[pdwestman]

Aluminum, BTW, does not have a fatigue limit. Even a very low stress, if repeated enough cycles, will eventually lead to cracking and fatigue failure. That’s why springs are not made of aluminum.

I'll ask you if this is an accidental mis-statement? If so, edit the posting and I'll edit this one.
If not, please try to explain.

And with that, I’ve probably “beat” this topic to “death.”

 

[Norton 850]

I'll ask you if this is an accidental mis-statement? If so, edit the posting and I'll edit this one.
If not, please try to explain.

No it is not a mis-statement. Aluminum has no endurance limit, meaning it can withstand only a finite number of stress cycles regardless of how low the stress is. Lookup Haviland aircraft failure to learn more. (I think it was Haviland)
Jason

 

[Damocles]

No it is not a mis-statement. Aluminum has no endurance limit, meaning it can withstand only a finite number of stress cycles regardless of how low the stress is. Lookup Haviland aircraft failure to learn more. (I think it was Haviland)
Jason

Seems like I vaguely recall from a class taught by Hugh Harrison Hurt, Jr. (or was it III?), author of, "The Hurt Report," (first comprehensive scientific study of motorcycle accidents), a British jet passenger aircraft, De Havilland Comet I,, . . with cracks in stressed aluminum, was "repaired" by technicians who drilled the aluminum at the ends of the cracks, to stop the fractures from propagating.

This link may (or, may not) shed some light:

. . . FATIGUE FAILURE OF THE DE HAVILLAND COMET I - ScienceDirect

Or, these videos & etc.:

havolind jet aircraft aluminum failure drilling cracks - Bing video

 

[PeteK]

Stop-drilling is a method for stopping the propagation of cracks that have already formed based on an impact. Poor weld, or some overload. Used in aluminum, plexiglass, sheet steel and other materials, it’s a quick field repair until the part can be serviced or replaced. If the cracks are due to cyclic fatigue, stop-drilling buys you very little additional time before other fatigue cracks develop.

 

[PeteK]

As for aluminum not having an endurance limit, Jason also is correct, although I can see how this way of saying it might be interpreted the other way around.

Put differently, aluminum will always fatigue eventually, depending on the stress and number of cycles. Low stress will take much longer to develop fatigue cracks, but eventually it will fail. To use another vehicular example, some racing engines use aluminum conrods instead of steel to allow higher RPMs. However those rods must be changed every so many hours—or even minutes!

Vibrations are a particular concern because they can impose very high and localized stress. This is what lead to the empennage cracking in the Comets. When I was a Navy pilot flying helicopters, we had a maintenance procedure that required using an FFT- based vibration measuring system and placed sensors in different parts of the helicopter, to measure the vibration forces in “g’s” that vibrations caused. If they exceeded certain values, we had to troubleshoot further to find and fix the source.

 

[pdwestman]

Aluminum has no endurance limit, meaning it can withstand only a finite number of stress cycles regardless of how low the stress is.

A finite number of stress cycles, seems to suggest an absolute "endurance limit" or "fatigue limit" to my way of comprehension of the English language.

Therefore, Aluminum does have a limited "endurance life" or "fatigue life" seems to be a more accurate description of aluminum under cyclic stresses.

 

[Norton 850]

A finite number of stress cycles, seems to suggest an absolute "endurance limit" or "fatigue limit" to my way of comprehension of the English language.

Therefore, Aluminum does have a limited "endurance life" or "fatigue life" seems to be a more accurate description of aluminum under cyclic stresses.

I didn't mean to confuse you. "Having no endurance limit" is a common description for aluminum and other certain materials as stated in many Strength of Materials books.
Jason

 

[DPelletier]

Has anyone figured out why the coil spring fails in the first place?

1) it's too long and coil binds right away. When it's loose it rattles around and wears on the case

2) the factory lever fits the shaft poorly allowing the spring to move slightly even when the lever is tight; this means the spring undergoes millions of duty cycles rather than just sitting there.

 

[Vgraf]

My second post on the forum. Don't have a klr....yet. I do have a tw200. Fantastic bike. I ride 2 up with the wife 95% of the time. It is great for dirt roads in the NC mountains, the blue ridge parkway, and short non-freeway rides. Low seat height. Actually the TW was the only bike my wife could get on without a ladder. I am looking for something now to take us for longer rides. Never even seen or ridden a klr but this 2021(?) caught my attention. I will be standing in line to check it out!

I've alway really liked the TW200 looks and concept and I arranged a 1 hour test ride of a lightly used TW at a dealer about 10 years ago. I'm 6'2" 240 lbs with gear and I felt like it was a mini-bike that didn't care much for hauling my fat self around. Now at 60, I suspect I'd appreciate it's qualities more than I did then. It's under consideration...

 

[gruff54]

I've alway really liked the TW200 looks and concept and I arranged a 1 hour test ride of a lightly used TW at a dealer about 10 years ago. I'm 6'2" 240 lbs with gear and I felt like it was a mini-bike that didn't care much for hauling my fat self around. Now at 60, I suspect I'd appreciate it's qualities more than I did then. It's under consideration...

Have both a KLR and TW in my garage. At 6'3" 190 lbs it does kinda feel like I'm on a minibike. They're similar yet different. You can't beat the TW for going slow, love being able to put both feet on the ground easily. Even with a 34" inseam the KLR is tall. At 66, I find myself enjoying the TW more.

Mike

 

[DPelletier]

nevermind; I wasn't responding to the latest posts and the discussion has moved on....