Specimen Thickness Effect on Cleavage Fracture Toughness of High and Intermediate Pressure Steam Turbine Rotor Materials
Hiromi UEMURA, Akira KIUCHI, Takao INOUE and Atsushi WAKAMI
Abstract:Fracture toughness tests of Cr-Mo-V steels were conducted by the CT specimens of various thickness (B=b=a, BFspecimen thickness, bFuncracked ligament, aFcrack 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, jic according to ASTM E399, provided that the following condition is met. B350(Jc^Đflow) or B1.0(Kc(J)^ĐY)2 Where Đflow is flow stress, andĐY 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 jic, 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, B350(Jc^Đflow). Key Words:Cleavage fracture toughness, Fracture toughness test, Cr-Mo-V steels, Specimen thickness effect, Plane strain fracture toughness, Valid Kic, Kic criterion