usermat.F in HIP process

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  • Last Post 29 March 2020
sobhanis posted this 26 March 2020

Hi 

 

I am working on HIP ( hot  isostatic pressing) by using usermat subroutine.

young modulus poisson ratio , yield stress  is a function of relative density and  density as a function of plastic strain. so density change by  each time step so the others material properties, too 

I use usermat code but the problem is the usermat works with constant material properties but whenever i change them as a function of density the code did not work. Can anyone tell me what is the problem?

 

 

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Wenlong posted this 26 March 2020

Hi, 

 

Your objective can be achieved with the Usermat.F, but it is not clear to me what specific issue you are encountering when you noted that it “did not work.”

 

If you received an error during compiling or during a solution when using density-dependent properties, can you provide the error message(s)?

 

On the other hand, if the results obtained for the density-dependent case are not as expected, I’d suggest that you use state variables to store intermediate results throughout your solution.  Then, use a simple 1-element cube model to check results with hand calculations (apply uniaxial load to just have 1 stress component, for example, for easier checking with hand calculations).  For example, you seem to already be storing state variable #3 as (relative) density, but by storing other variables (yield stress, etc.), you can then check results to see which quantity/quantities are not being updated correctly throughout the solution, which may give some clue regarding what is occurring in your usermat.F code.  (If you do not see state variables stored for all substeps, include OUTRES,SVAR,ALL in your “Commands (APDL)” object, so you can see all intermediate results.)

 

As a side note, it seems that you are updating relative density based on equivalent plastic strain (“dpleq”, if I am reading your code snippet correctly), but please note that equivalent plastic strain (“pleq&rdquo is the deviatoric component, and you want the volumetric component to calculate relative density.  The volumetric plastic strain needs to be calculated by taking the average of x, y, z plastic strain components.  Also, you seem to be replacing the “pleq_t” value with the first state variable, but “pleq_t” is an input parameter and should generally not be changed.  As noted above, by storing and reviewing state variables in a simple 1-element model, I think that it will be easier for you to debug your Fortran code and see what variables are problematic in your usermat.F code.

 

Regards,

Wenlong

 

 

 

sobhanis posted this 29 March 2020

thanks you. this is usermat original code I only add density to it. the problem is the density did not change during time steps. at the end i should hve plots of density vs time that density changes every step. the UPF ACT extension did not work with my academic version . i modeled in workbench and import the .inp fie to the APDL but it only solved the first time step . i use outres, all,all command.  i need the density  to change every time steps.

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