An evaluation of the precracked charpy test

In this testing program precracked Charpy tests were performed to evaluate fracture toughness parameters for a SA 508 C1.2 pressure vessel steel and to consider the validity of the proposed standard method of test for instrumented impact testing of precracked Charpy specimen. Test specimens machined from the test cylinder TSC-2 used for Thermal Shock Experiment were supplied by Oak Ridge National Laboratory (ORNL), USA. Two instrumented impact hammers were used: one having the normal test geometry and the other having an inverted test geometry. The present results of both testers are in good agreement with the data obtained by the Oak Ridge National Laboratory (ORNL). The validity of the test according to the proposed standard method, especially the conditions time to fracture and fracture before general yielding, is difficult to fulfill simultaneously. Further the available energy of standard impact tester is often inadequate to satisfy the energy requirements. Although the load cell of the new impact tester (inverted test geometry) needs further improvements, the results indicate that inaccuracies of the measured force values due to specimen oscillations can be diminished without significant damping of the load signal. This makes it possible to use high frequency response which is important when elastic or elastic-plastic behaviour of the material is to be tested.