NAS517 tensile strength 1

[dcascap]

Hi,

For NAS517 screws, which it suppose that they have a min tensile strength of 160 ksi according to the spec.
Can I use this value as max strength of the screw in tension? Or should I somehow calculate also if the countersunk head fails before the shank?
The later is quite difficult in the case of a countersunk, even though I could make some kind of approximation.
I attach to the post the link of the specs.

https://www.aircraftspruce.com/catalog/pdf/NAS517%20TDS.pdf

 

[3DDave]

There is going to be a stress concentration at the transition, so that will likely cause the shank to fail at that location, though there is a second stress concentration where the threads end.

I would caution that this is not a tensile rated fastener - there isn't a guaranteed load for each size of screw. If it was reasonable to do so, they would have done it. The fastener material strength is mainly a quality control and indication of resistance to stripping the recess.

 

[dcascap]

Thanks for your answer!
What about using the spec MIL-S-7839, which is the procurement spec of the screw? Then I can use the shear allowable from NAS498 and tension for a low alloy steel corresponding to MIL-S-7839 (which is 110 ksi instead of 160 ksi so it should be conservative).

 

[3DDave]

If it is critical, get a sample of them and do a pull test with the joint geometry you intend to use and see how they do.

 

[rb1957]

I'd probably go with Ftu over the min thread area. I might try to calibrate this with other fasteners or by simple test. I wouldn't use 110ksi for 160ksi.

 

[dcascap]

Thanks for the answers I'll check how critical it is, even though it should not as it is mostly for shear loading...