Performance of an advanced combat helmet with different interior cushioning systems in ballistic impact: Experiments and finite element simulations

This paper presents results from both experiments and numerical simulations of frontal and lateral ballistic impacts on a Hybrid III headform equipped with Advanced Combat Helmets (ACH) of two different interior cushioning designs, namely the strap-netting system and the Oregon Aero (OA) foam padding. It aims to study the differences between two different impact orientations for these two different interior cushioning systems. The experiments involve frontal and lateral ballistic impacts of a 11.9 g spherical steel projectile traveling at speeds of approximately 200 m/s, striking on the helmet-cushion-headform assemblies. The dynamic interaction between various components of the helmet-cushion-headform assemblies are investigated with the use of high-speed photography while post-test evaluation of the damaged helmets are performed using visual observation, optical microscopy and computed tomography (CT) scan. A series of ballistic impact simulations with finite element (FE) models of the two assemblies reconstructed from CT images, are performed to correlate with experimental results. The commercial software, Abaqus™, is used for the FE analyses. In general, there is reasonable correlation between numerical and experimental observations and on quantitative parameters, such as head accelerations, helmet damage and deflections. It is also found that softer foams with low stiffness are more effective as shock absorbing cushion against ballistic impacts under certain condition. Additionally, results of the two interior cushioning systems are compared with various injury criteria to assess their acceleration levels. It is found that, for frontal impact, the helmet with strap-netting system fails both the Wayne State Tolerance Curve (WSTC) and Federal Motor Vehicles Safety Standards (FMVSS) 218 criteria while the one with OA foam-padding passes both.