In this paper a mechanistic rationale for the fracture process is applied to the CVN impact test so that the J-R curve fracture toughness could be estimated for materials that have only a CVN energy value as the fracture toughness characterization. The method assumes that the fit to the J-R curve can be given a standard form by assuming that the product of J and the tearing modulus, T, is a constant. Given this standard fitting form, the CVN energy is used to estimate a point on the J-R curve. Using this single point and the constant J × T product, the J-R curve is estimated with the two-parameter power law fit specified in ASTM standards. The procedure is applied to metals that undergo purely ductile fracture, that is, those that have CVN energy that would be characterized as “upper shelf” or 100% shear.

The method requires a calibration between impact energy, which has energy contributions from factors other than the fracture process, and the J-R curve point used in the fit. It is calibrated using three steel alloys where both CVN energy on the upper shelf and J-R curve fracture toughness data exist. The results show that a consistent calibration factor can be assumed that applies to all of the steels. Using that factor and the standard J-R curve fit, the prediction was good for all the steels examined. From these J-R curves, the initiation toughness value J_IC can also be determined using the J_IC construction from ASTM Standard Method E 1820. The resulting determination of J_IC shows why the simple process of fitting data sets does not give a universal prediction of toughness. The material tensile strength plays a role in the determination of J_IC.