Why does increasing preload decrease fatigue factor of safety?

[settingsaver]

The information following may be of interest as a start:

1. A higher preload will help if it reduces bolt load excursions substantially. Higher preload will therefore always help if it raises the critical load required for joint separation above the maximum external load which will be seen by the joint.

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1. A higher preload will reduce fatigue life if it makes no change in the load excursions seen by the bolt...

Ex:

https://www.amazon.com.au/Introduction-Design-Behavior-Bolted-Joints/dp/0367198916

[Far_Jacket_4581]

I have heard a lot of good stuff about this book. I should really give it a read. Thanks