Biggadike,
The stress amplitude calculated is for the endurance limit. Below the calculated stress amplitude, no failures should occur. You can run at higher stresses as long as you keep the number of cylces down. You can draw a SN curve on a log-log plot with the calculated endurance limit at...
Biggadike,
Best source I have seen lately for axial fatigue strength in threads is the German spec VDI2230. The major consideration is if your threads are rolled before or after heat treat. If rolled after heat treat you get a higher fatigue strength.
For rolled before heat treat bolts...
In my experience there is not a relationship between tightening and loosening torque. Tightening torque is dynamic torque, while loosening torque is determined by the static torque. Static torque has very large variability and is affected by everything including materials, coating, friction...
Some methods to check current torque-
1. Return to mark check - Mark the bolt and abutment with a reference line, then loosen the bolt, retighten the bolt up to the reference line again while monitoring torque. You want the dynamic torque and not the static. (This method has pretty good...
