I’ve read a bit about the Zienkiewicz-Zhu Stress in the Calculix doc and I was wondering: is there a reason why I should not always look at this stress instead of the “regular” stress? According to the doc this method gives a more accurate stress at the nodes.
Notice that element variables are more accurate at the integration points. The values at the nodes are extrapolated values and consequently less accurate.
Why are node values displayed in the results and can these values actually be trusted?
I understand these are Calculix/general FEA questions rather than PrePoMax questions.
This output is typically used as an error measure. Abaqus offers similar outputs, they are meant to evaluate extrapolation errors due to too coarse meshes. CalculiX also has ERR for that (mutually exclusive with ZZS).
However, you could use ZZS for more accurate output if you take into account the differences in how it’s calculated with neighboring elements.
Unlike Abaqus or some other solvers, CalculiX provides only nodal averaged stress in .frd contour map results. However, you can use element history output (*EL PRINT) to print the integration point stresses from the seleted elements to .dat file (displayed in tabular form in PrePoMax too). There’s also this script: Stresses at the integration points in ParaView - #2 by mkraska