Master Curve analysis of inhomogeneous ferritic steels

Application of advanced master curve approaches on WWER-440 reactor pressure vessel steels

“…The SINTAP lower tail analysis contains three steps, and guides the user towards the most appropriate estimate of the reference temperature, T 0 SINTAP , describing the population having the lower toughness [8,9]. The procedure is briefly described next.…”

“…The MC-Ra procedure was developed for the analysis of data sets consisting of multiple populations [8]. Each population is characterised by T 0 , which is a random variable that is assumed to follow a Gaussian distribution characterized by mean T 0MML and standard deviation sT 0MML .…”

“…However, the need to assess RPV fracture toughness more accurately will drive some utilities to use modified surveillance specimens to measure MC fracture toughness, in addition to traditional Charpy V-notch testing. The basic MC method for analysis of brittle fracture test results, as defined in ASTM E1921 is intended for macroscopically homogeneous ferritic steels only [8]. A basic assumption in the weakest link cleavage fracture model used for the MC is the fixed, empirically determined temperature dependence of fracture toughness, K Jc , which is applied independently of the material.…”

“…Random inhomogeneity is much more difficult to handle. The structural integrity assessment procedures for European industry (SINTAP), contains a lower tail modification of the MC analysis [8,9]. This enables conservative lower bound type fracture toughness estimates also for inhomogeneous steels, which are then governed by the fracture toughness of the more brittle constituent.…”

“…Therefore, a probabilistic description of the complete material is not possible. New extensions [8] of the MC approach have been developed for inhomogeneities governed by two separate MC distributions i.e., the bimodal master curve (MC-Bi) and for the analysis of inhomogeneous materials consisting of random inhomogeneities (MC-Ra). The MC-Bi extension is shown to be extremely efficient in describing e.g.…”