Coordinate system and orthotropic materials
 

Hello all,

I'm trying to set up a cylindrical coordinate system in order to orient an orthotropic material correctly (Epoxy Carbon Woven (230 GPa) Wet) on a 2D axisymmetric model. The problem is, the radial direction defaults to x, whereas the properties I want to lie radially are defined as z on the material. I thought there may be two ways around this:

1. Change the coordinate system such that z is the radial axis.

2. Change the data so that the properties I want lie on the x axis.

I can't figure out how to do 1, so I tried doing 2 and I get an error

"The stress-strain matrix of material 1 is not positive definite, which
is required for real materials. Being positive definite means that
1.0 - PRXY**2*EY/EX - PRYZ**2*EZ/EY - PRXZ**2*EZ/EX -
2.0*PRXY*PRYZ*PRXZ*EZ/EX must be positive, but is equal to -0.4782336.
Consider reducing the Poisson's ratios.

EX = 7.5E+09 EY = 5.916E+10 EZ = 5.916E+10
PRXY = 0.3 PRYZ = 4.E-02 PRXZ = 0.3
GXY = 2.7E+09 GYZ = 1.75E+10 GXZ = 2.7E+09. "

I've checked that I placed the mechanical data in the correct place a load of times and I'm pretty sure it's right. Any suggestions? Thanks!

Ok, so I found http://148.204.81.206/Ansys/150/ANSY...0Reference.pdf, and section 2.1.2 is what I'm looking for, but I don't really understand what it's saying.

Would anyone be kind enough to explain what goes where in terms of moduli and poisson's ratios, such that the lowest Young's modulus is on the radial axis? Thanks!