Robust Determination of Fatigue Crack Propagation Thresholds from Crack Growth Data

Abstract

The robust determination of the threshold against fatigue crack propagation ∆Kth is of paramount importance in fracture mechanics based fatigue assessment procedures. The standards ASTM E647 and ISO 12108 introduce operational definitions of ∆Kth based on the crack propagation rate da/dN and suggest linear fits of logarithmic ∆K– da/dN test data to calculate ∆Kth. Since these fits typically suffer from a poor representation of the actual curvature of the crack propagation curve, a method for evaluating ∆Kth using a nonlinear function is proposed. It is shown that the proposed method reduces the artificial conservativeness induced by the evaluation method as well as the susceptibility to scatter in test data and the influence of test data density.