Fatigue analyisis

[AlanTomlinson]

Hello,

I am trying to conduct a fatigue analysis of two riveted plates with inputted residual stresses. to do this i am applying pressures to the outside area of the rivet to simulate the residual stresses and writing it to an inital LS file. Next i've applied the maximum load and written it to an LS file. Finally the max stress is removed and the minimum stress applied and written to LS file 3. i have then solved these three files and read them all within the Fatigue section.

The alternating stresses i obtain are almost identical to the values i get when no residual stresses are input and the only reason for this i can imagine is an incorrect analysis procedure.
Could anyone please comment on the manner in which i am carrying out this fatiuge analysis and suggest where i might be going wrong.

Thanks
Alan

 

[TGS4]

The residual stress is a constant on the stress state - fatigue requires an alternating stress state. Based on that, why would you expect to see a different result?

 

[AlanTomlinson]

Thanks for your reply,

I am applying an alternating stress to the end of the specimen by the form of a max and a min pressure. The residual stress needs to remain on the speciment throughout testing so i was applying it in an earlier LS file and leaving it on the file for the other loads.

How would you advise i incorporate this residual stress?

 

[TGS4]

Read my response above again - WHY do you expect to see a different result, based on the fact that fatigue is driven by ALTERNATING stress?

 

[AlanTomlinson]

I acknowledge your point and understand. only the fatigue life if affected by residual stresses from the cold working of the hole during riveting. These are the forces i am trying to include but cannot find the literature explaining how to incorporate them succesfully.