"CF Bike Shatters" - continued

the "CF Bike Shatters" thread is now too deep for me to follow on my
limited screen real estate - i'm starting a new thread.

peter cole wrote:
jim beam wrote:
Peter Cole wrote:

Find one to support your claim that carbon fibers aren't brittle
& I'll read along.

learn about yield before you /dare/ to lecture on deformation,
bull****ter.

Oh please. Typical "jim beam" switcharoo. We're talking about
fracture (see thread title).

you're confusing fracture of brittle materials with fracture of ductile
materials - the two mechanisms are completely different. but hey that
wouldn't be the first time that ignoring fundamentals suits your
argument, right?

Carbon fibers are brittle.

in isolation, they are. so is any high strength material. but cfrp is
not. what's why we use it!

They elongate
only between 0.8 - 1.4% before fracture in tension. E-glass is 3x
that, 6061 is ~20x that.

you're mixing apples with oranges. carbon fiber [and glass fiber] have
no deformation mechanism, no dislocation function. so they have no
ductility. so they are "brittle". again, this is not to be confused
with the behavior of their composites.

for glass and carbon, their stress/strain graphs are much extended -
what would be the hooke's law region of a ductile material.

If you have a source (other than yourself)
that says otherwise, I'm all ears.

go to a library!
you can also look at this:
http://www.flickr.com/photos/38636024@N00/1208725721/
the "x" points are the "failure" points for all the materials since
onset of yield is failure.


If you take the often cited 6x ultimate yield strength of CF, derate
it by the 4 plies (minimum, 0, 90 +-45) you need for isotropy, plus
the ratio of fiber to epoxy, you come out with nothing special wrt
overall strength.

eh? why do you need isotropy??? oh, you're trying to force an argument
where none exists. my bad.

That's why there isn't much difference in CF vs Al
handlebars and seatposts (except price).

incorrect. it's because it's relatively cheap fiber, relatively
imprecise manufacturing and a generous safety margin.

It's only when you exploit
anisotropy that CF makes sense, but then you're stuck with lack of
impact resistance and brittle failure as a trade off.

but you have that kind of trade off with /any/ high strength material,
even steel. the higher the strength, the more brittle.

CF is great for
some apps, marginal for others and crappy for the rest. It's an
engineering thing.

wow. condescension, massive over-generalization and naivety all in one.

jim beam wrote:
the "CF Bike Shatters" thread is now too deep for me to follow on my
limited screen real estate - i'm starting a new thread.

peter cole wrote:
jim beam wrote:
Peter Cole wrote:

Find one to support your claim that carbon fibers aren't brittle
& I'll read along.

learn about yield before you /dare/ to lecture on deformation,
bull****ter.

Oh please. Typical "jim beam" switcharoo. We're talking about
fracture (see thread title).

you're confusing fracture of brittle materials with fracture of ductile
materials -

I'm not "confusing" them, I'm comparing them.


Carbon fibers are brittle.

in isolation, they are. so is any high strength material. but cfrp is
not. what's why we use it!

I don't know who "we" is.

You're absolutely wrong about CFRP. You can't discuss an inherently
anisotropic material without qualifying by fiber orientation (pretty
much my whole point).

A unidirectional fiber composite will have characteristics very much
like those of the reinforcing fiber when loaded on-axis. Off-axis, those
properties change rapidly, becoming essentially those of the matrix at
90 degrees.


They elongate
only between 0.8 - 1.4% before fracture in tension. E-glass is 3x
that, 6061 is ~20x that.

you're mixing apples with oranges. carbon fiber [and glass fiber] have
no deformation mechanism, no dislocation function. so they have no
ductility. so they are "brittle". again, this is not to be confused
with the behavior of their composites.

On-axis, the behavior of composite and fiber are very similar.


for glass and carbon, their stress/strain graphs are much extended -

Extended from what?

what would be the hooke's law region of a ductile material.

I give up, what?


If you have a source (other than yourself)
that says otherwise, I'm all ears.

go to a library!
you can also look at this:
http://www.flickr.com/photos/38636024@N00/1208725721/
the "x" points are the "failure" points for all the materials since
onset of yield is failure.

Citing yourself again? Why am I not surprised. You're never going to
learn anything that way.


If you take the often cited 6x ultimate yield strength of CF, derate
it by the 4 plies (minimum, 0, 90 +-45) you need for isotropy, plus
the ratio of fiber to epoxy, you come out with nothing special wrt
overall strength.

eh? why do you need isotropy??? oh, you're trying to force an argument
where none exists. my bad.

