UC Berkeley

Traumatic brain injury (TBI) has become an serious concern for athletes and soldiers. Helmets used for preventing injury in athletics can borrow information gathered from au- tomobile safety studies. In contrast, TBI threats for soldiers exist at different scales than studied in those works, thus requiring specialized studies to address these threats. Combat helmets consist of a stiff composite shell and a foam liner system. The liners serve to mitigate injuries caused by the impact of the shell upon the head. The aim of this work is to develop a numerical simulation that is capable of recreating the micro-mechanical behavior of the foam liners at deformation rates anticipated in a combat environment.

In this work a three dimensional nonlinear beam network model and foam geometry creation tool were developed to recreate the microstructure of open-celled foam pads. The model is designed to be stable under high rates of compression and to be able to undergo self- contact to recreate a stiffening response seen at large strains. The beam network model was used to perform rapid compression tests at various impact speeds. Shock wave speeds were calculated for each test. The sock speed data was mapped back to macro-scale parameters using the rigid-perfectly-plastic-locking (RPPL) model of cellular deformation. The model’s prediction of the locking strain aligns with data studied at the macro-scale.

The work aims to demonstrate a tool that can be used to improve the protection provided foam liners at impact speeds that could be seen in combat.