In motorcycle traffic accidents, the human head is exposed to loads exceeding several times the loading capacities of its natural protection. Annually, approximately five thousand motorcyclists get killed in Europe as a result of traffic accidents. They account for 9% of all road fatalities. Wearing a helmet reduces the risk of fatality with about 50%. Over the years, helmet standards have evolved to be an effective means to assure helmet quality in terms of minimal performance. In general, helmet testing standards are the result of often rather pragmatic compromises in meetings of technical experts, more than scientific research. As helmet quality improves, the criteria of shock absorption tests are raised and impact severities are increased. The shock absorption test of the ECE Regulation 22 (ECE-R.22) is the focal point of this thesis. In this test, the helmet quality is assessed by measuring the acceleration time history of a headform during a helmeted headform impact. Helmet quality is expressed in terms of the injury parameters: maximum resultant translational headform acceleration (amax) of the headform's centre of gravity and Head Injury Criterion (HIC). The HIC is currently the leading head injury criterion in automotive research, however the ECE standard is still the only helmet standard that has implemented it in its shock absorption test. The head model used in this test is an aluminium alloy, "rigid" headform. The shock absorption test of the ECE-R.22 has two main limitations with respect to injury assessment. Firstly, the currently used headform may not properly mimic the response of the human head correctly in helmeted head impact. The rigid headform does not model the flexibility of the human brain and skull, which may be inadequate to model the helmet-head interaction correctly. Secondly, advances in injury biomechanics have resulted in other, possibly better, injury criteria that are not or can not be measured in the current shock absorption test. To date, little has been done to explore how helmet designs may change as a result of applying these different criteria. This thesis deals specifically with the question: How could motorcycle helmet designs change as a result of applying new and different head injury criteria in the shock absorption test of ECE-R.22? (Author/publisher)
Samenvatting