CF Bike Shatters Top Tube and Down Tube after hitting a Road Divot

[jim beam]

Tim McNamara wrote:
> In article <[email protected]>,
> damyth <[email protected]> wrote:
>
>> On Aug 16, 3:14 pm, Tim McNamara <[email protected]> wrote:
>>> In article <[email protected]>,
>>>
>>> damyth <[email protected]> wrote:
>>>> Yeah, you're a real Einstein.
>>> And the need to be gratuitously nasty comes from...?
>>>
>>>> The point here is not just post any random picture of a mangled
>>>> random frame. Show me a mangled frame with 2 (virtually) perfect
>>>> wheels, drivetrain, forks, & stays, etc., and then we can start
>>>> the discussion of whether it constitutes a case of JRA or not.
>>>> In the case of the OP's Scott CF bike, having the down tube break
>>>> in two places at the same time is akin to lightning striking the
>>>> same place twice.
>>> We don't know that this is what happened. You're making an
>>> unfounded assumption. The two breaks in the down tube could have
>>> happened sequentially rather than simultaneously and from two
>>> different causes. For example, the front end snaps off and as the
>>> bike falls to the pavement, the down tube end strikes something and
>>> breaks a second time.
>>>
>>> The break at the middle of "Scott" looks like the downtube was
>>> forced upwards, peeling off a "flap" of CF like the strings in a
>>> stick of celery. That, to me, suggests that it was the second
>>> break in the downtube.
>>>
>>> But it's all pretty baseless speculation, since all we have are
>>> three photos and a vague description of the crash.
>>>
>>>> What are the odds of that happening without some sort of
>>>> manufacturing defect? If you stuck a well-constructed CF tube in
>>>> a hydraulic bending mandrel, do you think it's going to section
>>>> off in two virtually perfect pieces like that? If you had paused
>>>> to think about this for more than a millisecond, this question
>>>> ought to have to occurred to you.
>>> That was one question. The other question that ought to have
>>> occurred to you was what might have happened to the bike *before*
>>> the accident. Was the downtube already damaged, perhaps by clamping
>>> it into a roof rack with a down tube grabber?
>>>
>>> Could it be a manufacturing defect? Sure. Could be be something
>>> else? Sure. We have almost no data from which to work, however.
>> It's obvious from your post that you've never handled carbon fiber
>> tubing, certainly not enough to be familiar with their properties.
>> Why don't you compare the typical breaking strength of carbon fiber
>> tubing with the yield strength of metal tubing used on bikes, and get
>> back to me whether you still think your theory of the second break of
>> the down tube by a "grounding crash" holds water. Quite frankly,
>> your theory is laughable to anyone with even the most rudimentary
>> understanding of the properties of (well-constructed) CF tubing.
>>
>> When I said "at the same time," I didn't actually mean the same
>> instantaneous moment in time, more like "on the same ride." I could
>> have been clearing in my original post but all you ditto-heads who
>> clung to the obvious "more than JRA" theory (despite lack of evidence
>> for or against it) was just getting plain annoying, especially if
>> you've never batted around a CF tube to understand how unlikely it is
>> to break transversely as in the OP's pictures.
>
> And yet you're illogical enough to claim that (1) a CF tube is so strong
> that it's almost impossible to break and (2) it can spontaneously blow
> apart when hitting a pothole. You must be partaking of the jim beam.
> You're also missing my point and that of the others- we don't have
> enough information to form an opinion as to what happened. Period. And
> yet for some reason you continue to waste time trying to convince us
> that there's a manufacturing defect. Unless you're clairvoyant or you
> were there when the crash happened, you don't have enough information
> either.

no, he means that carbon tube doesn't typically fail like that. your
non-comprehension is evidenced by the fact that you

1. don't understand that, even though it's been repeated here by several
posters.
2. clearly have no experience.

if you were smart enough, you'd have considered that he actually had
something to say rather than was just adding noise to the signal, unlike
you. retard.

