Scamdium strikes again!

jim beam wrote:
Phil Lee, Squid wrote:
jim beam wrote:
Phil Lee, Squid wrote:
http://weightweenies.starbike.com/ph...ic.php?t=19036

Aluminum BB axles are not a good material selection...

they're fine if they're dimensionally appropriate for the job.
aluminum shimano axles anyone?

the problem comes when you use the same size in aluminum as you do
in steel given aluminum's much lower strength. presence of
scandium in this situation is pretty much irrelevant.

It was tongue in cheek, of course.

I'm curious to know what proportion of high-mileage Ksyrium SSC SL
riders get broken spokes compared to standard-spoke riders.

well, those spokes are 3x the size...

That's what I mean. However, with aluminum's lack of a fatigue limit...

interestingly, when those wheels first came out, it seemed like i'd
see someone shipwrecked with a broken aluminum spoke once or twice a
month. the last few years though, i can't say i've seen one.

The lack of a fatigue limit would almost ensure that higher-mileage wheels
would have constant breakages, wouldn't it?

Does the ball-and-socket method of the SSC SL spoke heads resist breakage
better when compared to the J-bend of SS spokes?

--
Phil Lee, Squid

Phil Lee, Squid wrote:
jim beam wrote:
Phil Lee, Squid wrote:
jim beam wrote:
Phil Lee, Squid wrote:
http://weightweenies.starbike.com/ph...ic.php?t=19036

Aluminum BB axles are not a good material selection...

they're fine if they're dimensionally appropriate for the job.
aluminum shimano axles anyone?

the problem comes when you use the same size in aluminum as you do
in steel given aluminum's much lower strength. presence of
scandium in this situation is pretty much irrelevant.
It was tongue in cheek, of course.

I'm curious to know what proportion of high-mileage Ksyrium SSC SL
riders get broken spokes compared to standard-spoke riders.
well, those spokes are 3x the size...

That's what I mean. However, with aluminum's lack of a fatigue limit...

it has a definable fatigue limit, but not an endurance limit. stainless
steel doesn't have an endurance limit either, so traditional spokes have
no intrinsic advantage.


interestingly, when those wheels first came out, it seemed like i'd
see someone shipwrecked with a broken aluminum spoke once or twice a
month. the last few years though, i can't say i've seen one.

The lack of a fatigue limit would almost ensure that higher-mileage wheels
would have constant breakages, wouldn't it?

be careful of terminology. while there is a lot of confusion about
which term describes what in certain quarters, where i came from,
endurance limit describes the "knee" in the s-n graph of mild steel,
while fatigue limit describes the stress level to survive an arbitrary
number of stress cycles, say 10^7. it's the design, stress risers,
material quality, etc., that determine fatigue life more than anything
else, particularly once you get away from the simple alloys systems.
don't be afraid of properly deployed aluminum alloys - aluminum alloy
wings stay on planes for a good long time....


Does the ball-and-socket method of the SSC SL spoke heads resist breakage
better when compared to the J-bend of SS spokes?

in terms of design principle, yes it should do - no intrinsic bending.
all the broken aluminum spokes i've ever seen have broken at the
threaded end.

"jim beam" wrote in message
t...
[edit]
be careful of terminology. while there is a lot of confusion about which
term describes what in certain quarters, where i came from, endurance
limit describes the "knee" in the s-n graph of mild steel, while fatigue
limit describes the stress level to survive an arbitrary number of stress
cycles, say 10^7. it's the design, stress risers, material quality, etc.,
that determine fatigue life more than anything else, particularly once you
get away from the simple alloys systems. don't be afraid of properly
deployed aluminum alloys - aluminum alloy wings stay on planes for a good
long time....


And am I right in thinking they're held on with rivets, mostly? That got me
wondering about this cracking-round-eyelets thing that rattles on and on in
RBT. I saw someone on TV restoring an aircraft. drilling the holes for the
rivets involved at least a 3 step process (pilot, bigger drill, finishing
drill). I assumed this was to produce a smooth round hole. I'm willing to
believe that holes in rims are a one step process. This could leave a
comparatively rough and ovalised hole. Could this lead to more serious
crack propogation?

Skippy
E&OE

In article
,
"Skippy" wrote:

"jim beam" wrote in message
t...
[edit]
be careful of terminology. while there is a lot of confusion about which
term describes what in certain quarters, where i came from, endurance
limit describes the "knee" in the s-n graph of mild steel, while fatigue
limit describes the stress level to survive an arbitrary number of stress
cycles, say 10^7. it's the design, stress risers, material quality, etc.,
that determine fatigue life more than anything else, particularly once you
get away from the simple alloys systems. don't be afraid of properly
deployed aluminum alloys - aluminum alloy wings stay on planes for a good
long time....


