J-R curve evaluation from predominantly tensile specimen geometries

The J integral fracture mechanics methodology uses a single parameter, the J integral, to characterize the intensity of the crack tip field for both crack initiation and crack growth. This parameter is intended to be applicable whether the applied loading is predominantly tensile or predominantly bending and, in general, laboratory specimens are tested in a bending mode while the applications are often predominantly tensile. Several recent large scale tests conducted in the U.S. and in Europe and analyzed as part of the Committee on the Safety of Nuclear Installations (CSNI) project FALSHIRE have show that, in at least some cases, the J integral at initiation, and the J-R curve in general, can be distinctly elevated for predominantly tensile loadings when compared to bending specimen results. This paper reports that analysis proposes that a second parameter is needed to characterize the crack tip field in terms of the crack tip triaxiality or constraint, and that the JIc or J-R curve can vary markedly for specimens of distinctly different constraint. To understand this developing issue, specimen geometries with a predominantly tensile mode of loading must be developed and tested. In this work, double and single edge notched specimens are developed which produce a tensile mode of loading, can be easily precracked in bending, and can be loaded to produce ductile crack growth and failure in the test laboratory