 

[jim beam]

Peter Cole wrote:
> Michael Press wrote:
>> In article <[email protected]>,
>> Peter Cole <[email protected]> wrote:
>>
>>> The thing that concerns me about CF is that it's an inherently
>>> labor-intensive process. That, combined with the fact that the only
>>> real reason to use it is to shave weight means that parts won't be
>>> over-designed and manufacturers will constantly try to squeeze costs.
>>> Cheap CF seems like a recipe for disaster. I think it's much easier
>>> for a piece of sloppy work to slip through CF production than the
>>> highly-automated metal frame production.
>>
>> How is carbon fiber frame building more labor critical than steel
>> frame building? Overheating that steel head tube joint is a serious risk.
>>
>
> I said labor-intensive, not labor critical. It's labor-intensive simply
> because more manual operations are involved, more man-hours in the
> process. Other than small operations, most metal frames these days are
> fabricated by machine in highly automated processes. Tube cutting,
> shaping, welding and painting are often done with robots.
>
> Hand-made metal frames can suffer the same imperfections if
> manufacturers push the cost cutting too far, by rushing the work or
> using inadequately skilled workers. Since automated processes are so
> repeatable, quality is more uniform.
>
> Cheap CF is still constrained by the first law of bicycle design:
> "cheap, light, reliable -- pick any two". Unreliable CF is a bit scarier
> than unreliable metal due to the "sudden catastrophic failure" phenomenon.

a suddenly failed weld is just as scary.

what you would have said if you'd bothered to learn enough is that
what's scary about carbon is relying on manufacturers who cut corners,
then certify testing compliance. the material itself rarely, if ever,
just suddenly fails. as you'd know if you had experience.

 

[Tim McNamara]

In article <[email protected]>,
"Tom Nakashima" <[email protected]> wrote:

> "Tim McNamara" <[email protected]> wrote in message
> news:[email protected]...
> >
> > And yet you're illogical enough to claim that (1) a CF tube is so
> > strong that it's almost impossible to break and (2) it can
> > spontaneously blow apart when hitting a pothole. You must be
> > partaking of the jim beam. You're also missing my point and that of
> > the others- we don't have enough information to form an opinion as
> > to what happened. Period. And yet for some reason you continue to
> > waste time trying to convince us that there's a manufacturing
> > defect. Unless you're clairvoyant or you were there when the crash
> > happened, you don't have enough information either.
>
> We have worked and experimented with prepreg carbon-fiber sheets here
> at the Stanford Linear Accelerator Center. While working with the
> material, we noticed there are such things as "voids" in the epoxy as
> well as voids in the layers. We also noticed how important
> temperature and time is when layering the sheets together. So I can
> believe there could be manufacturing defects that could get by the
> quality control department.

I don't rule that out as a possibility, but I am not going to hang my
hat on that as the answer either. There is just not enough information
available to us.

> In a conversation with John Slawta of Landshark Bicycles, he told me
> about a few NEW carbon-fiber forks he has broken by gently squeezing
> the ends before he paints them. He would not mention the brand. -tom

Better to find them that way. I remain convinced that CF is an
inappropriate material for bike frames, even though saying so usually
nets me a few comments to the effect that I am a knuckle dragging mouth
breather who should go back to the trees.

 

[Kenny]

On Aug 18, 7:15 am, Tim McNamara <[email protected]> wrote:
> I remain convinced that CF is an
> inappropriate material for bike frames, even though saying so usually
> nets me a few comments to the effect that I am a knuckle dragging mouth
> breather who should go back to the trees.
An interjection: I would be curious as to what your opinion of the use
of CF in the building of aircraft?

