I am doing a certain analysis that requires to export stress values.
I created an element set where the max Von Mises is. After the analysis I see in PrePoMax the location of the max value VON MISES, which is 820 MPa. It is located on the surface.

Then, I exported the stress values of the element sets where the max value point is. I exported the stress tensor in Excel and then I added a column where I wrote the general Von Mises formula. But, when I use the MAX function, it finds 927 MPa.

Those are the stresses from history output save to .dat file, they are taken directly from integration points. Field output displayed as contour plots in PrePoMax is obtained differently - those are averaged nodal stresses and hence the difference.

It’s a standard problem in FEA. In fact, we usually look at both average and unaveraged stresses and check values directly at integration points to check the correctness of results. Such differences may indicate erroneous stress peaks. Check this region (around element number 78300) and see if there is any suspicious behavior there. Local mesh refinement in this area may help.

@FEAnalyst
Hi Jakub, i think in PrePoMax it is Not possible to show averaged and unaveraged Stress, or isn’t it?
Maybe this would be a nice tool in Future?

Because often a huge difference between averaged and unaveraged stress indicates a to coarse mesh. Therefore the comparison is useful for mesh validation.

I had a similar issue not too long ago. I did a simple analysis with a material model with complete yielding at yield stress. The model showed stresses above yield stress, which i found odd, but i then created a history output of the stresses and saw that no value went above yield stress.