3D Orthotropic Material Stiffness Relationships


When working with isotropic materials I've traditionally only chosen to leave one of the three properties blank (E,G,nu) for stiffness relationships to avoid warning messages and have NASTRAN/FEMAP calculate it. I've been looking over some models with 3D orthotropic materials and they've utilized the same method but I can't seem to find the documentation on how NASTRAN treats 3D materials and calculates that relationship. Is this method still valid for 3D materials or do all three values need an entry. If NASTRAN does calculate it does it use the traditional G=E/1(1+nu) or how does that work?


Re: 3D Orthotropic Material Stiffness Relationships

Siemens Phenom Siemens Phenom
Siemens Phenom

From the QRG for MAT11:

"G12, G13, G23 Shear modulus relating τ 12, 13, 23 and γ12, 13, 23. (Real > 0.0; No default, must be defined)"


For MAT1 an isotropic material:

"G Shear modulus. (Real ≥ 0.0 or blank)"

And in the remarks it says "If only one E, G, or NU is blank, then it will be computed from the equation: E = 2 · (1 + NU) · G" So you are correct about that.