Comparison of Auminium, Steel and Carbon forks?

[Nate Nagel]

Ben C wrote:
> On 2008-04-25, Peter Cole <[email protected]> wrote:
>
>>Ben C wrote:
>>
>>
>>>So let's say I'm bending it. It might be the top tube on a bike (that
>>>might be simpler than the fork). Suppose it's strong enough, but its
>>>fatigue life is too short. Would it help to make the tube fatter but
>>>thinner-walled, or vice versa, or not?
>>
>>Yes, the larger cross section will have lower stress for the same load.
>>
>>
>>>My second question is: if I make two tubes that are both just right for
>>>both yield strength and fatigue life for a particular application, one
>>>out of steel and one out of aluminium, is it inevitable that one tube
>>>will be stiffer than the other, or is there enough working range that
>>>after satisfying the strength and fatigue requirements the designer can
>>>also make them the same stiffness? (Of course they will have different
>>>diameters and thicknesses).
>>
>>The two materials are different, so that makes direct comparison
>>problematic. Generally, to get comparable fatigue life, the aluminum
>>will use a bit more material than needed for comparable strength, so you
>>have a choice of similar fatigue, but aluminum stronger, or similar
>>strength with aluminum less durable. The limit for steel tubing diameter
>>is dent/crumple resistance. This has been all pretty well worked out
>>empirically in bike frames over the last couple of decades.
>
>
> Thanks for the answer. I'm thinking then that it is quite likely that in
> practice aluminium frames and forks _will_ be stiffer than steel ones
> (when comparing similar styles of bike) as a consequence of designing
> them for sufficient fatigue life?
>
> But I still don't know really-- the aluminium frame may be stronger, but
> aluminium has a lower modulus than steel, so it's not obvious that it's
> going to be stiffer.

Aluminum fatigues much more easily than steel. In fact, it is possible
to design a steel part that will *never* fatigue given limited cyclic
loads, but it is *not* possible to do that with aluminum - only to
design one that will last long enough that it will *effectively* never fail.

Thus, I suspect that aluminum frames/forks/etc are designed with this in
mind and are somewhat overbuilt as a result WRT stiffness. Therefore my
guess is that they would tend to be stiffer, and the general rule of
thumb that "aluminum rides hard" is the result.

That said, I couldn't be much more happy with the craigslist Cannondale
I recently acquired; rides like a dream. (seems that conventional
wisdom, right after "aluminum rides hard" is "Cannondales ride hard.")
Only possible mitigating factors are the carbon fork and the 700x32C
tires. (I might have picked 28s or even full on road tires, but they
are acceptably smooth and easy rolling for the riding that I do.) Of
course, I'm the same guy whose primary car is a Porsche 944 with Koni
yellows on it, so apparently my priorities are definitely skewed toward
handling and I don't necessarily feel the need to be completely isolated
from tar strips, dropped change, etc.

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

 

[Ben C]

On 2008-04-25, Nate Nagel <[email protected]> wrote:
> Ben C wrote:
[...]
>> Thanks for the answer. I'm thinking then that it is quite likely that in
>> practice aluminium frames and forks _will_ be stiffer than steel ones
>> (when comparing similar styles of bike) as a consequence of designing
>> them for sufficient fatigue life?
>>
>> But I still don't know really-- the aluminium frame may be stronger, but
>> aluminium has a lower modulus than steel, so it's not obvious that it's
>> going to be stiffer.
>
> Aluminum fatigues much more easily than steel. In fact, it is possible
> to design a steel part that will *never* fatigue given limited cyclic
> loads

Only for mild steel. The steel that all half-decent steel bikes are made
of has no endurance limit (i.e. will always fatigue eventually).

But it still has much better fatigue life than aluminium.

> , but it is *not* possible to do that with aluminum - only to
> design one that will last long enough that it will *effectively* never fail.
>
> Thus, I suspect that aluminum frames/forks/etc are designed with this in
> mind and are somewhat overbuilt as a result WRT stiffness. Therefore my
> guess is that they would tend to be stiffer, and the general rule of
> thumb that "aluminum rides hard" is the result.

That's what I'm thinking, but it is difficult to be sure of this. It is
quite a complicated equation because of all the differences in the
materials.

> That said, I couldn't be much more happy with the craigslist Cannondale
> I recently acquired; rides like a dream. (seems that conventional
> wisdom, right after "aluminum rides hard" is "Cannondales ride hard.")
> Only possible mitigating factors are the carbon fork and the 700x32C
> tires.

The tyres at least have got to have a significant effect there.

For your next craigslist purchase get a nice lugless steel Peugeot and
then you can compare the two

 

[[email protected]]

Ben C? wrote:

> [...]

>>>> My second question is: if I make two tubes that are both just
>>>> right for both yield strength and fatigue life for a particular
>>>> application, one out of steel and one out of aluminium, is it
>>>> inevitable that one tube will be stiffer than the other, or is
>>>> there enough working range that after satisfying the strength and
>>>> fatigue requirements the designer can also make them the same
>>>> stiffness? (Of course they will have different diameters and
>>>> thicknesses).