And am I right in thinking they're held on with rivets, mostly? That got me
wondering about this cracking-round-eyelets thing that rattles on and on in
RBT. I saw someone on TV restoring an aircraft. drilling the holes for the
rivets involved at least a 3 step process (pilot, bigger drill, finishing
drill). I assumed this was to produce a smooth round hole. I'm willing to
believe that holes in rims are a one step process. This could leave a
comparatively rough and ovalised hole. Could this lead to more serious
crack propogation?

Bicycle rim holes should be finished with a grommet so
machining is a negligible contribution to rim hole
failure. Experience of many people show that thick
anodizing of bicycle rims is a much greater contributor to
rim failure.

--
Michael Press

Skippy wrote:
"jim beam" wrote in message
t...
[edit]
be careful of terminology. while there is a lot of confusion about which
term describes what in certain quarters, where i came from, endurance
limit describes the "knee" in the s-n graph of mild steel, while fatigue
limit describes the stress level to survive an arbitrary number of stress
cycles, say 10^7. it's the design, stress risers, material quality, etc.,
that determine fatigue life more than anything else, particularly once you
get away from the simple alloys systems. don't be afraid of properly
deployed aluminum alloys - aluminum alloy wings stay on planes for a good
long time....


And am I right in thinking they're held on with rivets, mostly? That got me
wondering about this cracking-round-eyelets thing that rattles on and on in
RBT. I saw someone on TV restoring an aircraft. drilling the holes for the
rivets involved at least a 3 step process (pilot, bigger drill, finishing
drill). I assumed this was to produce a smooth round hole. I'm willing to
believe that holes in rims are a one step process. This could leave a
comparatively rough and ovalised hole. Could this lead to more serious
crack propogation?

it could - the process you describe is designed to create the smoothest
surfaces possible and therefore mitigate fatigue. bike rim holes are
drilled or punched in a one-step process.

the bottom line is that rims are a component that wears in use. it
therefore has a limited lifetime. if the wear life is shorter than the
fatigue life [assuming spoke tension as specified by the rim
manufacturer], it's simply not worth the effort or expense to try
extending it even further.

Michael Press wrote:
In article
,
"Skippy" wrote:

"jim beam" wrote in message
t...
[edit]
be careful of terminology. while there is a lot of confusion about which
term describes what in certain quarters, where i came from, endurance
limit describes the "knee" in the s-n graph of mild steel, while fatigue
limit describes the stress level to survive an arbitrary number of stress
cycles, say 10^7. it's the design, stress risers, material quality, etc.,
that determine fatigue life more than anything else, particularly once you
get away from the simple alloys systems. don't be afraid of properly
deployed aluminum alloys - aluminum alloy wings stay on planes for a good
long time....

And am I right in thinking they're held on with rivets, mostly? That got me
wondering about this cracking-round-eyelets thing that rattles on and on in
RBT. I saw someone on TV restoring an aircraft. drilling the holes for the
rivets involved at least a 3 step process (pilot, bigger drill, finishing
drill). I assumed this was to produce a smooth round hole. I'm willing to
believe that holes in rims are a one step process. This could leave a
comparatively rough and ovalised hole. Could this lead to more serious
crack propogation?

Bicycle rim holes should be finished with a grommet so
machining is a negligible contribution to rim hole
failure. Experience of many people show that thick
anodizing of bicycle rims is a much greater contributor to
rim failure.

sorry, but there's no proven connection with anodizing. the originator
of this allegation used a dye penetrant test as "proof". all dye
penetrant testing shows is that cracking is present - it is entirely
uninformative as to cause. deployment of an inappropriate test should
warn of flawed theory, but the fact that cracking is often out of plane
with any potential anodizing cracks shows just how wildly off base it
really is. please don't propagate this old wives tale any more michael.
thanks.

Michael Press wrote:
In article
,
"Skippy" wrote:

"jim beam" wrote in message
t...

don't be afraid of properly
deployed aluminum alloys - aluminum alloy wings stay on planes for a good
long time....

Yeah. After 15 years in service, the FAA mandates frequent inspections
for cracks with an eddy current meter. This is one of the main reasons
Airbus and Boeing are so eager to shift to carbon: not just the weight
savings, but the wait savings. Current inspection procedures for carbon
parts are visual and perhaps a tap test and nothing more. As recent
discoveries show, these are inadequate. See latest New Scientist for
the story.
Ô

jim beam wrote:

Michael Press wrote:

Bicycle rim holes should be finished with a grommet so
machining is a negligible contribution to rim hole
failure. Experience of many people show that thick
anodizing of bicycle rims is a much greater contributor to
rim failure.

sorry, but there's no proven connection with anodizing. the originator
of this allegation used a dye penetrant test as "proof". all dye
penetrant testing shows is that cracking is present - it is entirely
uninformative as to cause. deployment of an inappropriate test should
warn of flawed theory, but the fact that cracking is often out of plane
with any potential anodizing cracks shows just how wildly off base it
really is. please don't propagate this old wives tale any more michael.

So then maybe you can explain the tremendously failure rates between
anodized rims and the same rim without anodizing (something I've seen
even with modern "thin anodized" rims. It's OK to try to shoot holes
in theory, but unless you have some other more plausible theory, it's
all hand-waving.

