Use of Instrumented Charpy Impact Tests for the Determination of Fracture Toughness Values

A number of techniques has been under development to estimate fracture mechanics parameters using the instrumented Charpy impact test. The evolution of elastic-plastic fracture mechanics has led to the use of small test specimens to achieve valid cleavage fracture toughness values based on the J-Integral concept, KJc, in the lower ductile-to-brittle transition temperature (DBTT) range. A successful concept bases on the statistical data treatment methodology with the Weibull-type statistic. It has been demonstrated that the probabilistic-based estimates of the median fracture toughness of ferritic steels tend to form transition curves of the same shape, the so-called "master curve", normalized to one common specimen size, namely the 1T (i.e. 25 mm thick) specimen. This method covers the determination of a reference temperature, T0, at a median fracture toughness, KJc, of 100 MPa m1/2. Furthermore toughness parameters in terms of J-Integral based ductile crack initiation toughness, KJi, have been also used for the integrity assessment of structures. The determination of KJi values by the instrumented impact test requires the detection of the ductile crack initiation on the dynamic load vs. displacement curve.