No, I'm trying to compare "apples to apples" -- material suitability for
isotropic loading.


That's why there isn't much difference in CF vs Al
handlebars and seatposts (except price).

incorrect. it's because it's relatively cheap fiber, relatively
imprecise manufacturing and a generous safety margin.

How do you know what the safety margin is?
How do you know what the fiber is?
How do you know what the process is?

In the past, you've made the rather obvious point that it's silly to
talk about metals without knowing the specific alloy. Now, you're making
gross generalizations about a material which has much greater
parameterization.

As far as I know, no component or frame manufacturer publishes layup
schedules. If you have any, please share. You claimed that a "visit to a
bike shop" would allow one to learn this. I fail to see how visual
inspection of a composite part would reveal the layup schedule. At best,
you could perhaps get a little information on the outermost ply, often,
not even that.


It's only when you exploit
anisotropy that CF makes sense, but then you're stuck with lack of
impact resistance and brittle failure as a trade off.

but you have that kind of trade off with /any/ high strength material,
even steel. the higher the strength, the more brittle.

You're missing the point about anisotropy.


CF is great for
some apps, marginal for others and crappy for the rest. It's an
engineering thing.

wow. condescension, massive over-generalization and naivety all in one.

No, just engineering basics. With CF bars and posts, you get (more
expensive) parts with similar weights. You also get susceptibility to
damage from clamping pressure and/or impact. Crappy (yet popular)
applications.

Peter Cole wrote:
jim beam wrote:
the "CF Bike Shatters" thread is now too deep for me to follow on my
limited screen real estate - i'm starting a new thread.

peter cole wrote:
jim beam wrote:
Peter Cole wrote:

Find one to support your claim that carbon fibers aren't brittle
& I'll read along.

learn about yield before you /dare/ to lecture on deformation,
bull****ter.

Oh please. Typical "jim beam" switcharoo. We're talking about
fracture (see thread title).

you're confusing fracture of brittle materials with fracture of
ductile materials -

I'm not "confusing" them, I'm comparing them.

but you are confusing them - you're not differentiating between ductile
and brittle - and that's pretty damned fundamental.



Carbon fibers are brittle.

in isolation, they are. so is any high strength material. but cfrp is
not. what's why we use it!

I don't know who "we" is.

prick.


You're absolutely wrong about CFRP. You can't discuss an inherently
anisotropic material without qualifying by fiber orientation (pretty
much my whole point).

eh? /you/ are defeating your own argument!!! first you b.s. about
"isotropic" cfrp, now you're admitting that it's inherently not!!!



A unidirectional fiber composite will have characteristics very much
like those of the reinforcing fiber when loaded on-axis. Off-axis, those
properties change rapidly,

they don't just "change rapidly", they're completely different. that's
why it's anisotropic!!!

becoming essentially those of the matrix at
90 degrees.

mince words whydontcha



They elongate
only between 0.8 - 1.4% before fracture in tension. E-glass is 3x
that, 6061 is ~20x that.

you're mixing apples with oranges. carbon fiber [and glass fiber] have
no deformation mechanism, no dislocation function. so they have no
ductility. so they are "brittle". again, this is not to be confused
with the behavior of their composites.

On-axis, the behavior of composite and fiber are very similar.

but composites rarely if ever use solely uniaxial layup. you're trying
to twist the facts again.



for glass and carbon, their stress/strain graphs are much extended -

Extended from what?

compared to the ductile materials with which you're confused.


what would be the hooke's law region of a ductile material.

I give up, what?

that wasn't a question. i missed the word "from" - which you'd have
spotted if you weren't so intent on being a prick.



If you have a source (other than yourself)
that says otherwise, I'm all ears.

go to a library!
you can also look at this:
http://www.flickr.com/photos/38636024@N00/1208725721/
the "x" points are the "failure" points for all the materials since
onset of yield is failure.

Citing yourself again? Why am I not surprised. You're never going to
learn anything that way.

prick. /you/ won't admit that you don't understand the difference
between ductile and brittle. if you won't open a book, then i have to
show you.




If you take the often cited 6x ultimate yield strength of CF, derate
it by the 4 plies (minimum, 0, 90 +-45) you need for isotropy, plus
the ratio of fiber to epoxy, you come out with nothing special wrt
overall strength.

eh? why do you need isotropy??? oh, you're trying to force an
argument where none exists. my bad.

No, I'm trying to compare "apples to apples" -- material suitability for
isotropic loading.

aha! more fundamental misunderstanding - there's no such thing as
isotropic loading. that's why we have poisson's ratio.




