Reply To: D3 failure parameter in *MAT_015 (JOHNSON_COOK)

[Armin]

Hi Rong,

Thanks for sharing this. I still think a negative sign might be missing in the definition of stress triaxiality in Equation 4 in your screenshot. Stress triaxiality is commonly defined as the ratio of mean stress (hydrostatic stress) over equivalent stress. Pressure is the negative of hydrostatic stress.

In Johnson-Cook fracture criterion, fracture strain is inversely related to stress triaxiality. In other words, fracture strain should decrease by increasing the stress triaxiality. You can do a few checks using single-element simulation to ensure that the expected fracture trend is resolved in your model.