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Generalized plane strain elements (eg CPE4G) with UMAT

Generalized plane strain elements (eg CPE4G) with UMAT

Generalized plane strain elements (eg CPE4G) with UMAT

(OP)
I have a UMAT for the material behaviour that works with CPE4 elements but not with CPE4G elements.
I did mention the ref node and restrict DOF 4 & 5.
CPE4G works fine for elastic material or plastic ones given with the appropriate keywords, but NOT with a UMAT.
Does anyone know if I have to specify smthg in the UMAT so that it works for CPE4G elements?

Thanks

RE: Generalized plane strain elements (eg CPE4G) with UMAT

What exactly do you mean by saying it does not work with UMAT ? Could you mention some details ?

RE: Generalized plane strain elements (eg CPE4G) with UMAT

(OP)
With CPEG4 elements, the solution is diverging. Here is what I have in the msg file:
...
AVERAGE FORCE                      0.785       TIME AVG. FORCE       0.785
 LARGEST RESIDUAL FORCE             -1.12       AT NODE          4   DOF  2
 LARGEST INCREMENT OF DISP.         1.000E-05   AT NODE          2   DOF  1
 LARGEST CORRECTION TO DISP.       -4.140E-06   AT NODE       1000   DOF  3
          FORCE     EQUILIBRIUM NOT ACHIEVED WITHIN TOLERANCE.

 AVERAGE MOMENT                     0.425       TIME AVG. MOMENT      0.425
 ALL MOMENT    RESIDUALS ARE ZERO
 LARGEST INCREMENT OF ROTATION      4.248E-37   AT NODE       1000   DOF  4
 LARGEST CORRECTION TO ROTATION     3.886E-52   AT NODE       1000   DOF  4
          THE MOMENT    EQUILIBRIUM EQUATIONS HAVE CONVERGED


 ***WARNING: THE SOLUTION APPEARS TO BE DIVERGING.

 ***ERROR: TIME INCREMENT REQUIRED IS LESS THAN MINIMUM SPECIFIED.  ANALYSIS
           ENDS


With CPE4, it works fine.
I don't know why it (yhe UMAT) works with CPE4 elements and not with CPEG4 elements!!!!!

RE: Generalized plane strain elements (eg CPE4G) with UMAT

If the non-convergence problem were caused by UMAT , I would check the data passed as input by Abaqus for the two element cases. It might happen to be some differences since CPEG4 allows for out-of-plane strains and the two type of elements are meant for ,let say, slightly different constitutive response.

For CPEG4 , I think, you should have NTENS=4 from which first 3 strain/stress components are the the direct stress/strain componets 11,22,33. And the 4th component should be the shear 12 component (for both stress and strains storage arrays)..i.e. (NDI=3,NSHR=1).

Anyhow , I do not know what your constitutive response described inside UMAT is , so I cannot speculate more...
but I would check the input data passed in by Abaqus for the two element types.



RE: Generalized plane strain elements (eg CPE4G) with UMAT

(OP)
In fact, that was the problem. So I sort it out, because in my UMAT the out of plane strain increment was forced to be equal to zero (DSTRAN(3)=0) which is ok for CPE4 elements.
By removing this condition, it works fine for CPEG4 element.

Anyway, thanks for answering my question

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