Heavy sectional structural steels for nuclear pressure vessel are severely required to prevent unstable fracture like a brittle fracture. From this point of view, it is important to know the fracture toughness characteristics concerning to the fracture mechanics criteria for evaluation of fracture toughness.
Dynamic fracture behaviors of the steel in tensile test using circumferentially notched round bar specimens were reported and discussed previously. In this report, dynamic fracture toughness test using three points bending specimens of the same steel are carried out, and the evaluations by the critical COD, J-value and dynamic transition temperature are investigated.
The conclusions obtained from the experimental test results were as follow;
1) Transition curves of dynamic fracture toughness shifted to a higher temperature, and transition curves were change in narrower temperature range abruptly as higher impact loading rate.
2) Transition temperature T
dδ(0.2) or T
dJ(10) based on the dynamic COD or J-value criteria re-spectively were almost constant or slightly increased to higher temperature with higher loading rate.
3) The difference of transition temperature between the static and dynamic fracture test was large in the bending fracture toughness test comparing with the tensile test.
4) The dynamic COD or J-value criteria in this test represented a favourable critical toughness of the structural steels depending to test temperature.
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