Orthotropic Materials in Nastran Plane Strain Analysis - CPLSTN4

[MrRogers1987]

I am trying to run a plane strain model that has several components which do not have isotropic properties. They are made from composite layups, but I have calculated equivalent orthopedic properties for the layup schedule. Now I have a plane strain model of a different section of this assembly. I am using the PPLANE property card with CPLSTN4 elements and MAT3 card to try and apply the orthotropic material properties. I looked into other options in Nastran for creating plane strain models, but (correct me if I'm wrong) it seems like this combination is the only one that will allow the inclusion of orthotropic materials. I also want to recover the stress results in a cylindrical coordinate system, so I am also using MAT3 for the isotropic materials so that I can assign material directions to all the elements. From what I understand, this is the only way to recover stress/strain components in a coordinate system other than global for CPLSTN* elements.

Once I had results I realized that there was an issue with the material orientations. Apparently FEMAP does not work very well with CPLSTN* elements; it does not understand how the elemental coordinate system is defined. It tries to treat them as CQUADs and defines the element x-axis relative to the "first-edge". This isn't how CPLSTN* element coordinates are defined however, so when it calculates the element orientation angle theta to define the material angle it provides an incorrect result. For CPLSTN* elements the x-axis is always aligned with the global (or basic) x-direction. Does anyone know a way around this in FEMAP? I tried using NX8.5 as well, but it does not support this element type at all (won't even read the elements in).

 

[jbrackin]

The issue with supporting plane strain elements correctly with orthotropic material(MAT3)is being addressed in the next release(11.3)
We are also aware of the material angle issue. Under Modify/Update Elements/Material angle then you should see the form below where you can pick a fixed angle instead of having Femap calculate it. I believe that will allow you to get the material oriented properly.

 

[MrRogers1987]

Good to know jbrackin. The only issue with your proposed solution is that the material angle needs to vary for each element; I want them aligned radially with a cylindrical system at the model's center. It would be prohibitively time consuming to manually calculate and assign an angle to each element...

 

[jbrackin]

See the picture below from the QRG, the elem cord system is the basic system, so all elements should have the same rotation angle.You are rotating from the basic x axis.

 

[MrRogers1987]

Yes I know the elemental CSys is the basic system. That means that each element will need a different rotation angle to have their x-axis aligned with the radial direction of a cylindrical CSys though. Basically the theta coordinate of each element centroid is the required rotation angle. The only way all elements would have the same rotation angle is if they lie on the same radial vector.