"brittle" vs. non-ductile

jim beam wrote:
Mike Jacoubowsky wrote:
Someone wrote:
Every time we've seen a CFRP bike part that has been hit or loaded
hard enough to break it, it has been broken completely through. That
seems to indicate the the energy to complete a fracture isn't much, at
least for carbon-epoxy such as we see in bikes.

This is both true and incredibly misleading. There are a lot of people
out there riding on damaged (broken) carbon frames & forks that aren't
aware of it. Few know what to look for, and even fewer *want* to look
for the damage, preferring instead to think "phew, looks like it came
out OK, I don't have to shell out a ton of money!"

indeed.

This is probably the best demonstration of why CF is bad for "prime time".


So yes, it's true that few have "seen" a carbon fiber product that's
broken and not yet completely failed, but that doesn't mean they're
not out there.

First you say that there are lots of people riding damaged CF without
knowing, then few have seen these (unless you're splitting "damaged" and
"broken" and "failed"). Seems contradictory, unless you mean there are
lots of damaged frames and forks that don't have symptoms? (something I
have no trouble believing).


absolutely - the warning signs are there but are frequently ignored.

He seems to say there aren't any.

jim beam wrote:
Peter Cole wrote:
jim beam wrote:
following peter cole's confusion on this subject, it seems we need a
little clarification of what constitutes "brittle" fracture.

"brittle" is where there is very little energy absorbed as the
fracture interface propagates through a material. glass is the
classic example of this - once a crack is present, it takes almost
nothing to continue the crack's progress to complete failure.

"ductile" however is a totally different animal. significant energy
is absorbed during ductile deformation. but ductile deformation is
not fracture, it's another process entirely! once ductile
deformation has occurred, fracture requires /further/ propagation
energy.

fracture energy absorption is what determines whether a material is
"brittle" or not. cfrp is not brittle like glass. it is not
ductile, [the apparent, er, "confusion"] but it is typically not
brittle - significant energy is absorbed as the fracture interface
progresses [depending on fabrication and constituent materials of
course].

indeed, fracture energy absorption in non-ductile composites can be
so high, they're actually used in applications /specifically/ for
this reason. anyone familiar with motorcycle helmet testing will be
aware of this. same for bullet-protective military helmets. both
are non-ductile composites with very high fracture energy absorption.
energy absorbed depends on constitution, but the principle applies,
and is worth repeating - it's energy absorbed on fracture interface
progression that determines toughness, not whether the material is
ductile.


What's this the 4th thread? You can keep going but it seems like you
haven't convinced anybody yet. It might help if you cited *any* source
supporting your unique view.

eh? i'm starting a new thread because your [typical] obfuscation is so
convoluted, i really can't be bothered to untangle it. and you keep
getting away from the central point - you don't understand materials.

Really? Prove it by citing anything other than your own opinions.




You're confusing fatigue with brittle failure

no i'm not - you're [wrongly] asserting that low ductility means brittle.

No, I'm not. What's the ductility of Kevlar?


and CF composites with Kevlar composites/hybrids (among other things).

no, but you'd love to put those words of deliberate deceit into my mouth.

OK, show me the "bullet-protective military helmet" made from CF composite.


Yes, CF is sometimes mixed with other materials in applications like
body armor, but the purpose is not to absorb energy, but to stiffen
the assembly to avoid blunt force trauma.

er, that is somewhat "confused".

No, it's factual.



Again, you're confusing force with energy,

no - that's a statement of deliberate deceit.

No, CF composites can withstand high forces but normally don't absorb
much energy. Otherwise, CF would be used instead of Kevlar for body
armor, since it's lighter.


which you have done consistently through these threads.

see above.

See below above.



CF composites can be used to design energy absorbing *structures* (F1
nose & tail boxes), but that involves crushable geometries that absorb
energy in a very specific manner.

no amount of "crushable geometries" would matter if the material were in
fact "brittle". truth is, the /material/ absorbs energy on fracture,
hence their use. "crushable geometry" would mean nothing if the parts
were made of glass.

Composite assemblies (like tubes) can absorb a lot of energy if the
failure mode is precisely controlled, like tube eversion, see
http://www.touchbriefing.com/pdf/11/auto031_r_dyckhoff.pdf

"The high amount of energy absorbed in
this comprises several components:
• the deformation energy of the aramid fibre
component;
• the rupture energy of the carbon fibre
component, including fractures in the matrix;
• the internal friction resulting from shear forces as
the angular structure of the fabric changes during
eversion and expansion of the tube; and
• a friction component caused as the partically
destroyed, everted laminate is forced over the
intact outer surface of the tube."


