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hill plasticity
Posted 19 mar 2013, 08:57 GMT-4 Structural Mechanics Version 4.3a 3 Replies
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Trying to make hill plasticity non-symmetric so my question is; is it possible with different yield stress level in tension and compression.
Then in addition the plastic stage is confusion. How are hardening parameters given? as a list or is there only one parameter for all planes?
In hope :)
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It’s not that easy. You cannot for example just use different Hill plasticity constants in tension and compression. That would lead to a discontinuous yield surface and convergence problems. One way to get different yield stresses in tension and compression is to make the yield surface a function of the mean stress or pressure. You will see that for example in the Mohr-Coulumb and Drucker-Prager soil material models (available in the COMSOL Geomechanics Module). These models are not anisotropic though like the Hill plasticity.
Nagi Elabbasi
Veryst Engineering
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If I understand you right; the yield stresses should be defined as variables in global definitions as functions of current stress state?
What with the actual plasticity stage, do you know if hardening parameters can be given as vector or is one parameter/perfect plasticity the only option?
Still in hope :)
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Yes, the yield function can be a user-defined function of the stress state, and so can the flow rule. The hardening affects the yield stress (part of the yield function) by making it also a function of a scalar measure of plastic strain (or a vector in your case). I believe that can be done too in COMSOL.
My advice when it comes to making significant changes to plasticity though is to select a well-established material model from the literature to implement since there are many subtle issues involved.
Nagi Elabbasi
Veryst Engineering