Learning Forum

[onur gorur]

Hello everyone,

I am currently facing a problem with implementing the cast iron plasticity model to simulate engineered cementitious concrete (ECC) strain-hardening behavior. For my master´s thesis, I need to use the Cast iron model to input the stress-strain relation of the ECC material for tension and compression zones separately. I used a command object to embed the properties of the material, but I could not get the solution as the solver threw errors every time I started the simulation. 

The stress-strain values from experimental data: The Young´s modulus is 20.6 GPa, and the Poisson´s ratio is 0.15.

 

Here are the error and warning messages shown in the solution information:

*** WARNING ***                         CP =       2.016   TIME= 12:12:37
 Material number 3 (used by element 213951) should normally have at     
 least one MP or one TB type command associated with it.  Output of     
 energy by material may not be available.                               

 *** ERROR ***                           CP =       2.016   TIME= 12:12:37
 For material 1 at temperature 22, the initial slope (205555.556) of the
 stress-strain curve based on the TB,UNIAXIAL table with option (COMP)  
 is less than EX (206000).                                              

 *** ERROR ***                           CP =       2.016   TIME= 12:12:37
 For material 1 at temperature 22, the initial slope (175000) of the    
 stress-strain curve based on the TB,UNIAXIAL table with option (TENS)  
 is less than EX (206000).                                              

 *** ERROR ***                           CP =       2.031   TIME= 12:12:37
 The step data was checked and there were errors found.                 
  Please check output or errors file (                                  
 C:\Users\gorur\Downloads\ECC_Model\_ProjectScratch\Scr011E\file0.err ) 
 for messages.                                                          

 *** NOTE ***                            CP =       2.031   TIME= 12:12:37
 This nonlinear analysis defaults to using the full Newton-Raphson      
 solution procedure.  This can be modified using the NROPT command.     

 *** NOTE ***                            CP =       2.031   TIME= 12:12:37
 The conditions for direct assembly have been met.  No .emat or .erot   
 files will be produced.               

[John Doyle]

The ratio of stress to strain from first data set (defined via TBPT commands) for tension and compression need to match the corresponding elastic modulus (defined by MP,ex,,). That is what the error messages are referring to.  The warning about Material 3 can probably be ignored, since you are not using Material 3, but you should confirm.

[onur gorur]

 

The elastic modulus for the tension and compression is different as you can see from the experimental data. I tried to correct the code, but the problem still persists. Here is the corrected code. I inserted an additional data point for zero strain and yield stress. However, the second data for tension and compression already has the yield stress values. Therefore, I am a bit confused about what to do. Do you have some other recommendations? I am also including the link to the paper where I got the input parameters for the FEM. 

https://www.sciencedirect.com/science/article/pii/S0950061823029884

/prep7

 

mp,ex,1,20600.0  !Elastic modulus

mp,nuxy, 1,0.15  !Poisson ratio

 

!Define cast iron model

TB,CAST,1,,,ISOTROPIC

 

TB,CAST,1,1,4,TENSION

TBPT,,0.0,3.50

TBPT,,0.0002,3.50

TBPT,,0.0007,3.9

TBPT,,0.0127,4.40

 

 

TB,CAST,1,1,3,COMPRESSION

TBPT,,0.0,18.50

TBPT,,0.0009,18.5

TBPT,,0.0023,47.3

 

[Ashish Khemka]

Hi,

Can you try modifying the Young's modulus to be equal to the initial slope of the stress strain curve?

Regards,

Ashish Khemka

[onur gorur]

The slope of the stress-strain curve is different for tension and compression. I am also including the mechanical properties of the composite.

[onur gorur]

Here is the download link to my model: 

https://we.tl/t-SS15Cfi1WX?utm_campaign=TRN_TDL_05&utm_source=sendgrid&utm_medium=email&trk=TRN_TDL_05

I appreciate your help. 

[sai.teja.potu]

@Onur gorur, did you manage to solve the issue with different slopes in tension and compression ? I'm facing a similar problem and would appreciate any insights or solutions you found.