Originally Posted by
closetbiker
not quite. Eps is supposed to deflect energy by compressing, not splitting. Splitting can occur after the maximum compression has occurred, or if the foam fails in it's compression. Once the EPS has split, it cannot provide any protection.
Yes, it took some energy to compress it to the point that it would split, and then some more to actually split, and that's energy that didn't go into splitting your head. The question is if this is a significant amount of energy, and I don't recall ever seeing anybody actually measuring this.
Yes, if the helmet split, it failed. But the assertion that it provided no protection up until that point is unsupported as far as I know. Common sense (or simply my own educated guess, take your pick) tells me that it probably provided a little protection up until that point -- but not very much -- but I have no evidence of this either way. Do you?
It wouldn't be a difficult thing to test -- get some sensor-laden crash test dummies, and throw them around (in a controlled and repeatable way, of course) in such a way that their heads have harder impacts than bicycle helmets are designed to protect against. Repeat with and without helmet, at varying impact levels. Keep track of the condition of the helmet after each impact, as well as the sensor readings and the intensity and other details of the impact.
Records of helmet failure has increased with newer designs. Older designs had lower rates of failure.
Common sense suggests to me that this is correct (simply due to the trend of adding more and more ventilation), but do you have any citations or other data to back this up?