Learning Forum

[ssagar]

I am performing the Charpy Impact Test simulation in LS-DYNA for specimens of various initial temperatures. I have the Johnson-Cook Parameters that are using a reference temperature of 298 K.

However, my initial temperatures of my specimens are 77 K, 298 K and 723 K. Do I have to scale the J-C parameters to match each temperature? Or do I conduct a coupled Structural and Thermal analysis using an initial temperature value using the thermal properties.

Thank you,

S.S

[Andreas Koutras]

Hello You can manually specify the material properties that correspond for each temperature and run a structural-only analysis. In that case, if you use MAT_015, you will need to deactivate the temperature dependence by setting m=0 and D5=0. In the J-C model, plastic work will cause temperature increase. For a tabulated version of the model you can consider MAT_224.
I hope this helps.

[ssagar]

Thank you very much for your response Andreas Just to make sure I am understanding your reply. If the plastic work results in temperature softening (expressed as the homologous temperature raised to the power of m), do I not consider its effect if I change each parameter to correspond to the initial temperature it was tested at (an experimental tensile test was performed at each temperature)?
I do not have the J-C parameters at each test temperature nor do I have the MAT_224 properties at each test temperature. What I do have is the J-C parameters at a reference temperature, tr = 298 K.
The only ways of of changing the initial temperature (or in the experiment, test temperature) in LS- DYNA are:
(1) Mat107: has T0 = Initial Temperature: Structural only analysis.
(2) Mat015 and Use Initial_Temperature: Will require a structural and thermal analysis.
So far, MAT107 did not work out well. The impact energy actually decreased with temperature which is not in agreement with published data and experiment.
Coupled Structural and Thermal is taking very long using MAT015 and Initial Temperature.
Thank you again SS

[Andreas Koutras]

For MAT_015 you can specify the initial temperature change T-Troom by using *INITIAL_STRESS_SOLID/SHELL and setting history variable #5. I'm not sure how well this will work. I think I would use the coupled analysis. Maybe you need to check your thermal solver parameters. Make sure that the units of the material parameters and thermal properties are consistent. It's better to stick with SI units everywhere. I hope this helps.

[ssagar]

Thank you Andreas, will recheck the coupled structural/thermal model. Yes SI units were used. I appreciate your responses.
S.S.