Thread Strength in 6061 Aluminum

[gbednar]

I would like to know how many tons of pressure it would take to "strip" 1/2"-13 threads x 1-1/4 deep in 6061 aluminum. The bolt would be grade 5. Thanks in advance!!

 

[sdananay]

A general rule of thumb is to allow 1-1/2 to 2 diameters of thread engagement in aluminum. This is so that the threads will not strip. Since you have more than two diameters, I would expect the failure mode to be in tension at the root area of an enengaged thread. There are add'l factors which come into play: stress concentration at the first engaged thread, nut dilation, wrenching stresses, etc. Always, always torque the fastener to its proof stress. This gives you the highest safety factor as safety factor is calculated by comparing the preload to the applied load.

Hope this helps. Good Luck.

sdananay

 

[diamondjim]

You may want to take a grade 8 bolts
make a steel collar 2 inches thick and turn
the bolt until it strips the threads
and record the amount of rotation that
it took. You can translate this into the
length of stretch and get a fair approximation.
You would want to do this at least 6 times
to get a fair sample. This test is only good
for static condition and not for dynamic
conditions. You could use about 57 percent of
this value for dynamic loads.
It seems that the cost to do this would be little.

There are formulas in Machineries handbook that
show how to calculate the depth of thread required
for different bolt strenghths. It allows you to
break the thread before stripping the internal threads
and I assume has a factor of safety of two.
Keep us posted with your results.