CF is not usually used in a direct energy absorption role but as in a
supporting strengthening/stiffening role (as in hoop strength
reinforcement in fiberglass vault poles) That's not how bike parts are
designed, so comparisons are misleading.

no, you're trying to deceive again.

No, take a look at current state of the art vaulting pole designs. Why
aren't they all CF?


As everyone in the industry seems to know, low velocity impacts

without numbers, "impact" is an utterly meaningless word - it's the
ephemeral straw-clutch by one desperately seeking to stir fear,
uncertainty and doubt.

The numbers are there, it's been intensively studied.


lead to microcracks in the matrix,

again, without numbers, that is a meaningless statement. [handily
deceitful though.] with composites, the discontinuity between fiber and
matrix accounts for a good deal of short range "problem". there are
ways of addressing but not overcoming this. different matrix materials,
even carbon nanotube in the matrix resin, has significant benefits -
hence easton's use for instance.

I guess that's an agreement?


which eventually coalesce into macro cracks and sudden failure.

and not if they don't.

Why wouldn't they? It's a cumulative process.


just like metal fatigue and dislocation migration.

You say that like it's a good thing.


This is cumulative and not easily detected.

just like metal fatigue and dislocation migration.

Similar, but worse in that it makes an already brittle material more
brittle.


interestingly, i don't see you ringing the bells of armageddon about
metal fatigue and how everyone needs x-ray and ultrasound on their metal
frames. but you're trying to deceive, so that's to be expected.

I don't use aluminum forks, either.


If a parts designer simply optimizes for CF specific strength and
modulus, they're stuck with low impact resistance and brittle failure.

bull****. you don't know what "brittle" means and you're trying to
deceive by misuse of that word.

That's how CF bike parts are generally designed.

that's suppositional bull****.

Two calls of "bull****" with no backup. Typical.

On Mon, 03 Sep 2007 14:32:04 -0700, jim beam
wrote:


eh? the privilege of arguing against me lies with /you/ big guy, not me
- so feel free to go ahead and present your own information. whenever
you're ready...

"privilege of arguing against me"?! Consider me truly debased at
receiving such a distinction! LOL!

My intent was not to argue, it was to know more. Up thread you wrote
that in your experience CF failure is preceded by much 'audible
warning'. Will you be more specific?

Peter Cole wrote:
jim beam wrote:
Mike Jacoubowsky wrote:
Someone wrote:
Every time we've seen a CFRP bike part that has been hit or loaded
hard enough to break it, it has been broken completely through. That
seems to indicate the the energy to complete a fracture isn't much, at
least for carbon-epoxy such as we see in bikes.

This is both true and incredibly misleading. There are a lot of
people out there riding on damaged (broken) carbon frames & forks
that aren't aware of it. Few know what to look for, and even fewer
*want* to look for the damage, preferring instead to think "phew,
looks like it came out OK, I don't have to shell out a ton of money!"

indeed.

This is probably the best demonstration of why CF is bad for "prime time".

er, you ought to let boeing into your secret then...




So yes, it's true that few have "seen" a carbon fiber product that's
broken and not yet completely failed, but that doesn't mean they're
not out there.

First you say that there are lots of people riding damaged CF without
knowing, then few have seen these (unless you're splitting "damaged" and
"broken" and "failed"). Seems contradictory, unless you mean there are
lots of damaged frames and forks that don't have symptoms? (something I
have no trouble believing).

misconstruction.



absolutely - the warning signs are there but are frequently ignored.

He seems to say there aren't any.

putting words into peoples mouths...

Peter Cole wrote:
snip crap

translation of the peter cole position: "cfrp is brittle. except for
when it's not."

tremendous. you should be a lawyer.

Luke wrote:
On Mon, 03 Sep 2007 14:32:04 -0700, jim beam
wrote:

eh? the privilege of arguing against me lies with /you/ big guy, not me
- so feel free to go ahead and present your own information. whenever
you're ready...

"privilege of arguing against me"?! Consider me truly debased at
receiving such a distinction! LOL!

My intent was not to argue, it was to know more. Up thread you wrote
that in your experience CF failure is preceded by much 'audible
warning'. Will you be more specific?

i think you should d.a.g.s. first.

