Response of the biped head physical model to low level shock waves

The BIPED headform is specifically developed by Defence R&D Canada (DRDC) to assess the relative reduction of the risk of injury to the human brain (Blast Induced TBI: b-TBI), offered by combat helmets, from low-level shockwaves. These low level shockwaves may be encountered in theatre due to exposure to an improvised explosive devices or other explosive threats and can cause serious long-term effect on health. A study to improve the understanding of the load transfer mechanism from a shockwave to the brain simulant of the headform was performed using a 400 x 400 mm square shock tube. The BIPED was mounted on a crash dummy neck and exposed to shockwaves of two different loading levels having a peak overpressures of 90 and 160 kPa respectively and a duration of 10-15 milliseconds. The response of the bare headform was compared to the response of the headform with an open-face and full-face combat helmet. Pressures on the headform surface, pressures in the brain simulant as well as strain on the skull were measured. Various phases in brain pressure responses were identified. Application of a helmet appears to decrease the peak pressures in the first phase of the response but increased pressure amplitude during the third phase. A Finite Element study was performed to study shockwave load transfer into the brain from skull modal resonance. The FE study revealed that increase of the third phase pressure is most likely due to rigid body motion of the skull exciting the brain simulant, suspended in water in the skull cavity, in its modal resonance frequency. This rigid body motion effect appears to increase with the presence of a helmet. The study resulted in a better understanding of the shockwave – head interaction and the potential protection offered by combat helmets. It also showed that modal resonance frequencies of skull and brain are crucial in the load transfer to the brain and should be included in the biofidelity requirement for a head simulant used to assess the protection potential of PPE
or operational protocols.