Experimental check of existing methods of fracture strength analysis

Tests were carried out with ST-2-type specimens and large-sized specimens of 15Kh2NMFA steel (1930×300×65 mm in size) with a central through crack and a semielliptic surface crack. It was established that theJ R -curves plotted for the large-sized specimens with a central through crack are located higher than the corresponding curves for the ST-2-type specimens. The fracture strength of the specimens with a central through crack was calculated according to the GE EPRI procedure. It was shown that the results of numerical calculations depend strongly on the technique of approximation of the stress-strain diagram by the Ramberg-Osgood relation and on the accuracy of the evaluation of the term (P/P0)n+1. By using the R6 method (version I), one can avoid all these difficulties and obtain a conservative estimate of the values of fracture loads. For the large-sized specimens with a semielliptic surface crack, we used the interpolation criterion and demonstrated the applicability of the method under consideration to the evaluation of fracture loads.