Fracture Toughness Testing With Cracked Round Bars: Feasibility Study (NUREG/CR-6342)
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Manuscript Completed: March 2000
Date Published: April 2000
J.H. Giovanola, J.E. Crocker
SRI International Poulter Laboratory
333 Ravenswood Avenue
Menlo Park, CA 94025
Under Contract to:
Oak Ridge National Laboratory
Managed by Lockheed Martin Energy Research Corporation
Oak Ridge, TN 37831-6158
C.J. Fairbanks, NRC Project Manager
Division of Engineering Technology
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001
NRC Job Code L1098
SRI International has investigated the feasibility of measuring representative toughness values for nuclear pressure vessel materials using small cracked round bars (CRBs). We tested a weldment material [Heavy-Section Steel Irradiation (HSSI) Weld 72W with 0.23% copper] at six temperatures (-150°, -80°, -50°, 0°, 23°, and 50°C) using CRBs and compared the fracture-toughness results with data obtained for HSSI Weld 72W by Oak Ridge National Laboratory using 1T-compact tension (CT) specimens.
The overall agreement between the toughness values measured with the CRBs and the 1T-CT was quite good over the entire range of temperatures and for both cleavage and ductile fracture. This agreement attests to the promise of the CRB geometry for providing valid toughness values from small specimens. Nevertheless, we observed some differences, mainly for cleavage toughness values below 0° C. We attribute the differences to (1) possible inaccuracies in the estimation formulas for the J-integral, (2) differences in constraint, and (3) statistical size effects.
We recommend that work be continued to validate the CRB test procedure and to adapt it to specimens that can be fabricated from halves of broken Charpy specimens.