抄録
Fracture toughness tests of Cr-Mo-V steels were conducted by the CT specimens of various thickness (B=b=a, B: specimen thickness, b: uncracked ligament, a: crack length), and 3-dimensional elastic-plastic finite element analyses of them have been performed. Based on the maximum tensile stress criterion for the cleavage fracture, specimen thickness effect on fracture toughness has been investigated analytically. It is proposed from the analyses that the fracture toughness is equivalent to the plane strain fracture toughness, KIc according to ASTM E399, provided that the following condition is met.
B≥350(Jc/σflow) or B≥1.0(Kc(J)/σY)2
Where σflow is flow stress, and σY is 0.2% offset yield stress. The thickness required from the criterion is about 40% of that from the requirement of ASTM E399.
Ikeda et al. proposed that Pmax=PQ as a validity criterion of KIc, which means that unstable fracture occurs before load-crack opening displacement curve intersects the 5% secant line. The present tests are same results as the proposal. It is demonstrated from the present analyses that the criterion of Pmax=PQ, which were obtained from only experimental results, satisfies the above requirement, B≥350(Jc/σflow).
