Transversly Isotropic Laminites

[ErikCarlson]

I am working on an analysis of a carbon (balanced cloth) laminate structure and was told that when assigning material properties, to assume that the lamina are transversely isotropic i.e. the G12=G13=G23. Does anyone have a reference as to why this is or is not a valid assumption? I feel that the stiffness in the transverse directions is going to be epoxy dominated and therefore much softer then the in-plane stiffness (610,000 psi for balanced cloth). Thanks in advance.

Erik Carlson

 

[SWComposites]

For a fabric composite ply it usually is assumed that G12 = G13 = G23 since all of the shear moduli are essentially matrix properties. E3 is however much less than E1 or E2 since it is also primarily a matrix property while the other two are fiber dominated. If you have properties for a tape material with the same fiber and matrix as the fabric material, then you can assume that E3(fabric) = E2(tape), nu13(fabric) = nu12(tape) and nu23(fabric) ~ 0.67*nu12(tape).