Zero Diagonal detected-Aborting Run

[Mohsen]

Hello,

I am a new user to FEBio and trying to re simulate The Junyan Li 2013 work "http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3688071/". when I selected cartilage material as hyperelastic, Neo Hooken or Moony Rivilin my simulation is run and converged but when I change it to Biphasic, it gives me the error like "Zero Diagonal detected.Aborting Run". I there any one who knows its reason and how it could be fixed?

Thanks,
Mohsen

[maas]

Hi Mohsen,

A zero diagonal may indicate incorrect material parameters, or a rigid body mode, caused by improperly constraining the body. If you can't figure out the cause, feel free to upload or email us the FEBio input file and we'd be happy to take a closer look.

Cheers,

Steve

[Mohsen]

Thank you for your email and suggestions. the bones in my model were rigid body but I change them to elastic and try to run but again faced to the same problem. I tried to send you the FEBio input through email but there is not any option to upload my model there. I was wondering if there is any possibility to send the model through private message?

Best,
Mohsen

[maas]

Hi Mohsen,

You can email me at steve dot maas at utah dot edu.

Best,

Steve

[Mohsen]

Dear Dr. Steve,


Thank you for your reply. I think my previous problem related to "zero diagonal detected" was solved and at least my model was converged by changing the constrain, residual tolerance and minimum residual. Now, I decided to take a step forward and model the cartilage as "fibril-reinforced biphasic materials" like Meng 2014 article (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4263820/). but I run to another problems:
1) I sat axes for all elements of cartilage and then define material and assign to them exactly like the same way mentioned by Dr. Ateshian in this post (http://mrlforums.sci.utah.edu/forums...astic-material). But when I want to export the file as .feb file the preview was crush and have to be close.
It's worth mentioning, if I assign fibril-reinforced biphasic materials to just one part, it will be exported well but when I assign to more than one part it was crash.I did not get its reason and how should fix it.
2) when I opened the crush exported .feb file in note++ to see the code, it seems that the material axis which I selected are missed.

for both case if I remove all the material axis and exported as .feb file, they'll works well. I think it related to material axis but I don't know how I should fix it and really appreciate if you could let me know how I should fix this problem.

Best,
Mohsen Sharifi Renani,

[Vaishakhraju]

Hi Steve,
I am also getting the same error when i changed the material property of cartilage to biphasic, crashed FEBio error is coming,
could you please help me with this issue.
I am attaching the febio file: https://drive.google.com/file/d/1NEt...a4OXV0RSU/view

Thanks
Vaishakh R

[maas]

Hi Vaishakh,

I think it is caused by the ImgLnk rigid bodies. They are connected to the femur or tibia via rigid connectors but are otherwise fully unconstrained and presumably the cause of the zero diagonals. I'm not sure I understand the purpose of these connects but they a closer look at them to see if they are setup correctly.

Cheers,

Steve

[lyra]

Hi,

I am using Preview's cube geometry, whenever I change the material from isotropic to a rigid body I get the same error. I have tried to add a displacement constraint in the x-direction to one of the surfaces to see if it will help but still, I get the same error. I have no forces applied to the cube, so I am suspecting if there is a bug or I am missing anything in using the rigid body material. I have attached the .feb file here.

Thank you for your help.

[ateshian]

Hi,

The file you have attached does not have any boundary conditions, so the analysis will fail since there is nothing to constrain the geometry.

Please keep in mind that the application of boundary conditions is different for deformable versus rigid bodies. For rigid bodies you should use Physics->Add Rigid Constraint... whereas for deformable bodies you should use Physics->Add Boundary Condition...

Best,

Gerard