[email protected] (ant) wrote in message
news:<
[email protected]>...
>
[email protected] (Carl Fogel) wrote in message
> >
> > Do carbon frames dent? If so, why can't they be dented back out?
>
> (apologies if this has been asnwered repeatedly already)
>
> carbon doesnt dent. it breaks. you could imagine it like a piece of glass. if you push hard
> enough on it, it wont finally dimple, it just snaps. push hard enough on steel, and you will make
> a dimple.
>
> this is, of course, a simplistic analogy. in truth, what is breaking is the fibers, and the
> epoxy that holds them together, so you wont get a clean break like a piece of glass. carbon will
> also bend a lot, compared to glass. if you put a carbon tube on two cinderblocks and pushed in
> the center, it would bend, and spring back to where it started. same with steel. if you kept
> pressing harder and harder, the steel would eventually permanently deform to the bend. the
> carbon would snap.
>
> if you push carbon to the point at which the fibers begin breaking, there is nothign you can do to
> 'heal' it. you cant go in and reconnect the individual fibers that make up the structural strength
> of the composite.
>
> that is the implied danger in carbon forks, that internal fibers could break under heavy load, but
> you wouldnt be able to tell by looking. if you crash your c.fork, do you know if there is internal
> damage? you can crush carbon fiber pieces and hear the fibers and epoxy crackling, but stop before
> the damage is complete and never be able to tell the difference (to my untrained eye). even if the
> fork is plenty strong enough to hold up to normal bicycling, if something went 'crackle' inside,
> it is weaker and you dont know by how much.
>
> the good news is that the forks these days can be made so dang strong that they are rarely
> loaded so heavily that damage is done. you just dont hear abotu too many forks snapping off
> these days, IME.
>
> anthony
Dear Anthony,
Your fiber explanation makes sense.
Given what you say, I suspect that Andrew meant that "you can't fix a dent in a carbon tube because
you can't get a dent in a carbon tube in the first place," which would have been clear to him
because he knows what he's talking about and is probably marvelling at my ignorance.
Thanks for clearing this up for me.
Carl Fogel