That's why there isn't much difference in CF vs Al
handlebars and seatposts (except price).

incorrect. it's because it's relatively cheap fiber, relatively
imprecise manufacturing and a generous safety margin.

How do you know what the safety margin is?
How do you know what the fiber is?
How do you know what the process is?

are you denying the facts?



In the past, you've made the rather obvious point that it's silly to
talk about metals without knowing the specific alloy. Now, you're making
gross generalizations about a material which has much greater
parameterization.

principle apply, big guy.


As far as I know, no component or frame manufacturer publishes layup
schedules.

they don't quantify, but they do illustrate. you should look some time.


If you have any, please share. You claimed that a "visit to a
bike shop" would allow one to learn this.

campy carbon cranks. you can see the exterior layup pattern -
inconvenient for you to admit though this may be.


I fail to see how visual
inspection of a composite part would reveal the layup schedule.

er, because you can see the exterior through the clearcoat? but you wan
tto talk substrate? well, you'll have to look online, won't you.


At best,
you could perhaps get a little information on the outermost ply, often,
not even that.

bingo.



It's only when you exploit
anisotropy that CF makes sense, but then you're stuck with lack of
impact resistance and brittle failure as a trade off.

but you have that kind of trade off with /any/ high strength material,
even steel. the higher the strength, the more brittle.

You're missing the point about anisotropy.

no i'm not. and that's a spectacular statement from a guy that doesn't
understand the difference between ductile elongation and brittle fracture.




CF is great for
some apps, marginal for others and crappy for the rest. It's an
engineering thing.

wow. condescension, massive over-generalization and naivety all in one.

No, just engineering basics. With CF bars and posts, you get (more
expensive) parts with similar weights. You also get susceptibility to
damage from clamping pressure and/or impact. Crappy (yet popular)
applications.

so when planes have warning labels on them telling crew not to walk on
wings, that can be ignored? bull****. carbon componentry has labels
saying "do not clamp", "do not exceed...", etc., that can be ignored?
bull****.

twist all you want - you're still missing the basics.

jim beam wrote:
Peter Cole wrote:
jim beam wrote:
the "CF Bike Shatters" thread is now too deep for me to follow on my
limited screen real estate - i'm starting a new thread.

peter cole wrote:
jim beam wrote:
Peter Cole wrote:

Find one to support your claim that carbon fibers aren't brittle
& I'll read along.

learn about yield before you /dare/ to lecture on deformation,
bull****ter.

Oh please. Typical "jim beam" switcharoo. We're talking about
fracture (see thread title).

you're confusing fracture of brittle materials with fracture of
ductile materials -

I'm not "confusing" them, I'm comparing them.

but you are confusing them - you're not differentiating between ductile
and brittle - and that's pretty damned fundamental.


You can keep saying that, but I'm not.




Carbon fibers are brittle.

in isolation, they are. so is any high strength material. but cfrp is
not. what's why we use it!

I don't know who "we" is.

prick.


You're absolutely wrong about CFRP. You can't discuss an inherently
anisotropic material without qualifying by fiber orientation (pretty
much my whole point).

eh? /you/ are defeating your own argument!!! first you b.s. about
"isotropic" cfrp, now you're admitting that it's inherently not!!!

Nonsense, read it again.



A unidirectional fiber composite will have characteristics very much
like those of the reinforcing fiber when loaded on-axis. Off-axis,
those properties change rapidly,

they don't just "change rapidly", they're completely different. that's
why it's anisotropic!!!

becoming essentially those of the matrix at 90 degrees.

mince words whydontcha

Nonsense, read it again.




They elongate
only between 0.8 - 1.4% before fracture in tension. E-glass is 3x
that, 6061 is ~20x that.

you're mixing apples with oranges. carbon fiber [and glass fiber] have
no deformation mechanism, no dislocation function. so they have no
ductility. so they are "brittle". again, this is not to be confused
with the behavior of their composites.

On-axis, the behavior of composite and fiber are very similar.

but composites rarely if ever use solely uniaxial layup. you're trying
to twist the facts again.

I simply stated a fact.



for glass and carbon, their stress/strain graphs are much extended -

Extended from what?

compared to the ductile materials with which you're confused.


what would be the hooke's law region of a ductile material.

I give up, what?

that wasn't a question. i missed the word "from" - which you'd have
spotted if you weren't so intent on being a prick.

Your statement is still incoherent.





If you have a source (other than yourself)
that says otherwise, I'm all ears.

go to a library!
you can also look at this:
http://www.flickr.com/photos/38636024@N00/1208725721/
the "x" points are the "failure" points for all the materials since
onset of yield is failure.

