Burner2k,
Not sure if this is what you are looking for (maybe you've already looked here) but there is some good info on using R-curves in the following:
Farahmand - Fatigue and Fracture of High Risk Parts - Section 3.4.3
Broek - The Practical Use of Fracture Mechanics - Section 10.6
Broek - Elementary Engineering Fracture Mechanics - Section 8.3
Damage Tolerance Assessment Handbook Volume 1 - Section 2.4.1
I might also go to the NASA Technical Reports Server and search for "r-curve". It may be beneficial to look at the list of references in any reports that come up. If you can track those down they may help you.
Keep em' Flying
//Fight Corrosion!