von Mises stress with algebraic sign
von Mises stress with algebraic sign
(OP)
Dear all,
for a part under triaxial stress condition i´d like to do a fatigue life estimation.
From a FE analysis i got the von Mises stresses (to compare uniaxial material props with triaxial stress in part)
material assumed to be ductile.
( so yield in tension and compression should be similar)
Question :
is it a legal way to add the alegebraic sign to the von Mises stress. I´d like to plot the results in a Haigh diagram where i take care of the algebraic sign of the mean stress. (just to visualize tension and compression)
for a part under triaxial stress condition i´d like to do a fatigue life estimation.
From a FE analysis i got the von Mises stresses (to compare uniaxial material props with triaxial stress in part)
material assumed to be ductile.
( so yield in tension and compression should be similar)
Question :
is it a legal way to add the alegebraic sign to the von Mises stress. I´d like to plot the results in a Haigh diagram where i take care of the algebraic sign of the mean stress. (just to visualize tension and compression)





RE: von Mises stress with algebraic sign
RE: von Mises stress with algebraic sign
Most of cases I deal with are proportional loading. The directions of principal stress do not change. I look at both the maximum and minimum principal stresses in three principal directions during the cycle and use the largest stress fluctuation for calculation of fatigue stress.
Thanks,
Gurmeet
RE: von Mises stress with algebraic sign
Your fatigue life calculation will of course depend on the principal stress range which you should calculate from the stress components if the principal direction varies. It has nothing to do with Von Mises stress which is for assessing stresses against a yield criteria.
corus
RE: von Mises stress with algebraic sign
http://www.machinedesign.com/ASP/strArticleID/5573...
AAY
http://www.geocities.com/fea_tek/
RE: von Mises stress with algebraic sign
You can use other equivalent stress with this sign function.
This is not good for everycase!!!! If the shear stress is high in this case this formula totally bad. This equation shows us that the volume of the "stress cubic" is growing or not. If it is growing in this case it is tension. The problem is the shear stress, because in this case the volume will not change, just the shape of it is deformed.
Other possible way is the "Critical cutting plane method", like in FEMFAT software. This is also not correct, but more than nothing.
Best regards,
Irwin