In article , jim beam
wrote:

Luke wrote:
On Mon, 03 Sep 2007 14:32:04 -0700, jim beam
wrote:

eh? the privilege of arguing against me lies with /you/ big guy, not me
- so feel free to go ahead and present your own information. whenever
you're ready...

"privilege of arguing against me"?! Consider me truly debased at
receiving such a distinction! LOL!

My intent was not to argue, it was to know more. Up thread you wrote
that in your experience CF failure is preceded by much 'audible
warning'. Will you be more specific?

i think you should d.a.g.s. first.

A quick search of rbt archives, key words "jim beam carbon failure"
yielded 397 results. A quick scan -- I don't have the time to wade
through the whole list -- reveals many rancorous threads; is there an
example among the results comprising a detailed description of a carbon
component failing you?

Luke wrote:
In article , jim beam
wrote:

Luke wrote:
On Mon, 03 Sep 2007 14:32:04 -0700, jim beam
wrote:

eh? the privilege of arguing against me lies with /you/ big guy, not me
- so feel free to go ahead and present your own information. whenever
you're ready...
"privilege of arguing against me"?! Consider me truly debased at
receiving such a distinction! LOL!

My intent was not to argue, it was to know more. Up thread you wrote
that in your experience CF failure is preceded by much 'audible
warning'. Will you be more specific?
i think you should d.a.g.s. first.

A quick search of rbt archives, key words "jim beam carbon failure"
yielded 397 results. A quick scan -- I don't have the time to wade
through the whole list

and i do???


-- reveals many rancorous threads;

that is not relevant to an innocent question.


is there an
example among the results comprising a detailed description of a carbon
component failing you?

the answers are out there.

bottom line, i smell "agenda" in this question, and it has nothing to do
with curiosity about materials.

In article , jim beam
wrote:

Luke wrote:
In article , jim beam
wrote:

Luke wrote:
On Mon, 03 Sep 2007 14:32:04 -0700, jim beam
wrote:

eh? the privilege of arguing against me lies with /you/ big guy, not me
- so feel free to go ahead and present your own information. whenever
you're ready...
"privilege of arguing against me"?! Consider me truly debased at
receiving such a distinction! LOL!

My intent was not to argue, it was to know more. Up thread you wrote
that in your experience CF failure is preceded by much 'audible
warning'. Will you be more specific?
i think you should d.a.g.s. first.

A quick search of rbt archives, key words "jim beam carbon failure"
yielded 397 results. A quick scan -- I don't have the time to wade
through the whole list

and i do???

Evidently not. So consult your memory, it's much quicker.


-- reveals many rancorous threads;

that is not relevant to an innocent question.

True. No need to have inserted it.


is there an
example among the results comprising a detailed description of a carbon
component failing you?

the answers are out there.

You have them, pass them along.


bottom line, i smell "agenda" in this question, and it has nothing to do
with curiosity about materials.

Lotta aromas circulating...I detect overtones of bull feces in your
evasiveness.

jim beam wrote:
Peter Cole wrote:
jim beam wrote:
Mike Jacoubowsky wrote:
Someone wrote:
Every time we've seen a CFRP bike part that has been hit or loaded
hard enough to break it, it has been broken completely through. That
seems to indicate the the energy to complete a fracture isn't much, at
least for carbon-epoxy such as we see in bikes.

This is both true and incredibly misleading. There are a lot of
people out there riding on damaged (broken) carbon frames & forks
that aren't aware of it. Few know what to look for, and even fewer
*want* to look for the damage, preferring instead to think "phew,
looks like it came out OK, I don't have to shell out a ton of money!"

indeed.

This is probably the best demonstration of why CF is bad for "prime
time".

er, you ought to let boeing into your secret then...

The aircraft industry works to higher standards than joe (jim) consumer.
That's the point.






So yes, it's true that few have "seen" a carbon fiber product that's
broken and not yet completely failed, but that doesn't mean they're
not out there.

First you say that there are lots of people riding damaged CF without
knowing, then few have seen these (unless you're splitting "damaged"
and "broken" and "failed"). Seems contradictory, unless you mean there
are lots of damaged frames and forks that don't have symptoms?
(something I have no trouble believing).

misconstruction.



absolutely - the warning signs are there but are frequently ignored.

He seems to say there aren't any.

putting words into peoples mouths...

Then how (if there are "warning signs") could there be:
"a lot of people out there riding on damaged (broken) carbon frames &
forks that aren't aware of it." ?