Preliminary results from biaxial shallow-flaw fracture toughness tests on reactor pressure vessel steel.

摘要

Reactor pressure vessel (RPV) operating life can be limited by postulated pressurized-thermal-shock (PTS) accident conditions. The calculated fracture initiation resistance of an RPV is based on the ASME K(sub Ic) fracture toughness curve which was developed using specimens with negligible out-of-plane strain (i.e. plane-strain conditions). However, PTS loads produce both a significant crack-opening load and a significant positive out-of-plane load along the crack front for both circumferential and axial flaws. Experimental evidence is scarce but seems to indicate that, for conditions prototypic of an RPV, a reduction in fracture toughness takes place associated with out-of-plane biaxial loading when compared with uniaxial loading conditions in shallow flaw specimens. Additional experimental fracture toughness dam under biaxial loading are necessary to evaluate the effect of biaxial loads in an RPV under PAS conditions. Previous testing of single-edge-notch bend (SEN) specimens with shallow and deep cracks indicates an increase in the fracture toughness of the shallow crack specimens compared with the deep crack specimens. The Heavy-Section Steel Technology (HAST) program sponsored by the US Nuclear Regulatory Commission (NRC) is conducting an exploratory, ''Proof-of-principle'' series of out-of-plane biaxial-bending fracture toughness tests using specimens with shallow flaws. Cruciform specimens with an approximate cross section of 100 (times) 100 mm (4 (times) 4 in.) with a straight through, two-dimensional, shallow flaw, are being loaded in bending across two perpendicular planes for biaxial loading. This paper presents the initial test results under uniaxial and biaxial loading and compares the test results with HAST shallow-crack data.