 

[Tom \Johnny Sunset\ Sherman]

Kenny ??? wrote:
> On Aug 18, 7:15 am, Tim McNamara <[email protected]> wrote:
>> I remain convinced that CF is an
>> inappropriate material for bike frames, even though saying so usually
>> nets me a few comments to the effect that I am a knuckle dragging mouth
>> breather who should go back to the trees.
> An interjection: I would be curious as to what your opinion of the use
> of CF in the building of aircraft?

Aircraft have mandatory certification and inspection programs that go
far beyond what is done for bicycles and bicycle components.

--
Tom Sherman - Holstein-Friesland Bovinia
BEER IS FOOD



--
Posted via a free Usenet account from http://www.teranews.com

 

[Tim McNamara]

In article <[email protected]>,
Kenny <[email protected]> wrote:

> On Aug 18, 7:15 am, Tim McNamara <[email protected]> wrote:
> > I remain convinced that CF is an inappropriate material for bike
> > frames, even though saying so usually nets me a few comments to the
> > effect that I am a knuckle dragging mouth breather who should go
> > back to the trees.
>
> An interjection: I would be curious as to what your opinion of the
> use of CF in the building of aircraft?

I don't know enough about aircraft or the applications of CF in aircraft
to be able to form an opinion.

 

[Derk]

Tim McNamara <[email protected]> wrote:
> I remain convinced that CF is an
> inappropriate material for bike frames, even though saying so usually
> nets me a few comments to the effect that I am a knuckle dragging mouth
> breather who should go back to the trees.
I agree with Tim: it wouldn't be my first choice either.

Derk

 

[Derk]

Tom "Johnny Sunset" Sherman wrote:

> Aircraft have mandatory certification and inspection programs that go
> far beyond what is done for bicycles and bicycle components.
And in spite of that there's a series on National Geographic channel about
planes that crashed.

Derk

 

[Artoi]

In article <[email protected]>,
Kenny <[email protected]> wrote:

> An interjection: I would be curious as to what your opinion of the use
> of CF in the building of aircraft?

An A300-600 series aircraft fell out of the sky because it lost its
vertical fin...
--

 

[jim beam]

Derk wrote:
> Tom "Johnny Sunset" Sherman wrote:
>
>> Aircraft have mandatory certification and inspection programs that go
>> far beyond what is done for bicycles and bicycle components.
> And in spite of that there's a series on National Geographic channel about
> planes that crashed.
>
> Derk

how many crash because of mechanical problems?

 

[jim beam]

Artoi wrote:
> In article <[email protected]>,
> Kenny <[email protected]> wrote:
>
>> An interjection: I would be curious as to what your opinion of the use
>> of CF in the building of aircraft?
>
> An A300-600 series aircraft fell out of the sky because it lost its
> vertical fin...
> --

a MD-83 fell out of the sky once too. does that mean planes are bad?

if you're trying to make the point that composites are different and
require different inspection and testing*, you're correct. if you're
trying to say that composites are somehow bad, you're wrong. they offer
better strength and fatigue properties than traditional materials.
really can't see why anyone would complain about that unless they're
underinformed.


* these days, what are in effect microphones are embedded in composite
componentry and connected to flight computers to detect early signs of
problems. creaking, cracking and groaning, remember?

 

[still me]

On Sat, 18 Aug 2007 07:14:37 -0700, jim beam
<[email protected]> wrote:

>if you're trying to make the point that composites are different and
>require different inspection and testing*, you're correct. if you're
>trying to say that composites are somehow bad, you're wrong. they offer
>better strength and fatigue properties than traditional materials.
>really can't see why anyone would complain about that unless they're
>underinformed.

My steel frame plane is 30 years old and it never fell out of the sky!

 

[jim beam]

still me wrote:
> On Sat, 18 Aug 2007 07:14:37 -0700, jim beam
> <[email protected]> wrote:
>
>> if you're trying to make the point that composites are different and
>> require different inspection and testing*, you're correct. if you're
>> trying to say that composites are somehow bad, you're wrong. they offer
>> better strength and fatigue properties than traditional materials.
>> really can't see why anyone would complain about that unless they're
>> underinformed.
>
> My steel frame plane is 30 years old and it never fell out of the sky!
>

how many flying hours?

what you really mean is that it hasn't fallen out of the sky /yet/.
high strength steels don't have a fatigue endurance limit - just in case
you thought fatigue didn't apply to you.

