I am in the process of learning how to implement a UMAT for my abaqus models.
I am starting small - using a single element and implementing isotropic linear-elasiticity theory so I can easily confirm my answers. I have implemented this behavior successfully on a single C3D8 brick element (verified by using Abaqus built-in *ELASTIC keyword).
I am trying the same thing on a single CPS4 element (plane strain). I am attempting to use the same UMAT file as in the 3-D case, with only the following exceptions:
1) Changing the definition of the Jacobian for a plane stress element. That is, using Hookes law for [URL= http://www.efunda.com/formulae/solid_mechanics/mat_mechanics/hooke_plane_stress.cfm?search_string=plane%20stress%20stiffness ]plane stress[/URL] as opposed to [URL= http://www.efunda.com/formulae/solid_mechanics/mat_mechanics/hooke_isotropic.cfm?search_string=hookes%20law ]3D isotropic[/URL] Hookes Law.
2) Using the strain indices appropriate for the CPS4 element (i.e., in plane stress, I have stress(3) referring to S12 as opposed to S33, as it would in the 3D case).
Something is still not working for my formulation. I submit my job, and in the Abaqus Model Tree, the job status goes from Submitted -> Running and hangs there indefinitely. Whats more, the .msg file only goes so far as writing INCREMENT 1 STARTS. ATTEMPT NUMBER 1, TIME INCREMENT 1.00 and then just ends - no warnings, no errors, no feedback. I have uploaded my plane stress UMAT as ELASTIC_PL_STRESS.txt.
I was hoping someone could help me with some feedback if they can identify what it is Im doing wrong. Im happy to answer any questions that would facilitate a response.
PS - Id be happy for some input regarding another quirk Ive noticed (that may be inconsequential). When testing/troubleshooting my code, Ill often write output text messages and the like to the .dat file. This works fine, but I find the output is printed 2X for each integration point (e.g., if I specify hello world to be output to the .dat file only at int. pt. 5 and increment 5 in a single step simulation, hello world is printed twice).