Re: "brittle" vs. non-ductile - getting through the jb rubbish

Jambo <-...@xxx> wrote:
Put it this way - imagine one carbon fiber as a pencil. It's very strong in
compression and tension, as long as the load is parallel to its length (or
axis). However, put a load perpendicular to its axis, and you can easily
break the pencil.

Ben C <spams...@xxxxxxxxx> wrote:
I think that's a herring.

Michael Press wrote:
Wood is a composite material, so the analogy is
excellent. No fishy smell. Wood easier to crush
transversely than longitudinally. That is why good
cutting blocks are made with the end grain on the
surface of the block. Wood is optimized to carry an
axial load. Tall timber. When wood is called upon act
as a beam as in a limb, it puts more material on the
side of the neutral axis that is in compression, the
underside.

Chalo wrote:
I've noticed jb likes to use the CFRP-wood analogy. I think it bears
pointing out that wood is a pretty terrible material for structural
tubing, which is why nobody uses it that way. It's also worth noting
that aerospace industries, brought up so often in this context, don't
seem to be going out of their way to use CFRP as tubing or framework
anywhere.

Wooden bicycle frames have been tried time and time again and always
found lacking. CFRP, being comparable to a very hard, very strong
wood, should be subject to many of wood's shortcomings-- which looks
to be true.

A Muzi wrote:
In fairness, true monocoque (some Kestrels for example) designs use the material to its best advantage, obviating tube-to-tube jointing issues.

jim beam wrote:
personally, i'm not so convinced about this. and few are true monocoque - giant aren't from what i've seen.

integrity of crfp depends on compaction during cure. enclosed structures like a true monocoque are very hard to get truly compacted. if not, then extra weight is required to build in more safety. while mistakes can be made, epoxied cfrp componentry like forks are proven quantities. when i get around to buying a full carbon frame, i'll probably go for a lugged frame like look.

Kestrel's patent (expired now?) is a pressurized internal bladder and a rigid separable outer mold case. No longer used for an entire frame, just sections, for a few reasons including overly complex and expensive tooling which makes frequent 'model year' changes prohibitive.

We occasionally see moisture problems in glued joints of all material combinations and a one-piece at least doesn't do that. I'm no expert but, looking at other industries' use of the material, many multi-layered directional fiber carbon designs look like those frames (then again, fishing rods don't... ).
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971
.

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