Problems with European-style Helmet Test Rigs
Summary: The European helmet rig places the helmet on a ring or "basket" for the guided drop. The headform inside the helmet and the helmet are free to move when the impact with the anvil takes place. If helmets were round, the center of the headform where acceleration is measured would always be over the center of the anvil, but bicycle helmets are not round. The problem can affect test results.
Shock absorption test according to EN 1077:
problem of helmet positioning:
Abstract and links to full study
According to EN 1077 the impact point, the anvil centre and the centre of gravity of the headform should be aligned for a shock absorption test. Depending on the helmet shape it is for geometrical reasons not always possible to align the three points, even if the position of the centre of gravity is known exactly.
Two possible interpretations of EN 1077
The following two positioning methods both seem consistent with standard EN 1077, see also figure:
1. Alignment of the marked impact point (=target impact point) with the anvil centre, whereby the anvil surface is approximately tangential to the helmet shell at the marked impact point. The impact is directed only approximatively towards the centre of gravity of the headform.
2. Alignment of the marked impact point with the centre of gravity of the headform and the anvil centre. Compared to positioning 1, the helmeted headform has to be rotated which leads to the fact that actually a point different from the marked impact point is impacted in the shock absorption test (this is evident from the analysis of the damage to the helmet liner, see photographs 1 and 2).
The full study
Adobe .pdf format (smaller)
Word format - .doc file