 

[still me]

On Sat, 18 Aug 2007 07:59:56 -0700, jim beam
<[email protected]> wrote:

>still me wrote:
>> On Sat, 18 Aug 2007 07:14:37 -0700, jim beam
>> <[email protected]> wrote:
>>
>>> if you're trying to make the point that composites are different and
>>> require different inspection and testing*, you're correct. if you're
>>> trying to say that composites are somehow bad, you're wrong. they offer
>>> better strength and fatigue properties than traditional materials.
>>> really can't see why anyone would complain about that unless they're
>>> underinformed.
>>
>> My steel frame plane is 30 years old and it never fell out of the sky!
>>
>
>how many flying hours?
>
>what you really mean is that it hasn't fallen out of the sky /yet/.
>high strength steels don't have a fatigue endurance limit - just in case
>you thought fatigue didn't apply to you.


Ah... I was only joking, doing a light parody on the steel frame vs.
carbon threads. You may have taken me too seriously.

 

[Peter Cole]

Derk wrote:
> Tim McNamara <[email protected]> wrote:
>> I remain convinced that CF is an
>> inappropriate material for bike frames, even though saying so usually
>> nets me a few comments to the effect that I am a knuckle dragging mouth
>> breather who should go back to the trees.
> I agree with Tim: it wouldn't be my first choice either.
>
> Derk

Composite failure modes is a very complicated subject which has been
researched heavily in recent years due to the importance of composites
in aircraft and, perhaps more importantly, the growing interest in the
automotive market.

Composites can provide extremely high levels of "specific energy
absorption" (the amount of energy absorbed per unit weight), in best
case scenarios higher than typical metals.

Metal structures absorb energy through deformation, while composite
absorption is much more complicated, involving interaction between the
reinforcing fiber and the matrix (epoxy typically). Much of the
composite absorption comes from friction as the (broken) fibers are
pulled from the matrix and/or the matrix deforms around/between the plies.

In worst case scenarios, when the fiber/matrix interaction is
compromised, the bulk material can exhibit the characteristics of the
underlying fiber, which is very brittle. This can cause "catastrophic"
as opposed to "progressive" failure. The amount of energy absorbed is
proportional to the area under the stress-strain curve. Plain fibers
(carbon) don't elongate much, so the area under the curve is small.

The actual performance of composite structures under failure loads is
subject to a number of parameters, such as part geometry, fabric weave
and layup angles, load axis, strain rate, layup order and fiber to
matrix ratios. From a geometric perspective, long thin walled tubes are
among the most likely shapes to have catastrophic failure tendencies.

While carbon fiber composites are still gaining experience in new
applications, a great deal is known about similar fiberglass composites
which have been used for many decades in consumer level products (boat
hulls, surfboards, snow skis, etc.). Historically, in those products,
structural problems (particularly from delamination) have been long
recognized.

While fiberglass is a much less attractive material for performance
applications (planes & bikes) than CF, it's a bit safer from a
catastrophic failure for at least a couple of reasons. First, the fiber
is less brittle (will elongate more), and second, it is often used
isotropically, with things like chopped fiber mats providing similar
strength (and stiffness) in all directions. To get the high performance
you want (strength to weight) out of CF you really want to exploit it in
anisotropic modes. This, unfortunately, increases the tendency to
catastrophic failure (lowers toughness).

I remember a group canoe trip years ago with several fiberglass, one
kevlar and one aluminum canoes used in white water. All the fiberglass
canoes were destroyed (smashed), the aluminum was badly dented, while
the kevlar showed hardly a mark. CF can have excellent toughness, but it
has to be designed for it.

