Hi Aadam,
The error messages indicate that you are using a nonlinear material, probably with a custom stress-strain curve entered. The first error says the strains need to be in order of increasing strain.
Are the strains not sorted by increasing value?
Perhaps the remaining errors are related to the first problem. Also, the modulus after the yield stress needs to be smaller than the elastic modulus. In other words, Et = (stress 3-stress 2)/(strain 3-strain2) and so on, and each of those need to be less than the elastic modulus.
John Holtz, P.E. Global Product Support
Autodesk, Inc. If not provided, indicate the version of Inventor Nastran you are using.If the issue is related to a model, attach the model! See What files to provide when the model is needed.
