[kolektiv]

In which case yes, just a very misinformed original author. Shattering, cracking, etc. are all known, planned features of a helmet impact - anything which can absorb energy in the helmet and not the head is a good thing (with some obvious caveats of course).

[moopling]

Depends, depends... Fracturing of a flaw requires much less energy than plastic deformation. So it is really a question of whether it deformed first and then cracked, or fractured early. In the latter case, possibly caused by a flaw or very sharp impact, not much energy would be absorbed at all!