Master Curve analysis of inhomogeneous ferritic steels

The basic Master Curve (MC) method for analysis of brittle fracture test results is intended for macroscopically homogeneous ferritic steels only. In reality, the steels in question are seldom fully macroscopically homogeneous. The materials' toughness may depend on the specimen location in the sample. Inhomogeneity may be deterministic or random (or a mixture of both) in nature. Deterministic inhomogeneity can be accounted for, provided that the specimen extraction histories are known and enough specimens are tested. Random inhomogeneity is much more difficult to handle. The structural integrity assessment procedure SINTAP contains a lower tail modification of the MC analysis. This enables conservative lower bound type fracture toughness estimates also for inhomogeneous materials. The problem is that the SINTAP method, does not provide information of the tougher material. Therefore, a probabilistic description of the complete material is not possible. In this paper, a new comparatively simple extension of the MC is introduced for inhomogeneities governed by two separate MC distributions. The extension is shown to be extremely efficient in describing e.g. weld heat-affected zone (HAZ) data. In addition, a simple method for the analysis of random inhomogeneous material consisting of mixed data is presented. The method is also applicable for data sets including several different materials.