Rivet factory head failure - can anyone tell me how this happens?

[mill2978]

While I was riveting ribs to rear spar on my RV8 wings and 5 AN470AD4-8 factory heads failed in the same way.





I was hand bucking these with a double offset cup and a tungsten bucking bar. I was using ~45PSI and the shop head was well formed. I had an assistant who was holding the rivet gun perpendicular to the work so I could focus on squeezing the trigger and forming the shop head. When we lifted the rivet gun the factory head just fell out of the cup. leaving the rest of the rivet in place.

Any ideas how this happens? Was this technique or could I have other rivets that are ready to fail in a similar way? I inspected(including some light prying on the rest with no failures) and don't see any indication of problems.

[Steve Melton]

I don't know much about rivets but could it be a defect in the rivet itself?

[Charles in SC]

I would say bad rivets, I would probably drill out some or all of them and see what they look like. I am sure someone else will chime in on this but if you do not get to the bottom of it you will always wonder. The only time I have seen rivet heads come off like that it was due to salt water corrosion on some old over seas containers.

[mill2978]

When I was cleaning up I mistakenly dumped the heads in the trash, i dug through it and found 3 of the 5, here they are in close up.

Top of factory head pre clean:


Bottom of factory head pre clean:


Top after rinse in MEK:


Bottom after rinse in MEK:

[aerhed]

Your offset set is clearly sideloading the mfg head. You can see where they sheared in the upside down shot. Also looks like the cup is slightly undersize leaving an extruded rim around the head. Drill em all out and try another setup.

[aeroaddict]

Yup, exactly what Arehed said. Even though the factory head appears ok (sans the ring) the bottom of the head show signs of shear; the area that has uniform parallel lines. The other part of the fracture area is the ductile failure after enough of the cross sectional area was reduced by the shearing action.

Corrective action; ensure the set is perpendicular (or in axial alignment with the rivet) to the piece being riveted.

[mill2978]

Aerhed and Dan thanks for the help. I would much rather this be an issue of technique than of defective rivets.

[airguy]

Yup, this is technique - the force was not perpendicular to the rivet head, there is some side load there that is shearing the rivet.

[PCHunt]

Can you squeeze these rivets instead of driving them? Much less likely to shear the heads, IMHO.

I personally prefer to squeeze a rivet than buck it, if I can.

As always: YMMV!

BTW: Very sharp eyes, AERHED!! Well done.

[ijustwannafly]

This is a good read for a newbie like me.

Sorry you are having some difficulty with that set but thanks for posting it up for new guys like me to read and learn about.