I'm also curious as to what might keep anodizing from cracking "in
plane" with typical rim-killing cracks. Seems to me that the same
stresses that kill the parent material would certainly be likely to
flex the brittle anodizing enough to create a crack in the same plane.

Or is this just another "Jobst said it so I'm going to try to convince
everyone it's not true" issue?

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $795 ti frame

Mark Hickey wrote:
jim beam wrote:

Michael Press wrote:

Bicycle rim holes should be finished with a grommet so
machining is a negligible contribution to rim hole
failure. Experience of many people show that thick
anodizing of bicycle rims is a much greater contributor to
rim failure.
sorry, but there's no proven connection with anodizing. the originator
of this allegation used a dye penetrant test as "proof". all dye
penetrant testing shows is that cracking is present - it is entirely
uninformative as to cause. deployment of an inappropriate test should
warn of flawed theory, but the fact that cracking is often out of plane
with any potential anodizing cracks shows just how wildly off base it
really is. please don't propagate this old wives tale any more michael.

So then maybe you can explain the tremendously failure rates between
anodized rims and the same rim without anodizing (something I've seen
even with modern "thin anodized" rims. It's OK to try to shoot holes
in theory, but unless you have some other more plausible theory, it's
all hand-waving.

so what rims are available both anodized and unanodized? and what's
your data? all i've seen is a bunch of misdiagnosed assertions that
happen to coincide with "tension as high as the rim can bear".


I'm also curious as to what might keep anodizing from cracking "in
plane" with typical rim-killing cracks. Seems to me that the same
stresses that kill the parent material would certainly be likely to
flex the brittle anodizing enough to create a crack in the same plane.

study this:
http://web.onetel.net.uk/~davidwgreen/rimpics/4.JPG
the crack is not radial, it's tangential, therefore it's not initiating
from any anodizing crack. anodizing cracks, as you'll know if you've
looked at them under a magnifier, extend strictly radially from the rim
hole.


Or is this just another "Jobst said it so I'm going to try to convince
everyone it's not true" issue?

there's nothing wrong with jobst's work when it's something within his
actual sphere of knowledge. but given that that sphere is apparently
much smaller than he cares to admit, the problem comes when he starts
making flawed presumptions about stuff he doesn't actually know or can
be bothered to research. and it gets worse when he tries to b.s. a
metallurgist on basic materials theory about which he hasn't got the
faintest clue.

In article
,
jim beam wrote:

Michael Press wrote:
In article
,
"Skippy" wrote:

"jim beam" wrote in message
t...
[edit]
be careful of terminology. while there is a lot of confusion about which
term describes what in certain quarters, where i came from, endurance
limit describes the "knee" in the s-n graph of mild steel, while fatigue
limit describes the stress level to survive an arbitrary number of stress
cycles, say 10^7. it's the design, stress risers, material quality, etc.,
that determine fatigue life more than anything else, particularly once you
get away from the simple alloys systems. don't be afraid of properly
deployed aluminum alloys - aluminum alloy wings stay on planes for a good
long time....

And am I right in thinking they're held on with rivets, mostly? That got me
wondering about this cracking-round-eyelets thing that rattles on and on in
RBT. I saw someone on TV restoring an aircraft. drilling the holes for the
rivets involved at least a 3 step process (pilot, bigger drill, finishing
drill). I assumed this was to produce a smooth round hole. I'm willing to
believe that holes in rims are a one step process. This could leave a
comparatively rough and ovalised hole. Could this lead to more serious
crack propogation?

Bicycle rim holes should be finished with a grommet so
machining is a negligible contribution to rim hole
failure. Experience of many people show that thick
anodizing of bicycle rims is a much greater contributor to
rim failure.

sorry, but there's no proven connection with anodizing. the originator
of this allegation used a dye penetrant test as "proof". all dye
penetrant testing shows is that cracking is present - it is entirely
uninformative as to cause. deployment of an inappropriate test should
warn of flawed theory, but the fact that cracking is often out of plane
with any potential anodizing cracks shows just how wildly off base it
really is. please don't propagate this old wives tale any more michael.

Aluminum oxide and aluminum have different bulk physical
characteristics. Among these are ductility and elastic
modulus. A bicycle rim undergoes considerable strain.
Different things can happen. The differential of
elasticity between the Al2O3 and Al results in a shear
stress at the boundary. This could result in a relative
displacement of the two layers, and this would be observed
as exfoliation of the Al2O3 in flakes. This is not
observed. The boundary between the Al and the Al2O3 is not
a sharp one, but gradual, so the shear stress is not
large.

Another possibility is that the low tensile strength of
the Al2¬3 results in fracture of the Al2O3 layer. This is
observed. The fractures produce a stress riser propogating
the crack into the Al progressively weakening it until the
rim fails.

The same phenomenon is experieneced when a scab forms over
a wound. If the skin is stretched the scab can crack and
open the wound.

--
Michael Press