Citing yourself again? Why am I not surprised. You're never going to
learn anything that way.

prick. /you/ won't admit that you don't understand the difference
between ductile and brittle. if you won't open a book, then i have to
show you.

Your diagram has no useful information.

If you take the often cited 6x ultimate yield strength of CF, derate
it by the 4 plies (minimum, 0, 90 +-45) you need for isotropy, plus
the ratio of fiber to epoxy, you come out with nothing special wrt
overall strength.

eh? why do you need isotropy??? oh, you're trying to force an
argument where none exists. my bad.

No, I'm trying to compare "apples to apples" -- material suitability
for isotropic loading.

aha! more fundamental misunderstanding - there's no such thing as
isotropic loading. that's why we have poisson's ratio.

Now who's mincing words?





That's why there isn't much difference in CF vs Al
handlebars and seatposts (except price).

incorrect. it's because it's relatively cheap fiber, relatively
imprecise manufacturing and a generous safety margin.

How do you know what the safety margin is?
How do you know what the fiber is?
How do you know what the process is?

are you denying the facts?

Show me a fact & I'll get back to you on that.




In the past, you've made the rather obvious point that it's silly to
talk about metals without knowing the specific alloy. Now, you're
making gross generalizations about a material which has much greater
parameterization.

principle apply, big guy.

That's informative!



As far as I know, no component or frame manufacturer publishes layup
schedules.

they don't quantify, but they do illustrate. you should look some time.

I tried. Why don't you post some of the examples you've found?



If you have any, please share. You claimed that a "visit to a bike
shop" would allow one to learn this.

campy carbon cranks. you can see the exterior layup pattern -
inconvenient for you to admit though this may be.


I fail to see how visual inspection of a composite part would reveal
the layup schedule.

er, because you can see the exterior through the clearcoat? but you wan
tto talk substrate? well, you'll have to look online, won't you.


At best, you could perhaps get a little information on the outermost
ply, often, not even that.

bingo.

That's your idea of a layup schedule?


It's only when you exploit
anisotropy that CF makes sense, but then you're stuck with lack of
impact resistance and brittle failure as a trade off.

but you have that kind of trade off with /any/ high strength
material, even steel. the higher the strength, the more brittle.

You're missing the point about anisotropy.

no i'm not. and that's a spectacular statement from a guy that doesn't
understand the difference between ductile elongation and brittle fracture.

Repeating that doesn't make it true. You, on the other hand, seem to be
the only one on the planet who doesn't see that CFRP has low impact
resistance.

CF is great for
some apps, marginal for others and crappy for the rest. It's an
engineering thing.

wow. condescension, massive over-generalization and naivety all in one.

No, just engineering basics. With CF bars and posts, you get (more
expensive) parts with similar weights. You also get susceptibility to
damage from clamping pressure and/or impact. Crappy (yet popular)
applications.

so when planes have warning labels on them telling crew not to walk on
wings, that can be ignored? bull****. carbon componentry has labels
saying "do not clamp", "do not exceed...", etc., that can be ignored?
bull****.

Who said anything about ignoring labels? I was talking about the need
for labels.

twist all you want - you're still missing the basics.

If you say so, but do try to scrape up a fact or two & perhaps we can go
from there.

jim beam wrote:

you're confusing fracture of brittle materials with fracture of ductile
materials - the two mechanisms are completely different.
....
carbon fiber [and glass fiber] have
no deformation mechanism, no dislocation function. so they have no
ductility. so they are "brittle". again, this is not to be confused
with the behavior of their composites.

for glass and carbon, their stress/strain graphs are much extended -

By "extended", I presume you mean that CFRP and GRP can accept more
stress and strain before failure than structurally comparable metals
can. But since the mechanisms of failure are so different, I think
it's fair to compare the amount of work required to reach brittle
failure for advanced composites and structural metals. You'd have to
seek out an a terribly temperamental metal to find one that is even in
the same ballpark in terms of the small amount of work required to
fracture it. And that's really the practical measure of toughness,
isn't it?

I am surprised at your apparent suggestion (though you don't actually
come out and say so directly) that CFRP could have a significant
amount of ductility or toughness in any of its commonly used
formulations for bicycles. I understand that toughness was one of the
goals, realized or not, for nylon thermoplastic-based CFRP bike frames
and parts. Those constituted a fleeting market experiment, and are
now all gone. The CFRP frames and parts that remain are epoxy-based
and therefore subject to vitreous fracture of both fiber and matrix,
without any useful amount of plastic deformation to absorb transient
overloads or point impacts. In other words, they exhibit extremely
poor toughness.

