HELP : finding law paramaters for ballistic impact in 3D ((Hydro) Johnson Cook), ball and plate

L_utbm
L_utbm Altair Community Member
in Community Q&A

Hello altair community,

For a class project, we are trying to simulate a ball piercing through an aluminium plate at high speed.

We did a first try with plate in Shell element using the Johnson Cook law, and the results were accurate enough.

Now we try it in 3D, but the simulation is unrealistic :

image.png
image.png

Message we get :

EXCEEDED EPS_MAX ON SOLID ELEMENT NUMBER      34877: DEVIATORIC STRESS SET TO 0 ON INTEGRATION POINT

I know that the eps_max is exceeded (set to 0.1), this is what we want, but how do I tell the software to make the rupture happen ?

I also read the wiki and I found this concerning element deletion in Jc law :

When εpεp reaches the value of εmaxpεpmax in one integration point, then based on the element type:

  • Shell elements: The corresponding shell element is deleted.
  • Solid elements: The deviatoric stress of the corresponding integral point is permanently set to 0; however, the solid element is not deleted

Some other info : Interface type 7, min gap 0.1, 200m/s, mass = 40g, E(ball) = 2 000 000 MPa

From here, we concluded that maybe the regular JC law cant work in our 3D case ??

Then, we tried Hydro Johnson Cook, but again, the results are not what we expected :

The closest we got is this :

image.png

Here are all the law parameters :

image.png
image.png
image.png

As for the value of the material constant and parameters, they are kind of random values we found there and there on the internet/ in thesis/ chat GPT…

Sorry for the long post, thank you for your help, we really need it as we are kinda lost and we think we tried everything we could.

I attached the files of the Hydro JC

Thanks, have a nice one !

essai_hyd_JCOOK_law4_0000.rad
essai_hyd_JCOOK_law4_0001.rad

Tagged:

Answers

  • Mathis
    Mathis
    Altair Employee

    Hi @L_utbm,

    The behavior you are describing is expected with the set of parameters you are using.

    You need to define a failure model and some erosion parameters. This will allow you to calibrate the damage initialization&evolution and the quality criteria to trigger element erosion.

    Here is a presentation that should be helpful for you:

    RADIOSS_FAILURE&EROSION.pdf

    I hope this helps.

    Regards,

    Mathis

Categories