Thread shear help 2

[ntonar]

I am looking to find out at what ft/lbs or in/lbs the threads in the aluminum will shear/strip. I have a steel post going into an aluminum plate, the thread is ¼-20 the aluminum is tool and jig. I am guessing it has a shear strength of around 30ksi. What is the equation I would use?

Here is a pic of what is going on

 

[boo1]

use the simplified equation to estimate the force required to strip (shear) the threads.
F=Su*Ats
Su= Ultimate shear strength of the plate or bolt
Ats=cross section where shear occurs

Assuming the plate is weaker than the bolt material the simplified expession for shear area (from FED-STD-H28) is:
Ats=3.14159*En*(3*Le/4)
En=the min pitch dia of the bolt
Le=Sst(2As)/Snt*3.14159*n*Dsmin((.5n)+0.57735(Dsmin-Enmax))

 

[Philrock]

1/4-20 UNC-2B female threads have a stripping area of 0.539 in^2 per inch of engagement, according to the Fastener Standards Handbook, published by the Industrial Fastener Institute.

Your estimate of the aluminum’s shear yield strength looks quite high. 6061-T6 or T651 would be 23.1 ksi; MIC-6 would be 8.6 ksi.

There’s a wealth of useful thread information at:

http://euler9.tripod.com/bolt-database/23.html