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Jumps in Shear Stress after a Step

Jumps in Shear Stress after a Step

Jumps in Shear Stress after a Step

(OP)
Hi I am fairly new to Abaqus. I am modeling the interaction of a steel probe
with a hyperelastic material. Both are 2-d shells. The hyperelastic material
is a square. The tool touches the square at the center of one edge. There
are 2 Static, General steps. In step-1, the tool pushes into the square
material with a displacement inwards. (Ramped). In step-2, nothing new is
added (the tool remains at the penetrated depth of about 0.5% of the
material length). The tool is constrained to move only into the
hyper-material and not along the edge, and the opposite edge of the
hyper-material is fixed.

After meshing and submitting the job, when I view the plot of the shear
stress of the hyper-material center node (where the tool touches it), it
gives me a sharp drop after step-1, as if the tool were lifting off the
material and then rises again, as if the tool had been pushed in again. (I
am not sure this is the possible case, though. It was the best way I could
interpret it)

I don't understand this effect- could someone please explain it to me?

Is it possible that Abaqus deletes the BCs of step-1, and then applies those
of step-2? Other quantities (like normal stresses and reaction force on tool
become zero after step-1).

Sorry for the long message.

RE: Jumps in Shear Stress after a Step

(OP)
Thank you for your reply. The boundary condition does get promoted to the next step. I also checked the contact pressure, and that is non-zero throughout the process, so I guess that loss of contact is not the problem. Could there be another reason for such a sharp change in shear? (It goes from 45 to -45 instantaneously). Is this kind of shear change noticed in any other situations, so that perhaps I could draw a parallel?

RE: Jumps in Shear Stress after a Step

(OP)
Nothing. That is, nothing new. The probe remains at the displacement that it reached at the end of step-1 (it deforms the tissue accordingly).

RE: Jumps in Shear Stress after a Step

(OP)
I am plotting it against time- I've plotted the odb field output (unique nodal, S12) for the node of the material in contact with the probe.

RE: Jumps in Shear Stress after a Step

(OP)
I'll try that. Thanks.

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