Adaptive head impact protection via a rate-activated helmet suspension

Abstract The design of an adaptive helmet suspension system that provides optimized head protection under variable impact conditions is reported. The adaptive response is achieved through the use of rate activated tethers (RATs), a flexible strap-like material that uses shear thickening fluids to generate speed-sensitive extensional resistance. The RATs are integrated into a helmet by replacing the webbing system of a traditional construction hardhat with a network of RATs, and performing impact attenuation testing over a range of velocities. Impacts to the crown region of the helmet demonstrate a 50% reduction in peak acceleration experienced by the headform for impact velocities between 1.5 and 3.5 m/s compared to the conventional webbing system, and comparable response to the conventional system at 4.5 m/s. Complementary RAT extensional testing and low velocity helmet compression tests confirm that the rate-sensitive response of the RATs contributes significantly to improved system performance. Additionally, calculations for suspension model systems show that the steady yield force exhibited by RATs over long strokes is a critical feature for minimizing head acceleration, and that the RAT suspension systems are achieving responses remarkably close to the ideal suspension response.