Learning Forum

[ssagar]

Hi,

The Johnson-Cook (JC) constitutive and damage parameters are usually expressed with a reference temperature as Room Temperature. I have a specimen that is not at Room Temperature and is running a dynamic analysis (Charpy Impact Test). The experiment entailed cooling specimens to -196 degrees Celsius. Another set of specimens is tested at room and another at 600 degrees Celsius.

I have in my possession, literature that show the JC parameters at a reference temperature = room temperature. Is it possible to used the same JC parameters for all 3 temperatures in LS-DYNA by changing the Initial Temperature, T0 in the MAT_107 material card? In this case the results was not much affected.

In this case, I would expect that LS-DYNA would scale each parameter to the corresponding temperature as by intuition, if the temperature increases from 25 to 600 degrees for metals, the yield stress, A in JC constitutive model would be less than that for at room temperature. Also, if we freeze specimen to -196 degrees Celsius, the plasticity parameters would be low as the metal becomes brittle (experiment show very low ductility).

OR

Is it that the JC parameters would be different for each temperature of specimen?

Thanks,

SS

[Chris Quan]

Reference temperature means the temperature where the test material is stress-free. Usually, it is the room temperature.
However, if you want to simulate the impact to a material at the elevated or the reduced temperature such as 600 C or -196 C and 600 C or -196 C is its stress-free temperature, the reference temperature should be changed to 600 C or -196 C.
At the same time, all JC material parameters should be set to the values at the new reference temperature. For example, the initial yield stress should be reduced in 600 C and increased in -196 C.