Effectively removing the helmet on one slick movement of the wrist left the Juggernaut's back turned on Hulk and vulnerable to the one and only blow it took.
you do know Juggy only wears that helmet to guard himself from a psychic attack? it has no bearing on his powers.
So it wouldn't be strong enough to keep his head from getting smashed in, plus I recall on a cartoon his powers being associated with a scrouny little guy, getting powers from it. I haven't read anything comic book related to him...