Notch sensitivity in a threaded fastener

First, I have to wonder how much bending there actually is across the threads. If it's a bolt in single shear, treat it like a fixed guided beam and find the moments at the ends. Using distributed loads instead of concentrated loads will yield lower moments.

I believe the radius for root radiused UNR fasteners is p/8, where p is the pitch (1/14 in here). That gives a radius of 0.0089 in. If it's a regular UN fastener the radius will be smaller.

The book Mechanical Engineering Design by Shigley has a figure for notch sensitivities for steels under reversing axial/bending loads. Here's what I get for a radius of ~0.009 in.

Ultimate Strength q

Most likely the q for your fastener would be 0.73 or less.

Also, if you considered bolt preload, remember that does not reverse with the other loads. There's a non-zero mean stress there. An equivalent reversing stress can be determined for that if needed.

Good luck.

Jeff F.

Hello. You get this stuff or what?

Yeah, I did... thanks.

I used the numbers you gave me to get in the ballpark, but ended up approximating notch sensitivity by the "peterson model", where:

q=1/(1+(a/r)) and a=.001*(300/Sut)^1.8.

The final result was a 'q' of about 0.63 or so. There is some bending across the threads, as it's an adapter that connects an actuator to a rod end.

I appreciate the > Jeff F> >

Good. Just wanted to make sure my post made it to news servers other than the one I'm on.

I ran across that formula once and had forgetten it. Good reminder thanks..