>>> The two materials are different, so that makes direct comparison
>>> problematic. Generally, to get comparable fatigue life, the
>>> aluminum will use a bit more material than needed for comparable
>>> strength, so you have a choice of similar fatigue, but aluminum
>>> stronger, or similar strength with aluminum less durable. The
>>> limit for steel tubing diameter is dent/crumple resistance. This
>>> has been all pretty well worked out empirically in bike frames
>>> over the last couple of decades.

>> To avoid the stiffness problem (that increases with the third power
>> of "beam height"), that causes failures elsewhere, some aluminum
>> forks were made to external steel dimensions but with greater wall
>> thickness.

> This sounds interesting but I'm not sure I understand exactly what
> you're saying. What's "beam height"-- is it tube diameter in this
> context-- and what were the failures elsewhere?

When bending a structural element (an I-beam) the height of the beam
is used to compute its bending stress. Because mainly the extreme
parts above and below the bending axis (for vertical loading) are the
ones that are stressed and that is where the action is.

>> That was a dud and you probably cannot find such a frame still in
>> regular use.

> What was wrong with it?

They looked like steel forks and frame tubes (Alan bicycles) but
readily bent forks and developed cracks. Today Alan is making
composite frames.

>> Weight weenies have done little good for the durability and
>> repairability of bicycles yet that is what sells.

> Well they are weight weenies not durability or repairability weenies.

....and they are often overweight.

Jobst Brandt

 

[jim beam]

Nate Nagel wrote:
> Ben C wrote:
>> On 2008-04-25, Peter Cole <[email protected]> wrote:
>>
>>> Ben C wrote:
>>>
>>>
>>>> So let's say I'm bending it. It might be the top tube on a bike (that
>>>> might be simpler than the fork). Suppose it's strong enough, but its
>>>> fatigue life is too short. Would it help to make the tube fatter but
>>>> thinner-walled, or vice versa, or not?
>>>
>>> Yes, the larger cross section will have lower stress for the same load.
>>>
>>>
>>>> My second question is: if I make two tubes that are both just right for
>>>> both yield strength and fatigue life for a particular application, one
>>>> out of steel and one out of aluminium, is it inevitable that one tube
>>>> will be stiffer than the other, or is there enough working range that
>>>> after satisfying the strength and fatigue requirements the designer can
>>>> also make them the same stiffness? (Of course they will have different
>>>> diameters and thicknesses).
>>>
>>> The two materials are different, so that makes direct comparison
>>> problematic. Generally, to get comparable fatigue life, the aluminum
>>> will use a bit more material than needed for comparable strength, so
>>> you have a choice of similar fatigue, but aluminum stronger, or
>>> similar strength with aluminum less durable. The limit for steel
>>> tubing diameter is dent/crumple resistance. This has been all pretty
>>> well worked out empirically in bike frames over the last couple of
>>> decades.
>>
>>
>> Thanks for the answer. I'm thinking then that it is quite likely that in
>> practice aluminium frames and forks _will_ be stiffer than steel ones
>> (when comparing similar styles of bike) as a consequence of designing
>> them for sufficient fatigue life?
>>
>> But I still don't know really-- the aluminium frame may be stronger, but
>> aluminium has a lower modulus than steel, so it's not obvious that it's
>> going to be stiffer.
>
> Aluminum fatigues much more easily than steel.

what kind of aluminum? what kind of steel?


> In fact, it is possible
> to design a steel part that will *never* fatigue given limited cyclic
> loads,

again, what kind of steel? most of the high strength steels don't have
this property. nor do stainless steels.


> but it is *not* possible to do that with aluminum - only to
> design one that will last long enough that it will *effectively* never
> fail.

it's basic engineering to figure out the nature of the application.
that includes service life.


>
> Thus, I suspect that aluminum frames/forks/etc are designed with this in
> mind and are somewhat overbuilt as a result WRT stiffness. Therefore my
> guess is that they would tend to be stiffer, and the general rule of
> thumb that "aluminum rides hard" is the result.
>
> That said, I couldn't be much more happy with the craigslist Cannondale
> I recently acquired; rides like a dream. (seems that conventional
> wisdom, right after "aluminum rides hard" is "Cannondales ride hard.")
> Only possible mitigating factors are the carbon fork and the 700x32C
> tires. (I might have picked 28s or even full on road tires, but they
> are acceptably smooth and easy rolling for the riding that I do.) Of
> course, I'm the same guy whose primary car is a Porsche 944 with Koni
> yellows on it, so apparently my priorities are definitely skewed toward
> handling and I don't necessarily feel the need to be completely isolated
> from tar strips, dropped change, etc.
>
> nate
>

 

[jim beam]

