One big fastener surrounded by several small
One big fastener surrounded by several small
(OP)
I am looking for the explanation why it is not a good idea to have one big fastener (5/16") in a repair that has otherwise 1/8" dia fasteners. I know it has to do with load distribution and the fasteners will not have an equal load. I have had a quick look through Bruhn and Niu and I can't find it.
Any help where I can find a published answer will help me.
Many thanks!
Any help where I can find a published answer will help me.
Many thanks!





RE: One big fastener surrounded by several small
Now, by replacing a 1/8" rivet with, say, a 5/16" screw, things change. Assuming a constant load along the length of the joint again, under that load, the 5/16" screw will displace much less than the 1/8" rivets. About 19 times less, in fact. This "hard point" prevents the adjacent rivets from taking their fair share of the load. The sheet transfers a large load locally through the screw.
Associated with installing a screw is the hole that isn't filled by an expanded fastener. The stress concentration is high at an overloaded, loose fastener, cutting down the fatigue life.
That's my off-the-cuff explanation. Flip through an article by Swift, or Eastin, and they can explain it in much more detail, plus some analytical rigour. Their articles can be found with a Google search.
Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout