For a 3D model, 3D Warp needs to run to produce the initial stress values to be converted into NASTRAN interface files. The 3D initial stress values are first saved in the *.tsp file in the project folder. After running the mpi2nas.vbs macro, they are converted to initial strains and saved in the *.ist file that NASTRAN can read in.
The mesh model and related material properties and initial stresses are converted to the NASTRAN Bulk Data Format, primarily using the free form in order to reduce the interface file size. The interface file extensions used are *.nas for the mesh model, *.mts for the material properties, and *.ist for the initial strains.
Before you can export data to NASTRAN, you must first run a Fill+Pack analysis, with or without fiber orientation analysis.