von Mises stress in fatigue
von Mises stress in fatigue
(OP)
I have a structure with combined mechanical and thernal loads. My thermal loads give raise to small von Mises stresses but large principal stresses. (almost hydrostatic) Will my large principal stresses give me fatigue problems, or can I forget it due to small von Mises stress?????
Thanks for any hints
Thanks for any hints





RE: von Mises stress in fatigue
In fatigue analysis usually shear stress criteria(Not Von mises stress criteria ) is used. For shear stress criteria
maximum principal and minimum principal stresses are used. Therefore you need to look at the both of the principal stress , not to one of them(as long as you are not using maximum principal stress criteria , where maximum stress is the stress you need to use to go to the S-N curve)
RE: von Mises stress in fatigue
Cheers
Greg Locock
RE: von Mises stress in fatigue
If the loads do cycle then the principal stress ranges need to be determined and the fatigue life can then be calculated.
A good example is in appendix C of BS5500.
pw
RE: von Mises stress in fatigue
GREGLOCOCK IS RIGTH ABOUT HYDROSTATIC LOADING CAUSE NO SHEAR
BUT IT DOES NOT MEAN NO MECHANISM FOR CRACK GROWTH. AS LONG AS YOU HAVE CYCLIC LOADING REGARDLESS OF YOU HAVE SHEAR OR NOT FATIGUE IS AN ISSUE.