On the whole, I think CF has been around long enough in bike frames to
make it reasonably trustworthy, although I'd still avoid cheap CF. I'd
rather crash a steel fork than a CF one, too.

 

[jim beam]

Peter Cole wrote:
> Derk wrote:
>> Tim McNamara <[email protected]> wrote:
>>> I remain convinced that CF is an
>>> inappropriate material for bike frames, even though saying so usually
>>> nets me a few comments to the effect that I am a knuckle dragging mouth
>>> breather who should go back to the trees.
>> I agree with Tim: it wouldn't be my first choice either.
>>
>> Derk
>
> Composite failure modes is a very complicated subject which has been
> researched heavily in recent years due to the importance of composites
> in aircraft and, perhaps more importantly, the growing interest in the
> automotive market.
>
> Composites can provide extremely high levels of "specific energy
> absorption" (the amount of energy absorbed per unit weight), in best
> case scenarios higher than typical metals.
>
> Metal structures absorb energy through deformation, while composite
> absorption is much more complicated, involving interaction between the
> reinforcing fiber and the matrix (epoxy typically). Much of the
> composite absorption comes from friction as the (broken) fibers are
> pulled from the matrix and/or the matrix deforms around/between the plies.
>
> In worst case scenarios, when the fiber/matrix interaction is
> compromised, the bulk material can exhibit the characteristics of the
> underlying fiber, which is very brittle. This can cause "catastrophic"
> as opposed to "progressive" failure. The amount of energy absorbed is
> proportional to the area under the stress-strain curve. Plain fibers
> (carbon) don't elongate much, so the area under the curve is small.

careful peter - you're presuming anybody would actually /use/ "brittle".

and carbon fibers don't elongate in any mode other than elastic. they
have no ductile deformation mechanism like metal.

>
> The actual performance of composite structures under failure loads is
> subject to a number of parameters, such as part geometry, fabric weave
> and layup angles, load axis, strain rate, layup order and fiber to
> matrix ratios. From a geometric perspective, long thin walled tubes are
> among the most likely shapes to have catastrophic failure tendencies.
>
> While carbon fiber composites are still gaining experience in new
> applications, a great deal is known about similar fiberglass composites
> which have been used for many decades in consumer level products (boat
> hulls, surfboards, snow skis, etc.). Historically, in those products,
> structural problems (particularly from delamination) have been long
> recognized.
>
> While fiberglass is a much less attractive material for performance
> applications (planes & bikes) than CF, it's a bit safer from a
> catastrophic failure for at least a couple of reasons. First, the fiber
> is less brittle (will elongate more),

absolutely not. neither glass not carbon fibers are ductile. the only
"elongation" you'll ever get out of them is elasticity.


> and second, it is often used
> isotropically, with things like chopped fiber mats providing similar
> strength (and stiffness) in all directions.

like campy carbon. like trek carbon.

> To get the high performance
> you want (strength to weight) out of CF you really want to exploit it in
> anisotropic modes. This, unfortunately, increases the tendency to
> catastrophic failure (lowers toughness).

massive over-generalization. any anisotropic material has different
properties in different directions. lower strength perpendicular to the
load axis is seldom a problem.

>
> I remember a group canoe trip years ago with several fiberglass, one
> kevlar and one aluminum canoes used in white water. All the fiberglass
> canoes were destroyed (smashed), the aluminum was badly dented, while
> the kevlar showed hardly a mark. CF can have excellent toughness, but it
> has to be designed for it.

but that wasn't a function of the carbon - that was s function of the
composition.


>
> On the whole, I think CF has been around long enough in bike frames to
> make it reasonably trustworthy, although I'd still avoid cheap CF. I'd
> rather crash a steel fork than a CF one, too.


then use the product of a manufacturer that worries about their
reputation and manufactures in a country where people know what they're
doing and aren't cutting corners. i've had a wheel-smashing impact on
my look carbon fork and it hasn't blinked.