Which is the point you're trying hard not to concede, right?

Chalo

Chalo Colina wrote:

By "extended", I presume you mean that CFRP and GRP can accept more
stress and strain before failure than structurally comparable metals
can. But since the mechanisms of failure are so different, I think
it's fair to compare the amount of work required to reach brittle
failure for advanced composites and structural metals. You'd have to
seek out an a terribly temperamental metal to find one that is even in
the same ballpark in terms of the small amount of work required to
fracture it....

Quenched plain carbon steel without tempering?

--
Tom Sherman - Holstein-Friesland Bovinia

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

Peter Cole wrote:
jim beam wrote:
Peter Cole wrote:
jim beam wrote:
the "CF Bike Shatters" thread is now too deep for me to follow on my
limited screen real estate - i'm starting a new thread.

peter cole wrote:
jim beam wrote:
Peter Cole wrote:

Find one to support your claim that carbon fibers aren't brittle
& I'll read along.

learn about yield before you /dare/ to lecture on deformation,
bull****ter.

Oh please. Typical "jim beam" switcharoo. We're talking about
fracture (see thread title).

you're confusing fracture of brittle materials with fracture of
ductile materials -

I'm not "confusing" them, I'm comparing them.

but you are confusing them - you're not differentiating between
ductile and brittle - and that's pretty damned fundamental.


You can keep saying that, but I'm not.

"6061 elongation is 26%". that's plastic deformation.
"carbon fiber elongation is 1.5%". that's elastic deformation.

there's a fundamental difference an "engineer" should understand.






Carbon fibers are brittle.

in isolation, they are. so is any high strength material. but cfrp is
not. what's why we use it!

I don't know who "we" is.

prick.


You're absolutely wrong about CFRP. You can't discuss an inherently
anisotropic material without qualifying by fiber orientation (pretty
much my whole point).

eh? /you/ are defeating your own argument!!! first you b.s. about
"isotropic" cfrp, now you're admitting that it's inherently not!!!

Nonsense, read it again.

evasive b.s.




A unidirectional fiber composite will have characteristics very much
like those of the reinforcing fiber when loaded on-axis. Off-axis,
those properties change rapidly,

they don't just "change rapidly", they're completely different.
that's why it's anisotropic!!!

becoming essentially those of the matrix at 90 degrees.

mince words whydontcha

Nonsense, read it again.

more evasive b.s.






They elongate
only between 0.8 - 1.4% before fracture in tension. E-glass is 3x
that, 6061 is ~20x that.

you're mixing apples with oranges. carbon fiber [and glass fiber] have
no deformation mechanism, no dislocation function. so they have no
ductility. so they are "brittle". again, this is not to be confused
with the behavior of their composites.

On-axis, the behavior of composite and fiber are very similar.

but composites rarely if ever use solely uniaxial layup. you're
trying to twist the facts again.

I simply stated a fact.

no, you twisted "facts" to state an untruth.





for glass and carbon, their stress/strain graphs are much extended -

Extended from what?

compared to the ductile materials with which you're confused.


what would be the hooke's law region of a ductile material.

I give up, what?

that wasn't a question. i missed the word "from" - which you'd have
spotted if you weren't so intent on being a prick.

Your statement is still incoherent.

eh? that you don't understand the difference between elastic and
plastic deformation?







If you have a source (other than yourself)
that says otherwise, I'm all ears.

go to a library!
you can also look at this:
http://www.flickr.com/photos/38636024@N00/1208725721/
the "x" points are the "failure" points for all the materials since
onset of yield is failure.

Citing yourself again? Why am I not surprised. You're never going to
learn anything that way.

prick. /you/ won't admit that you don't understand the difference
between ductile and brittle. if you won't open a book, then i have to
show you.

Your diagram has no useful information.

eh? it illustrates different deformation for different materials -
elastic and plastic. something you don't seem to understand.



If you take the often cited 6x ultimate yield strength of CF, derate
it by the 4 plies (minimum, 0, 90 +-45) you need for isotropy, plus
the ratio of fiber to epoxy, you come out with nothing special wrt
overall strength.

eh? why do you need isotropy??? oh, you're trying to force an
argument where none exists. my bad.

No, I'm trying to compare "apples to apples" -- material suitability
for isotropic loading.

aha! more fundamental misunderstanding - there's no such thing as
isotropic loading. that's why we have poisson's ratio.

Now who's mincing words?

eh? you want me to be more direct? ok. you're an "engineer" that
doesn't know the fundamentals of deformation on loading. that's pretty
****ing weak.

that unmincing enough for you?






