Rim cracks. Stress corrosion cracking? Brandt's law limited?

[Martyn Aldis]

I have followed the advice given when the general question of rims cracks was raised a few weeks ago
and searched back for contributions covering rim cracks around the eyelet in modern rims.

Some poster express a strongly held view that it is all cut and dried and the problem is caused by
cracks in anodised finish propagating into the underlying alloy in areas where there is a high
cyclic stress pattern. The argument appears to be based on the notch property of the cracks in the
anodisation.

This is said to be backed up by established airframe knowledge. There is some uncertainty about
whether or not this experience relates only to thick anodising or to the normal anodised finish seen
of most cycle and marine parts as well. (This is often silver but as far as I know the light
metallic looking colours are similar thickness to the common silver.)

In a sub-thread (a fibre?) from the recent thread The Book, The Wheel, No Taco, Jim Beam suggests
extrusion faults are to blame.

The cracks around the eyelets on our Mavic D521 (silver anodised) appeared in March after we had
used the tandem through a period when the roads were salted. We seldom have snow but our highways
authority salts when a hard frost is expected to avoid icy patches especially at roundabouts and
other road junctions. In settled high pressure weather the rock salt stays along the edges of the
road for several days and our rims are quite dusty with it at the end of a ride. Most of the cracks
in our rim follow the circumference but a few radiate a short distance from the spoke hole towards
the braking surface. They have extended to 6 or 8 mm quite fast but they are now growing more
slowly. I suspect this simply reflects that the stress from the spokes is localised.

I have only very limited knowledge of this area from welding training and what I have read in books
aimed at amateur and small scale boat builders and the more technically inclined yacht and boat
maintainer.

Here goes with what I have read:

A corrosive environment (specifically seawater) changes fatigue properties of many metals and their
alloys dramatically. For example mild steel does not show any fatigue limit in sea water as it does
in clean air and the strength of the common marine stainless steels after 100 million cycles in sea
water is half that in clean air.

In certain metals and alloys steady stress and a particular form of corrosive environment can lead
to stress corrosion cracking. My principal source book (Metal Corrosion in Boats by Nigel Warren)
states that aluminium alloys with a yield strength over 400 N/square mm are susceptible in seawater.

If the alloys used for rims are susceptible to stress corrosion cracking, it could mean that the
Jobst Brandt rule of spoke tension may not be valid because a level of steady stress that is safe in
clean air can a problem in a suitably corrosive environment. (Literally that is, not in postings.)

We are fairly casual about the electrolytic partnerships we set up in bicycles wheels. In marine
practice every effort is made to keep yellow metals away from aluminium. It is also normal to put a
layer of special paste under a pop-rivet on a mast even when the rivet is made of a safe alloy like
monel. The same paste is used by the aircraft industry but the rim maker and wheel builder happily
bring stainless steel, plated brass and aluminium alloy together dry.

So dipping wheels in the ocean is best reserved for the end of that trans-continental ride. Do bike
hire people near beaches get lots of rims problems? Do they see lots of cracked rims?

Has anyone who really knows what they are on about investigated corrosive processes in relation to
rim cracking?

Martyn e-mail [email protected]
==============================================================================

 

[Jim Beam]

> A corrosive environment (specifically seawater) changes fatigue properties of many metals and
> their alloys dramatically. For example mild steel does not show any fatigue limit in sea water as
> it does in clean air and the strength of the common marine stainless steels after 100 million
> cycles in sea water is half that in clean air.
>
yes! stress corrosion cracking is well known.

> In certain metals and alloys steady stress and a particular form of corrosive environment can lead
> to stress corrosion cracking. My principal source book (Metal Corrosion in Boats by Nigel Warren)
> states that aluminium alloys with a yield strength over 400 N/square mm are susceptible in
> seawater.

depends on the alloy, but aluminum is susceptible, yes.

>
> If the alloys used for rims are susceptible to stress corrosion cracking, it could mean that the
> Jobst Brandt rule of spoke tension may not be valid because a level of steady stress that is safe
> in clean air can a problem in a suitably corrosive environment. (Literally that is, not in
> postings.)

potentially, yes.

>
> We are fairly casual about the electrolytic partnerships we set up in bicycles wheels. In marine
> practice every effort is made to keep yellow metals away from aluminium. It is also normal to put
> a layer of special paste under a pop-rivet on a mast even when the rivet is made of a safe alloy
> like monel. The same paste is used by the aircraft industry but the rim maker and wheel builder
> happily bring stainless steel, plated brass and aluminium alloy together dry.
>
> So dipping wheels in the ocean is best reserved for the end of that trans-continental ride. Do
> bike hire people near beaches get lots of rims problems? Do they see lots of cracked rims?

not especially, but you're absolutely right that that it is a potential source of concern.

