Frame Fatigue Tests : Carbon, steel, alu.....

[amator]

... surprising results though not representative of all materials or framebuilders.

http://www.sheldonbrown.com/rinard/E...tigue_test.htm

[EDS]

Originally Posted by amator

... surprising results though not representative of all materials or framebuilders.

http://www.sheldonbrown.com/rinard/E...tigue_test.htm

A bit dated . . .

[amator]

http://www.tomsarazac.com/tom/opinions/frame-test.html


Many people have used this test to draw conclusions regarding regarding suitability of various materials for bicycle frames. In particular, since aluminum frames faired better in the tests than steel frames, this has led many to believe that aluminum is an all-around better frame material.

Unfortunately, the testing method does not fairly represent real-world riding stresses on frames, and the conclusions ignore some very basic information.

The test fixture is designed to mimic riding out of the saddle, which is generally believed to apply the most stress to a bike frame. The test applies 268 pounds of force to the cranks for 100,000 cycles, and then 291 pounds for another 100,000 cycles. The force is applied to the pedals at an angle that should be consistent with out-of-the-saddle riding.

Let's suppose that this is a valid test. Their test fixture caused failures in nine of fourteen frames tested. How could this be? At a cadence of 60 RPMs, 200,000 cycles is 55 hours of riding. The first frame failed in under 57,000 cycles -- a good rider at 90 RPMs would reach this point in about ten and a half hours of riding (out of the saddle). In real world terms, riders can expect their brand new very expensive bikes to fail during his first couple of weeks riding in the mountains. Right away we should know that something is wrong with this test.....

[goonster]

My rebuttal of the rebuttal:

I agree that the test is not entirely representative of real-world riding conditions, rather it represents an extreme worst-case scenario. The forces are very high, and the frames are clamped to maximize deflection.

However, since the same procedure is applied equally to all frames, and since the test is performed to destruction, it provides valid and useful data with respect to relative resistance to fatigue.

After all, we can argue all day about how long a frame should last in actual riding, but we cannot argue about the fact that these frames broke when they did.

Ideally, the test would be repeated for greater numbers of each frame, to eliminate variations from frame to frame for each model.

Finally, I think tests like this say more about a particular product (e.g. Cannondale CAAD 5) than a material (e.g. all aluminum frames).

[soulspinner]

Originally Posted by goonster

My rebuttal of the rebuttal:

I agree that the test is not entirely representative of real-world riding conditions, rather it represents an extreme worst-case scenario. The forces are very high, and the frames are clamped to maximize deflection.

However, since the same procedure is applied equally to all frames, and since the test is performed to destruction, it provides valid and useful data with respect to relative resistance to fatigue.

After all, we can argue all day about how long a frame should last in actual riding, but we cannot argue about the fact that these frames broke when they did.

Ideally, the test would be repeated for greater numbers of each frame, to eliminate variations from frame to frame for each model.

Finally, I think tests like this say more about a particular product (e.g. Cannondale CAAD 5) than a material (e.g. all aluminum frames).

.

The DT shifter bosses on the Merlin are problematic as there's no easy way to purge the welds on a solid machined bit like that. I'd bet a newer model without the bosses would not fail as early.

[Charles M]

That thing is 12 years old...



The fun part gets tossed in when you add the perspective of time...


LAST FEW YEARS OF TEST CERT'S FROM MANUFACTURERS WHO WOULD ALLOW THEIR RESLTS TO BE PUBLIC


Everythings developed but the weight, stiffness and durability of Carbon has changed fairly dramatically in the last 12 years compared to the other materials tested...

If you had the chance to talk to Manfred and had more feedback than they (EFBE) are allowed to share or publish, you would have a clearer view than what the two sets of tests show...

A substantial amount of todays carbon product weighing 30 - 50% less, with better stiffness (and in several cases a pretty damn nice ride quality) that that first test can sit in that test jig now and go through double the cycles without an issue...

[I Want Sachs?]

If it is not about the material, but about the design, then we have to admit that Trek and Cannondale were well designed since they did very well. Perhaps that is why they are now the biggies, unlike DeRosa, which was my dreambike for years.

Wonder how would well designed bikes revered by our forum members such as Parlee, Sachs, Vanilla, and Pegoretti hold up.