Preload in shear joints

[shingouz]

Hey everyone,
I was wondering if aircraft manufacturers are using preload tensionning to enhance fatigue life into shear joints, What I mean by preload tightening is instead of introducing a torque to induce a preload ( a lot of scattering, non accurate...), they introduce directy tension by using more accurate toolings ( hydraulic tensioning, strain gauges...)
Thanks

 

[rb1957]

controlling the preload isn't the problem; verifying and repeating the friction force is.

a better approach would be to bond the shear faces together with say a room temperature cure epoxy.

but why the interest in this ? you have a good static design (critical in bearing), but a poor fatigue result ?
sounds odd to me, but ...

 

[shingouz]

Screwman, I don't say that we will depend on friction as just an defined amount of load will be transmitted by friction between plates; the point is: now we transmit all of the load by bearing, if we put some preload in bolt's we can transmit even more load for the same fatigue life!
rb1957 Interest is in performance obviously, bonding is also a good solution but it's different from what I'm interested in
Sorry for my english, I perhaps don't use the right words to express what I mean

 

[rb1957]

ok, you have designed the joint to be critical in bearing. preloading the bolt will reduce the static shear allowable of the bolt.

but i don't see how preloading the bolt will improve the fatigue performance of the joint, presumably it's the lug that's critical in fatigue, not the bolt ?

i guess we're not saying it cannot be done, sure the technology is well understood for preloading a bolt.

i thin kwe're all saying that it's a pretty bad idea, at least a pretty odd (unusual) idea. i think it'd be an unusual joint that is designed to be critical (statically) for bearing and then it has a fatigue problem. if i did encounter this joint, i'd use an interference fit bush to improve the fatigue performance.

but it sounds like this is just a thought exercise. can we end on "this is a bad idea" ?