Ben C wrote:
> On 2008-04-25, Peter Cole <[email protected]> wrote:
>> Ben C wrote:
>>
>>> So let's say I'm bending it. It might be the top tube on a bike (that
>>> might be simpler than the fork). Suppose it's strong enough, but its
>>> fatigue life is too short. Would it help to make the tube fatter but
>>> thinner-walled, or vice versa, or not?
>> Yes, the larger cross section will have lower stress for the same load.
>>
>>> My second question is: if I make two tubes that are both just right for
>>> both yield strength and fatigue life for a particular application, one
>>> out of steel and one out of aluminium, is it inevitable that one tube
>>> will be stiffer than the other, or is there enough working range that
>>> after satisfying the strength and fatigue requirements the designer can
>>> also make them the same stiffness? (Of course they will have different
>>> diameters and thicknesses).
>> The two materials are different, so that makes direct comparison
>> problematic. Generally, to get comparable fatigue life, the aluminum
>> will use a bit more material than needed for comparable strength, so you
>> have a choice of similar fatigue, but aluminum stronger, or similar
>> strength with aluminum less durable. The limit for steel tubing diameter
>> is dent/crumple resistance. This has been all pretty well worked out
>> empirically in bike frames over the last couple of decades.
>
> Thanks for the answer. I'm thinking then that it is quite likely that in
> practice aluminium frames and forks _will_ be stiffer than steel ones
> (when comparing similar styles of bike) as a consequence of designing
> them for sufficient fatigue life?
>
> But I still don't know really-- the aluminium frame may be stronger, but
> aluminium has a lower modulus than steel, so it's not obvious that it's
> going to be stiffer.

indeed.

 

[Nate Nagel]

Ben C wrote:
> On 2008-04-25, Nate Nagel <[email protected]> wrote:
>
>>Ben C wrote:
>
> [...]
>
>>>Thanks for the answer. I'm thinking then that it is quite likely that in
>>>practice aluminium frames and forks _will_ be stiffer than steel ones
>>>(when comparing similar styles of bike) as a consequence of designing
>>>them for sufficient fatigue life?
>>>
>>>But I still don't know really-- the aluminium frame may be stronger, but
>>>aluminium has a lower modulus than steel, so it's not obvious that it's
>>>going to be stiffer.
>>
>>Aluminum fatigues much more easily than steel. In fact, it is possible
>>to design a steel part that will *never* fatigue given limited cyclic
>>loads
>
>
> Only for mild steel. The steel that all half-decent steel bikes are made
> of has no endurance limit (i.e. will always fatigue eventually).
>
> But it still has much better fatigue life than aluminium.
>
>
>>, but it is *not* possible to do that with aluminum - only to
>>design one that will last long enough that it will *effectively* never fail.
>>
>>Thus, I suspect that aluminum frames/forks/etc are designed with this in
>>mind and are somewhat overbuilt as a result WRT stiffness. Therefore my
>>guess is that they would tend to be stiffer, and the general rule of
>>thumb that "aluminum rides hard" is the result.
>
>
> That's what I'm thinking, but it is difficult to be sure of this. It is
> quite a complicated equation because of all the differences in the
> materials.
>
>
>>That said, I couldn't be much more happy with the craigslist Cannondale
>>I recently acquired; rides like a dream. (seems that conventional
>>wisdom, right after "aluminum rides hard" is "Cannondales ride hard.")
>>Only possible mitigating factors are the carbon fork and the 700x32C
>>tires.
>
>
> The tyres at least have got to have a significant effect there.
>
> For your next craigslist purchase get a nice lugless steel Peugeot and
> then you can compare the two

Heh. "but it's for an experiment! We all have to make sacrifices in
the name of SCIENCE!!!"

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

 

[Paul M. Hobson]

[email protected] wrote:
> Another aspect of this is that for the same deflection, stress is
> higher in the larger cross section element. For this reason, I have
> seen more wrinkled aluminum than steel tubes from bending. Before the
> advent of aluminum frames, steel frames wrinkled their downtubes at
> the transition from thick walled tube ends to thin wall.


Is the downtube in the pictures linked below an example of the
"wrinkling" that you mention?
<http://farm1.static.flickr.com/185/414152236_28706394eb_b.jpg>
and
<http://farm1.static.flickr.com/188/414152239_a51bb08255_b.jpg>

\\paul
--
Paul M. Hobson
..:change the f to ph to reply:.

 

[[email protected]]

Paul M. Hobson wrote:

>> Another aspect of this is that for the same deflection, stress is
>> higher in the larger cross section element. For this reason, I
>> have seen more wrinkled aluminum than steel tubes from bending.
>> Before the advent of aluminum frames, steel frames wrinkled their
>> downtubes at the transition from thick walled tube ends to thin
>> wall.

> Is the downtube in the pictures linked below an example of the
> "wrinkling" that you mention?

http://farm1.static.flickr.com/185/414152236_28706394eb_b.jpg

> and

http://farm1.static.flickr.com/188/414152239_a51bb08255_b.jpg

I'm not good at photo interpretation of under-exposed pictures. Try
taking another picture with a light background perpendicular to the
long axis of the tube, preferably with the principal axis of the tube
parallel to a straight lined background. As it is, I don't see the
bend or the wrinkle.

