Are CF frames really safe?

On Thursday, May 25, 2017 at 8:53:36 AM UTC-7, wrote:
itsnot road conditions ....who rides into potholes ?

prob is factory quality control

JB is prob keeping a close magnifier on his CF

we due for a JB CF Report any day now...

prob crack above The Hub

The Hub? http://hopworksbeer.com/ I'm waiting for Tom to post a link supporting his claim that CFRP "deteriorates rapidly" riding on rough California roads. I think the CF big-hit bike guys would be surprised to hear this. I can see UV and a harsh environment attacking the polymer (assuming no decent paint job and a bike chained-up outside), but fatigue cycles alone don't cause "rapid" deterioration. The deterioration is less rapid than with aluminum or steel in terms of the number of cycles to failure.

I've broken most bicycle-related things -- frames, cranks, pedals, seat posts, handlebars, hubs. I haven't broken a CF anything yet, but I would expect to break a CF frame one day, and I do keep an eye on the fork and steerer.. I'm not sure about the strength of CF steerers, although they seem to be working out fine. I sure wouldn't buy a Colnago. All my CF bikes (a SuperSix and a Roubaix) have lifetime warranties.

-- Jay Beattie.

On Thursday, May 25, 2017 at 8:53:36 AM UTC-7, wrote:
itsnot road conditions ....who rides into potholes ?

prob is factory quality control

JB is prob keeping a close magnifier on his CF

we due for a JB CF Report any day now...

prob crack above The Hub

What are you talking about? We aren't talking about pot holes, but just increasingly rough pavement that causes the frame and fork to flex. This required a lot of motion in the large fiberglass frames with very heavy construction but not very large for very thin and light cross sections of CF.

On Thursday, May 25, 2017 at 9:09:27 AM UTC-7, jbeattie wrote:
On Thursday, May 25, 2017 at 8:53:36 AM UTC-7, wrote:
itsnot road conditions ....who rides into potholes ?

prob is factory quality control

JB is prob keeping a close magnifier on his CF

we due for a JB CF Report any day now...

prob crack above The Hub

The Hub? http://hopworksbeer.com/ I'm waiting for Tom to post a link supporting his claim that CFRP "deteriorates rapidly" riding on rough California roads. I think the CF big-hit bike guys would be surprised to hear this.. I can see UV and a harsh environment attacking the polymer (assuming no decent paint job and a bike chained-up outside), but fatigue cycles alone don't cause "rapid" deterioration. The deterioration is less rapid than with aluminum or steel in terms of the number of cycles to failure.

I've broken most bicycle-related things -- frames, cranks, pedals, seat posts, handlebars, hubs. I haven't broken a CF anything yet, but I would expect to break a CF frame one day, and I do keep an eye on the fork and steerer. I'm not sure about the strength of CF steerers, although they seem to be working out fine. I sure wouldn't buy a Colnago. All my CF bikes (a SuperSix and a Roubaix) have lifetime warranties.

-- Jay Beattie.

Jay, did you read the reference John had? At the end of that paper they showed a graph of the reduction in the strength of the various resins via flexing.

The flexing of those thick sections vs the thing sections in a bicycle would show that simple road imperfections would vibrate or "flex" the tubing causing the drop in resin strength.

The Trek my friend had also had a lifetime warranty and it broke within a week of delivery. They replaced the frame (the problem was a rather harmless crack but a break none-the-less) but he had to pay for the disassembly of the old frame and the assembly of the new.

The pictures of the broken CF frames are of course all of the worst possible occurrences. And many of them are from collisions with a car which should not be in the same classification. But lifetime warranties are not the same thing same thing as a guarantee.

well, I lived 10 years in the deep freeze near Canada where frost goes 5' down

6 year in Lower Pa with antique road surface with frost maybe 2.5'

6 crossing California on too and back from the San Juans to Yuma/San Diego.

Cals roads are fairly good. Up in the Mtns on very secondary roads there may be some roughness bot on the whole...no the roads are OK

Down at the Beach many roads crack along the N-S road line from subsidence. Avoid.

