The partitioning point dividing ΔK into ΔKeff, denoted Kop. was determined for Al 7475-T7351 and the Ni-base alloy Nicrofer 5219 Nb annealed. The experimental testing technique used relies only on the fatigue crack propagation behavior, i.e. whether a fatigue crack can propagate or can not propagate. It was found that Kop for Al 7475-T7351 is a steadily increasing function of the R-ratio and Kmax, up to an upper bound value depending only on Kmax. This upper bound value is denoted as Kop(max. value). The Kop determined for Nicrofer 5219 Nb annealed is a steadily increasing function of the R-ratio and Kmax only; no upper bound value exists for this material. Kop, Kmax as a function of the R-ratio for both materials, and the locus of Aop(max. value) as a function of Kmax for Al 7475-T7351 are represented in the form of polynomial equations.
Marci, G. (1996). Determination of the partitioning point dividing δK into δKeff. Engineering Fracture Mechanics, 53(1), 23–36. https://doi.org/10.1016/0013-7944(95)00082-7