Estimation of Fracture Toughness Using Flat-Ended Cylindrical Indentation

A method is proposed to predict the fracture toughness of in-service structures using the instrumented indentation test. While previous studies have attempted to predict fracture toughness using spherical indenters, we propose the method to predict fracture toughness using flat-ended cylindrical indenters. Using the geometric similarity of a cylindrical indentation test and the Cracked Round Bar (CRB) fracture toughness test, fracture toughness values were derived from a single indentation test by assuming that the load–depth curve of the indentation test is the same as the load–displacement curve of the CRB fracture toughness test. To determine the crack initiation point, the concept of limit load in CRB testing is adopted, and a new load–depth curve is obtained using a suggestion in the standard of fracture toughness test. In order to apply the proposed method directly to in-service structures, the model uses mechanical parameters that can be obtained by indentation testing. The model was verified on metallic materials primarily used in nuclear power plants.