Modifying the Ernst method which takes into account the tension component of the plastic displacement in CT (Compact Tension) specimen, a useful J-evaluation formula is proposed when crack grows.
The use of the blunting-line concept in $J_{IC}$ determination, while reasonably well established in ASTM Standard, is subject to some uncertainty when applied to all kinds of materials and specimens. It seems necessary to determine the blunting line experimentally for each material in order to use it with confidence. Using Single-Specimen-Compliance method and rotational effect experimental blunting-line determination method is also presented.
In this study most of the specimens tested are side-grooved in order to provide a straight crack front. This modification is believed to result in a J value which is nearly constant through the crack front. This straight crack produces R curves of lower slope than those associated with curved crack fronts and seems to result in a conservative characterization of the toughness trends.
