bolt or helicoil pull out strength in G10

[Tmoose]

We have specified 240 1 inch long 1/2-13 helicoils in a modified G10.
Every one of the 240 helicoils is to be "proven" by torquing to 75 lb-ft.
Online I found some info that says a thread tapped in G-10 to 1.5 bolt diameters is "stronger" than a "hardened" bolt.
Despite that I am skeptical.

The helicoil folks say they only have pullout strength for metallic materials.

Before I go stirring things up, is there some non-proprietary info to help evaluate this un-built design?

Thanks,

Dan Timberlake

 

[Tmoose]

We drilled and tapped a 3.5 inch diameter bar of G-10 for
1/2-13 helicoils. Some axially and some radially. The inserts were 3/4 inch long. The axial insert failed right around about 100 lb-ft. The radial insert did not fail at slightly above 100 lb-ft.

Textron says a 1/2 UNC bolt tightened to ~ 150 lb-ft exerts ~ 17,000 lb tension.
So I say the insert tore out around 11,000 lb tension, which is about a grade 5 bolt.

 

[SWComposites]

What specifically is G10?

 

[Jick]

G10 is a glass cloth / epoxy laminated composite specified by NEMA, IIRC. It is often used as a structural element that can double as an electrical insulator, as when used for a PCB substrate.

 

[rnd2]

Tmoose
I personally would not recommend threading anything into G10, unless the the load requirement was neglible. The material is weak inter-layer and can split. This can easily be demonstrated by inserting a stress concentrator (chisel) between layers. If there is significant load suggest to drill through-holes and some sort of clamping mechanism.

 

[Tmoose]

rnd2 - this is a complete but unbuilt design we inherited along with a 'partner."
I'm just sniffing around, looking for trouble, and having those inserts tear out would be BIG trouble. My intuition was along the lines of your "don't so it" comment. So I was trying to quantify the danger. Amazingly I get the feeling I was the first one to do any testing like this. Or maybe just the only one willing to talk about it.

 

[misako]

Rule of thumb, don't ever thread a composite, as very weak in shear and matrix dependent which you don't want to be.