Sect VIII Div 2 Part 5 Elastic Plastic Local Failure

[rickfischer51]

Does anyone know the derivation of equation 5.6 for the limiting strain shown at 5.3.3.1.c? It looks like a variation on the triaxiality treatments I've seen from time to time. I googled a bit and found a paper by Deng, et al that uses it to evaluate some pressure vessle materials, but they dont give the derivation. IS this a curve fitting exercise?

 

[TGS4]

The derivation is in ASME PTB-1 (2009). It is from Prager (in a WRC Bulletin under development) and Bridgeman "Studies in Large Plastic Flow and Fracture with Special Emphasis on the Effects of Hydrostatic Stress" (1964).