Master Curve methodology

Fracture toughness tests are performed on a selection of materials and fluences. The test conditions comply with the Master Curve methodology. The results are compared to the indirect approach of end-of-Ufe toughness... 

The Master Curve methodology uses a mathematical model to describe the probability of cleavage fracture initiation in a material containing a distribution of postulated fracture initiators (flaws). The model includes the temperature dependence of Kj, which was estimated empirically from a data set including various ferritic structural steels. The scatter definition based on the Weibull distribution, the size adjustment and the definition of the temperature dependence are the basic elements of the Master Curve methodology as described in ASTM E 1921. 

A master curve can be constructed as indicated in Figure 22.8, where the zero-shear-rate viscosity t]q has to be evaluated for each one of the indicated viscosity curves. Both, the effect of temperature and pressure on the viscosity versus shear rate curve can be addressed by considering a shift factor that may be related, for instance, to the free volume of the system by means of the Williams, Landel, and Ferry (WLF) equation [9, 15, 23, 24]. With the aid of this shift factor, the new viscosity curve can be constructed from known viscosity values and the reference curve at the prescribed values of temperature and a pressure. The use of shift factors to take into account the temperature dependence on the viscosity curve was also used by Shenoy et al. [19-21] in their methodology for producing viscosity curves from MFI measurements. 

NRC (2001), Safety Evaluation by the Office of Nuclear Reactor Regulation to Include the Use of a Master Curve-based Methodology for Reactor Pressure Vessel Integrity Assessment, Docket No. 50-305, Kewaunee Nuclear Power Plant, May, US Nuclear Regulatory Commission, Washington, DC. 

Server W E et al. (1998), Application of Master Curve Fracture Toughness Methodology for Ferritic Steels, EPRI TR 108390, April 1998, Electric Power Research Institute, Palo Alto, CA. 

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