Re: GR&R for an "R" value instrument
R should be straight forward as it is a ratio calculated from four dimensional measures (two before and two after).
Have your operator(s) measure the samples multiple times before the test then again multiple times after the test. Next calculate R using the matched before/after results. That is, the two dimensions from sample 1, first repeat before and the two dimensions from sample 1 first repeat after.
While the test itself is destructive, the dimensions are not destructive. However, you must plan the before measurements and take them before performing the test.
I'll have to research on N before advising how to do that. Does the Instron software calculate N directly, or do you interpret it from a graph?