12 May 08 11:27
I've been using 3D continuum shell element (SC8R) to model elastic deformation in a global sphere. I'd like to express the stress directions in global coordinates rather than in the local shell coordinates abaqus provides (S11, S22, S12; S33 is radial and is always set to zero).
I accessed what abaqus terms the local coordinate system values in the odb file through the fieldOutput variable via python commands. In the scripting manual it says the variable localCoordSystem is a matrix of direction cosines relating the local coordinate system to the global coordinate system.
If this is the case, then using this rotation matrix (R) of direction cosines I should be able to get the stress values in terms of global coordinates by the following procedure:
Stress_global = R*stress_local*R'
However, when I do this the global stress values I get do not make sense at all.
Is there something I'm missing here or should the procedure I'm using give the correct stress values in terms of global x-y-z coordinates?
If someone knows a better way to go from shell local coordinates to global xyz coordinates any suggestions will be greatly appreciated!!!