MA3 rim failure, where to now

"Ian Smith" wrote in message
...

It is not reasonable, because it fails to explain the observed fact
that
with the spokes on which the hub stands removed, the hub remains
supported,

No it doesn't. The wheel collapses.


So in the limiting case where tension reaches zero in the lower spokes the
wheel spontaneously collapses? I think not. I think it will become
unstable, but it will not spontaneously collapse.

--
Guy
===

WARNING: may contain traces of irony. Contents may settle after posting.
http://www.chapmancentral.com

"Ian Smith" wrote in message
...

Like that, for example. If the bottom spokes were missing the wheel
would collapse - you'd get a flexural failure in the rim at the bottom
of the wheel.


Only if the force exceeded a certain limit. So now the degree of
"standingness" is not only dependent on the rigidty of the rim, it's also
affected by the mass applied at the hub. Or maybe "stand" is a pointless
way to describe the effect of rim deformation on the tension of the lower
spokes.

--
Guy
===

WARNING: may contain traces of irony. Contents may settle after posting.
http://www.chapmancentral.com

I saw no response to the question. I assume those who quibble about
the function of spokes did not see the following or were unable to
access the URL. Please consider the question.

================================================== ==================
This is not a semantic difference but a technical one, the book shows
an aluminum a common die-cast moped wheel that looks as though it
might have wire spokes.

http://mopedarmy.com/photos/brand/6/1681/

In such wheels, knowing that they are not tensioned, evokes the
response that "of course, this wheel stands on its bottom spokes."
However, by selective cooling in the die cast process, these spokes
can be tensioned, and the answer becomes unclear. Visually it appears
to be between a wire spoked wheel and a wooden wagon wheel.

Does prestress of a spoke change its function and that of the wheel?
================================================== ==================

Jobst Brandt

"Java Man (Espressopithecus)" wrote in message
ble.net...

It is worse than that: it is actively misleading. Consider a more rigid
rim.

But we're discussing bicycle wheels, which have a very flexible rim.

Irrelevant. The relatively large change in tension in the bottom spokes is
entirely a function of rim deformation, as far as my reading of the FEA
goes, so if you take a more rigid rim, some of the standingness becomes
hangingness. IOW, "hang" and "stand" obscure rather than illuminating the
issue.

--
Guy
===

WARNING: may contain traces of irony. Contents may settle after posting.
http://www.chapmancentral.com

On Thu, 11 Sep 2003 09:05:02 GMT, Simon Brooke wrote:
Ian Smith writes:

Sorry, no. My argument is that the north team pulls less hard, and
teh handkerchief moves. Which team caused teh handkerchief to move?
You're saying the south team did, but they are doing nothing
different, so it's not sensible (by cause and effect) to say they
caused teh change.

The South team _do_ cause the change. That's simply an observable
fact, and no amount of distortion of reality can alter it. They are
still doing work, whereas the North team are driking beer.

Read what I said - the north team are still pulling, just less hard.

Regardless, evenb if the north team _did_ drop teh rope, they caused
teh change, by dropping theg rope. Cause and effect. Very simple.

regards, Ian SMith
--
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On Thu, 11 Sep 2003 15:42:04 +0100, Just zis Guy, you know? wrote:
"Ian Smith" wrote in message
...

Actually, they elongate at teh bottom - alongside teh contact patch.
In fact, the greatest elongation is in the lower half of the wheel.

They have a negative modulus then?

No, the spoke in highest tension is near the bottom of the wheel.

What I said is accurate, and is discussed (with numerical values) on
my web page. I also state the value of modulus used, so you can see
what it is if you want. It now looks like you're deliberately
selectively misrepresenting what those that disagree with you said,
since I have trouble believing you seriously think I'd spontaneously
change the modulus of spokes as they move round the wheel.

regards, Ian SMith
--
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In article ,
says...
"Java Man (Espressopithecus)" wrote in message
ble.net...

