Joint Separation Analysis

[albeckom]

Hi,

I refer to Joint Slip Analysis for fasteners. One reference for such an analysis is NASA-STD-5020.
I have been wondering if there is merit to apply this analysis beyond bolts, and on countersunk fasteners.
Can countersunk fasteners slip?

I'm questioning this because I have been tasked to prove that all fasteners used in my design, including countersunk screws, satisfy the non-slip condition.

Thanks!

 

[Screwman1]

Be careful that you have the proper load capability for your flush head fasteners. Because of the penetration of the recess, many of these designs are down rated on their tensile strength to account for failure through the head prior to full potential load being reached. most flush head parts are designed for non-structural or shear loaded applications where they are used in shear, rather than for use in slip-critical designs.

 

[tbuelna]

I don't recall any part of NASA-STD-5020 prohibiting use of flush head fasteners. The joint-slip analysis approach described in section 6.4 is for "Friction as a Load Path for Shear Loading". This relies on axial preload in the joint fasteners to create sufficient clamped friction at the joint interface to prevent any relative sliding between the contact surfaces. I think it would be safe to assume that if there is sufficient axial preload in the fasteners to meet the joint-slip safety analysis margin, then there should be more than enough friction at the flush head bolt contact to prevent any sliding there.