When a downtube becomes bent from a frontal impact on the bicycle, it
generally raises a welt on its underside and bows upward at the end of
the tube butting.

Jobst Brandt

 

[Marian]

On 4ÔÂ21ÈÕ, ÉÏÎç9ʱ33·Ö, Mike <[email protected]> wrote:
> In article <[email protected]>, [email protected] says...
>
>
>
> > On 18 Apr, 00:55, Hobbes@spnb&s.com wrote:
> > > On Thu, 17 Apr 2008 15:23:53 -0700 (PDT), blackhead <[email protected]>
> > > wrote:
>
> > > >Are there any impartial tests that have been done on Auminium, Steel
> > > >and Carbon forks? Some people say carbon absorbs vibration better than
> > > >steel and Aluminium, others say it makes little difference... etc etc
>
> > > The differences of design, materials quality and manufacture are greater than
> > > the differences in the materials themselves. Even in weight there is an
> > > intersection between the three. I've got bikes with all three and they've all
> > > got something going for them.
>
> > > Really depends on what you're doing with the bike and which forks you're
> > > choosing from.
>
> > So do Carbon forks really absorb vibration significantly better than
> > Aluminium, so giving a better ride?
>
> Hmmm, my carbon-forks (attached to a carbon frame road bike - tyres at 110-115psi) don't do a hell of a lot of
> absorbing when I ride over the coarse chip road surface that our wonderfulcity council decided to plaster all over my
> commuting route, whereas my aluminiun forks (attached to a full-suspensionmountain bike - 120 mm front travel) does a
> fine job of absorbing all the bumps induced by fist-sized cobbles on a fast down-hill track. Can I make any conclusions
> from this - only that the geometry, tyres, build and whatever is probably of far more significance.
>
> To compare apples with apples, my CF road-bike is a lot lighter than th eold steel-frame, but I don't think there is a
> _significant_ change in vibration absorption.

Apples to Apples - aluminum bike with carbon fork all parts switched
over to a titanium frame (including same carbon fork) ... slightly
different geometry but same end result for handlebar to saddle to
pedal ratio when everything was tweaked and despite the wheel under
the ass tri -frame the ti bike is a much softer ride.

(and as I'm not the person who bought the new frame I get to say that
impartially)

-M

 

[Mike]

In article <[email protected]>, [email protected] says...
> Mike wrote:
> > In article <[email protected]>, [email protected] says...
> >> blackhead wrote:
> >>> On 17 Apr, 23:23, blackhead <[email protected]> wrote:
> >>>> Are there any impartial tests that have been done on Auminium, Steel
> >>>> and Carbon forks? Some people say carbon absorbs vibration better than
> >>>> steel and Aluminium, others say it makes little difference... etc etc
> >>> For the fork to attenuate vibration, it has to do what a shock
> >>> absorber in a car shock does; store the energy when flexed similar to
> >>> a spring and dissipate it via some dampening mechanism, otherwise
> >>> you'll get the vibration released through the whole frame as a
> >>> resonance. It certainly stores energy when flexed, but I don't see how
> >>> the energy is dissipated.
> >> word of the day: "hysteresis". all polymers have hysteresis, hence they
> >> absorb/dissipate energy.
> >>
> > Yep, and steel and aluminium forks absorb and dissipate energy too - otherwise I could wander out into the corridor
> > (where I store my bike during the day) and observe the forks still 'humming' from the morning's ride.
>
> er, no. in that misconceived example, energy is dissipated into the
> environment, not in some bizarre internal absorption mechanism.
>
It doesn't matter what the dissipative mode is. As long as the vibrational energy is not dissipated into the hands or
bum of the rider, the forks (and frame) are doing their job. And the fact that hysteresis is a phenomenon that occrs in
polymers does not 'magically' guarantee that any fork made with cf will provide a better damped ride than any fork made
with aluminium or steel.

Mike

 

[jim beam]

Mike wrote:
> In article <[email protected]>, [email protected] says...
>> Mike wrote:
>>> In article <[email protected]>, [email protected] says...
>>>> blackhead wrote:
>>>>> On 17 Apr, 23:23, blackhead <[email protected]> wrote:
>>>>>> Are there any impartial tests that have been done on Auminium, Steel
>>>>>> and Carbon forks? Some people say carbon absorbs vibration better than
>>>>>> steel and Aluminium, others say it makes little difference... etc etc
>>>>> For the fork to attenuate vibration, it has to do what a shock
>>>>> absorber in a car shock does; store the energy when flexed similar to
>>>>> a spring and dissipate it via some dampening mechanism, otherwise
>>>>> you'll get the vibration released through the whole frame as a
>>>>> resonance. It certainly stores energy when flexed, but I don't see how
>>>>> the energy is dissipated.
>>>> word of the day: "hysteresis". all polymers have hysteresis, hence they
>>>> absorb/dissipate energy.
>>>>
>>> Yep, and steel and aluminium forks absorb and dissipate energy too - otherwise I could wander out into the corridor
>>> (where I store my bike during the day) and observe the forks still 'humming' from the morning's ride.
>> er, no. in that misconceived example, energy is dissipated into the
>> environment, not in some bizarre internal absorption mechanism.
>>
> It doesn't matter what the dissipative mode is.

eh?

