I am attempting to make some quick predictions for failure of some notched composite specimens using the Whitney-Nuismer point stress or average stress criterion. I have no data (yet). The default values of d0 and a0 are approx d0=.04 inches and a0=.15 inches respectively but I think I can make much more accurate failure predictions if I calculate these values specific to the laminate. Does anyone know of a purely analytical technique for calculating d0 and/or a0 ?
ESPcomposites [Brian at http://www.espcomposites.com]
The W-N criteria are simply an attempt to capture the “hole size effect” for composite laminates. d0 (or a0) can only be determined via test (at least in an accurate manner). Also note that the predicted capability can significantly change with relatively small changes of d0.
While there are some approximate d0 values for different material systems and typical layups, these should only be used as reference and to get a feel for what to expect. If you want to make a quick prediction, you are probably better off using preliminary design values that are established for your given type of material system (these would account for notches, mechanically fastened joints, environment, post-impact strength, etc.)
Above is a snippet.