If there's no frost n no building with triax, roads are ok

'asphalt' is flexible. Todays ripples from yesterdays weather may settle out tomorrow

On Thursday, May 25, 2017 at 10:46:30 AM UTC-7, wrote:
On Thursday, May 25, 2017 at 9:09:27 AM UTC-7, jbeattie wrote:
On Thursday, May 25, 2017 at 8:53:36 AM UTC-7, wrote:
itsnot road conditions ....who rides into potholes ?

prob is factory quality control

JB is prob keeping a close magnifier on his CF

we due for a JB CF Report any day now...

prob crack above The Hub

The Hub? http://hopworksbeer.com/ I'm waiting for Tom to post a link supporting his claim that CFRP "deteriorates rapidly" riding on rough California roads. I think the CF big-hit bike guys would be surprised to hear this. I can see UV and a harsh environment attacking the polymer (assuming no decent paint job and a bike chained-up outside), but fatigue cycles alone don't cause "rapid" deterioration. The deterioration is less rapid than with aluminum or steel in terms of the number of cycles to failure.

I've broken most bicycle-related things -- frames, cranks, pedals, seat posts, handlebars, hubs. I haven't broken a CF anything yet, but I would expect to break a CF frame one day, and I do keep an eye on the fork and steerer. I'm not sure about the strength of CF steerers, although they seem to be working out fine. I sure wouldn't buy a Colnago. All my CF bikes (a SuperSix and a Roubaix) have lifetime warranties.

-- Jay Beattie.

Jay, did you read the reference John had? At the end of that paper they showed a graph of the reduction in the strength of the various resins via flexing.

The flexing of those thick sections vs the thing sections in a bicycle would show that simple road imperfections would vibrate or "flex" the tubing causing the drop in resin strength.

The Trek my friend had also had a lifetime warranty and it broke within a week of delivery. They replaced the frame (the problem was a rather harmless crack but a break none-the-less) but he had to pay for the disassembly of the old frame and the assembly of the new.

The pictures of the broken CF frames are of course all of the worst possible occurrences. And many of them are from collisions with a car which should not be in the same classification. But lifetime warranties are not the same thing same thing as a guarantee.

Yes, CFRP has a fatigue life. For a bike frame, its longer than steel -- at least for the frames that were tested and reported on Sheldon's site.

The more interesting question is why CFRP forks or frames fail in use, and whether the failure rate is higher than with other frame or fork materials.

The fact is that the vast majority of light-weight road bikes (CF, steel and aluminum) are shipped with CFRP forks. Cannondale started shipping the 2.8 with Kinesis CF forks in about '95 (after three years of the dreadful sub-one aluminum forks). Trek 5500 with CF forks was 1992 -- so 22-25 years of mass-produced bikes with CF forks.

I bought a pair of Kestrel after-market forks in '92 to replace the aluminum forks on my 2.8, so contrary to my 30 year statement previously, I've been riding CFRP forks since '92 -- a scant 25 years. I even had some cheap-o Nashbar CF forks that I bought for my old SP steel racing bike and my Cannondale T1000. They all had aluminum steerers and were not bleeding edge technology. Anyway, none of them broke, but I would be interested in some real investigation of the frequency and causes of CF fork failures. The failures I've seen involved objects stuck in spokes with the sole exception of one pair where the blade was not bonded to the crown.

-- Jay Beattie.

On Thursday, May 25, 2017 at 11:42:39 AM UTC-7, wrote:

Cals roads are fairly good. Up in the Mtns on very secondary roads there may be some roughness bot on the whole...no the roads are OK

Down at the Beach many roads crack along the N-S road line from subsidence. Avoid.

If there's no frost n no building with triax, roads are ok

'asphalt' is flexible. Todays ripples from yesterdays weather may settle out tomorrow

Not around and in the cities. Even out in farm country the roads have been torn up from trucks and lack of repair.

On 26/05/17 08:19, jbeattie wrote:


Yes, CFRP has a fatigue life. For a bike frame, its longer than
steel -- at least for the frames that were tested and reported on
Sheldon's site.


What that test demonstrates is that the steel frames are not designed
well enough to cope with the applied cyclic stress input. You can see
from the graph here https://en.wikipedia.org/wiki/Fatigue_limit that
if the applied cyclic stress is below a certain magnitude, the cyclic
fatigue life of steel is near infinite.