That's why there isn't much difference in CF vs Al
handlebars and seatposts (except price).

incorrect. it's because it's relatively cheap fiber, relatively
imprecise manufacturing and a generous safety margin.

How do you know what the safety margin is?
How do you know what the fiber is?
How do you know what the process is?

are you denying the facts?

Show me a fact & I'll get back to you on that.

denial. prick.






In the past, you've made the rather obvious point that it's silly to
talk about metals without knowing the specific alloy. Now, you're
making gross generalizations about a material which has much greater
parameterization.

principle apply, big guy.

That's informative!

from someone that doesn't know basic engineering principles like the
difference between elastic and plastic, that's a real dumb-ass statement.





As far as I know, no component or frame manufacturer publishes layup
schedules.

they don't quantify, but they do illustrate. you should look some time.

I tried. Why don't you post some of the examples you've found?

why do i have to do all the heavy lifting??? you're the prick
contesting the issue.





If you have any, please share. You claimed that a "visit to a bike
shop" would allow one to learn this.

campy carbon cranks. you can see the exterior layup pattern -
inconvenient for you to admit though this may be.


I fail to see how visual inspection of a composite part would reveal
the layup schedule.

er, because you can see the exterior through the clearcoat? but you
wan tto talk substrate? well, you'll have to look online, won't you.


At best, you could perhaps get a little information on the outermost
ply, often, not even that.

bingo.

That's your idea of a layup schedule?

no. but you're my idea of an evasive prick.



It's only when you exploit
anisotropy that CF makes sense, but then you're stuck with lack of
impact resistance and brittle failure as a trade off.

but you have that kind of trade off with /any/ high strength
material, even steel. the higher the strength, the more brittle.

You're missing the point about anisotropy.

no i'm not. and that's a spectacular statement from a guy that
doesn't understand the difference between ductile elongation and
brittle fracture.

Repeating that doesn't make it true.

no, being true makes it true. repeating denial can't make it untrue.


You, on the other hand, seem to be
the only one on the planet who doesn't see that CFRP has low impact
resistance.

bull****.

1. who the **** wants their frame to be resistant to artillery fire.
2. "impact resistance" is a function of the fiber itself, the layup, the
fiber length, density, orientation and matrix - among other things.
"CFRP has low impact resistance" is such a BULL**** dumb-ass statement,
it beggars belief.


CF is great for
some apps, marginal for others and crappy for the rest. It's an
engineering thing.

wow. condescension, massive over-generalization and naivety all in
one.

No, just engineering basics. With CF bars and posts, you get (more
expensive) parts with similar weights. You also get susceptibility to
damage from clamping pressure and/or impact. Crappy (yet popular)
applications.

so when planes have warning labels on them telling crew not to walk on
wings, that can be ignored? bull****. carbon componentry has labels
saying "do not clamp", "do not exceed...", etc., that can be ignored?
bull****.

Who said anything about ignoring labels? I was talking about the need
for labels.

so what would your labels say then? "er, this may be elastic or it may
be plastic - we really don't know"?



twist all you want - you're still missing the basics.

If you say so,

damned right i say so!

but do try to scrape up a fact or two & perhaps we can go
from there.

i have. but you seem too intent on being a persistently ignorant prick
to absorb anything.

Chalo wrote:
jim beam wrote:
you're confusing fracture of brittle materials with fracture of ductile
materials - the two mechanisms are completely different.
...
carbon fiber [and glass fiber] have
no deformation mechanism, no dislocation function. so they have no
ductility. so they are "brittle". again, this is not to be confused
with the behavior of their composites.

for glass and carbon, their stress/strain graphs are much extended -

By "extended", I presume you mean that CFRP and GRP can accept more
stress and strain before failure than structurally comparable metals
can.

need to be vary careful with that statement.

1. comparison of strain is debatable with a higher modulus material like
carbon - if the slope is steeper, stress has to rise more for a given
strain. but that greater stiffness on the other hand can be a
significant overall benefit.

2. metal structures like bikes are not used in their plastic zone, only
elastic. the elastic strain before onset of deformation is very limited.

But since the mechanisms of failure are so different, I think
it's fair to compare the amount of work required to reach brittle
failure for advanced composites and structural metals.

disagree - because the mechanisms are different, we /cannot/ compare them.

You'd have to
seek out an a terribly temperamental metal to find one that is even in
the same ballpark in terms of the small amount of work required to
fracture it. And that's really the practical measure of toughness,
isn't it?

well, composites do have a degree of toughness - because they're
composites, but bike frames are not made to be sustain damage - as the
definition of toughness means. frames need to /resist/ damage - and for
that, composites that can have much higher strength and much better
fatigue can be a huge benefit.


