I can help you with one half of it. Look up the Scripting Reference Guide, 34.6 FieldOutput object, that describes you how to save a custom field output. That way you can save all your data for each critical plane. Then if you want you can create the envelope of them in CAE or just create another from your script to write the maximum value as well.

If you want to keep the outputs, you need to open the odb without the read-only flag, or even better create a new odb file.

For the theory on critical planes, if you have access to FE-Safe, you can check their manual, as that code implements the approach. You likely won't find the actual code, but the theory will be described properly.

Good luck with your research!

Thank you David for you helpful points. Actually I have generated stress and strain fields from fieldoutput by getscalarfield command and then in a for loop in my script rotated the costum stress and strain dields. The problem I have before finding the maximum values of them is how to concatenate the data before applying envelope command. Could you please guide me how to do them?

Thanks

Well the question is what do you store in those fields and what do you count as results? Maybe create a new step, where field output is the expected damage or some other scalar. If you have a tensor, how would you say which tensor is bigger than the other? Then perhaps you create a separate frame for each angle of the inspected planes? Then you can get the maximum damages at every node over the frame.