Evaluation of Plane Strain Fracture Toughness is the Ductile-Brittle Transition Temperature Region. 3rd Report, Evaluation by Using Small Fatigue Test Specimen.

Fracture toughness tests have been made in a transition temperature region at stress ratio R=-1.0 using 1TCT specimens which were cut out from SM41C carbon steel. Considerations of a plane strain fracture toughness and a plane strain condition at a brittle fracture were performed. The main results obtained were as follows. (1) The plane strain fracture toughness in the transition temperature region was simply obtained from a test which was carried out at R=-1.0 using a few small specimens. (2) A stress condition occurring in front of a crack at a brittle fracture satisfied the plane strain condition. (3) da/dN from the fatigue test data at stress ratio R=-1.0 can be extrapolated by ΔJ even in the transition temperature region. (4) The plane strain fracture toughness can be obtained from the minimum value of the fracture toughness test data using 20 three-point bend specimens in the transition temperature region.