> As long as the vibrational energy is not dissipated into the hands or
> bum of the rider, the forks (and frame) are doing their job.

it's not the "job" of a solid [as opposed to suspension] fork to do
anything other than hold the wheel, regardless of material. the fact
that cfrp happens to offer some attenuation is just gravy.


> And the fact that hysteresis is a phenomenon that occrs in
> polymers does not 'magically' guarantee that any fork made with cf will provide a better damped ride than any fork made
> with aluminium or steel.
>

eh? like leading a horse to water [explaining physical principle]
doesn't mean it will drink [understand] you mean?

 

[Mike]

In article <[email protected]>, [email protected] says...
> Mike wrote:
> > In article <[email protected]>, [email protected] says...
> >> Mike wrote:
> >>> In article <[email protected]>, [email protected] says...
> >>>> blackhead wrote:
> >>>>> On 17 Apr, 23:23, blackhead <[email protected]> wrote:
> >>>>>> Are there any impartial tests that have been done on Auminium, Steel
> >>>>>> and Carbon forks? Some people say carbon absorbs vibration better than
> >>>>>> steel and Aluminium, others say it makes little difference... etc etc
> >>>>> For the fork to attenuate vibration, it has to do what a shock
> >>>>> absorber in a car shock does; store the energy when flexed similar to
> >>>>> a spring and dissipate it via some dampening mechanism, otherwise
> >>>>> you'll get the vibration released through the whole frame as a
> >>>>> resonance. It certainly stores energy when flexed, but I don't see how
> >>>>> the energy is dissipated.
> >>>> word of the day: "hysteresis". all polymers have hysteresis, hence they
> >>>> absorb/dissipate energy.
> >>>>
> >>> Yep, and steel and aluminium forks absorb and dissipate energy too - otherwise I could wander out into the corridor
> >>> (where I store my bike during the day) and observe the forks still 'humming' from the morning's ride.
> >> er, no. in that misconceived example, energy is dissipated into the
> >> environment, not in some bizarre internal absorption mechanism.
> >>
> > It doesn't matter what the dissipative mode is.
>
> eh?
>
> > As long as the vibrational energy is not dissipated into the hands or
> > bum of the rider, the forks (and frame) are doing their job.
>
> it's not the "job" of a solid [as opposed to suspension] fork to do
> anything other than hold the wheel, regardless of material. the fact
> that cfrp happens to offer some attenuation is just gravy.
>
Maybe I shouldn't bother...but I have a few minutes to spare so why not poke at the troll (because - surely - that's
what you must be). You seem to be suggestng that every bicycle designer in history has got to the point where he/she
has to draw out the front fork. "Ahh, yes.." our designer mutters "...the front fork. Let's keep it simple. After all -
_all_ it has to do is hold the wheel. Guess I may as well make it a solid, rigid, vertical rod. No need to complicate
matters with castor, trail, curvature, variable diameter, head-tube angle, length, etc."

> > And the fact that hysteresis is a phenomenon that occrs in
> > polymers does not 'magically' guarantee that any fork made with cf will provide a better damped ride than any fork made
> > with aluminium or steel.
> >
>
> eh? like leading a horse to water [explaining physical principle]
> doesn't mean it will drink [understand] you mean?

With, perhaps some prejudice, I believe that a thirty year career in materials physics has provided me some insight to
the basic properties of matter and how they relate to the function and behaviour of materials and structures. Once
again, hysteresis is not the only mechanism available to attenuate vibration. As a simple example, simple enough
perhaps for you to grasp, a coil spring with a moderately low resonance frequency will not transmit high-frequency
vibration... and not a polymer in sight.

To reiterate, I fully understand the nature of hysteresis in polymers and how this provides an intrinsic ability for
these materials to dampen and absorb vibrational energy. I also understand, but you appear to be either unable to admit
or unable to understand, that there are other mechanisms available by which vibrational energy can be dissipated.
Despite your claims, you have provided no evidence of what you appear to claim, that is: that a fork built from cf will
inevitably and invariably be better at reducing the transfer of vibrational energy, from the axle of the front wheel to
the riders hands, than any fork built from steel or aluminium.

You may re-parrot "hysteresis in polymers" but without evidence that this provides a measurable reduction in the
transfer of vibrational energy _taking into account the differing geometry, mass and design of forks built from
differing materials_ you have not proved your case. If you _can_ supply such evidence, I will be willing to admit to
the accuracy of your hypothesis.

