Learning Forum

[Peter Yip]

Hello Forum,

I have been running many impact simulations where the metals are best modeled with the Johnson-Cook model. What I noticed in many papers that provide JC params is that they forget/omit the specific heat. However, when I try to run LS-DYNA without a CP, the job errors out with a message saying that the JC model has "an invalid specific heat value of 0.000E+00". 

Can someone explain to me where the specific heat enters the equation and why there is a requirement for this on the JC model?

Thanks,

Peter

[Armin]

Hi Peter,

The specific heat is required for calculation of the adiabatic temperature rise. It is stored as a history variable even in cases of mechanical-only analysis. Please see the screenshot below from the documentation:

[Peter Yip]

 

Thank you, Armin. Greatly appreciated. Can you provide the link to the documentation you have? When I look at this link online for the LS-DYNA Keyword Manual Vol II (https://ftp.lstc.com/anonymous/outgoing/jday/manuals/LS-DYNA_manual_Vol_II_R7.1.pdf) the Johnson-Cook Homologous Temperature doesn't show that form you have in your screenshot.

Thanks again,

Peter

 

[Peter Yip]

Hi Armin,

Please disregard my last comment. I was able to find a newer version of the LS-DYNA Materials Manual Volume II that has the same formulation provided. 

Thanks,

Peter

[Peter Yip]

I assumed that the current temp value was calculated using an equation of state. If that's not the case, why does the JC model require an equation of state for solid elements only? Why wouldn't an EOS be required for shells?

Thanks,

Peter