I wonder how many more years of service I'll get from my steel frame,
aluminium steerer and CFRP forks? According to Strava, I'll have ridden
over 75,000km on it in a few more months. Currently 72,302.5 km. Mind
you, I don't weigh anything like 120kg (75kg more like), so it would be
difficult for me to ever press on the pedals with 1200N as per the test.

--
JS

On Fri, 26 May 2017 14:22:48 +1000, James
wrote:

On 26/05/17 08:19, jbeattie wrote:


Yes, CFRP has a fatigue life. For a bike frame, its longer than
steel -- at least for the frames that were tested and reported on
Sheldon's site.


What that test demonstrates is that the steel frames are not designed
well enough to cope with the applied cyclic stress input. You can see
from the graph here https://en.wikipedia.org/wiki/Fatigue_limit that
if the applied cyclic stress is below a certain magnitude, the cyclic
fatigue life of steel is near infinite.

I wonder how many more years of service I'll get from my steel frame,
aluminium steerer and CFRP forks? According to Strava, I'll have ridden
over 75,000km on it in a few more months. Currently 72,302.5 km. Mind
you, I don't weigh anything like 120kg (75kg more like), so it would be
difficult for me to ever press on the pedals with 1200N as per the test.

Regarding testing it might be remembered that all tests are designed
to be severe enough to fail the item being tested. If the item never
fails the test has proven nothing.

Had the test been carried out with 75 kg. or 62% of the load actually
used the test might well be still going on and your bike might,, as a
Chinese bike shop assured me when discussing a Flying Pidgin, "be a
bike that you can pass on to your descendents" :-)
--
Cheers,

John B.

On Thursday, May 25, 2017 at 9:22:54 PM UTC-7, James wrote:
On 26/05/17 08:19, jbeattie wrote:


Yes, CFRP has a fatigue life. For a bike frame, its longer than
steel -- at least for the frames that were tested and reported on
Sheldon's site.


What that test demonstrates is that the steel frames are not designed
well enough to cope with the applied cyclic stress input. You can see
from the graph here https://en.wikipedia.org/wiki/Fatigue_limit that
if the applied cyclic stress is below a certain magnitude, the cyclic
fatigue life of steel is near infinite.

I wonder how many more years of service I'll get from my steel frame,
aluminium steerer and CFRP forks? According to Strava, I'll have ridden
over 75,000km on it in a few more months. Currently 72,302.5 km. Mind
you, I don't weigh anything like 120kg (75kg more like), so it would be
difficult for me to ever press on the pedals with 1200N as per the test.

That curve shows that steel at 75% of it's max loading lasts forever. The chart that John gave us showed that carbon forks should probably be replaced every couple of years. The aluminum steerer on your chart suggests that the fork should be replaced reasonably often as well.

You will probably ignore this warning and you probably won't have any problems. But if my theory about the vibrations being the sort of loads that can wear CF components you do so at your own risk.

On 5/26/2017 12:22 AM, James wrote:
On 26/05/17 08:19, jbeattie wrote:


Yes, CFRP has a fatigue life. For a bike frame, its longer than
steel -- at least for the frames that were tested and reported on
Sheldon's site.


What that test demonstrates is that the steel frames are not designed
well enough to cope with the applied cyclic stress input. You can see
from the graph here https://en.wikipedia.org/wiki/Fatigue_limit that
if the applied cyclic stress is below a certain magnitude, the cyclic
fatigue life of steel is near infinite.

I'm not sure "not designed well enough" is accurate. I think in various
competitive situations, engineers design things knowing they won't last
forever. I think it was John who referenced Colin Chapman's words on
race cars falling apart as they cross the finish line. A less
theoretical example might be "top fuel dragsters," where engines are
torn down and parts replaced after each 1/4 mile run.

Of course, you wouldn't want that situation for the car you drive on a
vacation journey or a trip to the store. But at least some supposedly
normal bicycles are designed with light weight a bigger priority than
long service life.

I think the reason it pays off for the manufacturers is that at least in
the U.S., most bikes spend almost their entire life hanging in garages.
Very few ever accumulate even 10,000 miles.


--
- Frank Krygowski