Unloading step of indentation problem

[acrozhao]

Hello. I am simulating indentation on an elastic-plastic material. It is an axisymmetric contact problem. The indenter is modeled as a rigid cone. The indentation is displacement controlled.

In the loading step, the indenter is driven into the material up to the indentation depth of 1 micron. Then the indenter is withdrawn from the material in the unloading step.

Since the material is plastically deformed in the loading step, the indenter will be detached from the material before the indenter is withdrawn to its original position in the unloading step. But I cannot predict where the indenter will be detached from the material. So, in the input file, I let the indenter be withdrawn to its original position. Hence I waste some computation time on withdraw the indenter after the indenter is detached from the material.

Is there a way to stop the unloading step once the indenter detached from the material where the resistant force is zero?

Thank you very much.
******************************************
*STEP,NLGEOM,AMPLITUDE=RAMP,INC=9000
loading: indent to 1 micron
*STATIC
2E-4,1.0,1.0E-9,0.01
*BOUNDARY
indenter,2,2,-1.0
*END STEP

*STEP,NLGEOM,AMPLITUDE=RAMP,INC=9000
unloading: withdraw to 0.0
*STATIC
2E-4,1.0,1.0E-9,0.01
*BOUNDARY
indenter,2,2,0.0
*END STEP

 

[xerf]

I think you could try to adjust the parameters of the automatic incrementation in the second step in order to save some computational time. For example your maximum allowed value of the increment si very small, i.e. 0.01. You can try larger values, up to 1.0. If you do not have contact, the convergence will occur much easier at larger increments.

For example:

*STEP,NLGEOM,AMPLITUDE=RAMP,INC=9000
unloading: withdraw to 0.0
*STATIC
2E-2,1.0,1.0E-9,0.5
....
*END STEP

 

[bassmanjax]

It would be nice if you could end the step when the reaction load on the indenter is zero, but I don't think it's possible in this case.

As Xerf said, you could leave the maximum increment at default rather than defining it in the data line, i.e;

*STEP,NLGEOM,AMPLITUDE=RAMP,INC=9000
unloading: withdraw to 0.0
*STATIC
2E-2,1.0,1.0E-9

 

[koetue]

there is the possibility to write a user subroutine, you can connect a spring(high stiffness) to the refnode of the rigid cone and control the force in the 2nd step.
happy easter