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

[rji229]

Thanks for the reply. What I would like to simulate is the AZ31B magnesium alloy. The material parameters are cited from the paper linked: A constitutive and fracture model for AZ31B magnesium alloy in the tensile state - ScienceDirect

The fracture material parameters are defined below:

which are very similar to the formula in LS-DYNA user manual. In real experiment, the parameters are calculated by fitting the data measured, and the result for the paper is shown:

So when using the negative D3 value, we can generate the correct stress-strain curve. However, in LS-DYNA manual, it indicates that D3 must be positive (if negative, use the absolute value). I don't know why we need to do that.

 

Besides, I also get the same result by using both positive and negative values for the material property for calculation (same absolute value, keeping all other JC parameters the same).