Frame Fatigue

[Dylan Solms]

Hi

I would like to know a bit more about frame fatigue.

Is it really true that alumnium frames fatigue and do the different alloys fatigue less. I've heard 7005 doesn't fatigue as bad as 6061!

Does steel fatigue?

 

P.S. GT makes this kinesis superlight frames. What is this and does it resist fatigue better?

And does rigid forks in a 29er fatigue the frame more?

Edited June 7, 2011 by Dylan Solms

[TNT1]

Start here:

http://www.epi-eng.com/mechanical_engineering_basics/fatigue_in_metals.htm

http://www.materialsengineer.com/CA-fatigue.htm

http://en.wikipedia.org/wiki/Fatigue_%28material%29

 

There are some clever boys here, but I'd suggest read up a bit before they lose you with their engineer-ese...

[The Drongo]

In short:

 

6 series aluminums contain more magnesium, and are more ductile. That means they are 'softer' in terms of buckling, and also 'melting' during welding. Softer than 7 series, but more flexible. Used more for frames.

 

7 series aluminums have a larger zinc content. They are harder and stronger but more brittle. So they are good material for components that wear, like chainrings for example.

 

They are then all heated, or tempered to different hardnesses.

 

Often the strength lies, not just in the alloy grade, but in the way it is extruded. ie: profile and wall thickness. eg. Double butted tube.

Hollow crankarms are often stronger than arms machined out of a solid piece of alloy.

Edited June 7, 2011 by The Drongo

[Johan Bornman]

I won't give a thought to frame fatigue at all. A good quality frame from any of the reputable manufacturers have for all practical purposes, an infinite life.

 

Yes, the odd heat treatment and welding flaw exists, but that's nothing to worry about.

 

Alu is a great material for frames.

 

A rigid fork over a suspended fork won't have any effect on the frame either.

[NotSoBigBen]

If frame fatigue was an issue I would have a bike or 2 that should have fallen apart by now ....

[brussel]

Johan I must disagree..

I had a Niner air nine scandium that I cracked within 3 months NOT on a weld but at a bend in the chainstay

[Slowbee]

was nasty ... sani2c ...... guy in front of us cracked his frame ... the top tube snapped right off the headset tube.

[_im_from_earth]

Why isn't there an emoticon for "sitting back and eating popcorn"?

[The Drongo]

Johan I must disagree..

I had a Niner air nine scandium that I cracked within 3 months NOT on a weld but at a bend in the chainstay

 

fatigue, or failure?

[The Drongo]

Why isn't there an emoticon for "sitting back and eating popcorn"?

 

http://wiki.urbandead.com/images/9/98/Popcorn.gif

[dirtrider]

A solid steel frame made from 20mm round bar will fatigue . It just takes longer .

[TNT1]

http://wiki.urbandead.com/images/9/98/Popcorn.gif

 

You mean:

http://wiki.urbandead.com/images/9/98/Popcorn.gif

[TNT1]

This is neat, it's like the rolling resistance crap.

[The Drongo]

You mean:

http://wiki.urbandead.com/images/9/98/Popcorn.gif

 

Indeed. Ta. I just don't know how.

[The Drongo]

A solid steel frame made from 20mm round bar will fatigue . It just takes longer .

 

But it could fail quicker than a 20mm round tube might fatigue!

[Tumbleweed]

This is neat, it's like the rolling resistance crap.

 

Oh, ja, was that super-formula ever produced? I remember that jmacceleri said my goldie had a good grasp of rolling resistance which sealed the argument.