from NASTRAN help ...
MAT2 Shell Element Anisotropic Material Property Definition
Defines the material properties for linear anisotropic materials for two-dimensional elements.

defines Gij such that stress_i = Gij*strain_j (i think !?)
field3 = G11,
field4 = G12,
field5 = G13,
field6 = G22,
field7 = G23,
field8 = G33

and MAT8 Shell Element Orthotropic Material Property Definition
Defines the material property for an orthotropic material for isoparametric shell elements

field3 = E11 = G11 (ie field3 from MAT2)
field4 = E22 = G22 (ie field6 from MAT2)
field5 = nu12 = G12/G11 (MAT2 field4/field3)
field6 = G12 = G33 (ie field8 from MAT2)
field7 = G13 = field5 on MAT2
field8 = G23 = field7 on MAT2

i tried to copy the manual, but the tables wouldn't show properly.

GL

at one time you could input a PCOMP/MAT8 set and NASTRAN would calculate the effective PSHELL/MAT2 card set.

In general there is no unique solution for going from homogeneous PSHALL/MAT2 stiffness to layered PCOMP/MAT8 stiffness.

"In general there is no unique solution for going from homogeneous PSHALL/MAT2 stiffness to layered PCOMP/MAT8 stiffness."

if that means determining individual ply properties from the composite, then yes (FWIW) i agree.

but if you're going from bulk section property to bulk section property ... ie you've got a CQUAD with a MAT2 material definition, and you want to use (for whatever reason) a MAT8 card, then (again, FWIW) i'd disagree ... i think i've shown that the MAT8 fields can be calculated from the MAT2 data (and vis versa)

I'm sorry for my delayed response. The inputs are very helpful.
@rb1957 ur tipp for converting MAT2/Shell to MAT8/Shell worked.

Thanks a lot!!

Cheers!