A new helmet testing method to assess potential damages in the Brain and the head due to rotational energy

Abstract: Preservation and protection of the head segment is of upmost importance due to the criticality of the functions entailed in this section of the body by the brain and the nervous system. Numerous events in daily life situations such as transportation and sports pose threats of injuries that may end or change a person’s life. In the European Union, statistics report that almost 4.2 million of road users are injured non-fatally, out of which 18% is represented by motorcyclist and 40% by cyclists, being head injuries 34% for bicyclists, and 24% for two-wheeled motor vehicles. Not only vehicles, are a source of injuries for the human head according to the injury report, 6,1 million people are admitted in hospitals for sports related injuries, where sports such as hockey, swimming, cycling presented head injuries up to 28%, 25% and 16% respectively (European Association for Injury Prevention and Safety Promotion, 2013).  According to records the vast majority of head crashes result in an oblique impact (Thibault & Gennarelli, 1985). These types of impacts are characterized for involving a rotation of the head segment which is correlated with serious head injuries. Even though there is plenty of evidence suggesting the involvement of rotational forces current helmet development standards and regulations fail to recognize their importance and account only for translational impact tests. This thesis contains an evaluation for a different developed method for testing oblique impacts. In consequence a new test rig was constructed with basis on a guided free fall of a helmeted dummy head striking an oblique (angled) anvil which will induce rotation. The results obtained are intended to be subjected to a comparison with another oblique test rig that performs experiments utilizing a movable sliding plate which when impacted induces the rotation of a dropped helmeted dummy head. The outcome will solidify the presence of rotational forces at head-anvil impact and offer an alternative testing method. After setting up the new test rig; experiments were conducted utilizing bicycle helmets varying the velocities before impact from 5m/s to 6m/s crashing an angled anvil of 45°. Results showed higher peak resultant values for rotational accelerations and rotational velocities in the new test rig compared to the movable plate impact test, indicating that depending on the impact situation the “Normal Force” has a direct effect on the rotational components. On the other hand a performed finite element analysis predicted that the best correlation between both methods is when the new angled anvil impact test is submitted to crashes with a velocity before impact of 6 m/s at 45° and the movable sliding impact test to a resultant velocity vector of 7,6m/s with an angle of 30° . In conclusion the new test method is meant to provide a comparison between two different test rigs that will undoubtedly have a part in the analysis for helmet and head safety improvements.