Extrapolation from INTEGRATION POINTS to NODES - How is it done in Abaqus?

Does anybody know how abaqus extrapolates values (like stress, plastic
strain etc) from integration points to nodes ? If suppose I have a 2D
bi-linear quad element with 9 integration points, then does it form a
2D polynomial function (like using Legendre polynomials upto order 3
or so) and then use it to extrapolate to the nodes? Or is it simpler
than that ? I know it must be using some form functions but what are
they?

Can somebody throw some light?
Thanks,
uday.





------------------------ Yahoo! Groups Sponsor --------------------~--> 
Make a clean sweep of pop-up ads. Yahoo! Companion Toolbar.
Now with Pop-Up Blocker. Get it for free!
http://us.click.yahoo.com/L5YrjA/eSIIAA/yQLSAA/PMYolB/TM
--------------------------------------------------------------------~->