Problems with European-style Helmet Test Rigs
Summary: The European helmet rig rests the helmet on a ring or "horseshoe" for the guided drop. The ring passes around the anvil at the impact level and drops down, leaving the headform
inside the helmet and the helmet 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 helmet must also be lightly secured in the ring at the moment the drop begins to prevent it from shifting. These problems can affect test results.
Shock absorption test according to EN 1077:
problem of helmet positioning:
Abstract and links to full study
Problem
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 approximately
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).
A second problem involves maintaining the helmet position
when the drop begins
When the rig's horseshoe or ring begins to descend, the helmet is momentarily left hanging
in space until gravity propels it downward. It catches up with the horseshoe, due to the friction in the bearings of the monorail that guides the horseshoe during the drop. But in that split second when the helmet is in actual freefall, it changes position. To avoid that, European testers generally tape the helmet to the horseshoe. Upon impact with the anvil, the helmet tears the tape loose. There is a whole science to trying to use the weakest possible tape that can hold the helmet in place without adding to the impact force as the tape tears. Most testers apply tape, slit it about half way through and then drop the helmet. Since there is no specification for the tape or the slit, this introduces another element of potential variance between labs.