 

[A Muzi]

>>> jim beam <[email protected]> wrote:
>>>> if you're trying to make the point that composites are different and
>>>> require different inspection and testing*, you're correct. if you're
>>>> trying to say that composites are somehow bad, you're wrong. they offer
>>>> better strength and fatigue properties than traditional materials.
>>>> really can't see why anyone would complain about that unless they're
>>>> underinformed.

>> still me wrote:
>>> My steel frame plane is 30 years old and it never fell out of the sky!

> jim beam <[email protected]> wrote:
>> how many flying hours?
>> what you really mean is that it hasn't fallen out of the sky /yet/.
>> high strength steels don't have a fatigue endurance limit - just in case
>> you thought fatigue didn't apply to you.

still me wrote:
> Ah... I was only joking, doing a light parody on the steel frame vs.
> carbon threads. You may have taken me too seriously.

Some homebuilt aircraft use nice seamless CrMo steel with brazed joints.
(their suppliers carry suitable materials for special-project bicycle
frames such as replacement mixte stays)
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

 

[Peter Cole]

jim beam wrote:
> Peter Cole wrote:
>> Derk wrote:
>>> Tim McNamara <[email protected]> wrote:
>>>> I remain convinced that CF is an
>>>> inappropriate material for bike frames, even though saying so usually
>>>> nets me a few comments to the effect that I am a knuckle dragging mouth
>>>> breather who should go back to the trees.
>>> I agree with Tim: it wouldn't be my first choice either.
>>>
>>> Derk
>>
>> Composite failure modes is a very complicated subject which has been
>> researched heavily in recent years due to the importance of composites
>> in aircraft and, perhaps more importantly, the growing interest in the
>> automotive market.
>>
>> Composites can provide extremely high levels of "specific energy
>> absorption" (the amount of energy absorbed per unit weight), in best
>> case scenarios higher than typical metals.
>>
>> Metal structures absorb energy through deformation, while composite
>> absorption is much more complicated, involving interaction between the
>> reinforcing fiber and the matrix (epoxy typically). Much of the
>> composite absorption comes from friction as the (broken) fibers are
>> pulled from the matrix and/or the matrix deforms around/between the
>> plies.
>>
>> In worst case scenarios, when the fiber/matrix interaction is
>> compromised, the bulk material can exhibit the characteristics of the
>> underlying fiber, which is very brittle. This can cause "catastrophic"
>> as opposed to "progressive" failure. The amount of energy absorbed is
>> proportional to the area under the stress-strain curve. Plain fibers
>> (carbon) don't elongate much, so the area under the curve is small.
>
> careful peter - you're presuming anybody would actually /use/ "brittle".
>
> and carbon fibers don't elongate in any mode other than elastic. they
> have no ductile deformation mechanism like metal.
>
>>
>> The actual performance of composite structures under failure loads is
>> subject to a number of parameters, such as part geometry, fabric weave
>> and layup angles, load axis, strain rate, layup order and fiber to
>> matrix ratios. From a geometric perspective, long thin walled tubes
>> are among the most likely shapes to have catastrophic failure tendencies.
>>
>> While carbon fiber composites are still gaining experience in new
>> applications, a great deal is known about similar fiberglass
>> composites which have been used for many decades in consumer level
>> products (boat hulls, surfboards, snow skis, etc.). Historically, in
>> those products, structural problems (particularly from delamination)
>> have been long recognized.
>>
>> While fiberglass is a much less attractive material for performance
>> applications (planes & bikes) than CF, it's a bit safer from a
>> catastrophic failure for at least a couple of reasons. First, the
>> fiber is less brittle (will elongate more),
>
> absolutely not. neither glass not carbon fibers are ductile. the only
> "elongation" you'll ever get out of them is elasticity.

Who said anything about ductility? That's your red herring.

