Determination of the partitioning point dividing Delta K into Delta K-eff

The partitioning point dividing Delta K into Delta K-eff, denoted K-op, 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 K-op for Al 7475-T7351 is a steadily increasing function of the R-ratio and K-max up to an upper bound value depending only on K-max. This upper bound value is denoted as K-op(max. value). The K-op determined for Nicrofer 5219 Nb annealed is a steadily increasing function of the R-ratio and K-max only; no upper bound value exists for this material. K-op / K-max as a function of the R-ratio for both materials, and the locus of K-op(max. value) as a function of K-max for Al 7475-T7351 are represented in the form of polynomial equations.