Ultegra Road triple crank cracks due to fatigue.

http://www.pbase.com/gearoidmuar/image/63965535.jpg

http://www.pbase.com/gearoidmuar/image/63965536.jpg

My friend Mick Lehane had this happen today. Fortunately he was only
slightly hurt. Chainset about 4-5 years old. Shimano Ultegra. Mick's a
60 year old light fit cyclist who probably does about 5000 miles per
year on this bike.

Anyone seen this happen? I never have before and I'm cycling all my
life. I've had bottom bracket axles crack in the past

wrote:
http://www.pbase.com/gearoidmuar/image/63965535.jpg

http://www.pbase.com/gearoidmuar/image/63965536.jpg

My friend Mick Lehane had this happen today. Fortunately he was only
slightly hurt. Chainset about 4-5 years old. Shimano Ultegra. Mick's a
60 year old light fit cyclist who probably does about 5000 miles per
year on this bike.

Anyone seen this happen? I never have before and I'm cycling all my
life. I've had bottom bracket axles crack in the past

but do you see how scratched up that thing is??? aluminum, like most
other structural metals, is notch sensitive. if the surface of the
component is scratched and damaged, it creates a multitude of small
notches from which fatigue can nucleate and grow. it's not simply
aesthetics which dictate the surface finish on these things.

for the future, your friend has got to learn to treat this stuff with
more respect. a campy [or any other brand] crank would have failed
identically in the same circumstances. when the f.a.a. investigates an
engine falling off a plane in flight, it's not going to have an issue
with the plane's manufacturer if it finds the service crew were using a
forklift to "massage" the engine's fixing bolts into position.

" wrote:

http://www.pbase.com/gearoidmuar/image/63965535.jpg

http://www.pbase.com/gearoidmuar/image/63965536.jpg

My friend Mick Lehane had this happen today. Fortunately he was only
slightly hurt. Chainset about 4-5 years old. Shimano Ultegra. Mick's a
60 year old light fit cyclist who probably does about 5000 miles per
year on this bike.

Anyone seen this happen? I never have before and I'm cycling all my
life. I've had bottom bracket axles crack in the past

The photos seem to show that the inner (BB side) of the break is
smoother and shinier that the outer part. That suggests that the crack
had been propogating for some time, starting at the inner surface. A
sudden break would be rough all the way across.

It's quite possible that the crank has been striking a maladjusted front
derailer, deeply scratching the crank and resulting in a stress riser
which led to the break.

This is a potentially disastrous failure. A more thorough/frequent
inspection schedule may have prevented it.

Please note that I have no specific expertise in metallurgy or failure
analysis.

May contain traces of nuts.

--
Ted Bennett

Yes.
I'm aware of crack propogation in aluminium.

It looks to me as if the fatigue occurred in the inner half (bike side)
and the outside bit was sudden.
The inner bit looked all powdered, like a salt of aluminium.

I've never seen a crank crack before. I've had several frames crack on
me, a couple of seat-posts, axles etc.

wrote:
Yes.
I'm aware of crack propogation in aluminium.

It looks to me as if the fatigue occurred in the inner half (bike side)
and the outside bit was sudden.
The inner bit looked all powdered, like a salt of aluminium.

I've never seen a crank crack before. I've had several frames crack on
me, a couple of seat-posts, axles etc.

I broke this same crank about a year ago, a little higher and maybe
less mileage. I have broken six or seven cranks, mostly 70s/80s
vintage Campy NR. One Shimano -- that one. I think cranks can fatigue
from bending at the bottom of the stroke, and, in my experience, this
is a common failure mode for people who weigh more than a few pounds
and who climb out of the saddle. I have broken cranks with and without
heel/shoe polishing, and if polishing or surface scratches are enough
to cause a crank to fail, then a serious redesign is in order. I have
big feet, and there is no way I am going to avoid hitting my crank arm
somewhere with my shoes. -- Jay Beattie.

Jay Beattie wrote:
wrote:
Yes.
I'm aware of crack propogation in aluminium.

It looks to me as if the fatigue occurred in the inner half (bike side)
and the outside bit was sudden.
The inner bit looked all powdered, like a salt of aluminium.

I've never seen a crank crack before. I've had several frames crack on
me, a couple of seat-posts, axles etc.

I broke this same crank about a year ago, a little higher and maybe
less mileage. I have broken six or seven cranks, mostly 70s/80s
vintage Campy NR. One Shimano -- that one. I think cranks can fatigue
from bending at the bottom of the stroke, and, in my experience, this
is a common failure mode for people who weigh more than a few pounds
and who climb out of the saddle. I have broken cranks with and without
heel/shoe polishing, and if polishing or surface scratches are enough
to cause a crank to fail, then a serious redesign is in order. I have
big feet, and there is no way I am going to avoid hitting my crank arm
somewhere with my shoes. -- Jay Beattie.

my shoes are size 13, and i /never/ "polish" the crank. ever. in fact,
i find it hard to understand how it's possible if cleats are positioned
correctly.

but shoes strike is not the only problem here - the inside of the crank
is scratched to blazes by repeated chain derailment. again, i find it
hard to understand how this problem is allowed to even occur in the
first place, let alone persist to the extent that this crank has
sustained the damage seen. there is a fundamental disconnect between
this rider's actions and the perception of consequences.