>
> Has anyone who really knows what they are on about investigated corrosive processes in relation to
> rim cracking?

i've done a little, but there's a limit to where you want to go with this stuff.

the truth is, aluminum has no fatigue endurance limit, so ultimately, it's going to break at some
point anyway. next, rims are subject to constant wear from the brakes. after that, they have to
endure pot-holes, drain covers, railroad tracks, car doors, bike racks, etc. and add to that, the
fact that there are more bikes sold in the u.s. than there are bike tires, and you quickly get the
idea that having a rim that can pass super-high milage limits is really an exercise in
pointlessness. why carry the extra weight? i have a pair of hard anodized open pros that are coming
up to 15,000 miles, and they're doing fine. the rear is a little buckled, but hey, that happens when
you actually ride a bike! i'll retire it if it gets worse, but the point is, it's good enough for
the job. and if you have a problem with one particular manufacturer, use another. we have choices.
your dollar counts for more than opinions on this newsgroup.

jb

 

[Terry Morse]

jim beam wrote:

> the truth is, aluminum has no fatigue endurance limit, so ultimately, it's going to break at some
> point anyway.

All things being equal, breaking later is better than breaking sooner, especially when "later" means
tens of thousands of miles instead of a few thousand. This type of lifetime can be designed into a
rim with little or no weight penalty. And the shame is that well designed and market tested rims are
being pushed out of the market by ones that cater to fashion over function.

> next, rims are subject to constant wear from the brakes. after that, they have to endure
> pot-holes, drain covers, railroad tracks, car doors, bike racks, etc. and add to that, the fact
> that there are more bikes sold in the u.s. than there are bike tires, and you quickly get the idea
> that having a rim that can pass super-high milage limits is really an exercise in pointlessness.

Is it really pointless to sell a rim that will last a long time? I can think of a couple of reasons
to want highly durable wheels. One is to avoid the hassle and cost of replacing them every year or
so--and you will have to replace poorly designed rims yearly if you're putting enough miles on them.
Another is having enough faith in a wheel's durability that you can take them on a tour and not have
to worry about a rim failure leaving you stranded in the middle of nowhere.
--
terry morse Palo Alto, CA http://www.terrymorse.com/bike/

 

[Ted Bennett]

and if you have a problem with one
> particular manufacturer, use another. we have choices. your dollar counts for more than opinions
> on this newsgroup.
>
> jb

Okay, Jim, tell us where we can buy non-anodized rims with no machined rims so we know that we are
starting with a consistent thickness.

In this case, I'd prefer to NOT have these technological "advances". Newer rims are worse
than old ones.

--
Ted Bennett Portland OR

 

[Jim Beam]

well, i /was/ going to suggest sun-ringle.com, but it seems they've gone to the dark side [all
anodized & machined] these days...

http://fixedgear.americancyclery.com/Store/Rims still stocks fiamme rims, which certainly looked
unanodized to me last time i was there. only trouble is they're all tubular.

honestly ted, it's good to be concerned, but just because a couple of people are still griping about
their experiences from 10 years ago, does /not/ mean the world is about to end today. i know others
do higher milage than me, but 15k miles on open pro cd's is not bad, especially for rims that are
allegedly such a cracking risk. outlasting the bearings in my campy record hubs at any rate.

jb

Ted Bennett wrote:
> and if you have a problem with one
>
>>particular manufacturer, use another. we have choices. your dollar counts for more than opinions
>>on this newsgroup.
>>
>>jb
>
>
>
> Okay, Jim, tell us where we can buy non-anodized rims with no machined rims so we know that we are
> starting with a consistent thickness.
>
> In this case, I'd prefer to NOT have these technological "advances". Newer rims are worse than
> old ones.

 

[Jim Beam]

> Is it really pointless to sell a rim that will last a long time?

of course not! but we live in an age where certain [*high end!!!*] auto makers spend millions of
dollars making transmissions that are deliberately and stringently life limited [so much so, it
costs them 30% more in q.c. to ensure this goal is met], but i don't hear people complaining about
that! same for rims, the /market/ doesn't seem to think it's a problem.

reality is, the market supports shortened life and disposability. again, using the auto biz as an
example, that's not a bad thing because new vehicles are significantly more fuel efficient and much
cleaner to operate. shortened vehicle life promotes this, big picture, regardless of any
individual's distaste with this concept.

re: bike components, i /do/ believe rim quality today is better than yesterday, so big picture, it's
good to keep moving on.

 

[Jobst Brandt]

Jim Beam writes:

>> Is it really pointless to sell a rim that will last a long time?

> Of course not! But we live in an age where certain [*high end!!!*] auto makers spend millions of
> dollars making transmissions that are deliberately and stringently life limited [so much so, it
> costs them 30% more in q.c. to ensure this goal is met], but i don't hear people complaining about
> that! Same for rims, the /market/ doesn't seem to think it's a problem.

Oooh! A conspiracy nut. And you believe that stuff enough to pass it on as fact. I've worked in the
auto industry and life tests are substantial hurdles for designers. You don't make money in
aftermarket transmissions, you only become a customer's enemy. Just look at FIAT (aka Fix It Again
Tony) in the USA.

