Study of an advanced helmet liner concept to reduce TBI : experiments & simulation using sandwich structures

Abstract

A large percentage of combat troops suffered Traumatic Brain Injuries (TBI) due to Improvised Explosive Devices (IEDs) in recent wars in the Middle East. The majority of TBIs were caused by exposure to blast waves. Use of advanced body armor has decreased the number of fatalities due to impacts after the explosions, increasing the number of observed non-fatal brain injuries from the blast waves. A large number of TBIs due to impact hits are also reported in skiers, bicyclists, football players etc. A new design concept for the helmet liners is being proposed that introduces solid or fluid filler material in channels inside the helmet liner. The main emphasis has been to improve the attenuation of incoming shock waves in the Army helmets; however, some impacts studies were also carried out for sports helmets. Directed blast experiments in collaboration with Purdue University and numerical studies using the ConWep module available in ABAQUS v6.10 are carried out. Fluid fillers are modeled using the coupled Eulerian-Lagrangian (CEL) functionality of ABAQUS. Preliminary results using flat plate sandwich structures with rectangular channels show that the use of high density filler material results in higher levels of blast mitigation. The peak transmitted overpressure is substantially reduced, while the duration of the positive pressure pulse and the rise time are increased leading to reduced pressure gradients. Fluid filler materials were also found to be promising. Viscosity was not found to be a potential mechanism for blast mitigation as hypothesized. No significant advantage of using circular or criss-cross channel geometries was observed. Prototypes of the first design of the helmet liner with channels have been fabricated, and their testing is under way. Development of a numerical model to observe the response to blast of the modified liner coupled with the Army's Advanced Combat Helmet (ACH) and a human head is also currently in progress. Experimental impact studies were carried out comparing POC ski helmets with standard ski helmets. Over multiple impacts, POC ski helmets showed substantially lower peak accelerations. Different filler materials in the sandwich structures were drop tested. Both the numerical model and the experiments showed higher impact attenuation by the use of viscous fluid in the sandwich structures subjected to drop tests.