Abatraet-The application of a ductile fracture methodology to predict structural behavior in components requires the use of two inputs. One of them is the material fracture toughness, usually characterized by the J-R curve of the material. The second input is the calibration functions, which represent the relation between load, P, displacement, u, and crack length, a. These three variables uniquely determine the behavior of a structure. When considering only the plastic component of this displacement, vr,, the calibration functions am usually stated in the form P = G(L?/W)H(U~/W), in which b is the untracked ligament, W-u, and Wis a characteristic dimension (width) of the fracture test specimen. In this relation, G is a geometry-dependent function, whereas H is a material-dependent hardening function.
The calibration functions may be obtained analytically, empirically, or numerically. Most often, the latter two forms are more readily available. Numerical solutions for the most commonly employed fracture testing geometries are normally obtained from the GE-EPRI Handbook, in which the plastic components of such quantities as J, CTOD, or load-line displacement, are related to the load by means of a power law. The behavior of the test specimen is described by using the Ramberg-Osgood stress-strain parameters, geometry-dependent variables, a crack length-dependent function, and a constraint factor.
The GE-EPRI Handbook approach therefore assumes that a component or a test specimen behaves in a predictable pattern, given by the material stress-strain behavior and by appropriate geometry-dependent functions. A unique feature of the Handbook approach is that it infers that specimens or components "inherit" the basic stress-strain properties to account for their fracture behavior. In other words, it implicitly assumes that, for a given material, any geometry one chooses to test follows the same pattern of behavior.
The purpose of this work is to show that, based on the EPRI approach, but not stated explicitly in the Handbook, there exists a common format for fracture test specimen calibration curves, hence for common two-dimensional structural components containing defects. The concept of load separation into components G and H is essential to the purposes of stating the common format, since the only differentiating feature between the various test geometries, for any given material, is the G function. Based on this, and on the experimental fracture behavior data of ductile steels with different test geometries, a few examples will be presented that confirm the existence of a common format.