Bolt design with heli-coil insert: stiffness of a joint with Heli-Coil type insert

[tomcrooks]

Hey all, first time posting here...

I've been wondering how a Heli-Coil insert (or similiar type threaded insert) would affect the stiffness calculations in a blind tapped hole.

We are working with #6-32 A286 strain hardened fasteners with 180 ksi yield strength, with 6061-T6 aluminum clamped material. Initially I am thinking that you would just assume that the Heli-Coil and the fastener are "one" in the area that the Heli-Coil and the fastener are in contact (threaded region of bolt)...Then you would have a series stiffness calculation for the fastener something like:

k_fastener_total = [(1/k_head) + (1/k_shank) + (1/k_fastener-helicoil)]^-1

Does that sounds right? Anyone else do this differently? Appreciate the comments.

Thanks,

T.J. Crooks

 

[CoryPad]

Strainsert can do more than just 2XXX series aluminium screws. However, their central inserts may be a little big for such a small screw. You may need to use foil strain gages on the outer diameter of your screw. Multiple foil gages in a half-bridge or full-bridge arrangement are the most accurate method for measuring screw force. Here is one supplier:

http://www.vishaypg.com/micro-measurements/stress-analysis-strain-gages/