I am surprised at your apparent suggestion (though you don't actually
come out and say so directly) that CFRP could have a significant
amount of ductility or toughness in any of its commonly used
formulations for bicycles.

that's not what i say or mean. it can have greater strength - a limited
degree of toughness [but only really during failure] but definitely no
ductility.

I understand that toughness was one of the
goals, realized or not, for nylon thermoplastic-based CFRP bike frames
and parts. Those constituted a fleeting market experiment, and are
now all gone.

toughness is work to deform. metals can be tough. composites not so
much. and if they /do/ evidence their ability to absorb deformation,
it's essentially failed, metal or composite.

The CFRP frames and parts that remain are epoxy-based
and therefore subject to vitreous fracture of both fiber and matrix,
without any useful amount of plastic deformation to absorb transient
overloads or point impacts. In other words, they exhibit extremely
poor toughness.

is wood brittle? [composites are modeled on wood.] it doesn't absorb
energy like a ductile metal does. true, energy absorption may be low,
but they still absorb work during failure so they don't just shatter
like glass. and many high strength metals aren't exactly tough either.
not in the habit of dropping cobalt drill bits are you?


Which is the point you're trying hard not to concede, right?

no, i'm "trying" to illustrate that a blanket statement like "carbon is
brittle" is way too ignorant and simplistic. it doesn't address
fatigue. it doesn't address stiffness. it doesn't address strength.
if a material is superior on all these counts, you're further from the
point where failure is even an issue. and even if we /are/ talking
failure mode, we need to compare like with like - saying that 6061
elongates 26% and carbon only 1.5% completely misses the fundamental
point that 24.5% of the aluminum's deformation is plastic, not elastic!
and anything post-elastic is failure in these kinds of applications.

jim beam wrote:
Chalo wrote:
jim beam wrote:
you're confusing fracture of brittle materials with fracture of
ductile materials - the two mechanisms are completely different.
...
carbon fiber [and glass fiber] have
no deformation mechanism, no dislocation function. so they have
no
ductility. so they are "brittle". again, this is not to be
confused with the behavior of their composites.

for glass and carbon, their stress/strain graphs are much
extended -

By "extended", I presume you mean that CFRP and GRP can accept more
stress and strain before failure than structurally comparable
metals
can.

need to be vary careful with that statement.

1. comparison of strain is debatable with a higher modulus material
like carbon - if the slope is steeper, stress has to rise more for a
given strain. but that greater stiffness on the other hand can be a
significant overall benefit.

2. metal structures like bikes are not used in their plastic zone,
only elastic. the elastic strain before onset of deformation is
very
limited.

But since the mechanisms of failure are so different, I think
it's fair to compare the amount of work required to reach brittle
failure for advanced composites and structural metals.

disagree - because the mechanisms are different, we /cannot/ compare
them.

You'd have to
seek out an a terribly temperamental metal to find one that is even
in the same ballpark in terms of the small amount of work required
to
fracture it. And that's really the practical measure of toughness,
isn't it?

well, composites do have a degree of toughness - because they're
composites, but bike frames are not made to be sustain damage - as
the
definition of toughness means. frames need to /resist/ damage - and
for that, composites that can have much higher strength and much
better fatigue can be a huge benefit.


I am surprised at your apparent suggestion (though you don't
actually
come out and say so directly) that CFRP could have a significant
amount of ductility or toughness in any of its commonly used
formulations for bicycles.

that's not what i say or mean. it can have greater strength - a
limited degree of toughness [but only really during failure] but
definitely no ductility.

I understand that toughness was one of the
goals, realized or not, for nylon thermoplastic-based CFRP bike
frames and parts. Those constituted a fleeting market experiment,
and are now all gone.

toughness is work to deform. metals can be tough. composites not
so
much. and if they /do/ evidence their ability to absorb
deformation,
it's essentially failed, metal or composite.

The CFRP frames and parts that remain are epoxy-based
and therefore subject to vitreous fracture of both fiber and
matrix,
without any useful amount of plastic deformation to absorb
transient
overloads or point impacts. In other words, they exhibit extremely
poor toughness.

is wood brittle? [composites are modeled on wood.] it doesn't
absorb
energy like a ductile metal does. true, energy absorption may be
low,
but they still absorb work during failure so they don't just shatter
like glass. and many high strength metals aren't exactly tough
either. not in the habit of dropping cobalt drill bits are you?