Glass fiber typically has 3x the elongation at failure vs CF.


>
>
>> and second, it is often used isotropically, with things like chopped
>> fiber mats providing similar strength (and stiffness) in all directions.
>
> like campy carbon. like trek carbon.

I think you misunderstand.


>
>> To get the high performance you want (strength to weight) out of CF
>> you really want to exploit it in anisotropic modes. This,
>> unfortunately, increases the tendency to catastrophic failure (lowers
>> toughness).
>
> massive over-generalization. any anisotropic material has different
> properties in different directions. lower strength perpendicular to the
> load axis is seldom a problem.

That's the opposite/inverse of what I said.

>>
>> I remember a group canoe trip years ago with several fiberglass, one
>> kevlar and one aluminum canoes used in white water. All the fiberglass
>> canoes were destroyed (smashed), the aluminum was badly dented, while
>> the kevlar showed hardly a mark. CF can have excellent toughness, but
>> it has to be designed for it.
>
> but that wasn't a function of the carbon - that was s function of the
> composition.

Just an illustration of toughness.


>>
>> On the whole, I think CF has been around long enough in bike frames to
>> make it reasonably trustworthy, although I'd still avoid cheap CF. I'd
>> rather crash a steel fork than a CF one, too.
>
>
> then use the product of a manufacturer that worries about their
> reputation and manufactures in a country where people know what they're
> doing and aren't cutting corners. i've had a wheel-smashing impact on
> my look carbon fork and it hasn't blinked.

I think this is just a windy restatement.

 

[jim beam]

Peter Cole wrote:
> jim beam wrote:
>> Peter Cole wrote:
>>> Derk wrote:
>>>> Tim McNamara <[email protected]> wrote:
>>>>> I remain convinced that CF is an
>>>>> inappropriate material for bike frames, even though saying so usually
>>>>> nets me a few comments to the effect that I am a knuckle dragging
>>>>> mouth
>>>>> breather who should go back to the trees.
>>>> I agree with Tim: it wouldn't be my first choice either.
>>>>
>>>> Derk
>>>
>>> Composite failure modes is a very complicated subject which has been
>>> researched heavily in recent years due to the importance of
>>> composites in aircraft and, perhaps more importantly, the growing
>>> interest in the automotive market.
>>>
>>> Composites can provide extremely high levels of "specific energy
>>> absorption" (the amount of energy absorbed per unit weight), in best
>>> case scenarios higher than typical metals.
>>>
>>> Metal structures absorb energy through deformation, while composite
>>> absorption is much more complicated, involving interaction between
>>> the reinforcing fiber and the matrix (epoxy typically). Much of the
>>> composite absorption comes from friction as the (broken) fibers are
>>> pulled from the matrix and/or the matrix deforms around/between the
>>> plies.
>>>
>>> In worst case scenarios, when the fiber/matrix interaction is
>>> compromised, the bulk material can exhibit the characteristics of the
>>> underlying fiber, which is very brittle. This can cause
>>> "catastrophic" as opposed to "progressive" failure. The amount of
>>> energy absorbed is proportional to the area under the stress-strain
>>> curve. Plain fibers (carbon) don't elongate much, so the area under
>>> the curve is small.
>>
>> careful peter - you're presuming anybody would actually /use/ "brittle".
>>
>> and carbon fibers don't elongate in any mode other than elastic. they
>> have no ductile deformation mechanism like metal.
>>
>>>
>>> The actual performance of composite structures under failure loads is
>>> subject to a number of parameters, such as part geometry, fabric
>>> weave and layup angles, load axis, strain rate, layup order and fiber
>>> to matrix ratios. From a geometric perspective, long thin walled
>>> tubes are among the most likely shapes to have catastrophic failure
>>> tendencies.
>>>
>>> While carbon fiber composites are still gaining experience in new
>>> applications, a great deal is known about similar fiberglass
>>> composites which have been used for many decades in consumer level
>>> products (boat hulls, surfboards, snow skis, etc.). Historically, in
>>> those products, structural problems (particularly from delamination)
>>> have been long recognized.
>>>
>>> While fiberglass is a much less attractive material for performance
>>> applications (planes & bikes) than CF, it's a bit safer from a
>>> catastrophic failure for at least a couple of reasons. First, the
>>> fiber is less brittle (will elongate more),
>>
>> absolutely not. neither glass not carbon fibers are ductile. the
>> only "elongation" you'll ever get out of them is elasticity.
>
> Who said anything about ductility? That's your red herring.
>
> Glass fiber typically has 3x the elongation at failure vs CF.

