Approximate method of elastic--plastic fracture analysis for nozzle corner cracks

Two intermediate test vessels with inside nozzle corner cracks have been pressurized to failure at ORNL by the HSST Program. Vessel V-5 leaked without fracturing at 880C (1900F), and Vessel V-9 failed by fast fracture at 240C (750F) as expected. The nozzle corner failure strains were 6.5 and 8.4 percent, both considerably greater than pretest plane strain estimates. The inside nozzle corner tangential strains were negative, implying transverse contraction along the crack front. Therefore, both vessels were reanalyzed, considering the effects of partial transverse restraint by means of the Irwin β/sub Ic/ formula. In addition, it was found possible to accurately estimate the nozzle corner pressure-strain curve by either of two semiempirical equations, both of which agree with the elastic and fully plastic behavior of the vessels. Calculations of failure strain and fracture toughness corresponding to the measured final strain and flaw size are made for both vessels, and the results agree well with the measured values