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Sometimes metal fatigued and cracks... and breaks.


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On 8/29/2019 at 5:51 AM, DXB said:

My ignorance of metallurgy and engineering leads to some nightmares here. This thread illustrates an example of a very beefy piece of aluminum fatiguing over time under repeated loads until failure.  The Mooney wing spar is also a beefy piece of aluminum that is loaded repeatedly.  We generally say these planes have no limit to their service life if maintained, and so I imagine the same concern does not apply.  But I have no idea why it wouldn't?

The bike part is machined  from a solid piece of aluminum. Do we have any idea what kind of aluminum it is made from? Is it heat treated after machining to relieve any machining stresses? Is the type of aluminum susceptible to stress cracking? Is it heat treated for strength? Different aluminums have different properties for ductability, crack resistance, strength, etc. 3003, 5052, 6061, 7075 all have different properties. Our airplanes are mostly 2024 aluminum. 

Maybe the bike maker didn't take all this into consideration before he decided to use what ever aluminum he picked? Did he consult a metallurgist to help him pick the correct aluminum or was his decision based on cost alone?  Might be an interesting conversation to have with him.  

Just think- the last time you rode that bike it had that crack in it!!!!!!    :-)

The wing spars in Mooneys are many layers of aluminum of which the type and heat treatment is specified. The design allows for a layer to crack and the adjacent layers to carry the load unlike a one piece head stem that will crack all the way through. Obviously many have flown with unacceptable corrosion for years before discovery due to the failure safety mode designed into the wing.   

Harmon designed it right!

 

 

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On 8/27/2019 at 6:42 PM, aviatoreb said:

Here’s a picture I took today on my bicycle during bicycle “preflight”.

yikes!  That’s my stem.  If the stem breaks st 35mph down a hill - forgetabout it.

That’s a break a shoulder break a nose loose some teeth get a concussion wake up in a helicopter crack.

its aluminum.  It’s a top of the line al stem. Glad I caught that one...

F23975E4-EE45-4A35-B59D-80FD2300F0DA.jpeg

I've run Thompson stems from time to time and I've never seen such rough machining in any of them.  The steerer pinch bolt holes look like they were opened up with a hand held power drill.  Is that the way it came from the factory?

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32 minutes ago, Cyril Gibb said:

I've run Thompson stems from time to time and I've never seen such rough machining in any of them.  The steerer pinch bolt holes look like they were opened up with a hand held power drill.  Is that the way it came from the factory?

Yes - that is their road model.

https://www.bikethomson.com/product/elite-x4-stems/

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