Simple semi-empirical correlation to estimate quasi-static fracture toughness from the Charpy impact energy

The Charpy impact test is the main mechanical test used in surveillance programs to monitor reactor vessel degradation as a result of neutron irradiation. Recent development of the master curve for frac-ture mechanics characterization using small size specimens triggered alternative approaches for ex-tracting fracture toughness from the Charpy impact test. Given the large amount of the available Charpy impact data worldwide collected over decades from surveillance programs and also experimental data generated in research reactors together with fracture toughness measurements, it becomes possible to correlate the Charpy impact properties to fracture toughness. A methodology was recently successfully developed using the instrumented Charpy impact tests to derive an estimate of the dynamic and static fracture toughness. However, in many cases, the tests were performed without instrumentation. So, based on the more detailed methodology to extract fracture toughness from the instrumented tests, a closed form simplified equation was developed to overcome the difficulties encountered when instru-mented tests are not available to still provide a reasonable estimate of static fracture toughness. The final equations allowing to estimate fracture toughness from the Charpy impact test are given
where CVN is the absorbed energy (in J) of the Charpy impact specimen tested at Ttest CVN (in °C) and USE is the upper shelf energy level (in J). The procedure was calibrated on a known database and validated on a new experimental database containing 14 data sets.
These simple semi-empirical equations were applied to a variety of reactor materials and proved to be in reasonably good agreement when compared to measured static fracture toughness data. Moreover, this new procedure is also compared to other existing correlations and showed clear improvements.