Bad Material definition in element number

[mina30]

Hi every body
I have written a VUMAT subroutine for anisotropic hyperelastic material Also, I have introduced material orientation for fiber directions by keywords. . but I have received the error " Bad Material definition in element number".
please give me any suggestion if anyone can help me

 

[IceBreakerSours]

How did you verify your subroutine in the first place?

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[mina30]

I do not know your meant about verifying.
But, I am sure about the material parameters. the code is run without local coordinate. but when I use local cylindrical coordinate, I received the mentioned error.

 

[IceBreakerSours]

By verification, I mean, did you try a single element FE model and compare the results from with Mathematica or something in a simple/biaxial tension or shear etc.? The code does not need a local coordinate system, the model does. In the code, you are assuming 1 or X-direction is the fiber direction, aren't you? So, you have to provide an orientation system to the model. Are you trying your subroutine on a single element model or something similar?

Are you new to this forum? If so, please read these FAQ:

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083

 

[mina30]

thanks for your suggestion. I will verify it and then report the results to you.
about orientation, I have defined a cylindrical orientation for model. I think it must not been specified fiber direction in the keyword for model.In fact, I have considered R direction as direction-1 in the code and I determined angle of fiber direction toward this coordinate for calculating invariant I4 and I6.
In addition, I would like to ask you about calculate cauchy stress. The potential energy function is incompressible, but I add a term of compressibility to function and determine it's coefficient 3 order bigger then other parameters. At the end, I calculate cauchy stress=USU , which S and U are second piola and right cauchy green deformation.