Are massive tension yield stress still solvable?


i do some test of deep slender beam (steel), the webs is thin and subjected to shear due to patch loads. using elastic material, large deformation and contact analysis is solvable for both full model and half symmetry, deformation result modes shown as expected and captured well to experimental.

however, it’s divergences when using nonlinear material applied. i seen from the stress elastic distribution has yield about 5 to 15 times higher, massively in large area of webs.

any hints about the problems? thanks in advances.

Do you mean that there’s no convergence in these cases with large plastic strains? Maybe adjusting the plasticity model could help. Or refining the mesh in critical regions. I would also try with different types of elements - the choice of element type can be particularly important in analyses involving plasticity in CalculiX.

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right, as i described.

it seems had been, i use multilinear elastoplastic not simplified bilinear near perfectly elastoplastic.

the original FE models from the report of authors does not taken refinement.

my model using a general purpose element, quadratic tetrahedral.

i’ll try using structured mesh (hexahedral element) or quad shell element as the original FE models from the author.

but, still in doubt and questionable if all it be can help to solvable due to membrane behavior of structural beams.

may the cause of solver algorithm between Newton-Raphson and modified Riks?

I think that it’s a good idea and I would try this.

If the original author used Riks solver and this problem involves large instabilities then it’s very likely that ccx’s traditional NR algorithm can’t handle them. The lack of an arc length solver is one of the most significant disadvantages of CalculiX.

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that’s another problems, the author not to mention the algorithm selected in Abaqus 6.11.

the element type being used by the authors are shell (S4R) and the material is simple bilinear elastoplastic with strain hardening.

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Can you share the title of that article ?

sorry. probably not now, i’m on the way making of test and benchmark and did not yet published since it’s unfinished.

here i’m seeking an advice and hints from someone who has experienced similar problems.

You could try reducing the step size. The plastic models I have run so far were very sensitive to a too large step size.

thanks, i forgot about this and i’ll try.


Hi xyont,

How do this post end up?.
I can’t achieve consistent results on my plastic analysis with Calculix. Only for very simple uniaxial tensile / compressive stress patterns.
As soon as the problem involve more complex stress distributions with shear or noticeable bending the results do not agree with other references.

By other hand, I suspect that ccx cannot manage sign reversal on the strains during the loading path on plastic models. I have found that PEEQ doesn’t stop when the model is unloaded. ¿Do you know if plasticity in ccx is limited to monotonic load patterns?

I really apreciate and consider your opinion and would like to ear about any update you can provide about your findings ( and the element that better perform to you if possible)

Sorry if this are too much question. Any answer you could provide is appreciated.

Thanks in advance


i’m not further investigate the problem, it did not finished yet. been trying to compares with different opensource solver with arch length algorithm capabilities.

it seems not only related to material plasticity, but equilibrium path at large deformation (shear buckling). theoretically the element stiffness is very low or nearly zero at areas with yielded materials. Newton Raphson algorithm sometimes is hard to find the path were Arch length is not.

Thank you very much for the update.