 

[Tom Sherman]

Mike ? wrote:
> In article <[email protected]>, [email protected] says...
>> Mike wrote:
>>> In article <[email protected]>, [email protected] says...
>>>> Mike wrote:
>>>>> In article <[email protected]>, [email protected] says...
>>>>>> blackhead wrote:
>>>>>>> On 17 Apr, 23:23, blackhead <[email protected]> wrote:
>>>>>>>> Are there any impartial tests that have been done on Auminium, Steel
>>>>>>>> and Carbon forks? Some people say carbon absorbs vibration better than
>>>>>>>> steel and Aluminium, others say it makes little difference... etc etc
>>>>>>> For the fork to attenuate vibration, it has to do what a shock
>>>>>>> absorber in a car shock does; store the energy when flexed similar to
>>>>>>> a spring and dissipate it via some dampening mechanism, otherwise
>>>>>>> you'll get the vibration released through the whole frame as a
>>>>>>> resonance. It certainly stores energy when flexed, but I don't see how
>>>>>>> the energy is dissipated.
>>>>>> word of the day: "hysteresis". all polymers have hysteresis, hence they
>>>>>> absorb/dissipate energy.
>>>>>>
>>>>> Yep, and steel and aluminium forks absorb and dissipate energy too - otherwise I could wander out into the corridor
>>>>> (where I store my bike during the day) and observe the forks still 'humming' from the morning's ride.
>>>> er, no. in that misconceived example, energy is dissipated into the
>>>> environment, not in some bizarre internal absorption mechanism.
>>>>
>>> It doesn't matter what the dissipative mode is.
>> eh?
>>
>>> As long as the vibrational energy is not dissipated into the hands or
>>> bum of the rider, the forks (and frame) are doing their job.
>> it's not the "job" of a solid [as opposed to suspension] fork to do
>> anything other than hold the wheel, regardless of material. the fact
>> that cfrp happens to offer some attenuation is just gravy.
>>
> Maybe I shouldn't bother...but I have a few minutes to spare so why not poke at the troll (because - surely - that's
> what you must be). You seem to be suggestng that every bicycle designer in history has got to the point where he/she
> has to draw out the front fork. "Ahh, yes.." our designer mutters "...the front fork. Let's keep it simple. After all -
> _all_ it has to do is hold the wheel. Guess I may as well make it a solid, rigid, vertical rod. No need to complicate
> matters with castor, trail, curvature, variable diameter, head-tube angle, length, etc."
>
>>> And the fact that hysteresis is a phenomenon that occrs in
>>> polymers does not 'magically' guarantee that any fork made with cf will provide a better damped ride than any fork made
>>> with aluminium or steel.
>>>
>> eh? like leading a horse to water [explaining physical principle]
>> doesn't mean it will drink [understand] you mean?
>
> With, perhaps some prejudice, I believe that a thirty year career in materials physics has provided me some insight to
> the basic properties of matter and how they relate to the function and behaviour of materials and structures. Once
> again, hysteresis is not the only mechanism available to attenuate vibration. As a simple example, simple enough
> perhaps for you to grasp, a coil spring with a moderately low resonance frequency will not transmit high-frequency
> vibration... and not a polymer in sight.
>
> To reiterate, I fully understand the nature of hysteresis in polymers and how this provides an intrinsic ability for
> these materials to dampen and absorb vibrational energy. I also understand, but you appear to be either unable to admit
> or unable to understand, that there are other mechanisms available by which vibrational energy can be dissipated.
> Despite your claims, you have provided no evidence of what you appear to claim, that is: that a fork built from cf will
> inevitably and invariably be better at reducing the transfer of vibrational energy, from the axle of the front wheel to
> the riders hands, than any fork built from steel or aluminium.
>
> You may re-parrot "hysteresis in polymers" but without evidence that this provides a measurable reduction in the
> transfer of vibrational energy _taking into account the differing geometry, mass and design of forks built from
> differing materials_ you have not proved your case. If you _can_ supply such evidence, I will be willing to admit to
> the accuracy of your hypothesis.

I ain't holding my breath.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

 

[Mike]

In article <[email protected]>, [email protected] says...
> Mike ? wrote:
> > You may re-parrot "hysteresis in polymers" but without evidence that this provides a measurable reduction in the
> > transfer of vibrational energy _taking into account the differing geometry, mass and design of forks built from
> > differing materials_ you have not proved your case. If you _can_ supply such evidence, I will be willing to admit to
> > the accuracy of your hypothesis.
>
> I ain't holding my breath.
>
Hey - I was just feeling benevolent. But I don't want to run the risk of breathlessness either...

Mike

 

[Paul M. Hobson]

[email protected] wrote:
>>> Another aspect of this is that for the same deflection, stress is
>>> higher in the larger cross section element. For this reason, I
>>> have seen more wrinkled aluminum than steel tubes from bending.
>>> Before the advent of aluminum frames, steel frames wrinkled their
>>> downtubes at the transition from thick walled tube ends to thin
>>> wall.

> Paul M. Hobson wrote:
>> Is the downtube in the pictures linked below an example of the
>> "wrinkling" that you mention?
>
>> http://farm1.static.flickr.com/185/414152236_28706394eb_b.jpg
>> and
>> http://farm1.static.flickr.com/188/414152239_a51bb08255_b.jpg

[email protected] wrote:
> I'm not good at photo interpretation of under-exposed pictures. Try
> taking another picture with a light background perpendicular to the
> long axis of the tube, preferably with the principal axis of the tube
> parallel to a straight lined background. As it is, I don't see the
> bend or the wrinkle.
>
> When a downtube becomes bent from a frontal impact on the bicycle, it
> generally raises a welt on its underside and bows upward at the end of
> the tube butting.