> Reality is, the market supports shortened life and disposability. Again, using the auto biz as an
> example, that's not a bad thing because new vehicles are significantly more fuel efficient and
> much cleaner to operate. Shortened vehicle life promotes this, big picture, regardless of any
> individual's distaste with this concept.

Oh BS!

> re: Bike components, I /do/ believe rim quality today is better than yesterday, so big picture,
> it's good to keep moving on.

With the low pay in the bicycle industry, it's hard to see how they pass any life tests. Fortunately
there are some dedicated bikies among those engineers who operate under the thumb of marketing most
of the time.

Jobst Brandt [email protected] Palo Alto CA

 

[Jim Beam]

> Oooh! A conspiracy nut. And you believe that stuff enough to pass it on as fact. I've worked in
> the auto industry and life tests are substantial hurdles for designers.

ok, explain a certain high end manufacturer coming to /my/ faculty and paying for research on how to
*induce* fatigue cracks at gear tooth roots. i repeat, *induce* /not/ mitigate.

when did you work auto? before the 80's i'll guess.

 

[Java Man]

In article <[email protected]>, [email protected] says...
> > Is it really pointless to sell a rim that will last a long time?
>
> of course not! but we live in an age where certain [*high end!!!*] auto makers spend millions of
> dollars making transmissions that are deliberately and stringently life limited [so much so, it
> costs them 30% more in q.c. to ensure this goal is met], but i don't hear people complaining about
> that! same for rims, the /market/ doesn't seem to think it's a problem.
>
> reality is, the market supports shortened life and disposability.

Nonsense. The average car on the road today lasts many more miles than cars from past decades, and
with less maintenance and repairs. Sure there are examples of old ______s that lasted 500,000 mi.
But on average, they're more durable today.

Rick

 

[Jose Rizal]

jim beam:

> > Oooh! A conspiracy nut. And you believe that stuff enough to pass it on as fact. I've worked in
> > the auto industry and life tests are substantial hurdles for designers.
>
> ok, explain a certain high end manufacturer coming to /my/ faculty and paying for research on how
> to *induce* fatigue cracks at gear tooth roots. i repeat, *induce* /not/ mitigate.
>

Research gets done on damage inducement all the time, not just on gears. Many fatigue tests have
this aim. The results help pinpoint areas of possible weaknesses. This by itself does not imply what
you claim. As far as saying that planned obsolescence is beneficial to the customers and the
environment, yikes! You must be in the pocket of auto manufacturers.

 

[Jim Beam]

these guys were plenty good at getting cracks to start. they were having problems getting them up to
the design milage, but no further. quite tricky.

not really any different from light bulbs failing at 1000 hrs. commonly accepted by consumers, but
hard to achieve technically.

 

[John Albergo]

jim beam wrote:

>> Is it really pointless to sell a rim that will last a long time?
>
>
> of course not! but we live in an age where certain [*high end!!!*] auto makers spend millions of
> dollars making transmissions that are deliberately and stringently life limited [so much so, it
> costs them 30% more in q.c. to ensure this goal is met], but i don't hear people complaining about
> that! same for rims, the /market/ doesn't seem to think it's a problem.
>
> reality is, the market supports shortened life and disposability. again, using the auto biz as an
> example, that's not a bad thing because new vehicles are significantly more fuel efficient and
> much cleaner to operate. shortened vehicle life promotes this, big picture, regardless of any
> individual's distaste with this concept.

Well, someone's been sleeping on the job, because longevity of automobiles is way beyond 40, or even
20 years ago, with much less rigorous maintenance required.

 

[David L. Johnso]

On Sat, 23 Aug 2003 02:14:06 +0000, jim beam wrote:

> of course not! but we live in an age where certain [*high end!!!*] auto makers spend millions of
> dollars making transmissions that are deliberately and stringently life limited [so much so, it
> costs them 30% more in q.c. to ensure this goal is met], but i don't hear people complaining about
> that! same for rims, the /market/ doesn't seem to think it's a problem.
>
> reality is, the market supports shortened life and disposability. again, using the auto biz as an
> example, that's not a bad thing because new vehicles are significantly more fuel efficient and
> much cleaner to operate. shortened vehicle life promotes this, big picture, regardless of any
> individual's distaste with this concept.

Clearly you did not deal with cars over the last 40 years. 40 years ago, wild claims about "life
limited" transmissions may have seemed true, since no one could make an automatic transmission that
lasted well (well, no one except the Germans). But cars now are vastly longer-lived than cars then.
In the 60s and 70s it was rare to be able to economically keep a car running for 100,000 miles. Now,
it is expected to get much more mileage than that. Everything about modern cars lasts longer than
the old ones. My daughter now drives my old (94) Honda; it has 150,000 miles, and no engine trouble,
not a speck of rust, and still gets 40mpg.

--

David L. Johnson

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