Hello everyone,
I have coded an anisotropic hyperelastic constitutive model using user-defined umat subroutine with
cm(1) = isotropic material parameter in GPa
cm(2-3) = IHYPER and IBULK (mandatory for user-defined material modeling) in GPa
cm(4-5) = anisotropic material parameters in GPa
cm(6-8) = {0, 1, 0} = components of anisotropic fibre vector, a_0
The fiber a_0 in the reference configuration is directed towards global Y-axis (also the loading direction) in a unit milimeter hexahedral element. Also, the hexahedral element's local coordinate system is same as the global coordinate system.
My question is: using solid finite element, IHYPER=1, IORTH=1 and AOPT=2.0, isn't the material card definition correct?
Thank you very much in advance.
Bhattarai
Hi @bhattarai,
This seems like a really interesting topic. Disclaimer: I have never used user defined materials so I'm not sure how much help I can add to the implementation, but I am happy to help spot check what you are doing.
I'm not sure what the "cm" is that you are referring to. Are these defined variables within your equation?
I think you may want to try an AOPT that uses the element local coordinate system. I just wouldn't trust a material whose response is dependent on it's orientation to the global system.
Dear @Negative Volume
Yes you are right, "cm" are the material parameters of the strain energy equation in the user-defined umatXX subroutines which are equal to the P_i in the LS_PrePost material card.
I am happy to help spot check what you are doing.
The first question in this thread was the simplest example of my integrated implementation considering the vector m_0 (p6=m_0x=0, p7=m_0y=1, p8=m_0z=0) only. The integrated or complete strain energy function consists of four vector families (a_0, b_0, m_0, n_0) as shown in the global coordinate system XYZ. My question is how is it possible to describe them in the material card using AOPT=2.0? Or do you think there is other possibility to define this anisotropy using another AOPT on solid element?
Thank you very much in advance.
Bhattarai
@bhattarai Okay got it. Yeah that’s what I was thinking, that it wouldn’t make sense to use AOPT=2 since that would use the global coordinate system. I would try to use one of the other options that use the local coordinate system of the element itself. There are a few choices so it just depends on how you want the orientation to behave.
Thank you Negative Volume. I know it is not the part of your job, but it would be a great help if you could define the correct material card for above mentioned vector distribution. My simulation has been stuck since weeks for which I suspected the above provided incorrect material card was the culprit. Thank you again.
Bhattarai