Hi all,
I have a problem in using Johnson cook model in DEFORM 3D. I am trying to use this model for pure aluminum after a cycle of deformation in a severe plastic deformation, and I obtained all necessary parameters from other scientific papers but the problem is that when I try to input these parameters to use this model, the software shows an error which indicates that some flow stresses are negative, consequently, the software does not run the simulation.
Can any one help me to solve this problem? Any ideas would be highly appreciated.
Best Regards,
Farhad
Dear Mr. Shunmugavel,
Thank you for your kind response. I obtained these data from scientific papers and they have already used those data and it seems that I have problem in using these kind of information in DEFORM, I have to mention that when i use ABAQUS I do not have any problems, however, I will certainly double check my data as you suggested.
Regards,
Farhad
Have you done any mesh sensitivity test? Materials volume constancy and so forth. If your die geometry is complicated and re-meshing criteria has not been defined properly you sometimes get such errors in DEFORM
Dear Dr. Ghassemali,
Thanks for your comment. I did not get a clear idea about mesh sensitivity test as you have indicated. could you please explain more?
I have to say that the die is defined as rigid body and I have meshed the sample in different mesh number and it seems that the mesh size has nothing to do with this error.
When I input these information, DEFORM shows the error that I have explained, even before generating the database.
The parameters I obtained for Johnson Cook model for pure aluminum from ISI papers are as follows:
A: 80 MPa / B: 120 MPa / n: 0.73 / c: 0.008 / m: 1.7 / Tm: 933 k
Any Ideas?
Mesh sensitivity test: you change the mesh size from "coarse" to "fine" in steps and follow your desired value (e.g. local strain/stress, hardness etc.) So you get a curve on that desired value vs. mesh size. The mesh size, after which the curve becomes constant, should be considered as your optimum mesh size. Coarser meshes would lead to a unreliable result, finer mesh just increases your computing time!
The other factor is the mesh-die geometry relativity. If the mesh size is too large compare to the geometry of your dies and its edges (i.e. r value, when you define your parts in DEFORM), then some meshes might virtually move inside your die and this cause an error. The way to deal with this is changing the remeshing criteria and see if that helps, which I think it will!
Thank you Dr. Ghassemali for your kind response and your clarification. I will certainly do what you suggested.
Hi farhad
May I ask you from which paper did you obtain these parameters?
i have a similar problem like yours in severe plastic deformation
thank you
Dear Reza,
I have sent you the requested paper. Hope you can solve your issue.
Regards,
Farhad
Mr. Farhad, I am facing a similar issue while trying to use the Johnson Cook model, could you share the paper with me too..?
Avneesh,
It's been a long time, I can't remember unfortunately!
But I am looking at my Archive, if I find that paper, I will send it to you.
Regards,
F.
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