Development and validation of a 3d fe model of advanced combat helmet and biomechanical analysis of human head and helmet response to primary blast insult

Blast-induced traumatic brain injury (bTBI) has emerged as a signature injury in combat casualty care. Present combat helmets are designed primarily to protect against ballistic and blunt impacts, but the current issue with helmets is protection from primary blast effects. In order to delineate wave interaction and propagation with the combat helmet and human head, a detailed finite element (FE) model of Advanced Combat Helmet (ACH) was developed and validated. A series of finite element analyses was undertaken to evaluate blast wave attenuating capability of the ACH by comparing the head/brain responses against blast loadings between the validated FE human head models with and without helmet. The integrated FE helmet/head model was subjected to blast insults at various overpressures (0.27-0.66 MPa) according to Bowen\u27s lung iso damage threshold curves. Effectiveness of the helmet with respect to various head orientations was also investigated. The resulting biomechanical responses of the brain to blast threats were compared for the human head with and without the helmet. For all Bowen\u27s cases, the peak intracranial pressures sustained by the head without helmet ranged from 0.68-1.8 MPa in the coup cortical region. ACH was found to mitigate intracranial pressures in the head by 10-35%. The helmeted head resulted in average 30% lower peak brain strains and product of strain and strain rate. Among three blast-loading directions with ACH in use, the highest reduction in peak intracranial pressure (44%) was from backward blast, whereas the lowest reduction in peak intracranial pressures and brain strains was due to forward blast (27%). The biomechanical responses of a human head to primary blast insult exhibited directional sensitivity owing to the different geometric contours and coverage of the helmet construction and asymmetric anatomy of the human head. Thus, direction-specific tolerances for bTBI are needed in helmet design in order to offer omni-directional protection for the human head. A series of FE analyses was also conducted to evaluate the effects of blast overpressure on the brain of a new blast anatomical headform model constructed with the actual human head geometry and simulant materials for skull and brain. Biomechanical parameters within the intracranial cavity of the blast headform model were compared to those from the human head model. Results suggested that differences in mechanical properties between the simulant materials and human skull/brain tissue properties influenced shock propagation through the head