pic: Team 3647 West Coast Drive

[JamesCH95]

Originally Posted by Ninja_Bait

I looked it up: Pop Rivets vs. Bolts

These are two kind of arbitrary sources, but it shows that while rivets are not quite as strong, they're comparable. The steel 1/4" rivet (shear: 2750 lbs.) beats Grade 2 1/4" bolts (shear:~2200 lbs.). However, the higher grades outmatch the rivets by a lot.

I assume they did a straight shear-strength calculation, which is good, but doesn't describe the whole situation.

Friction matters a lot, especially when clamping aluminum to aluminum. The static coefficient of friction is generally over 1, sometimes well over. You'd be looking at (to use my own numbers) 75%*1750lbf (proof load GR2 1/4-20) * 1.2 (coefficient of friction Al-Al) = 1575lb, so it would require 1575 lb of force to overcome the friction generated by the bolt's clamping force before the bolt sees a single pound of shear force, assuming the bolt was properly torqued.

Edit: I looked at the bearing strength of aluminum, assuming 6061 T6 it is 56ksi. Doing the math on an 1/4" diameter hole in an 1/8" thick plate says that anything over 1750lbf will start to yield the material around the fastener, so the excess strength of the rivet over a grade 2 bolt is meaningless because that will not be the mode of failure. The bolt's clamping force now makes it a clear winner.