Learning Forum

[rafi151021]

I would like to ask how to differentiate static load and dynamic load in structural analysis. I want to simulate the fatigue of bolt, I already set up the bolt pretension and the external load but when seeing the result I think the bolt pretension considered as dynamic load also

please give me a guidline

Thank you

[Ravikrishna K V S]

 

Type of structural analysis is decided by type of Analysis system not by type of loading. Also elaborate what makes you think the  bolt load behavior is dynamic.

 

 

[peteroznewman]

Rafi,

To get an accurate estimate of the fatigue in a bolt, you must use the Bolt Pretension load correctly. That means having a 3 step solution where step 1 applies the bolt pretension load, step 2 sets the bolt pretension to a locked state and step 3 applies the external load. Have you done that?  If so, look at the Working load in steps 2 and 3 to find out the force after preload (which is equal to the force you requested, unless you loaded it by Adjustment), and the force in the bolt after the external load is applied to the structure in step 3. In the example below, the force varies from 999 N to 1064 N.

Once you know the min and max forces in the bolt, calculate the min and max stress in the bolt including any stress concentration factors due to the thread geometry. Now you will have a mean stress and a stress amplitude. Use a mean stress theory equation such as Goodman to calculate the Equivalent Alternating Stress and look up the cycles to failure of the bolt from the SN curve of the bolt material.  Do you have the SN curve for the bolt material? 

These steps do not require the use of the Fatigue Tool.

-Peter