Correlation of stable crack growth with J-integral and crack tip opening for plane stress

The experimental investigation was aimed at establishing empirical criteria for the limits up to which the J-integral and the crack tip opening displacement, δ5, measured over a gage length of 5 mm can serve as correlation parameters for stable crack growth. The relevant quantities which may affect crack growth were systematically varied: material (Al alloys, 35 NiCrMo16 = 1.2766), specimen geometry, pre-crack length, and specimen width. Under plane stress conditions, both J and δ5 correlate crack growth much better on CCT specimens than on CT or SENB specimens. Furthermore, on CT and SENB specimens δ5 correlates about 5 times as much crack growth as J. In plane stress, the CCT geometry has a much bigger measurement capacity than in plane strain, the actual value for the JR-curve depending on the strain hardening properties of the material. (orig./HP)