UMAT- history variables

- February 9, 2024 at 5:53 am
  
  fatemesafarieng
  Subscriber
  
  Hi, I am trying to use my umat in LS-DYNA. I encountered a problem while using my UMAT in LS-DYNA. My model incorporates a damage parameter crucial for subsequent steps. In each step, I store the damage parameter as an hsv (history variable). However, I've noticed that the value of this hsv at the beginning of a step (e.g., -0.7) is significantly different from what was calculated in the previous step (e.g., 0.03). According to its formulation, it should be positive.
  
  I am confused as to why this discrepancy happens. Are there any tips about history variables?
  
  I would greatly appreciate your assistance and guidance in resolving this issue.
  
  If further information is needed please let me know.
- February 10, 2024 at 12:13 am
  
  Ushnish Basu
  Ansys Employee
  
  This is a debugging issue, and unfortunately, we cannot help with that. Please make sure that NHV is set correctly, and you can check the history variables in e.g. urmathn using no_hsvs and hsvs
- February 10, 2024 at 1:03 am
  
  fatemesafarieng
  Subscriber
  
  Thanks for your response. Where can I find this "urmathn" subroutine you mentioned?
- February 10, 2024 at 1:13 am
  
  Ushnish Basu
  Ansys Employee
  
  dyn21umat.F in recent versions, dyn21.F in older versions
- February 20, 2024 at 12:05 am
  
  fatemesafarieng
  Subscriber
  
  I checked my umat in a single-element model and it works. However, when I employ my umat in a multi-element model, I face the following warning and the model fails to run. Does anybody know what may cause this problem?
- February 20, 2024 at 2:53 am
  
  Ushnish Basu
  Ansys Employee
  
  It seems the built-in umat41 is being used. This is also a debugging issue, and we are not able to help with that
- February 20, 2024 at 5:32 am
  
  fatemesafarieng
  Subscriber
  
  It seems it is related to the following statement in umat:
  if (ncycle.eq.1) then
  if (cm(16).ne.1234567) then
  call usermsg('mat41')
  endif
  endif
  I could not find the definition of "ncycle" parameter. Could you please guide me on what this if condition is associated with?
- February 20, 2024 at 5:50 am
  
  Ushnish Basu
  Ansys Employee
  
  ncycle is the number of the current timestep, and is available from bk06.inc
  If you wrote yur own code for umat41, you don't have to keep this pice of code. You should put print statements in your own code to see what might be going wrong