Fracture toughness assessment for JN 1 austenitic stainless steel rolled plate at liquid helium temperature

In order to evaluate the fracture toughness of CSUS-JN 1 austenitic stainless steel rolled plate for superconducting magnet structures of magnetic fusion reactors, we have performed elastic-plastic fracture toughness testing at 4.2K. 1T compact test specimens and computer controlled unloading compliance method are used for the JIC tests. The effects of specimen thickness and side-groove on JIC and Tmat are examined. SEM fractograph reveals the effect of specimen thickness on fracture surface. The effect of crack tunneling on determination of J-R curve and JIC, and a difference between ASTM E813-81 and E813-87 are also discussed. (author)