Parametrizing ductile tearing resistance by four parameters

The energy dissipation rate, R, is considered as a measure of resistance to crack extension in elasto-plastic fracture mechanics. It can be re-evaluated from J_R test records of bend and tensile specimens. Three types of R(Δa)-curves are identified. If crack initiation occurs close to or at maximum load, the energy dissipation rate is decreasing with crack extension and approaches a stationary value. This type of R(Δa)-curves can be described by an exponential function with three parameters, namely the initial value, the final stationary value, and a transition length. The cumulative J_R-curves for different specimen geometries can be derived by integration. The three parameters of the R(Δa)-fit together with an integration constant, the initiation value, J_i, characterize ductile fracture resistance both quantitatively and physically interpretable. Constraint effects on R-curves can be quantified in terms of these parameters. A procedure for transferring J_R-curves from one geometry to another is proposed.