Hi everyone,
the Von Mises (VM) stress norm (already provided by CalculiX in a standard element output) is typically used to evaluate the “level of stress” for materials that can undergo at least a bit of plastic deformations, and which typically yield (and possibly fail) at opposite but “equal” (in absolute value) VM norm values.
For brittle materials, which cannot develop plastic deformations, and generally have very different stress limits in compression and traction, a very common criterion used for assessing the “level of stress” is the so-called Mohr Coulomb stress ratio.
Software like Ansys offer an element output with this stress criterion.
The formula is this:
I recently had to use the Mohr Coulomb stress ratio and had to write an equation in the Filed Output Editor:
Here the formula:
=if(STRESS.PRINCIPAL_MIN<0 and STRESS.PRINCIPAL_MAX>0,STRESS.PRINCIPAL_MAX/210-STRESS.PRINCIPAL_MIN/630, if(STRESS.PRINCIPAL_MAX<0 and STRESS.PRINCIPAL_MIN<0,-STRESS.PRINCIPAL_MIN/630,if(STRESS.PRINCIPAL_MAX>0 and STRESS.PRINCIPAL_MIN>0,STRESS.PRINCIPAL_MAX/210,0)))
In this case, as you can guess, the compression limit is 630 MPa and the traction limit is 210 MPa.
What I did is a tedious and error-prone tasks.
My suggestion would be to add the compression and traction limits among the material properties of brittle materials, and offer this output by default among the Field Outputs.
Best regards