Using Small Cracked Round Bars to Measure the Fracture Toughness of a Pressure Vessel Steel Weldment: A Feasibility Study

摘要

The research objectives were to demonstrate the feasibility of using small fatigue pre-cracked round bars to measure the initiation fracture toughness of ductile nuclear pressure vessel steels and weldments and to refine and validate experiment and analysis procedures. Initiation fracture toughness values were measured for a duplicate of HSSI Weld 72W, unirradiated, in the temperature range -150° to 50°C, using small cracked round bar (CRB) specimens. The results were compared with the values obtained with 1T-CT specimens. The good agreement between the toughness values measured with CRB and 1T-CT specimens indicates that using small CRB specimens (possibly cut from Charpy bars) to measure fracture toughness is feasible. A relationship between J and the displacement due to the crack δ_(cr), where δ_(cr) is obtained from extensometer measurements, was established experimentally. Fracture initiation in CRBs of the size investigated here occurred at or near maximum load, with the crack growth prior to maximum load being less than 200 μm. This observation, together with the unique relationship between J and δ_(cr), open the possibility of greatly simplified testing and data reduction procedures for fracture experiments with CRB.