Measurement of fracture toughness transition behaviour of Cr-Ni-Mo-V pressure vessel steel using pre-cracked Charpy specimens

The potential application of small pre-cracked Charpy specimens for the pre diction of the fracture toughness of the 1T-thickness specimens and the ref erence temperature T-0 has been examined. Transition fracture behaviour of plane sided, side-grooved and IT SENB specimens, respectively, was investig ated over a wide temperature range. The fracture toughness regions with var ious fracture initiation mechanisms were defined and ductile to brittle tra nsition temperatures denoted. The fracture toughness transition region of s mall pre-cracked specimens a as shifted to lower temperatures as compared w ith that of 1T SENB specimens. The fracture toughness data of small pre-cra cked specimens have been size corrected (weakest link) to 1T thickness and used to establish the reference temperature T-0 and K-Jc(mean) fracture tou ghness vs. temperature curve. The calculated temperature T-0 has been in co nsistence with that of the 1T SENB specimen. However, some corrected fractu re roughness data lay outside the scatter band of 1T thickness specimens an d the shape of the K-Jc(mean) curve has been quite different from the K-Jc( med)(1T) curve. It was found out that the original measured fracture toughn ess results df corrected data points lying outside the scatter band violate d the validity condition b(0)R(p)0.2/J(c) greater than or equal to 30, Bear ing in mind the work of Koppenhoefer and Dodds Jr. (Engng Fract Mechanics ( 1997);58:249-270), and the most recent analysis of Ruggieri et al. (Engng F ract Mechanics (1998);60:19-36), the fracture data of small pre-cracked spe cimens having the validity parameter lower than 50 have been first constrai nt adjusted using the cleavage fracture toughness scaling model of Dodds an d coworkers (J Testing Evaluation (1991);19. 123-134; Int J Fracture (1995) ; 74:131-161; Engng Fract Mechanics (1997),58:249-270), and only then size corrected. The K-J (mean) curve of such treated data was identical with K-J c(med)(1T). (C) 1999 Elsevier Science Ltd. All rights reserved.