Reference fracture toughness curve

Reference fracture toughness curve and safety factors... 

SI method Methodology Reference flaw Safety factor(s) Fracture toughness curve Comments... 

With the reference toughness curve approach, the RT m index first came into use as the reference nil-ductility temperature which is determined in accordance with the ASME Code, Section III, Subsection NB-2331. The reference toughness Km curve and the Ki curve for static crack initiation later came into use as part of Section XI where the Km curve was called the crack arrest Xia curve. Thus, the RTndt reference temperature index has become the key material parameter in determining the allowable (P-T) limits for plant operation and for evaluating RPV integrity as the result of extreme transients such as PTS. Note that several years ago, the concept of a different, directly measured fracture toughness Master Curve approach was accepted in the ASME Code based on the index parameter RTjq. This development is covered in detail in Chapter 10. 

Alternatively, the ASME Code, through Code Cases N-629 (ASME, 1999a) and N-631 (ASME, 1999b), allows the use of RTt , the reference temperature using To from the Master Curve fracture toughness approach in ASTM E 1921 (ASTM, 2008). RTt is defined as ... 

As with the RT m, the parameter Tq can be used as a reference temperature to normalize the fracture toughness of RPV steels. Figures 10.5a, b and c (Sokolov, 1998) show the same fracture toughness data as in Fig. 10.2a, but demonstrate that, although these are valid plane strain Aic data from relatively large specimens, the Master Curve provides a good representation of the results when normalized to IT specimen size. 

Because the Ki, and Ki curves in the ASME Code are normalized to REndt, potential application of the Master Curve procedure within the ASME Code structure is not straightforward. Figure 10.7 from Sokolov and Nanstad (1999) shows the relationship between REndt and the Master Curve Eo for the steels used to construct the A curve shown in Fig. 10.2. To overcome the lack of correlation between Eo and REndt, the Pressure Vessel Research Council and the Electric Power Research Institute (EPRI) in the USA developed a separate reference temperature based on Eo (Server et al, 1998 Van Der Sluys et al., 2000, 2001a, b). This reference temperature, RTj, was developed by determination of a temperature offset to Eo that would bound the fracture toughness data similar to that of the Ric curve in the ASME Code and has been incorporated into the ASME Code by Code Cases N-629 (ASME, 2013b) and N-631 (ASME, 2013c). Thus, in this scheme, Eq. 10.11 is contained in both Code Cases ... 

Van Der Sluys W A, et al. (2000), Fracture Toughness Master Curve Development Fracture Toughness of Ferritic Steels and ASTM Reference Temperature (To), WRC Bulletin 457, December, Welding Research Council, New York. 

In the third group of toughness descriptions various authors proposed to consider particular specimen dimensions and certain parts of the stress-strain or load-deflection curve. The term fracture toughness is also used by certain authors for the critical value of the stress intensity factor fC,. For further details of various fracture toughness descriptions the reader is referred to the abovementioned book by Bentur and Mindess (2006). Only a few proposals are presented below that seem to have both physical meaning and practical importance and gained more universal acceptance than others. 

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