Lumadyne shear strength

[Cameron Anderson]

https://www.apogeerockets.com/Building-Supplies/Misc-Hardware/Aluminum-4-40-Tube-Fasteners-3-pk
Anyone know the shear strength of these fasteners off-hand?
The screw is steel but the nut and washer are aluminium which complicates calculating the strength of the entire set up.

 

[Antares JS]

Shear strength should just be whatever the strength of the steel screw is...

 

[mtnmanak]

I agree, the aluminum washer/PEM should not affect shear strength. It is possible for the aluminum or the airframe to fail, but that would not be a "shear", just a material failure under load.

The shear strength of the bolt is the only shear force involved.

However, maybe you are asking "will the aluminum washer/PEM give out before the steel screw shears"? Are you picturing a scenario where the steel screw stays intact and rips through the aluminum and fiberglass like a zipper? If so, I am not aware of any way to properly calculate that except by testing.

 

[Cameron Anderson]

The larger surface are of the Al nuts versus the stronger steel screw is concerning, but in this specific set up I was wondering if anyone knew the precise shear fail point. I'm curious if lumadyne even knows.

 

[Antares JS]

The larger profile of the aluminum nuts is a good thing when it comes to preventing shear problems... More area = force distributed over that larger area = lower stress. Remember the formula for stress is force/cross-sectional area.