Re: elastic/plastic fundamentals

Tom 'Johnny Sunset' Sherman said:

jim beam aka Evan Williams said:

Jambo said:

"jim beam" <[email hidden]> wrote in message
news:[email hidden]...
> to continue the peter cole's recent pollution on the subject of
> confusing plastic deformation with elastic deformation:
>
> apparently, carbon fibers are inferior to 6061 aluminum because they
> only elongate 1.5% before failure vs 6061 which he alleged elongates
> 25% before failure.
>
> first up, he needs to stop exaggerating. 6061 is typically more
> like 16% in t4 temper - the common bike application. [various
> online sources]

http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MA6061T4

This clearly shows that elongation at break for 6061-t4 is between 22
and 25%.

alcoa 6061, 16%
http://www.alcoa.com/adip/catalog/pdf/Extruded_Alloy_6061.pdf

Quoted message said:

> for a 6061 with E = 69GPa, and 275MPa yield, that gives an elastic
> deformation limit of 0.275/69 x 100% = 0.04%.
>
> how does that compare again?

It's actually 0.4% - do your calculation again.

whoops!

Quoted message said:

It compares quite favorably.

ok, at the low end of the scale. i guess the point here is, this is
the upper limit for al, the lower for carbon.

Yes, but the point in avoiding "catastrophic" failure is how much energy
can be adsorbed prior to fracture, is it not?

absolutely.

Quoted message said:

And when metals exhibit
ductile fracture, does not the deformation in the plastic range
contribute to the amount of energy absorbed

indeed it does.

Quoted message said:

(or does the Charpy test lie)?

no it doesn't. and now you're getting to the point - those that want to
use the word "brittle" need to define that term with real data, not
hysterical bleating that the sky is going to fall when the last decade+
of reality says different.

Quoted message said:

Quoted message said:

Quoted message said:

It's in the area of elongation to failure that we need to be
concerned with, since this is the difference between walking and
riding home.

Elongation to failure of carbon fiber is typically 1.5%
(http://www.matweb.com/ - pick a carbon fiber).
Elongation to failure of 6061-t4 is 22-25%

but that's on plastic deformation. and the load the carbon will
sustain, because of its higher modulus [E = 300GPa for carbon vs 69GPa
for 6061] is /much/ higher for the same strain!!!

.

Quoted message said:

I'd rather have the Al alloy in this case.

only if you want to ignore superior strength.

Quoted message said:

The other issue is the ability to detect when

i think you mean "if".

Quoted message said:

CFC is damaged - it's very likely that critical damage can occur with
CFCs without visible clues.

but not audible clues. the stuff creaks and groans and makes cracking
noises. you don't walk in a timber that cracks under your weight to you?

Quoted message said:

There is plenty of literature available in the aerospace industry on
this. It's why NDT techniques are crucial to maintaining CFC
components on aircraft systems. Again there is plenty of
publications on this.

indeed. and the current state of the art involves embedding what are
essentially microphones to "listen" for signs of failure....

When (and if) will this technology be feasible for bicycle components?

what you really mean is, "when is it going to be cheap?". you /could/
install it today, but i seriously doubt you'd care for a 5+digit price
tag. in fact, all kinds of testing/inspection is available for all
existing bike materials today, but when is the last time you hard of
anyone going to the expense of crank x-ray? or frame weld x-ray? or
ultrasound? or even cheapo stuff like dye penetrant?

jim beam said:

Tom 'Johnny Sunset' Sherman said:

jim beam aka Evan Williams said:

Jambo wrote:
> "jim beam" <[email hidden]> wrote in message
> news:[email hidden]...
>> to continue the peter cole's recent pollution on the subject of
>> confusing plastic deformation with elastic deformation:
>>
>> apparently, carbon fibers are inferior to 6061 aluminum because
>> they only elongate 1.5% before failure vs 6061 which he alleged
>> elongates 25% before failure.
>>
>> first up, he needs to stop exaggerating. 6061 is typically more
>> like 16% in t4 temper - the common bike application. [various
>> online sources]
>
> http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MA6061T4
>
> This clearly shows that elongation at break for 6061-t4 is between
> 22 and 25%.

alcoa 6061, 16%
http://www.alcoa.com/adip/catalog/pdf/Extruded_Alloy_6061.pdf

>
>> for a 6061 with E = 69GPa, and 275MPa yield, that gives an elastic
>> deformation limit of 0.275/69 x 100% = 0.04%.
>>
>> how does that compare again?
>
> It's actually 0.4% - do your calculation again.

whoops!

>
> It compares quite favorably.

ok, at the low end of the scale. i guess the point here is, this is
the upper limit for al, the lower for carbon.

Yes, but the point in avoiding "catastrophic" failure is how much
energy can be adsorbed prior to fracture, is it not?

absolutely.

let me restate that - /during/ fracture.

Quoted message said:

Quoted message said:

And when metals exhibit ductile fracture, does not the deformation in
the plastic range contribute to the amount of energy absorbed

indeed it does.

Quoted message said:

(or does the Charpy test lie)?

no it doesn't. and now you're getting to the point - those that want to
use the word "brittle" need to define that term with real data, not
hysterical bleating that the sky is going to fall when the last decade+
of reality says different.

Quoted message said:

Quoted message said:

> It's in the area of elongation to failure that we need to be
> concerned with, since this is the difference between walking and
> riding home.
>
> Elongation to failure of carbon fiber is typically 1.5%
> (http://www.matweb.com/ - pick a carbon fiber).
> Elongation to failure of 6061-t4 is 22-25%

but that's on plastic deformation. and the load the carbon will
sustain, because of its higher modulus [E = 300GPa for carbon vs
69GPa for 6061] is /much/ higher for the same strain!!!

.
>
> I'd rather have the Al alloy in this case.

only if you want to ignore superior strength.

>
> The other issue is the ability to detect when

i think you mean "if".

> CFC is damaged - it's very likely that critical damage can occur
> with CFCs without visible clues.

but not audible clues. the stuff creaks and groans and makes
cracking noises. you don't walk in a timber that cracks under your
weight to you?

> There is plenty of literature available in the aerospace industry on
> this. It's why NDT techniques are crucial to maintaining CFC
> components on aircraft systems. Again there is plenty of
> publications on this.

indeed. and the current state of the art involves embedding what are
essentially microphones to "listen" for signs of failure....

When (and if) will this technology be feasible for bicycle components?

what you really mean is, "when is it going to be cheap?". you /could/
install it today, but i seriously doubt you'd care for a 5+digit price
tag. in fact, all kinds of testing/inspection is available for all
existing bike materials today, but when is the last time you hard of
anyone going to the expense of crank x-ray? or frame weld x-ray? or
ultrasound? or even cheapo stuff like dye penetrant?

jim beam aka Evan Williams said:

jim beam said:

Tom 'Johnny Sunset' Sherman said:

...
Yes, but the point in avoiding "catastrophic" failure is how much
energy can be adsorbed prior to fracture, is it not?

absolutely.

let me restate that - /during/ fracture....

Should that not be "during fracturing"?

--
Tom Sherman - Holstein-Friesland Bovinia
A Real Cyclist [TM] keeps at least one bicycle in the bedroom.

--
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