On 23 Jul 2006 12:01:32 -0700, "
wrote:


Yes.
I'm aware of crack propogation in aluminium.

It looks to me as if the fatigue occurred in the inner half (bike side)
and the outside bit was sudden.
The inner bit looked all powdered, like a salt of aluminium.

I've never seen a crank crack before. I've had several frames crack on
me, a couple of seat-posts, axles etc.

Dear G.,

I think that you have the sequence backward.

This picture . . .

http://www.pbase.com/gearoidmuar/image/63965536.jpg

.. . . shows a crank that began cracking on the pedal side.

The small dark area with the (| shape is where the failure began.

You'll see a series of fine lines (((( from the pedal-side. That's
where the original crack kept cracking a little more. These lines are
often called beachmarks or clamshell marks.

| | undamaged arm, pedal side

| (| first tiny crack starts at surface damage

| ((| crack extends a little further

| (((| a third crack lays down another line

|/\/\(((| sudden disaster when cracks reach central hole corners

(The actual pattern looks like a set of ripples expanding from a point
on the pedal side, but ASCII diagrams are crude.)

This fine cracking takes time, so the inner surface of that part of
the failure will often show corrosion.

When a critical point was reached, the rest of the arm broke off
abruptly, with a strikingly ragged, irregular surface that's going to
be uncorroded. The slowly cracking initial area also tends to be
rubbed smooth, while the area of abrupt failure is left rough.

The half-moon series of fine lines is well-known.

You can see similar crank failures he

http://pardo.net/pardo/bike/pic/fail/000.html

This one is nice because it shows how the crack began on the pedal
side:

http://pardo.net/pardo/bike/pic/fail/FAIL-010.html

See figures 4 & 5 here for a quick description and diagram of
beachmarks:

http://www.sv.vt.edu/classes/MSE2094...y/fatigue.html

Note that the abrupt failure clearly occurs when the cracking from the
pedal side finally reaches the corners of the hole in the center of
the arm.

Cheers,

Carl Fogel

jim beam wrote in
t:

wrote:
http://www.pbase.com/gearoidmuar/image/63965535.jpg

http://www.pbase.com/gearoidmuar/image/63965536.jpg

My friend Mick Lehane had this happen today. Fortunately he was only
slightly hurt. Chainset about 4-5 years old. Shimano Ultegra. Mick's a
60 year old light fit cyclist who probably does about 5000 miles per
year on this bike.

Anyone seen this happen? I never have before and I'm cycling all my
life. I've had bottom bracket axles crack in the past

but do you see how scratched up that thing is??? aluminum, like most
other structural metals, is notch sensitive. if the surface of the
component is scratched and damaged, it creates a multitude of small
notches from which fatigue can nucleate and grow. it's not simply
aesthetics which dictate the surface finish on these things.

for the future, your friend has got to learn to treat this stuff with
more respect. a campy [or any other brand] crank would have failed
identically in the same circumstances. when the f.a.a. investigates an
engine falling off a plane in flight, it's not going to have an issue
with the plane's manufacturer if it finds the service crew were using a
forklift to "massage" the engine's fixing bolts into position.

I wonder if Hollowtech can be to blame; it's a delamination with sharp
corners.

--
Mike DeMicco

Mike DeMicco wrote:
jim beam wrote in
t:

wrote:
http://www.pbase.com/gearoidmuar/image/63965535.jpg

http://www.pbase.com/gearoidmuar/image/63965536.jpg

My friend Mick Lehane had this happen today. Fortunately he was only
slightly hurt. Chainset about 4-5 years old. Shimano Ultegra. Mick's a
60 year old light fit cyclist who probably does about 5000 miles per
year on this bike.

Anyone seen this happen? I never have before and I'm cycling all my
life. I've had bottom bracket axles crack in the past

but do you see how scratched up that thing is??? aluminum, like most
other structural metals, is notch sensitive. if the surface of the
component is scratched and damaged, it creates a multitude of small
notches from which fatigue can nucleate and grow. it's not simply
aesthetics which dictate the surface finish on these things.

for the future, your friend has got to learn to treat this stuff with
more respect. a campy [or any other brand] crank would have failed
identically in the same circumstances. when the f.a.a. investigates an
engine falling off a plane in flight, it's not going to have an issue
with the plane's manufacturer if it finds the service crew were using a
forklift to "massage" the engine's fixing bolts into position.

I wonder if Hollowtech can be to blame; it's a delamination with sharp
corners.

have you ever seen the crack nucleate from inside?

On 23 Jul 2006 12:01:32 -0700, "
wrote:

I've never seen a crank crack before.

I have.

JT

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