no red herring. the /composite/ will elongate. you said "fiber".
fibers don't. and carbon composites can do that too.


>
>
>>
>>
>>> and second, it is often used isotropically, with things like chopped
>>> fiber mats providing similar strength (and stiffness) in all directions.
>>
>> like campy carbon. like trek carbon.
>
> I think you misunderstand.

what? campy /don't/ use randomly oriented fiber like glass fiber
commonly is? what abut trek? i think you need to check your facts.

>
>
>>
>>> To get the high performance you want (strength to weight) out of CF
>>> you really want to exploit it in anisotropic modes. This,
>>> unfortunately, increases the tendency to catastrophic failure (lowers
>>> toughness).
>>
>> massive over-generalization. any anisotropic material has different
>> properties in different directions. lower strength perpendicular to
>> the load axis is seldom a problem.
>
> That's the opposite/inverse of what I said.

you said: "you really want to exploit it in anisotropic modes. This,
unfortunately, increases the tendency to catastrophic failure".

so, are you or are you not saying that anisotropy leads to failure? you
may have /meant/ something different, but that's what you said.

>
>>>
>>> I remember a group canoe trip years ago with several fiberglass, one
>>> kevlar and one aluminum canoes used in white water. All the
>>> fiberglass canoes were destroyed (smashed), the aluminum was badly
>>> dented, while the kevlar showed hardly a mark. CF can have excellent
>>> toughness, but it has to be designed for it.
>>
>> but that wasn't a function of the carbon - that was s function of the
>> composition.
>
> Just an illustration of toughness.

no, it's an illustration of composition. carbon fibers are not brittle.

>
>
>>>
>>> On the whole, I think CF has been around long enough in bike frames
>>> to make it reasonably trustworthy, although I'd still avoid cheap CF.
>>> I'd rather crash a steel fork than a CF one, too.
>>
>>
>> then use the product of a manufacturer that worries about their
>> reputation and manufactures in a country where people know what
>> they're doing and aren't cutting corners. i've had a wheel-smashing
>> impact on my look carbon fork and it hasn't blinked.
>
> I think this is just a windy restatement.

yeah. like a bunch of windy generalizations about composites that end
up being misleading and unhelpful.

 

[Artoi]

In article <[email protected]>,
jim beam <[email protected]> wrote:

> Artoi wrote:
> > In article <[email protected]>,
> > Kenny <[email protected]> wrote:
> >
> >> An interjection: I would be curious as to what your opinion of the use
> >> of CF in the building of aircraft?
> >
> > An A300-600 series aircraft fell out of the sky because it lost its
> > vertical fin...
> > --
>
> a MD-83 fell out of the sky once too. does that mean planes are bad?
>
> if you're trying to make the point that composites are different and
> require different inspection and testing*, you're correct. if you're
> trying to say that composites are somehow bad, you're wrong. they offer
> better strength and fatigue properties than traditional materials.
> really can't see why anyone would complain about that unless they're
> underinformed.
>
> * these days, what are in effect microphones are embedded in composite
> componentry and connected to flight computers to detect early signs of
> problems. creaking, cracking and groaning, remember?

Relax. It was just a piece of factual data. Pointing out that CF even at
aerospace standard of QC can have unplanned failures.
--