Due to the fact that pipe flanges rely on bolts, and bolts rely on friction, it seems obvious to me that in deflecting to meet the load, the nut will immeasurably turn. So my question is - how much?

In other words, given a time based varying load on a given threaded fastener, what would be the rotation of the nut? Has there been any experiments done to show an equation between a simply varying load (like a sine wave in the axial direction) and the rotation of a threaded nut?

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    $\begingroup$ You may be forgetting that bolts are made to elastically elongate under load. That is what is happening when the bolt is pretensioned initially; it stretches. $\endgroup$
    – hazzey
    Jul 3 '15 at 13:22
  • $\begingroup$ I know that the bolt deflects. But if bolts loosen over time, what's the mechanism? Deflection by stretching of the bolt forcing the nut back down the threads causing a rotation makes sense. My question is how much does it rotate vs stretch? $\endgroup$
    – Mark
    Jul 3 '15 at 13:31
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    $\begingroup$ Search on "overhauling" in the context of threads. There is a critical angle at which the forces on an object on an "inclined plane" either do or do not cause it to move when loaded. Threads are designed (except in very special cases) to not overhaul. ie increasingly loading a threaded coupling will ultimately always break it and never "back it off". $\endgroup$ Jul 3 '15 at 20:56
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    $\begingroup$ @Mark If you found something that helped to answer this based on Russell and hazzey's comments, consider writing up your own answer for the benefit of future readers. $\endgroup$
    – Air
    Jul 8 '15 at 23:40

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