Here's the best my point&click, skills, and CFL lighting could do:
http://www.prism.gatech.edu/~gtg611a/pics/jobst/

I also threw in a photo of a 9spd SRAM chain that just about landed me
in the hospital.

\\paul
--
Paul M. Hobson
..:change the f to ph to reply:.

 

[[email protected]]

Paul M. Hobson wrote:

>>>> Another aspect of this is that for the same deflection, stress is
>>>> higher in the larger cross section element. For this reason, I
>>>> have seen more wrinkled aluminum than steel tubes from bending.
>>>> Before the advent of aluminum frames, steel frames wrinkled their
>>>> downtubes at the transition from thick walled tube ends to thin
>>>> wall.

>>> Is the downtube in the pictures linked below an example of the
>>> "wrinkling" that you mention?

http://farm1.static.flickr.com/185/414152236_28706394eb_b.jpg

>>> and

http://farm1.static.flickr.com/188/414152239_a51bb08255_b.jpg

>> I'm not good at photo interpretation of under-exposed pictures.
>> Try taking another picture with a light background perpendicular to
>> the long axis of the tube, preferably with the principal axis of
>> the tube parallel to a straight lined background. As it is, I
>> don't see the bend or the wrinkle.

>> When a downtube becomes bent from a frontal impact on the bicycle,
>> it generally raises a welt on its underside and bows upward at the
>> end of the tube butting.

> Here's the best my point&click, skills, and CFL lighting could do:

http://www.prism.gatech.edu/~gtg611a/pics/jobst/

> I also threw in a photo of a 9spd SRAM chain that just about landed me
> in the hospital.

The chain picture shows tat the chain didn't break, but that it had
been improperly re-assembled and had a loose fitting pin.

The frame pictures are axial aspects that don't show ow the tube was
overloaded. As I mentioned, a side view with straight background
features shows the bend and wrinkle unambiguously. I can't make much
of the paint flaking scenes in that set.

Jobst Brandt

 

[Paul M. Hobson]

[email protected] wrote:
> Paul M. Hobson wrote:
>
>>>>> Another aspect of this is that for the same deflection, stress is
>>>>> higher in the larger cross section element. For this reason, I
>>>>> have seen more wrinkled aluminum than steel tubes from bending.
>>>>> Before the advent of aluminum frames, steel frames wrinkled their
>>>>> downtubes at the transition from thick walled tube ends to thin
>>>>> wall.
>
>>>> Is the downtube in the pictures linked below an example of the
>>>> "wrinkling" that you mention?
>
> http://farm1.static.flickr.com/185/414152236_28706394eb_b.jpg
>
>>>> and
>
> http://farm1.static.flickr.com/188/414152239_a51bb08255_b.jpg
>
>>> I'm not good at photo interpretation of under-exposed pictures.
>>> Try taking another picture with a light background perpendicular to
>>> the long axis of the tube, preferably with the principal axis of
>>> the tube parallel to a straight lined background. As it is, I
>>> don't see the bend or the wrinkle.
>
>>> When a downtube becomes bent from a frontal impact on the bicycle,
>>> it generally raises a welt on its underside and bows upward at the
>>> end of the tube butting.
>
>> Here's the best my point&click, skills, and CFL lighting could do:
>
> http://www.prism.gatech.edu/~gtg611a/pics/jobst/
>
>> I also threw in a photo of a 9spd SRAM chain that just about landed me
>> in the hospital.
>
> The chain picture shows tat the chain didn't break, but that it had
> been improperly re-assembled and had a loose fitting pin.

The chain had been assembled only once with the provided connecting
link. This failure occurred about halfway around from the master link.
Poor manufacturing? Design?

> The frame pictures are axial aspects that don't show ow the tube was
> overloaded. As I mentioned, a side view with straight background
> features shows the bend and wrinkle unambiguously. I can't make much
> of the paint flaking scenes in that set.

The photos you want have been added.

--
Paul M. Hobson
..:change the f to ph to reply:.

