In order to address the need to monitor local contact forces during head impacts, a custom transducer was designed to monitor local force distribution patterns on an ISO size E magnesium headform concurrently with linear acceleration measures from an accelerometer located at the center of gravity of the headform. The response characteristics of the transducer were found to be predictable and acceptable given the limitations of high speed data collection in a confined environment. During bicycle helmet testing, the output from the transducer was also found to be sensitive to ventilation openings and ventilation channels located on the underside of the helmet liner.

The effect of helmet liner density upon local contact forces and headform acceleration was evaluated using an identical bicycle helmet model fabricated in four different helmet liner densities. The study found that peak headform acceleration and peak local contact sensor force values were significantly lower for the low density helmet liners when compared to the highest density of helmet liners during low to moderate energy impacts. During the high energy impact tests against the hemispherical anvil, the lower density helmets bottomed out, resulting in high local contact forces and high peak headform acceleration values relative to the higher density helmets. These results suggest that a tradeoff does exist in terms of the protection offered by low density helmets at low to moderate energy impacts compared to the performance of higher density helmets during the higher energy impacts.

The study also found that a poor correlation exists between peak headform acceleration and local contact force suggesting that future head protection standards should include evaluation of the load distribution characteristics of the helmet.