Which is the point you're trying hard not to concede, right?

no, i'm "trying" to illustrate that a blanket statement like "carbon
is brittle" is way too ignorant and simplistic. it doesn't address
fatigue. it doesn't address stiffness. it doesn't address
strength.
if a material is superior on all these counts, you're further from
the
point where failure is even an issue. and even if we /are/ talking
failure mode, we need to compare like with like - saying that 6061
elongates 26% and carbon only 1.5% completely misses the fundamental
point that 24.5% of the aluminum's deformation is plastic, not
elastic! and anything post-elastic is failure in these kinds of
applications.

However a bent metal frame can still get you home. A carbon frame
that has failed turns you into a pedestrian.

--
--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)

J. Clarke wrote:
jim beam wrote:
Chalo wrote:
jim beam wrote:
you're confusing fracture of brittle materials with fracture of
ductile materials - the two mechanisms are completely different.
...
carbon fiber [and glass fiber] have
no deformation mechanism, no dislocation function. so they have
no
ductility. so they are "brittle". again, this is not to be
confused with the behavior of their composites.

for glass and carbon, their stress/strain graphs are much
extended -
By "extended", I presume you mean that CFRP and GRP can accept more
stress and strain before failure than structurally comparable
metals
can.
need to be vary careful with that statement.

1. comparison of strain is debatable with a higher modulus material
like carbon - if the slope is steeper, stress has to rise more for a
given strain. but that greater stiffness on the other hand can be a
significant overall benefit.

2. metal structures like bikes are not used in their plastic zone,
only elastic. the elastic strain before onset of deformation is
very
limited.

But since the mechanisms of failure are so different, I think
it's fair to compare the amount of work required to reach brittle
failure for advanced composites and structural metals.
disagree - because the mechanisms are different, we /cannot/ compare
them.

You'd have to
seek out an a terribly temperamental metal to find one that is even
in the same ballpark in terms of the small amount of work required
to
fracture it. And that's really the practical measure of toughness,
isn't it?
well, composites do have a degree of toughness - because they're
composites, but bike frames are not made to be sustain damage - as
the
definition of toughness means. frames need to /resist/ damage - and
for that, composites that can have much higher strength and much
better fatigue can be a huge benefit.

I am surprised at your apparent suggestion (though you don't
actually
come out and say so directly) that CFRP could have a significant
amount of ductility or toughness in any of its commonly used
formulations for bicycles.
that's not what i say or mean. it can have greater strength - a
limited degree of toughness [but only really during failure] but
definitely no ductility.

I understand that toughness was one of the
goals, realized or not, for nylon thermoplastic-based CFRP bike
frames and parts. Those constituted a fleeting market experiment,
and are now all gone.
toughness is work to deform. metals can be tough. composites not
so
much. and if they /do/ evidence their ability to absorb
deformation,
it's essentially failed, metal or composite.

The CFRP frames and parts that remain are epoxy-based
and therefore subject to vitreous fracture of both fiber and
matrix,
without any useful amount of plastic deformation to absorb
transient
overloads or point impacts. In other words, they exhibit extremely
poor toughness.
is wood brittle? [composites are modeled on wood.] it doesn't
absorb
energy like a ductile metal does. true, energy absorption may be
low,
but they still absorb work during failure so they don't just shatter
like glass. and many high strength metals aren't exactly tough
either. not in the habit of dropping cobalt drill bits are you?

Which is the point you're trying hard not to concede, right?
no, i'm "trying" to illustrate that a blanket statement like "carbon
is brittle" is way too ignorant and simplistic. it doesn't address
fatigue. it doesn't address stiffness. it doesn't address
strength.
if a material is superior on all these counts, you're further from
the
point where failure is even an issue. and even if we /are/ talking
failure mode, we need to compare like with like - saying that 6061
elongates 26% and carbon only 1.5% completely misses the fundamental
point that 24.5% of the aluminum's deformation is plastic, not
elastic! and anything post-elastic is failure in these kinds of
applications.

However a bent metal frame can still get you home. A carbon frame
that has failed turns you into a pedestrian.


that depends. if it's completely fallen apart, obviously not. and if
it looks like it's about to fall apart, obviously not. however, while
is entirely "case by case", a carbon frame /can/ be ridden while
starting to fail. just be real slow and real careful. a friend rode an
mtb frame home with a bb that was starting to break loose. i've ridden
one of those crappy cracking chinese kestrel forks home. carbon rarely
completely vaporizes "jra" as some would have you believe - it's people
that ignore the warning signs that have the problems.