 

[jim beam]

Mike wrote:
> In article <[email protected]>, [email protected] says...
>> Mike wrote:
>>> In article <[email protected]>, [email protected] says...
>>>> Mike wrote:
>>>>> In article <[email protected]>, [email protected] says...
>>>>>> blackhead wrote:
>>>>>>> On 17 Apr, 23:23, blackhead <[email protected]> wrote:
>>>>>>>> Are there any impartial tests that have been done on Auminium, Steel
>>>>>>>> and Carbon forks? Some people say carbon absorbs vibration better than
>>>>>>>> steel and Aluminium, others say it makes little difference... etc etc
>>>>>>> For the fork to attenuate vibration, it has to do what a shock
>>>>>>> absorber in a car shock does; store the energy when flexed similar to
>>>>>>> a spring and dissipate it via some dampening mechanism, otherwise
>>>>>>> you'll get the vibration released through the whole frame as a
>>>>>>> resonance. It certainly stores energy when flexed, but I don't see how
>>>>>>> the energy is dissipated.
>>>>>> word of the day: "hysteresis". all polymers have hysteresis, hence they
>>>>>> absorb/dissipate energy.
>>>>>>
>>>>> Yep, and steel and aluminium forks absorb and dissipate energy too - otherwise I could wander out into the corridor
>>>>> (where I store my bike during the day) and observe the forks still 'humming' from the morning's ride.
>>>> er, no. in that misconceived example, energy is dissipated into the
>>>> environment, not in some bizarre internal absorption mechanism.
>>>>
>>> It doesn't matter what the dissipative mode is.
>> eh?
>>
>>> As long as the vibrational energy is not dissipated into the hands or
>>> bum of the rider, the forks (and frame) are doing their job.
>> it's not the "job" of a solid [as opposed to suspension] fork to do
>> anything other than hold the wheel, regardless of material. the fact
>> that cfrp happens to offer some attenuation is just gravy.
>>
> Maybe I shouldn't bother...but I have a few minutes to spare so why not poke at the troll (because - surely - that's
> what you must be). You seem to be suggestng that every bicycle designer in history has got to the point where he/she
> has to draw out the front fork. "Ahh, yes.." our designer mutters "...the front fork. Let's keep it simple. After all -
> _all_ it has to do is hold the wheel. Guess I may as well make it a solid, rigid, vertical rod. No need to complicate
> matters with castor, trail, curvature, variable diameter, head-tube angle, length, etc."
>
>>> And the fact that hysteresis is a phenomenon that occrs in
>>> polymers does not 'magically' guarantee that any fork made with cf will provide a better damped ride than any fork made
>>> with aluminium or steel.
>>>
>> eh? like leading a horse to water [explaining physical principle]
>> doesn't mean it will drink [understand] you mean?
>
> With, perhaps some prejudice, I believe that a thirty year career in materials physics

well, krygowski picks up a check for being an "engineering" professor,
but he doesn't know his ass from his elbow, and jobst brandt, esteemed
stanford alumni, doesn't know a damned thing about fatigue, deformation
or strength of materials. your conspicuous absence from all /those/
debates doesn't show me you have credentials.


> has provided me some insight to
> the basic properties of matter and how they relate to the function and behaviour of materials and structures. Once
> again, hysteresis is not the only mechanism available to attenuate vibration. As a simple example, simple enough
> perhaps for you to grasp, a coil spring with a moderately low resonance frequency will not transmit high-frequency
> vibration... and not a polymer in sight.
>
> To reiterate, I fully understand the nature of hysteresis in polymers and how this provides an intrinsic ability for
> these materials to dampen and absorb vibrational energy. I also understand, but you appear to be either unable to admit
> or unable to understand, that there are other mechanisms available by which vibrational energy can be dissipated.
> Despite your claims, you have provided no evidence of what you appear to claim, that is: that a fork built from cf will
> inevitably and invariably be better at reducing the transfer of vibrational energy, from the axle of the front wheel to
> the riders hands, than any fork built from steel or aluminium.
>
> You may re-parrot "hysteresis in polymers" but without evidence that this provides a measurable reduction in the
> transfer of vibrational energy _taking into account the differing geometry, mass and design of forks built from
> differing materials_ you have not proved your case. If you _can_ supply such evidence, I will be willing to admit to
> the accuracy of your hypothesis.

you've still gotten your approach inverted. as stated before, the
behavior of polymers are a given. even you admit it. now what /you/
have to do is argue the extent to which cf reinforcement mitigates that.
your "30 year career in materials physics" should make it easy, yes?

 

[Tom Sherman]

"jim beam" wrote:
> [...]
> well, krygowski picks up a check for being an "engineering" professor,
> but he doesn't know his ass from his elbow, and jobst brandt, esteemed
> stanford alumni, doesn't know a damned thing about fatigue, deformation
> or strength of materials. your conspicuous absence from all /those/
> debates doesn't show me you have credentials.[...]
>
Gee "jim", ever consider the possiblity that "Mike" is a newcomer to the
group? That would explain his lack or participation in previous debates, no?

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

 

[jim beam]

Tom Sherman wrote:
> "jim beam" wrote:
>> [...]
>> well, krygowski picks up a check for being an "engineering" professor,
>> but he doesn't know his ass from his elbow, and jobst brandt, esteemed
>> stanford alumni, doesn't know a damned thing about fatigue, deformation
>> or strength of materials. your conspicuous absence from all /those/
>> debates doesn't show me you have credentials.[...]
>>
> Gee "jim", ever consider the possiblity that "Mike" is a newcomer to the
> group? That would explain his lack or participation in previous debates,
> no?
>

gee tom, don't you think that pulling the "30 year veteran" card carries
some responsibility to do some homework?

goddamned lightweight.