The Use of Finite Element Analysis and Notch Tensile Testing to Determine the Cryogenic Fracture Toughness of Thick Section Weldment in Forged CSUS-JN1 Plate with Inconel 625 Type Filler Metals

The use of the notch tensile test to estimate the elastic-plastic fracture toughness (JIC) of structural alloys and weldments for superconducting magnets in fusion energy systems was studied. Notch tensile tests were performed with small round bar specimens containing an electro discharge machined (EDM) notch at liquid helium temperature (4 K) using crosshead rates of 3.3×10−3 and 20 mm/s. Notch tensile test specimens were 5 mm in diameter with a 30-mm reduced section. In the mid section of the specimen a 1 mm deep EDM notch of 0.2 mm width was machined around the girth, thus maintaining a starting diameter of 3 mm. Correlations between notch tensile strength, failuar energy absorption, and JIC were assessed. A finite element analysis was also performed to compute directly the J-values. Comparisons of the predicted JIC with results obtained from conventional JIS Z 2284 standard tests were made.