It is worse than that: it is actively misleading. Consider a more rigid
rim.

But we're discussing bicycle wheels, which have a very flexible rim.

Irrelevant.

If this was rec.wheels.carriages I'd agree. But it isn't.

The relatively large change in tension in the bottom spokes is
entirely a function of rim deformation, as far as my reading of the FEA
goes, so if you take a more rigid rim, some of the standingness becomes
hangingness. IOW, "hang" and "stand" obscure rather than illuminating the
issue.

That depends on how you define "the issue".

For an understanding of bicycle wheels, which was the point of JB's
book, eliminating the myth of "hanging" is useful. I suspect the
"standing" metaphor was intended to help with this.

Rick

On Thu, 11 Sep 2003 15:43:22 +0100, Just zis Guy, you know? wrote:
"Ian Smith" wrote in message
...

It is not reasonable, because it fails to explain the observed fact
that with the spokes on which the hub stands removed, the hub remains
supported,

No it doesn't. The wheel collapses.

So in the limiting case where tension reaches zero in the lower spokes the
wheel spontaneously collapses? I think not. I think it will become
unstable, but it will not spontaneously collapse.

In teh limitting case ONE spoke becomes unstressed. However, that's
not what your argument depends on - it depends on (and I quote)
"spokes on which teh hub stands". Spokes - plural, multiple, more
than
one.

If you remove the compressive spokes (of which tehre are several)
(which is what you proposed), the wheel is dramatically weakened. I
estimate a factor of 5 to 10, but haven't done any analysis to confirm
that. That's what you proposed, what I commented on, but not what
you've now decided to argue against.

That's called a strawman.

regards, Ian SMith
--
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|o o|
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On Thu, 11 Sep, Just zis Guy, you know? wrote:
"Java Man (Espressopithecus)" wrote in message
ble.net...

It is worse than that: it is actively misleading. Consider a more rigid
rim.

But we're discussing bicycle wheels, which have a very flexible rim.

Irrelevant.

It is not irrelevant. A bicycle wheel is what is termed statically
indeterminate. That measn that you cannot calculate the loads in the
component elenments unless you know the relataive stiffneses. A
corollary of that is that if you change the stiffness of some element,
you will change the distribution of the loads.

For this reason, if talking about a bicycle wheel, you need to confine
yourself to a reasonable range of stiffnesses - ones taht are close to
those of a bicycle wheel. Some other wheel, spoked with spokes 100
times more flexible, or with a rim of extruded diamond or whatever,
will work in a different way, with potentially a very different load
path and a very different behaviour.

However, that's not the discussion, is it - no-one ever starts "hey,
if you made a wheel with elastic spokes and extruded diamond for teh
rim, would it stand or would it hang". The discussion is about
bicycle wheels, and in bicycle wheels teh spokes that make by far the
biggest contribution to holding up the hub are the ones immediately
below the hub, it is therefore sensible to say the hub stands on teh
spokes.

goes, so if you take a more rigid rim, some of the standingness becomes
hangingness.

Yes, but you haven't got a bicycle wheel any more, and we were
discussing bicycle wheels.

Back to your post a little up teh thread, you said: "Consider a more
rigid rim. Suddenly the change in tension in the lower spokes is
significantly reduced." This isn't true. You need a _lot_ stiffer
rim, or a lot more flexible spokes to get a significant reduction.
Once again, the premise on which you are basing sweeping conclusions
is not sound.

regards, Ian SMith
--
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|o o|
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On Fri, 12 Sep 2003 18:49:33 +0000 (UTC), Ian Smith
wrote:


However, that's not the discussion, is it - no-one ever starts "hey,
if you made a wheel with elastic spokes and extruded diamond for teh
rim, would it stand or would it hang".

I'm afraid I have to correct you here - this is probably the second
most common troll, right after the "if you cut the bottom spokes..."
red herring.

Painfully funny stuff. g

--
Chris Bird