% of cyclic load a preloaded joint is subject to.

[uberchad]

I am trying to determine the % of a total cyclic load a preloaded joint sees when compared to a non preloaded joint. For example, a joint with .010" slop is subject to the entire cyclic load of the system (fatigue). However, a threaded connection does not sustain the full effect of the system’s applied cyclic load because the connection is preloaded above the cyclic load. This greatly increases the fatigue life of the coupler. But how much? Is there a rule of thumb/formula? I have had no luck.

FYI,

http://www.boltscience.com

is a great website!

Thanks!
-Chad

 

[uberchad]

I should mention that the joint is loaded axially in tension and compression.

 

[israelkk]

If for example the preloaded joint slope is 0.001 (10 times stiffer) the cyclic stress will be 10% of the non preloaded joint. Now check the S-N fatigue curve (and/or Goodman curve) and see how much longer it will last.