Scamdium strikes again!

Michael Press wrote:
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.

yes it is.

The fractures produce a stress riser propogating
the crack into the Al progressively weakening it until

in theory, yes.

the
rim fails.

but not in practice. the anodizing cracks are very observable and
they're not aligned with the rim cracking! yet again, examine this pic:
http://web.onetel.net.uk/~davidwgreen/rimpics/4.JPG
rim cracking /is/ however aligned with the extrusion axis, so much so
that long cracks jump back and forth between different extrusion lines,
but keep the same direction. /that/ is not anodizing.


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.

jim beam wrote:
Michael Press wrote:

Another possibility is that the low tensile strength of
the Al2?3 results in fracture of the Al2O3 layer. This is
observed.

yes it is.

Th e fractures produce a stress riser propogating
the crack into the Al progressively weakening it until

in theory, yes.

the
rim fails.

but not in practice. the anodizing cracks are very observable and
they're not aligned with the rim cracking! yet again, examine this pic:
http://web.onetel.net.uk/~davidwgreen/rimpics/4.JPG
rim cracking /is/ however aligned with the extrusion axis, so much so
that long cracks jump back and forth between different extrusion lines,
bu t keep the same direction. /that/ is not anodizing.

Yet another bit of photographic "evidence" from you which is not
evidence at all. Cracks from anodizing are not so evident in this photo
and it is not evident that the rim is anodized at all. If one can
discern such cracks, there do seem to be corresponding cracks in the
rim. Whatever: it is not at all clear enough. What IS evident is that
the rim has all sorts of stress risers from scoring, on the inward
facing surface that is not contacted by the brake pads. This is not a
polished aluminum rim, it has either been deliberately scored or poorly
manufactured. If there are cracks in the rim aligned with that scoring,
big deal: that is the whole reason why the manufacturer is supposed to
polish aluminum rims in the first place. But your photo isn't really
clear enough to even be sure those are cracks, and not just well-placed
dirt.

MANY posters in this group have seen the difference between the
otherwise identical polished aluminum MA2 and the heavily anodized
MA40. They know anodizing rims encourages crack formation, the more so
the heavier the anodizing. With your long track record of phony
photographic "evidence", you'll have to do A LOT better.

41 wrote:
jim beam wrote:
Michael Press wrote:

Another possibility is that the low tensile strength of
the Al2?3 results in fracture of the Al2O3 layer. This is
observed.

yes it is.

Th e fractures produce a st ress riser propogating
the crack into the Al progressively weakening it until

in theory, yes.

the
rim fails.

but not in practice. the anodizing cracks are very observable and
they're not aligned with the rim crac king! yet again, examine this pic:
http://web.onetel.net.uk/~davidwgreen/rimpics/4.JPG
rim cracking /is/ however aligned with the extrusion axis, so much so
that long cracks jump back and forth between different extrusion lines,
bu t keep the same direction. /that/ is not anodizing.

Yet another bit of photographic "evidence" from you which is not
evidence at all. Cracks from anodizing are not so evident in this photo
and it is not evident that the rim is anodized at all. If one can
discern such cracks, there do seem to be corresponding cracks in the
rim. Whatever: it is not at all clear enough. What IS evident is that
the rim has all sorts of stress risers from scoring, on the inward
facing surface that is not contacted by the brake pads. This is not a
polished aluminum rim, it has either been deliberately scored or poorly
manufactured. If there are cracks in the rim aligned with that scoring,
big deal: that is the whole reason why the manufacturer is supposed to
polish aluminum rims in the first place. But your photo isn't really
clear enough to even be sure those are cracks, and not just well-placed
dirt.

So, I looked at the other pictures and see they are not from the above
but that they have been well commented on already. I note that,
contrary to Jack Daniel's assertion in that original thread, that the
rims were low mileage and in good shape, the brake track is heavily
scored and there is corrosion on the outside. He also fails here to
link JPEGs 1-3, which show the inner surface of the rim pulling out in
a large circle around the eyelet. In short: manufacturing defect, too
short sockets. And like I say above, the rim is heavily scored, these
are natural stress risers so why shouldn't cracks be expected there? It
is not an anodized rim anyway. Lastly: with the too short sockets, once
could easily see how the tension could get too high without this being
seen by the stress-relief method, since only one wall was at first
getting all the load.

In short: again another piece of photographic "evidence" from this
poster which is nothing of the kind.

jim beam wrote:

Mark Hickey wrote:
jim beam wrote:

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".

There have been many of them over the years. Recently, I've seen the
diffence even between the black and silver versions of the Mavic Open
Pro rims (probably 20% of the wheels I've sold have had black rims,
but 100% of the rim failures have been with black rims).

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.

I'm still not following how it's impossible for the brittle anodizing
to crack where there's enough tension to eventually crack the parent
material. In fact, I can't imagine that the anodizing would NOT crack
first (it being much more brittle than the parent material). The fact
that the initial "typical" anodizing cracks might not match the
profile of a particular failure doesn't seem to be much of a "proof"
of anything, IMHO.

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.

Perhaps, but I'm still not convinced you are doing anything different
than you claim Jobst does above. There is enough anecdotal evidence
over the last couple decades to support Jobst's claims on this matter,
and little I've seen to refute it. IMH0, you're well short of
countering the evidence of thousands of anodized rims.

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