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Different results with explicit and implicit method

Different results with explicit and implicit method

(OP)
Hello everybody,

I´m simulating a problem of indentation of a tungsten needle tip on an aluminum layer. Before I was using just the module "Static Structural" from ANSYS, which is based on an implicit solver. Now I wanted to do the same simulation with the module "Explicit Dynamics" of ANSYS, performing a quasi-static simulation. So my aim is to obtain the same results with both modules.

The process is rather slow and I have checked that the kinetic energy is negligible (<<5%). Most deformation is plastic. I have tried different stress-strain curves for the aluminum, changing the strain hardening during the plastic deformation.

Results:
1- When using large strain hardenings I get the same results from both modules, which I expected.

2- HOWEVER, when using small strain hardenings, the results differ a lot between both modules. This is to say: the more plastic I do the aluminum, the higher the differences in the results between both modules.

Question:

Is this something due to the physics or could I "fix" this difference by tunning the parameters in the explicit module?

Some ideas:

I know that the plastic waves travel slower than the elastic ones. The lower the hardening, the slower the plastic wave is. Maybe this is the reason for the observed results.

I have already changed many parameters (time step size, mass scaling, damping factor and loading rate) and they do not have influence in the observed behavior for lower strain hardening.
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I would appreciate a lot any idea or reference in relation to this.

Best regards!

Angel Ochoa

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