressure (analogue of intracranial pressure) increases linearly with increase in reflected blast overpressures (ROP) for a given shell thickness. When the ROP is kept constant, fluid pressure increases linearly with the decrease in shell thickness. For understanding the blunt induced head injuries, the complaint (acrylic gel complex) and rigid (aluminum body) head surrogates with an identical mass are impacted on target surfaces of different stiffnesses. The study indicates that the acceleration field in the gel-filled head surrogate varies from coup to counter-coup region, whereas the field is uniform in the rigid surrogate. The variation in the acceleration field is influenced by the shell deformation that in turn depends on the stiffness of the target surface. Impact studies on the helmet padding currently being used by the US Army are also carried out at different loading conditions. Our results indicate that for a fixed thickness of a foam pad, an increase in the stiffness of the pad will result in the increased absorption of the impact energy. Advisor: Namas Chandr