Thank you for your responses. I have the strength of the brass material and the sterngth of the plastic material, I guess I was looking for a way to predict failure strength without testing to a particular margin of error. How do I go about assigning a safety factor. I also know the thread stress area of the botl and would conversely be able to kno wthe stread stress area of the insert. The inserts I am speaking of are threaded inserts which are molded-in, thermally inserted or ultrasonically inserted into plastics. Most fastener manufacturers of these kinds of hardware list strength data, but for specific materials. I am would be deigning a new part with a different material, I thougth there would be a way to estimate within a margin of error what it would take to pull insert out or rotate it in the plastic. I will check out the Mohr's circle method. Thanks for your inputs.
DS