A Comparison of J-Integral and CTOD as Fracture Toughness Parameters

The J-integral and the crack-tip opening displacement (CTOD) are widely used throughout the world to measure the fracture toughness of structural materials. There are many similarities between these two parameters, as well as a number of important differences. Because of these differences, the CTOD parameter tends to be more conservative when applied to structures.

The J-integral and CTOD were compared qualitatively and analytically. This work differs from previous comparisons in that the present study compared engineering estimates of J and CTOD, which are not necessarily equal to the true values of J and CTOD. However, the fracture toughness of a material is nearly always characterized in terms of the engineering approximations of J or CTOD.

The main difference between J and CTOD as measures of toughness is that J is directly proportional to the area under the load-displacement curve whereas CTOD is proportional to the clip gage displacement. This means that the relationship between the two parameters depends on strain hardening and constraint.