Von Mises Stress Formula

[lindejos]

Hi All,

Does anyone know where to find the von Mises stress
calculation formula that Mechanica uses? I have looked in
the documentation and the only description is:

"An equivalent stress that is a combination of all stress
components. The von Mises yielding criterion states that
a material reaches its elastic limit if the von Mises
stress is equal to the material's yield stress in simple
tension."

I am curious if it is the same as the classic von Mises
yield criterion (second deviatoric stress invariant
definition) or if it is simply some RSS calculation that
the post processor is making to combine the stress states
over each mesh element.

Thanks in advance,

lindejos

 

[lindejos]

Anybody? I guess I'll contact PTC.

 

[preeti]

Hi lindejos,

you read von misses theory on this site,
http://web.njit.edu/~sengupta/met 301/theory of failu
re.pdf

 

[lindejos]

Thanks for the link. I know what the von Mises failure
theory is, and how to calculate it. I am not sure, however,
if this is what Mechanica is using to calculate the "von-
Mises" stresses that it reports in the post processing.

 

[moriarty]

run a problem you know the answer for and check it

 

[bettina]

Hi,


I talked to the Mechanica Product Manager and he told me that
Mechanica calculates von Mises stress as follows:<?:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" />

sigma_vm = sqrt (3 * J_2) = sqrt ( (1/2) *( (sigma_11 - sigma_22)^2 + (sigma_22 - sigma_33)^2 + (sigma_11 - sigma_33)^2 + 6 * ( sigma_12^2 + sigma_23^2 + sigma_31^2)))

where J_2 is the second deviatoric stress invariant.


Hope this helps.