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The primary purpose of this work was to develop analytical relationships which could be used to assess the safety of irradiated nuclear reactor pressure vessels against unstable fracture. The need for such a calculation occurs when the Charpy uppershelf energy of the vessel steel is predicted to fall below the required 50 ft ∙ lb (67.8 J) level from accumulated neutron radiation damage. The method used was based on “tearing instability” concepts under “J-controlled growth” conditions for the crack stability criterion. The aforementioned purpose was served by developing fracture mechanics methods of wider applicability than previously available and applying them in analyses at uppershelf conditions (above the transition temperature). Elastic-plastic fracture mechanics concepts were used to extend recognized linear elastic fracture mechanics flaw analysis equations for through-the-thickness flaws and surface flaws into the plastic range. The approach also made use of J-R curve characterization of the material fracture resistance.
A crack stability diagram in the form of J as a function of Tplot was shown to be useful in demonstrating safe levels of loading (applied J) by comparison with the material J-R curve, reduced onto the same diagram. Consequently, a safe level of applied load, J50 [for J/T = 50 in. ∙ lb/in.2 (8.756 kJ/m2)], was suggested and the possibility of its correlation with upper-shelf Charpy energy values discussed.
fracture mechanics, elastic-plastic fracture, analysis, J-integral, J-R curve, tearing modulus, pressure vessel, surface flaw, through-wall flaw, crack growth instability, yielding, Charpy (energy), upper shelf (energy)
Professor of mechanics, Washington UniversityFracture Proof Design Corporation, St. LouisSt. Louis, Mo.Mo.
Task manager, U.S. Nuclear Regulatory Commission, Washington, D.C.